EP4709909A1

EP4709909A1 - Improvements to electro-synthetic or electro-energy cells

Info

Publication number: EP4709909A1
Application number: EP24834985.4A
Authority: EP
Inventors: Aaron Hodges; Gerhard Frederick Swiegers; Adam Warburton; David John Cox; Atiyeh Ebrahimi; Kieren Searle; Ganga Shankar; Kai Jian Yap
Original assignee: Hysata Pty Ltd
Current assignee: Hysata Pty Ltd
Priority date: 2023-07-05
Filing date: 2024-06-26
Publication date: 2026-03-18
Also published as: CN121399300A; MX2025015633A; CL2025004026A1; WO2025007181A1; AU2024290995A1; KR20260035893A

Abstract

Disclosed is an electro-synthetic or electro-energy cell, comprising a first gas diffusion electrode, and a second electrode. A spacer, including but not limited to a porous capillary spacer, is positioned at least partially between the first gas diffusion electrode and the second electrode. In one form the liquid electrolyte is transferred onto a side surface of the spacer beyond the electrodes. In one example there is also provided a liquid electrolyte reservoir, where the first gas diffusion electrode, the second electrode and the spacer are positioned outside of the liquid electrolyte reservoir. In one example the liquid electrolyte reservoir includes an aperture to release liquid electrolyte. In another form, an intermediate liquid feed structure is located at least partially between the spacer and the liquid electrolyte reservoir, wherein the liquid electrolyte is transferred by the intermediate liquid feed structure. Methods of operation and cell stacks are also disclosed.

Description

IMPROVEMENTS TO ELECTRO SYNTHETIC

OR ELECTRO-ENERGY CELLS

TECHNICAL FIELD

[001] The invention broadly relates to electrochemical cells, for example used as electrosynthetic cells or electro -energy cells. Example embodiments of the invention more particularly relate to zero-gap electrochemical cell architectures that are inherently energy efficient and that employ effects that minimize the need for macro-level external management of the electrochemical cell.

BACKGROUND

[002] An electro-energy cell is an electrochemical cell that generates electrical power continually or continuously, over indefinite periods of time, for use outside of the cell. Electroenergy cells are distinguished from galvanic cells in that they may need to be provided with a constant external supply of reactants during operation. The products of the electrochemical reaction are generally also constantly removed from such cells during operation. Unlike a battery, an electro -energy cell does not store chemical or electrical energy within it.

[003] An electro- synthetic cell may similarly be considered to be an electrochemical cell that manufactures one or more chemical materials continually or continuously, over indefinite periods of time, for use outside of the cell. The chemical materials may be in the form of a gas, liquid, or solid. Like an electro-energy cell, an electro-synthetic cell also requires a constant supply of reactants and a constant removal of products during operation. Electro-synthetic cells generally further require a constant input of electrical energy.

[004] Because of the large quantities of electrical energy involved in operating electroenergy and electro-synthetic cells, a key challenge in their development is to make them as energy efficient as possible during operation. This may be achieved, in part, by minimizing their electrical impedance. Impedance is the opposition that a cell circuit presents to an electrical current when a voltage is applied. One method of minimizing impedance is to employ a cell architecture in which the anode and cathode electrodes of the cell are placed facing each other, as close as possible to each other, without touching (which would create a short circuit). The gap between the two electrodes should ideally also be occupied by an electrolyte having the highest possible ionic conductance.

[005] To this end, a range of ‘zero-gap’ cell architectures have been developed for electrosynthetic or electro-energy cells. In such architectures, two electrodes are sandwiched tightly against opposite sides of an electrically insulating membrane, diaphragm, or ionomer (known as a ‘spacer’) that may have inherently high ionic conductance or may be imbued with a liquid electrolyte having a high ionic conductance. Zero -gap spacers of this type are generally less than 2 mm thick in zero-gap cells. Some examples of zero-gap cell architectures are provided in the scientific paper by R. Phillips and C. W. Dunnill, “Zero gap alkaline electrolysis cell design for renewable energy storage as hydrogen gas” in RSC Advances (2016), Vol 6, pages 100643-100651.

[006] A key challenge in electro-synthetic and electro-energy cells is to maintain the spacer in a hydrated or wetted state or imbued with liquid electrolyte during operation, in such a way that the energy efficiency of the electrochemical reaction is simultaneously maximised. In many traditional electro- synthetic cells (for example, water electrolysis cells), one or both half-cells must be filled with liquid electrolyte in order to maintain the spacer in a hydrated or wetted state or imbued with liquid electrolyte during operation. This typically leads to poor energy efficiency in the electrochemical reaction since one or both of the electrodes are then overwhelmed and oversaturated with liquid, and can only produce gases in the form of gas bubbles in the liquid electrolyte (e.g. in the form of a froth or foam). Such multi-phase mixtures require extra energy to produce and are more complex and energy intensive to handle. Similarly, in many traditional electro-energy cells (for example, hydrogen -oxygen fuel cells) in which the half-cells are filled with gases, the spacer can only be maintained in a hydrated or wetted or liquid-imbued state by constantly circulating externally humidified gases through one or both half-cells. The humidity (water vapour) in the gases condenses and forms liquid water on or in the spacer. This process is, however, extremely difficult to control. Excess condensation may occur, leading to the spacer, and thereby the electrodes, becoming over-wetted and oversaturated with liquid. The excess liquid on the electrode(s) may block access of the gas(es) to the electrode(s), causing poor energy efficiency in the electrochemical reaction. Insufficient condensation may, alternatively, occur, causing the spacer, and thereby the electrodes, to dry out, which also causes a loss in the energy efficiency of the reaction. This approach is therefore also challenging to control, wasteful of energy and complex to implement. [007] A class of electro-synthetic or electro-energy cell that spontaneously maintains its spacers optimally imbued with liquid electrolyte during operation, without a need for either of its half-cells to be filled with liquid electrolyte, or to circulate humidified gases through either of the half-cells, is ‘capillary-based’ electro- synthetic or electro-energy cells, for example of the types described in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, which are hereby incorporated by reference.

[008] Cells of this type are characterised by the use of a ‘porous capillary spacer’ between the electrodes. A porous capillary spacer is a porous spacer that draws in and confines the liquid electrolyte within itself by a capillary effect. The liquid electrolyte may be induced to spontaneously move inside the porous capillary spacer by the capillary effect, and/or by other effects, including but not limited to diffusion or osmosis. Liquid electrolyte may therefore be spontaneously and continuously or continually supplied to, or removed from the porous capillary spacer by a liquid reservoir, into which one end of the spacer is dipped.

[009] Several physical properties are characteristic of porous capillary spacers, including: (1) a capillary pressure, this being the pressure arising from the capillary effect with which liquid is held within the porous capillary spacer, (2) a ‘column height’ and ‘maximum column height’ , these being the actual height or maximum theoretical height, respectively, of a column of liquid drawn into and confined within a porous capillary spacer by capillary action from a liquid reservoir at its base, including during operation of a cell, and (3) ‘flow rates’ at particular heights, these being the rates of liquid transport inside the porous capillary spacer at particular heights above a liquid reservoir at its base, during operation of embodiment cells. When liquid is drawn up a porous capillary spacer from a reservoir at its base, these flow rates generally decline with increasing elevation above the reservoir, limiting the practical height of such cells.

[010] Figure 1 (prior art) schematically depicts a cross-section of a previously described electro-synthetic or electro-energy cell 10 as disclosed in the Applicant’s International Patent Publication No. W02022056603. Cell 10 has a reservoir 140 for containing a liquid electrolyte 100 at its base; a first gas diffusion electrode 120 positioned outside of the reservoir; a second electrode 130 positioned outside of the reservoir; and a porous capillary spacer 110 positioned between the first gas diffusion electrode 120 and the second electrode 130, the porous capillary spacer 110 having an end 150 that extends beyond the electrodes and into the reservoir 140; wherein, the porous capillary spacer is able to fill itself with the liquid electrolyte 100 when the end 150 of the porous capillary spacer 110 is in liquid contact with the liquid electrolyte 100 in the reservoir 140. The assembly of first electrode 120, porous capillary spacer 110, and second electrode 130 comprises the ‘electrode-spacer-electrode’ assembly 139 of the cell 10. The first gas diffusion electrode 120 may be configured to generate or consume a first gas that forms a first gas body 125. The second electrode 130 may be a gas diffusion electrode and may be configured to generate or consume a second gas that forms a second gas body 135. As can be seen, neither of the two half-cells in cell 10 are filled with liquid. Rather, the first half-cell is filled with the first gas body 125, while the second half-cell is filled with the second gas body 135. Despite this, the porous capillary spacer 110 is maintained imbued with liquid electrolyte during operation. Nor is there a need for one or both of the gas bodies to be externally humidified and re-circulated through its respective half-cell to maintain the spacer imbued with liquid electrolyte during operation.

[011] The cell may be surrounded by a liquid-impermeable and gas-impermeable external housing 151, through which external gas lines 127, 137 and liquid lines 152 penetrate. The first gas may be transported to or from the first gas body 125 via an external gas line 127 to or from an external storage volume 128. The second gas may be transported to or from the second gas body 135 via an external gas line 137 to or from an external storage volume 138. The first and second electrodes 120 and 130 respectively, may be connected to a power supply or power receiving unit 180 via electrical cables 160 and 170 respectively. Liquid electrolyte in reservoir 140 may be replenished from (if it is consumed in the electrochemical reaction) or removed to (if it is produced in the electrochemical reaction), an external store of liquid electrolyte 153 via an external pipe 152.

[012] During operation of the cell 10, at the molecular-level, liquid-phase materials produced by or consumed by the electrochemical reaction preferably spontaneously migrate to or from the reaction zones within or about the inside surfaces of the electrodes 120 and 130, where they face the spacer 110, in the liquid electrolyte inside the inter-electrode spacer 110, along the length of the inter-electrode spacer 110 to or from the reservoir 140. That is, the liquid-phase reactants and/or products preferably undertake ‘in-plane ’ migration in the liquid electrolyte 100 inside the spacer 110, along the length of the inter-electrode spacer 110 to or from the reservoir 140. The liquidphase reactants and/or products may so migrate under capillary and/or diffusion and/or osmotic control, which is ‘ self -regulated’ by the concentration differentials present in the liquid electrolyte and at and about the reaction zones at the electrodes. As a result of these self-regulated migrations, liquid-phase reactants may be replenished to the cell by adding fresh liquid-phase reactants to the reservoir, and liquid-phase products may be removed from the cell by removing them from the reservoir.

[013] At the molecular- level, gas-phase materials produced by or consumed by the electrochemical reaction may migrate in an orthogonal (90°) direction to the migration direction of the liquid-phase materials, along continuous gas phase pathways that are separate from and do not interfere with the liquid-phase pathways. That is, gaseous molecules or atoms may migrate to I from their respective gas bodies 125 or 135 through the relevant interface/s to or from the gas diffusion electrode(s) 120 or 130 respectively, i.e. into or out of the reaction zones within or about the inside surface of the electrodes 120 and 130 respectively, where they face the spacer 110. Such migrations may occur under (gas) capillary and/or diffusion control along continuous gas-phase pathways connecting each electrode 120 or 130 to each gas body 125 or 135, respectively. For this reason, gas-phase materials (reactants or products) may also exhibit self-regulation. Because the pathway of migration of each gas does not overlap with, or interfere with that of the other gas, or with the pathway of liquid migration inside the porous capillary spacer, gas movements may be independently self-regulated, separately to the self-regulation of the liquid movements. That is, the different gas- and liquid-phase reactants and products may each be subject to their own selfregulation, which does not interfere with the movements of the other reactants and products.

[014] The liquid electrolyte 100 in the reservoir 140 may be separated from the gas diffusion electrodes 120 and 130 by a barrier wall 155. The barrier wall 155 may be formed of a material that is impermeable to liquid electrolyte 100. A slit, gap, or orifice 145 in the barrier 155 may allow for the porous capillary spacer 110 to tightly fit and pass through into the reservoir 140.

[015] The barrier wall 155 may, optionally, have tubes 149 perforating it, to thereby ensure that the pressures of the first gas body 125 and the second gas body 135 are transmitted to the liquid electrolyte 100 in the reservoir 140.

[016] In the absence of tubes 149, where only a single slit, gap, or orifice 145 is present in the barrier wall 155, the cell may be immune to orientation effects. That is, if the slit, gap, or orifice 145 is completely filled with the porous capillary spacer 110, and the reservoir contains liquid electrolyte 100, then the cell may be operated in any orientation, including, for example, with the reservoir 140 at the top of the cell. [017] Figure 2 depicts a representation of the body of cell 10 in an inverted orientation, where gravity is directed downwards towards the bottom of the page with respect to orientation of the figure, with the reservoir 140 at the top of the cell. The external gas lines 127, 137 and liquid lines 152, and their associated gas volumes 128, 138 and liquid 153 volumes, as well as the electrical equipment 160, 170, and 180, are not depicted in Figure 2 for clarity. Direction 250 shows the direction of the ‘in-plane ’ migration of liquid-phase reactants in the liquid electrolyte 100, along the length of the inter-electrode spacer 110 from the reservoir 140. As can be seen, the porous capillary spacer 110 extends outside the region of the electrochemical cell itself (denoted by region 204) into locations beyond the electrodes (denoted by region 260), where the porous capillary spacer 110 does not have electrodes abutting it on one or both sides. The part of the porous capillary spacer 110 beyond the electrodes 120 and 130, being in region 260, is wholly inside the reservoir 140 / barrier wall 155. The volume between the electrodes 239 contains the porous capillary spacer 110. The first gas diffusion electrode 120 and the second electrode 130 are separated by an average inter-electrode distance 270.

[018] In this orientation, the capillary pressure with which the liquid electrolyte 100 is held within the porous capillary spacer 110 prevents the liquid electrolyte 100 in the reservoir 140 from flowing out and filling (flooding) the gas volumes 125 and 135 with liquid. That is, the capillary pressure of the porous capillary spacer 110 exceeds and counteracts the hydrostatic pressure created by the head of liquid in the reservoir 140. If the spacer 110 had a capillary pressure that was just too low relative to the hydrostatic pressure, liquid electrolyte would dribble out of spacer 110 at its bottom-most end, where the hydrostatic pressure is greatest, and progressively fill (flood) the gas chambers 125 and/or 135. If the porous spacer 110 had no capillary pressure at all, liquid electrolyte 100 would pour out at all heights of the spacer 110, immediately flooding chambers 125 and 135.

[019] The operation of cell 10 in the orientation shown in Figure 2 is therefore reliant on the capillary effect of the porous capillary spacer 110 and the relationship between its capillary pressure and the hydrostatic pressure created by the reservoir. This, same, capillary effect may be harnessed to maintain the electrodes 120 and 130 properly wetted (and not oversaturated or overwhelmed) with liquid electrolyte 100, and therefore able to operate with high energy efficiency. [020] Figure 3 (prior art) schematically depicts the structure of another capillary-based electrosynthetic or electro-energy cell 11 as disclosed in the Applicant's International Patent Publication No. W02022056603. Cell 11 differs from cell 10 in that no barrier wall 155 is present between the reservoir 140 and the electrodes 120 and 130. Liquid electrolyte 100 in the reservoir 140 may therefore be in direct contact with one or both electrodes 120 or 130. The extent of the contact may be relatively small (e.g. 5-10% of the electrode outer facial area, as depicted at A in Figure 3) or relatively large (e.g. 50-70% of the electrode outer facial area, as depicted at B in Figure 3). The extent of the contact between the liquid electrolyte and an electrode may be fixed, or may change, rapidly or slowly, transiently, or permanently, during operation of the cell, and the specific values of A and B may lie anywhere between 0% and 100%, inclusive.

[021] The example in Figure 3 demonstrates another approach to controlling the extent to which the electrodes 120 and 130 are wetted, namely by adjusting the physical contact between the electrodes 120 and 130, and the liquid electrolyte 100 in the reservoir 140. This may be achieved by pressurising the gas bodies 125 and 135 and applying a differential in their pressures. A higher pressure in gas body 125 relative to the pressure of gas body 135 will result in a smaller contact area A and a larger contact area B (as shown in Figure 3), potentially providing for electrode 130 to be more wetted overall than electrode 120. By contrast, a higher pressure in gas body 135 over gas body 125 will result in the contact area A being larger and the contact area B being smaller, thereby potentially reversing the extent of wetting overall of the electrodes 120 and 130. This approach is potentially important because it can be applied on the fly, in real time, during operation of the cell, to systematically maximise the energy efficiency of the electrochemical reaction. It is, of course, a relatively gross and not a fine effect.

[022] Electro- synthetic or electro-energy cells of the type depicted in Figures 1-3 can operate with remarkably high energy efficiencies, because they provide fundamentally improved control of spacer-, and thereby also electrode- wetting. That is, the spacer may be spontaneously maintained in a suitably hydrated or wetted or liquid-imbued state, whilst the electrodes are simultaneously properly wetted and not over- or under- saturated with liquid electrolyte. Thus, gas-generating electrodes in the systems described above may, for example, produce gases without substantially forming gas bubbles within the liquid electrolyte (i.e. they may operate ‘bubble-free’).

[023] However, cells of the type depicted in Figures 1-3, may suffer from some important limitations, a key one of which may be a limitation on their physical height. With a reservoir at the base of the cell, this limitation arises from the need for high, threshold flow rates to be exceeded at all heights within the porous capillary spacer above the reservoir, including at the top of the cell, during operation. This, under circumstances where the flow rates within a porous capillary spacer during operation, declines non-linearly with increasing height above the reservoir at the cell’s base. With a reservoir at the top of the cell, this limitation arises from the need for the capillary pressure within the porous capillary spacer to counteract and overcome the hydrostatic pressure of the head of liquid in the reservoir. The greater the cell height, the larger the hydrostatic pressure, and the larger the capillary pressure within the porous capillary spacer needs to be to avoid filling (flooding) of the gas chambers.

[024] New and improved configurations incorporating spacers (including but not limited to porous capillary spacers) that remain hydrated, wetted, or imbued with liquid electrolyte during operation of the cell, whilst allowing for the electrodes to be simultaneously properly wetted are therefore still needed. Improved configurations in this respect may potentially provide for further improvements in control, thereby avoiding the need for one or both of the half-cells to be filled with liquid electrolyte, or be supplied with externally humidified circulating gases, and thereby provide for high energy efficiency during operation.

[025] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

SUMMARY

[026] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify all of the key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[027] In various example aspects, embodiments relate to electrochemical cell architectures, particularly zero-gap electrochemical cell architectures with spacers, including but not limited to ‘porous capillary spacers’, between the electrodes, wherein the cell is configured to transfer liquid electrolyte from a liquid electrolyte reservoir onto a surface of the spacer, preferably a side surface of the spacer, to thereby maintain or help maintain the spacer hydrated, wetted, or imbued with liquid electrolyte during operation of the cell. The term ‘transfer’ includes any mode by which liquid may move, including but not limited to: drip, drop, flow, pour, run, spray, migrate, or pass. Preferably but not exclusively, the spacer extends beyond the electrodes, and consequently a side surface of the spacer extends beyond the electrodes, and the cell is configured to transfer liquid electrolyte from the liquid electrolyte reservoir onto a side surface of the spacer that lies or extends beyond the electrodes (i.e. onto a side surface of the spacer where the side surface lies or extends outside of the ‘electrode-spacer-electrode’ assembly of the cell). Preferably but not exclusively, liquid electrolyte is transferred from the liquid electrolyte reservoir only onto the side surface of the spacer and not onto the surface of an electrode, to thereby ensure proper wetting of the electrode, without overs aturation of the electrode with liquid electrolyte, thereby providing for high energy efficiency during operation. In another example, the cell is configured to transfer liquid electrolyte from the liquid electrolyte reservoir onto two side surfaces of the spacer that lie or extend beyond the electrodes. In another example, the cell is configured to transfer liquid electrolyte from the liquid electrolyte reservoir onto both side surfaces of the spacer that lie or extend beyond the electrodes, when the spacer is generally configured as a planar sheet structure. Preferably, though not necessarily, embodiments of the types described above and embodiments described herein overcome the limitations on physical height that exist for cells of the type depicted in Figures 1-3.

[028] In some embodiments, an end of the spacer that lies beyond the electrodes is located within the reservoir, that is an end surface of the spacer is positioned beyond the electrodes and the end surface of the spacer is positioned within the liquid electrolyte reservoir, whilst the reservoir is also configured to transfer liquid electrolyte onto a side surface of the spacer outside of the reservoir. In other embodiments the spacer abuts or is close to the outside of the reservoir, with the reservoir configured to transfer liquid electrolyte onto a side surface of the spacer abutting or close to the outside of the reservoir. In some embodiments, a structure with a gap, preferably a small gap, may be formed above the side surface of the spacer, termed here a ‘narrow gap’ structure, and this narrow gap structure may facilitate or help control the transfer of the liquid from the reservoir to the side surface of the spacer. In still other embodiments, the spacer may be physically separated from the reservoir, wherein an intervening structure, termed here a ‘liquid feed structure’, is configured to transfer liquid electrolyte from the reservoir to the side surface of the spacer. The liquid electrolyte reservoir may be located at one of, some of, or all of: the top, a first side, a second side, both of the sides, and/or the bottom of the cell.

[029] Example embodiments are particularly relevant to zero-gap electro-synthetic or electroenergy cells that facilitate gas-to-liquid or liquid-to-gas processes. Such cells may operate continually or continuously over indefinite periods of time, consuming reactants and generating products that are too voluminous to be accommodated within the cell, and may instead be supplied from or removed by or to external storage and supply/removal systems. Preferably, the example embodiments are inherently energy efficient. Preferably but not exclusively, the electrodes are properly wetted and not oversaturated (over-wetted) or undersaturated (under-wetted) with liquid electrolyte.

[030] In one example aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein the cell is configured to transfer liquid electrolyte from the liquid electrolyte reservoir to a side surface of the spacer that lies beyond the electrodes. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto a side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer.

[031] In another example aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein an end of the spacer that lies beyond the electrodes is positioned inside the liquid electrolyte reservoir. That is, in another aspect, an end surface of the spacer is positioned beyond the first gas diffusion electrode and the second electrode, and the end surface of the spacer is positioned within the liquid electrolyte reservoir. Preferably, the cell is also configured to transfer liquid electrolyte from the hquid electrolyte reservoir to a side surface of the spacer that lies beyond the electrodes and outside the reservoir. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto a side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer.

[032] In another example aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein the cell is configured to transfer liquid electrolyte from the liquid electrolyte to a side surface of the spacer that lies beyond the electrodes, and wherein that side surface of the spacer abuts or is close to the outside of the reservoir. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto a side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer.

[033] In another example, a structure with a small gap may be formed above the side surface of the spacer, termed here a ‘narrow gap’ structure, and this narrow gap structure facilitates or helps control the transfer of the liquid electrolyte from the liquid electrolyte reservoir to the side surface of the spacer that lies beyond the electrodes. Preferably but not exclusively, a narrow gap structure is sufficiently narrow to utilise a capillary action to help distribute the liquid evenly and uniformly on the side surface of the spacer.

[034] In another example the aperture is an overflow weir. In another example when a height of the liquid electrolyte in the liquid electrolyte reservoir is at a height of the overflow weir, and further liquid electrolyte is added, then the liquid electrolyte transfers onto the side surface of the porous capillary spacer. In another example the aperture is constricted or is associated with a valve, and the aperture is located below a height of the liquid electrolyte in the liquid electrolyte reservoir. Optionally, the constricted aperture and/or the valve regulates the transfer of the liquid electrolyte out of the liquid electrolyte reservoir. Preferably, the first gas diffusion electrode is positioned below the liquid electrolyte reservoir, and the second electrode is positioned below the liquid electrolyte reservoir, with respect to the direction of gravity. [035] In another example aspect there is provided an electro- synthetic or electro-energy cell, comprising: a first gas diffusion electrode; a second electrode; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein an intermediate ‘liquid feed structure ’ is physically located between, or at least partially between a side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, and the liquid electrolyte reservoir. Preferably, the spacer, including but not limited to a porous capillary spacer, does not directly contact liquid electrolyte that is within the liquid electrolyte reservoir. Preferably, the spacer, including but not limited to a porous capillary spacer, is spaced apart from, and/or does not directly contact, and/or is not positioned within, the liquid electrolyte reservoir. Preferably, liquid, such as liquid electrolyte, is transferred between the liquid electrolyte reservoir and the spacer, including but not limited to a porous capillary spacer, which may be to a side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, by the intermediate liquid feed structure. Preferably, the intermediate liquid feed structure is separate and distinct from the spacer, including but not limited to a porous capillary spacer. Preferably but not exclusively, the intermediate liquid feed structure is in direct contact with the liquid electrolyte reservoir. Preferably but not exclusively, the intermediate liquid feed structure is in direct contact with a side surface of the spacer, including but not limited to a porous capillary spacer, at one or more locations of the spacer that lie beyond the electrodes. Preferably but not exclusively, the intermediate liquid feed structure, or a second intermediate liquid feed structure, is in direct contact with a side surface of the spacer, including but not limited to a porous capillary spacer, at one or more locations of the spacer that lie beyond the electrodes. Preferably but not exclusively, during operation, liquid electrolyte movement along or within the intermediate liquid feed structure is ‘regulated’-, that is, liquid movement occurs in a pre-determined and controlled manner. Preferably but not exclusively, liquid electrolyte movement along or within the intermediate liquid feed structure is ‘ self -regulated’-, that is, liquid electrolyte movement occurs spontaneously in response to concentration differentials between liquid electrolyte in the intermediate liquid feed structure / reservoir, and liquid electrolyte at the side surface of the spacer, including but not limited to a porous capillary spacer, where it contacts with the intermediate liquid feed structure.

[036] In a first example, the intermediate liquid feed structure is a ‘porous capillary liquid feed structure ’ that spontaneously draws in and maintains a volume of the liquid electrolyte within it by a capillary action. Preferably, liquid electrolyte moves within the porous capillary liquid feed structure under the influence of capillary and/or diffusion and/or osmotic control, in the same way that liquid may move within a porous capillary spacer. Preferably, during operation of the cell, at the molecular-level, liquid-phase materials produced by or consumed by the electrochemical reaction spontaneously undertake ‘in-plane ’ migration along the length of the porous capillary liquid feed structure to or from the spacer, including but not limited to a porous capillary spacer. Preferably, this migration occurs under capillary and/or diffusion and/or osmotic control that is ‘self-regulated’ by the concentration differentials present between liquid electrolyte in the porous capillary liquid feed structure/reservoir and liquid electrolyte at the side surface of the spacer, including but not limited to a porous capillary spacer, at its contact points with the porous capillary liquid feed structure. Preferably, the rate at which liquid-phase materials transfer along the porous capillary liquid feed structure to or from the side surface of the spacer, including but not limited to a porous capillary spacer, is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products. (The factors that determine the rate at which liquid may move in a porous capillary material and their use in the selection of a suitable porous capillary material are taught in some detail in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, and are not repeated here).

[037] In a second example, the intermediate liquid feed structure is a ‘surface liquid feed structure ’ that is capable of moving a liquid electrolyte between a side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, and the liquid electrolyte reservoir by a different physical effect to those mentioned above, on the surface of the liquid feed structure, such as a ‘textured surface’, including but not limited to a surface tension effect, a contact angle effect, a hydrophilic-hydrophobic effect, or the like. Preferably but not exclusively, liquid electrolyte is spontaneously induced to move along the surface of the intermediate liquid feed structure by the effect in operation. Preferably but not exclusively, this migration is ‘self-regulated’ by the concentration differentials present between liquid electrolyte at the interface of the (textured) surface liquid feed structure and the reservoir, and liquid at the surface of the spacer, including but not limited to a porous capillary spacer, at its contact points with the intermediate (textured) surface liquid feed structure. Preferably, the rate of migration of liquid-phase materials along the surface of the intermediate surface liquid feed structure to or from the side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products. [038] In a third example, the intermediate liquid feed structure is an ‘ engineered liquid feed structure ’ such as a pipe, a conduit, a channel, a tube, a chamber, a trough, or a construction of any type for conveying a liquid between the side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, and the liquid electrolyte reservoir (other than a porous capillary liquid feed structure and a surface liquid feed structure, as discussed above). Preferably but not exclusively, liquid electrolyte is induced to move within the liquid feed structure by one or a combination of the following: the influence of gravity, or the influence of a physical effect, such as, for example, a siphon effect, or the influence of an engineering device, such as a pump, an ejector, an evactor, eductor, aspirator, vacuum ejector, venturi, venturi pump, jet pump, exhauster, a compressor, or of a man-made component of any type that is capable of moving a liquid-phase fluid. Preferably but not exclusively, during operation of the cell, the ‘flow rate’ of liquid electrolyte between the liquid electrolyte reservoir and the side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, is regulated to occur in a controlled, pre-determined manner. Preferably, the flow rate of the liquid-phase materials along the liquid feed structure to or from the side surface of the spacer, including but not limited to a porous capillary spacer, is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products.

[039] In another aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to transfer the liquid electrolyte from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir. In one example, the cell is configured to continuously or continually allow liquid electrolyte to transfer onto a side surface of the spacer. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[040] In another aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to transfer the liquid electrolyte from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir, and wherein an end surface of the spacer is positioned beyond the first gas diffusion electrode and the second electrode, and the end surface of the spacer is positioned within the liquid electrolyte reservoir. In one example, the cell is configured to continuously or continually allow liquid electrolyte to transfer onto a side surface of the spacer. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[041] In another aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to transfer the liquid electrolyte from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir. In one example, the cell is configured to continuously or continually allow liquid electrolyte to transfer onto a side surface of the spacer. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[042] In example aspects, there are provided example electro- synthetic or electro -energy cells as disclosed herein, wherein liquid electrolyte is transferred from a liquid electrolyte reservoir located at the top or sides of the cell in order to utilise the effect of gravity. In further example aspects, there are additionally, or alternatively, provided example electro-synthetic or electroenergy cells as disclosed herein that remove or consume liquid during operation, wherein liquid electrolyte is transferred from a liquid electrolyte reservoir onto a side surface of the spacer at a feed rate greater than that required to replenish liquid that is removed or consumed during the electrochemical reaction. In further example aspects, there are additionally, or alternatively, provided example electro- synthetic or electro-energy cells as disclosed herein that retain or produce excess liquid during operation, wherein liquid electrolyte is transferred from a liquid electrolyte reservoir onto a side surface of the spacer at a feed rate greater than that required to remove the excess liquid that is retained or produced during the electrochemical reaction. The above are referred to herein as ‘over-feeding’ the cell. In further example aspects, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein liquid electrolyte is transferred at an ‘over-feed’ rate that is 2-times to 20-times the feed rate required to: (i) replenish liquid that is removed or consumed during the electrochemical reaction, or (ii) remove excess liquid that is produced or retained during the electrochemical reaction. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[043] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein the transfer of liquid electrolyte is carried out at a high feed rate that is more than 0.1 g of liquid electrolyte per minute (for a 1 cm wide strip of spacer, which is the normalisation factor). In other examples, the feed rate is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute.

[044] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein, when the transfer of liquid electrolyte is carried out at the abovementioned high feed rate, the high feed rate produces a high flow rate of more than 0.1 g of liquid electrolyte per minute (for a 1 cm wide strip of spacer, which is the normalisation factor) inside the spacer between the first gas diffusion electrode and the second electrode. In other examples, the flow rate in the spacer between the first gas diffusion electrode and the second electrode is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[045] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein the abovementioned high flow rate keeps the concentration of the liquid electrolyte within the spacer between the first gas diffusion electrode and the second electrode, in a narrow range during operation of the cell, thereby avoiding concentration-related changes in the properties of the liquid electrolyte, including but not limited to changes in its conductivity, viscosity or density. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[046] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein, even at the abovementioned high feed rates of liquid electrolyte transfer and accompanying high flow rates of liquid electrolyte within the spacer, the first gas diffusion electrode and the second electrode are properly wetted, and not over- saturated with liquid electrolyte. In example aspects, there are provided example electro -synthetic or electro-energy cells as disclosed herein, wherein the average capillary pressure in the pores of the spacer is sufficient to maintain the first gas diffusion electrode and the second electrode properly wetted, and not over- saturated with liquid electrolyte, including at the abovementioned high feed rates of liquid electrolyte transfer and accompanying high flow rates of liquid electrolyte within the spacer. In example aspects, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the first gas diffusion electrode and / or the second electrode has no capillary pressure whatsoever, or wherein the first gas diffusion electrode and I or the second electrode has a capillary pressure of any particular value, and wherein the capillary pressure in the pores of the spacer is sufficient to maintain the first gas diffusion electrode and the second electrode properly wetted, and not over- saturated with liquid electrolyte. In example aspects there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the capillary pressure in the pores of the spacer exceed the hydrostatic pressure of the head of liquid above the pores, thereby ensuring that the liquid electrolyte is substantially confined within the spacer and does not continuously leak out of the spacer to flood the gas volumes. Preferably, though not necessarily, the spacer is a porous capillary spacer. In example embodiments wherein liquid electrolyte is transferred from a liquid electrolyte reservoir at the top or sides of the cell, onto a side surface of the spacer that extends beyond the electrodes, and wherein no part of the spacer is located within the liquid electrolyte reservoir, the head of liquid includes only liquid in and on the surface of the spacer, and not liquid inside the liquid electrolyte reservoir. Preferably but not exclusively, the lower hydrostatic pressure resulting from the lesser quantity of liquid in the head of liquid, provides for higher maximum cell heights than can be achieved in cells of the types depicted in Figures 1-3.

[047] Accordingly, in example aspects, there are provided example electro-synthetic or electroenergy cells as disclosed herein, wherein the maximum height of the cell is greater than 15 cm. In other examples, the maximum height of the cell is greater than 18 cm, greater than 20 cm, greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm.

[048] In further example aspects, there are provided example electro -synthetic or electroenergy cells as disclosed herein, wherein the first gas diffusion electrode and the second electrode are compressed against the spacer by more than 2 bar. That is, an ‘electrode compression’ or ‘electrode clamping force’ or ‘electrode pressure’ of more than 2 bar is applied in the cell. In other examples, the electrodes are compressed by more than 3 bar, more than 4 bar, more than 5 bar, more than 7 bar, or more than 10 bar against opposite sides of the spacer. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[049] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein the average pore diameter of the spacer is larger than 0.03 pm. In further example aspects, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the average pore diameter of the spacer is, additionally, or alternatively, smaller than 400 pm. In other examples, the average pore diameter of the spacer is smaller than 200 pm, smaller than 100 pm, smaller than 50 pm, smaller than 25 pm, smaller than 15 pm, smaller than 8 pm, smaller than 5 pm, smaller than 3 pm, smaller than 2 pm, or smaller than 1 pm. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[050] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein the thickness of the spacer is less than 0.2 mm, to thereby advantageously diminish the impedance of the cell. In other example aspects, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the thickness of the spacer is less than 0.2 mm, and the height of the cell is greater than 20 cm. In still other example aspects, there are provided example electro -synthetic or electro-energy cells as disclosed herein, wherein the thickness of the spacer is less than 0.2 mm, and the height of the cell is greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm. Preferably, the cell is capable of operating continuously or continually in a sustained fashion under these conditions. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[051] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein a first gas, forming a first gas body, is associated with the first gas diffusion electrode. For example, the first gas diffusion electrode is configured to generate or consume the first gas of the first gas body.

[052] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas within the cell is greater than atmospheric pressure. In other examples, the pressure of the first gas in the cell is greater than 1.1 bara, greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara (where ‘bara’ means bar (absolute), and is distinct from ‘barg’, which means bar (gauge)).

[053] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the second electrode is also a gas diffusion electrode, i.e. a second gas diffusion electrode, and a second gas, forming a second gas body, is associated with the second gas diffusion electrode. For example, the second gas diffusion electrode is configured to generate or consume the second gas of the second gas body.

[054] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the second gas within the cell is greater than atmospheric pressure. In other examples, the pressure of the second gas in the cell is greater than 1.1 bara, greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara (where ‘bara’ means bar (absolute), and is distinct from ‘barg’, which means bar (gauge)).

[055] In example aspects, there are provided example electro- synthetic or electro -energy cells as disclosed herein, wherein the spacer has a bubble point of more than 50 mbar. In other examples, the bubble point is more than 70 mbar, more than 100 mbar, more than 200 mbar, more than 500 mbar, more than 750 mbar, more than 1 bar, more than 2 bar, or more than 5 bar. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[056] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas on the first side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than or less than the pressure of the second gas on the opposite side of the spacer. In examples, the differential in the pressures between the first gas and the second gas may occur or may be made to occur during startup, shutdown or operation of the cell. For example, the differential in the pressure of the first gas and the pressure of the second gas may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the first gas and the second gas may be more than 10 mbar. In other examples, the differential in the pressures between the first gas and the second gas may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar. [057] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir, has a contact area with the liquid electrolyte that is greater than or equal to 1 cm². In other examples, the contact area is greater than or equal to 2 cm², greater than or equal to 3 cm², greater than or equal to 4 cm², or greater than or equal to 5 cm². Preferably but not exclusively, a large contact area of the side surface of the spacer provides for more rapid and higher volume liquid electrolyte transfer. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[058] In example aspects, there are provided example electro-synthetic or electro -energy cells as disclosed herein, wherein the liquid electrolyte contacts the first gas diffusion electrode and / or the second electrode only after first being transported along the spacer from the side surface of the spacer that extends beyond the electrodes, upon which it was transferred from the liquid electrolyte reservoir. Preferably, though not necessarily, the spacer is a porous capillary spacer.

[059] In another aspect there is provided a stack of electro- synthetic or electro-energy cells, comprising: a first electro-synthetic or electro -energy cell; and a second electro- synthetic or electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell; wherein each electro- synthetic or electro-energy cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to allow the liquid electrolyte to transfer from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir.

[060] In another aspect there is provided a method of operating an electro- synthetic or electroenergy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; the method including the steps of: allowing the liquid electrolyte to transfer from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir; transporting the liquid electrolyte via the spacer to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

[061] In another aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; a spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the spacer is positioned outside of the liquid electrolyte reservoir; and an intermediate liquid feed structure, located at least partially between the side surface of the spacer and the liquid electrolyte reservoir, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir to at least part of the side surface of the spacer by the intermediate liquid feed structure.

[062] In another aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a porous capillary spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the porous capillary spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the porous capillary spacer is positioned outside of the liquid electrolyte reservoir; wherein, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto at least part of the side surface of the porous capillary spacer.

[063] In another aspect there is provided a method of operating an electro- synthetic or electroenergy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte reservoir for containing a liquid electrolyte, wherein the liquid electrolyte reservoir includes an aperture; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a porous capillary spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the porous capillary spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the porous capillary spacer is positioned outside of the liquid electrolyte reservoir; the method including the steps of: allowing the liquid electrolyte to transfer from the liquid electrolyte reservoir via the aperture onto at least part of the side surface of the porous capillary spacer; transporting the liquid electrolyte via the porous capillary spacer to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

[064] In one example, liquid electrolyte transfers from the liquid electrolyte reservoir onto the side surface of the spacer, including but not limited to a porous capillary spacer. In another example, liquid electrolyte transfers from a side surface of the spacer that lies or extends beyond the electrodes, including but not limited to a porous capillary spacer, into the liquid electrolyte reservoir. Preferably, the liquid electrolyte transfers continuously or continually. Preferably but not exclusively, the transfer of liquid is induced by one of, or a combination of the following: the influence of gravity; or the use of a device or construction that dispenses liquid continuously or continually fed to it, such as a constricted aperture, an overflow weir (i.e. a waterfall, a dam, a dike, a levee, a barrier, a cataract, a boom, a wall, or a similar construction over which liquid may pass), or the like; or the use of a pump, an ejector, an evactor, eductor, aspirator, vacuum ejector, venturi, venturi pump, jet pump, exhauster, a compressor, or of a man-made component of any type that is capable of moving a liquid-phase fluid.

[065] Preferably but not exclusively, during operation of the cell, the rate at which liquid electrolyte transfers between the reservoir and the side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, is regulated to occur in a controlled, pre-determined manner. Preferably, the rate at which liquid electrolyte transfers is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products.

[066] In one example form, the first gas diffusion electrode is in direct contact with a first gas body. In another example form, the spacer, including but not limited to a porous capillary spacer, is filled with liquid electrolyte. In another example form, an average pore diameter of the porous capillary spacer is more than 0.03 pm and/or less than 400 pm. In another example form, the first gas diffusion electrode is in contact with and adjacent to the first gas body. In another example form, the second electrode is a second gas diffusion electrode and is in contact with and adjacent to a second gas body.

[067] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas on the first side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than the pressure of the second gas on the opposite, second side of the spacer, or wherein the pressure of the second gas on the second side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than the pressure of the first gas on the opposite, first side of the spacer. In examples, the differential in the pressures between the first gas and the second gas may occur or may be made to occur during startup, shutdown or operation of the cell. For example, the differential in the pressures between the first gas and the second gas may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the first gas and the second gas may be more than 10 mbar. In other examples, the differential in the pressures between the first gas and the second gas may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

[068] In another example aspect there is provided an electro-synthetic or electro-energy cell, comprising: a reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the reservoir; a second electrode positioned outside of the reservoir; a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, a side surface of the spacer that lies or extends beyond the electrodes, including but not limited to a porous capillary spacer, being in contact with a liquid feed structure that contacts the reservoir; wherein, the spacer, including but not limited to a porous capillary spacer, is able to fill itself with the liquid electrolyte via the liquid feed structure when liquid electrolyte is placed in the reservoir.

[069] In a further example aspect there is provided an electro- synthetic or electro-energy cell, comprising: a reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the reservoir; a second electrode positioned outside of the reservoir; a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein the spacer, including but not limited to a porous capillary spacer, is able to become hydrated, become wetted, or fill itself with the liquid electrolyte when liquid electrolyte continuously or continually transfers out of the reservoir onto a side surface of the spacer that lies or extends beyond the electrodes, including but not limited to a porous capillary spacer.

[070] In another example aspect there is provided an electro-synthetic water electrolysis cell, comprising: a first gas diffusion electrode configured to generate a first gas and be in direct contact with a first gas body comprising the first gas; a second electrode; and a porous capillary spacer configured to be filled with a liquid electrolyte and positioned at least partially between the first gas diffusion electrode and the second electrode; wherein an average pore diameter of the porous capillary spacer is more than 0.03 pm and/or less than 400 pm, and wherein a side surface of the porous capillary spacer that lies or extends beyond the electrodes is in contact with a liquid feed structure that contacts the reservoir.

[071] In a further example aspect there is provided an electro-synthetic water electrolysis cell, comprising: a first gas diffusion electrode configured to generate a first gas and be in direct contact with a first gas body comprising the first gas; a second electrode; and a porous capillary spacer configured to be filled with a liquid electrolyte and positioned at least partially between the first gas diffusion electrode and the second electrode; wherein an average pore diameter of the porous capillary spacer is more than 0.03 pm and/or less than 400 pm, and wherein liquid electrolyte that continuously or continually transfers out of the reservoir contacts a side surface of the porous capillary spacer that lies or extends beyond the electrodes.

[072] In further example aspects, there are provided example electro-synthetic or electroenergy cell as disclosed herein, wherein the distance between the first gas diffusion electrode and the second electrode is 0.2 mm or less. That is, the inter-electrode separation within the cell is 0.2 mm or less.

[073] In another example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell is an example cell as disclosed herein, and the method comprises applying a voltage across the first gas diffusion electrode and the second electrode, or generating a voltage across the first gas diffusion electrode and the second electrode. [074] In another example aspect there is provided a stack of electro-synthetic or electro-energy cells, comprising: a first electro -synthetic or electro-energy cell; and a second electro-synthetic or electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell; wherein each electro- synthetic or electro-energy cell comprises: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, and the spacer, including but not limited to a porous capillary spacer, positioned outside of the liquid electrolyte reservoir. Preferably, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto a side surface of the spacer that lies or extends beyond the electrodes, including but not limited to a porous capillary spacer.

[075] Preferably, the first electro-synthetic or electro-energy cell is a cell according to any cell as described herein, and the second electro-synthetic or electro-energy cell is a cell according to any cell as described herein. The liquid electrolyte reservoir may be provided as a distinct liquid electrolyte reservoir for each cell, or the liquid electrolyte reservoir may be provided as a common liquid electrolyte reservoir for supplying liquid electrolyte to both the first cell and the second cell.

[076] In another example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, and the spacer, including but not limited to a porous capillary spacer, positioned outside of the liquid electrolyte reservoir; wherein, the liquid electrolyte reservoir includes an aperture. The method including the steps of: allowing the liquid electrolyte to transfer from the liquid electrolyte reservoir via the aperture onto a side surface of the spacer that lies or extends beyond the electrodes, including but not limited to a porous capillary spacer; transporting the liquid electrolyte via the spacer, including but not limited to a porous capillary spacer, to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode. [077] Optionally, when a height of the liquid electrolyte in the liquid electrolyte reservoir is at a height of the overflow weir, and further liquid electrolyte is added, then the liquid electrolyte transfers onto the side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer. Optionally, a feed rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, is regulated by regulating a rate at which the liquid electrolyte is added to the liquid electrolyte reservoir. Optionally, a feed rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, is regulated by a size of the aperture.

[078] In another example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, the electro -synthetic or electroenergy cell comprising: a liquid electrolyte reservoir containing a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the spacer that lies or extends beyond the electrodes, including but not limited to a porous capillary spacer, is in contact with a liquid feed structure that contacts liquid electrolyte within the liquid electrolyte reservoir. The method comprising the steps of: contacting the first gas diffusion electrode and the second electrode with the liquid electrolyte; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

[079] In another example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, the electro -synthetic or electroenergy cell comprising: a liquid electrolyte reservoir containing a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein liquid electrolyte that continuously or continually transfer out of the liquid electrolyte reservoir contacts a side surface of the spacer that lies or extends beyond the electrodes, including but not limited to a porous capillary spacer.

[080] In another example aspect there is provided a stack of electro-synthetic or electro-energy cells, comprising: a first electro -synthetic or electro-energy cell; and a second electro-synthetic or - Z1 - electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell; wherein each electro -synthetic or electro -energy cell is an example cell as disclosed herein.

[081] In another example aspect there is provided a method of operating a stack of electrosynthetic or electro-energy cells to perform an electrochemical reaction, wherein the stack of electro-synthetic or electro -energy cells is an example stack of electro -synthetic or electro-energy cells as disclosed herein, and the method comprises applying a voltage across the first gas diffusion electrode and the second electrode in each stack of electro -synthetic or electro-energy cells, or generating a voltage across the first gas diffusion electrode and the second electrode in each stack of electro-synthetic or electro-energy cells.

[082] In a further example aspect, there is provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the porosity of the spacer is more than 60%, this being preferred for low impedance and high rates of flow of liquid electrolyte, including within but not limited to, porous capillary spacers and porous capillary flow structures. In other examples, the porosity of the spacer is more than 70%, more than 80%, or more than 90%.

[083] In another example aspect, there are provided example electro -synthetic or electroenergy cells as disclosed herein, wherein, when the spacer is filled with liquid electrolyte, it has an ionic resistance of less than 140 m cm² at room temperature.

[084] In another example aspect, there are provided example electro -synthetic or electroenergy cells as disclosed herein, wherein the liquid electrolyte comprises a hydroxide salt and has a pH of at least 10.

[085] In another example aspect, there are provided example electro-synthetic or electroenergy cells as disclosed herein, wherein the first gas diffusion electrode and the second electrode each have a side with a geometric surface area of greater than or equal to 10 cm².

[086] In another example aspect, there are provided example electro-synthetic or electroenergy cells as disclosed herein, wherein the first gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

[087] In another example aspect, there are provided example electro-synthetic or electroenergy cells as disclosed herein, wherein the second electrode is also a gas diffusion electrode and the second gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

[088] In another example aspect, there are provided example electro -synthetic or electroenergy cells as disclosed herein, wherein the movement of liquid electrolyte with the cell is self- regulated.

[089] In another example aspect, there are provided example electro -synthetic or electroenergy cells as disclosed herein, wherein drippers are placed on the liquid electrolyte inlet and outlet of the cell in order to avoid ‘shunt’ currents (also called ‘by-pass’ currents or ‘leakage’ currents) that may occur between cells when multiple cells are stacked into cell stacks. That is, the drippers on the liquid electrolyte inlet and outlet of a cell make the cell immune to shunt currents.

[090] In another example aspect, there are provided example cells as disclosed herein, wherein the cells are reversible, being electro-synthetic cells when operated in one direction and electroenergy cells when operated in the reverse direction. In one example, the cells are water electrolysis cells that produce hydrogen and oxygen from water when operated as electro- synthetic cells, and hydrogen-oxygen fuel cells that produce electricity when provided with hydrogen and oxygen reactants and operated in the reverse direction as electro-energy cells.

BRIEF DESCRIPTION OF THE FIGURES

[091] Illustrative embodiments will now be described solely by way of non-limiting examples and with reference to the accompanying figures. Various example embodiments will be apparent from the following description, given by way of example only, of at least one preferred but nonlimiting embodiment, described in connection with the accompanying figures.

[092] Figure 1 (prior art) depicts, in schematic form, a cross-sectional view of an example electro-synthetic or electro-energy cell as described in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, which are incorporated by reference.

[093] Figure 2 (prior art) depicts, in schematic form, a cross-sectional view of an example electro-synthetic or electro-energy cell of the type depicted in Figure 1, oriented in an upside-down disposition. [094] Figure 3 (prior art) depicts, in schematic form, a cross-sectional view of a second example electro- synthetic or electro -energy cell as described in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, which are incorporated by reference.

[095] Figure 4 depicts a schematic cross-sectional view of the inner elements of a preferred example embodiment electro- synthetic or electro-energy cell, in which an end surface of the spacer is positioned beyond the first gas diffusion electrode and the second electrode, and the end surface of the spacer is positioned within the liquid electrolyte reservoir, and showing the incorporation of additional apertures in the slit in the barrier wall between the reservoir and the cell itself.

[096] Figure 5 depicts an example reservoir plate that may be used to construct a reservoir of the type depicted in Figure 4, showing several apertures at the base of the plate through which liquid electrolyte may transfer onto a spacer.

[097] Figure 6(a) depicts how two reservoir plates of the type shown in Figure 5 may be sandwiched against a spacer to create a liquid reservoir. Figure 6(b) shows a cross-sectional view of the resulting assembly, showing the reservoir that is formed by the two reservoir plates.

[098] Figure 7 depicts a schematic cross-sectional view of the inner elements of a preferred example embodiment electro- synthetic or electro-energy cell wherein a side surface of the spacer beyond the electrodes, abuts or is close to a liquid electrolyte reservoir.

[099] Figure 8 depicts schematic cross-sectional views of the inner elements of preferred example embodiment electro- synthetic or electro-energy cells.

[0100] Figure 9, comprising of Figure 9A and Figure 9B, shows an example electro-synthetic or electro-energy cell with: (a) a spacer, including but not limited to a porous capillary spacer, welded to a polymer cell frame (Figure 9A), (b) a porous capillary liquid feed structure immersed in a liquid electrolyte reservoir on end and pressed up against a spacer, including but not limited to a porous capillary spacer, at the other end (Figure 9A), (c) a ‘top-reservoir’ (Figure 9B), (d) a ‘sidereservoir’ (Figure 9B). [0101] Figure 10 shows an example overall process for assembling an example embodiment electro-synthetic or electro-energy cell.

[0102] Figure 11 illustrates the operation of an example electro-synthetic or electro-energy cell.

[0103] Figure 12 depicts how the example electro -synthetic or electro-energy cells in Figure 12 may be stacked into filter-press-type ‘cell stacks’.

DETAILED DESCRIPTION

[0104] The following modes, features or aspects, given by way of example only, are described to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments.

Definitions

[0105] A ‘reactant’ is a chemical material that is consumed during an electrochemical reaction. A ‘product’ is a chemical material that is produced during an electrochemical reaction. A ‘liquid electrolyte’ is a liquid containing ions in solution that has the capacity to conduct electricity. A ‘conduit’ is a channel, a tube, a chamber, or a trough for conveying a fluid. A ‘manifold’ is one or more pipes, one or more tubes, one or more chambers, or one or more channels with multiple openings, for conveying a fluid. ‘Room temperature’ is defined as 21 °C.

[0106] A ‘liquid-gas’ cell is defined as an electrochemical cell that has at least one liquid-phase reactant or product, and at least one gas-phase reactant or product.

[0107] An ‘electro-energy cell’ is an electrochemical cell that generates electrical power continually or continuously, over indefinite periods of time, for use outside of the cell. Electroenergy cells may require a constant external supply of reactants during operation. The products of the electrochemical reaction may also be constantly removed from such cells during operation. An electro-energy cell may be a liquid-gas cell. An example of an electro-energy cell is a hydrogenoxygen fuel cell. This example is also a liquid-gas cell. [0108] An ‘electro-synthetic cell’ is an electrochemical cell that manufactures one or more chemical materials continually or continuously, over indefinite periods of time, for use outside the cell. The chemical materials may be in the form of a gas, liquid, or solid. Like an electro -energy cell, an electro-synthetic cell may also require a constant supply of reactants and a constant removal of products during operation. Electro- synthetic cells may generally further require a constant input of electrical energy during operation. An electro-synthetic cell may be a liquid-gas cell. An example of an electro- synthetic cell is a water electrolysis cell. This example is also a liquid-gas cell.

[0109] Electro-energy and electro -synthetic cells differ from other types of electrochemical cells, such as batteries, sensors and the like, in that they do not incorporate within the cell body all/some of the reactants they require to operate, nor all/some of the products they generate during operation. These may, instead, be constantly brought in from, or removed to the outside of the cell during operation. For example, electro-energy cells are distinguished from galvanic cells in that galvanic cells store their reactants and products within the cell body. Unlike a battery, an electroenergy cell does not store chemical or electrical energy within it. Similarly, while some electrochemical sensors may consume reactants and generate products in limited quantities during the sensing operation, all / some of these are stored within the cell body itself.

[0110] A ‘ spacer’ is defined as a thin membrane, diaphragm or ionomer that may have inherently high ionic conductance or may be filled or imbued with a liquid electrolyte having a high ionic conductivity, that may be placed between the electrodes of an electro-synthetic or electro-energy cell. A spacer may also be termed a ‘ separator’ . Examples of spacers include but are not limited to: (1) Agfa’s Zirfon PERL® UTP 500, which is used separator in commercial alkaline electrolysis cells, (2) Chemours’ Nafion® membrane separators such as Nafion 115 and Nafion 117 membrane separators, which are used in commercial Polymer Electrolyte Membrane (PEM) electrolysis cells, and (3) Dioxide Materials’ X37-50, which is an anion exchange membrane (AEM) separator used in anion exchange membrane (AEM) electrolysis cells. While Zirfon PERL® UTP 500 is a porous material that becomes filled with conductive alkaline liquid electrolyte during operation and thereby becomes conductive, the Nafion and AEM separators are inherently ion conductive and formally not porous at all. Their ionic conductivity derives, at least in part, from their polymeric structure, which contains ionizable groups that facilitate ion migration through them. They may, however, become imbued with a liquid electrolyte that amplifies their conductivity. For example, AEM separators are typically used and operated with highly conductive aqueous KOH electrolyte that becomes imbued into the polymer lattice of the separator, thereby significantly increasing their ionic conductivity.

[0111] The ‘electrode-spacer-electrode’ assembly of an electro-synthetic or electro-energy cell is that portion of the cell wherein the spacer lies between the two electrodes.

[0112] A ‘zero-gap’ electrochemical cell is a cell in which there is no gap between the electrodes and the inter-electrode spacer. That is, in a ‘zero-gap’ cell, the electrodes are tightly sandwiched against, or abut, opposite sides of the inter-electrode spacer.

[0113] The ‘reaction zone’ of an electrode in an electro-energy or electro- synthetic cell is a region in and about the surface of the electrode, where it faces the spacer. If the electrode is porous, for example if it is a gas diffusion electrode, the reaction zone may extend from the spacer-facing surface of the electrode some distance into the thickness of the electrode. The reaction zone of a cell, being an electro-energy or electro -synthetic cell, is a region that incorporates the reaction zones of both electrode in the cell.

[0114] A ‘half-cell’ is that part of an electro-energy or electro-synthetic cell that is associated with only one of the electrodes. For example, a cathode half-cell may be the chamber within the electro-energy or electro-synthetic cell that contains the cathode electrode and that lies on the cathode- side of the inter-electrode spacer. An anode half-cell may be the chamber within the electro-energy or electro -synthetic cell that contains the anode electrode and that lies on the anodeside of the inter-electrode spacer. In many traditional electro-synthetic cells, for example water electrolysis cells, the half-cells are completely flooded with liquid electrolyte.

[0115] The term ‘liquid electrolyte’ as used herein is defined to mean the liquid that is present and used in an electro- synthetic or electro-energy cell. In some cells, the liquid may be conductive (such as, for example, 1 M KOH, 6 M NaOH, 1 M H2SO4, or 4.5 M HC1). In other cells the liquid may be non-conductive (such as, for example, the de-ionized water that is used in Polymer Electrolyte Membrane electrolysis cells or fuel cells).

[0116] A ‘porous material’ is a solid material containing open space (‘void’ space) not occupied by the main framework of atoms or molecules that make up the structure of the solid. [0117] The ‘porosity’ of a porous material is defined as the ratio of the volume of void space divided by the total volume of the porous material, expressed as a percentage.

[0118] A ‘capillary’ or a ‘pore’ is a minute structure within a porous material through which a liquid or gas may pass.

[0119] The ‘pore diameter’ of a pore within a porous material is the idealised diameter of the pore.

[0120] The ‘average pore diameter’ of pores within a porous material is the average idealised diameter of the pores present in the porous material, by number, as measured using a gas porometer.

[0121] ‘Capillary action’ involves liquids being drawn into, held in and induced to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. It can be seen in the drawing up and holding of liquids between the hairs of a paint brush, in a thin tube, or in porous materials like paper or plaster. Such capillary-induced action is typically driven by intermolecular forces between the liquid and the surrounding solid surfaces. Within porous materials, capillary action occurs because of the combination of surface tension (which is created by cohesion within the liquid) and attractive forces between the liquid and the container wall. Once drawn up, the liquids may typically be held indefinitely at up to an elevated height, known as the maximum column height.

[0122] ‘Capillary pressure’ is the external pressure that needs to be applied to wholly counteract the capillary action. That is, it is the pressure that, if exerted upon a liquid drawn up by a capillary action, will cause the liquid to return to the location it would have occupied if the capillary action had not occurred. Capillary pressure may also be considered to be the pressure with which such a liquid is held within the pores or capillaries of a material that exerts the capillary action. The ‘capillary pressure’ of a porous material containing liquid, is therefore defined as the gas pressure required to push the liquid out of the average diameter capillaries within the porous material, as measured using a gas porometer.

[0123] The ‘bubble point’ of a porous material containing liquid, is defined as the gas pressure required to push the liquid out of the largest capillaries within the porous material, as measured using a gas porometer, and described in the Applicant's International Patent Publication Nos.

W02022056603, W02022056604, W02022056605, and W02022056606.

[0124] A ‘porous capillary spacer’ is a type of spacer, which comprises a porous material that uses a capillary action to draw in and maintain a column height of liquid electrolyte within the porous capillary spacer itself, where the liquid electrolyte forming the column height is confined within the volume of the porous capillary spacer and displays a capillary pressure. Porous capillary spacers and their properties are described in detail in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, which are incorporated by reference. It should be understood the ‘porous capillary spacer’ alternatively can be described as: ‘a porous spacer’, ‘a porous electrode spacer’, ‘a porous capillary electrode spacer’, ‘a porous spacer with fluidic pathways’, ‘a porous electrode spacer with fluidic pathways’, ‘a porous capillary separator’, ‘a porous separator’, ‘a porous electrode separator’, ‘a porous capillary electrode separator’, ‘a porous separator with fluidic pathways’, or ‘a porous electrode separator with fluidic pathways’.

[0125] ‘Column height’ is defined as the (actual) ‘height’ of a column of liquid confined within a porous capillary spacer by capillary action, including during operation of an example embodiment cell. The term ‘height’ is defined as the height above the surface of a reservoir of liquid into which the porous capillary spacer is dipped. If the porous capillary spacer is not dipped into a reservoir of liquid, then it is defined as the height above the bottom end (bottom distal end) of the porous capillary spacer.

[0126] ‘Maximum column height’ is defined as the highest (theoretical) ‘height’ of a column of liquid that can be maintained within a porous capillary spacer by capillary action when the porous capillary spacer itself has hypothetically infinite height. The term ‘height’ is defined as the height above the surface of a reservoir of liquid into which the porous capillary spacer is dipped. If the porous capillary spacer is not dipped into a reservoir of liquid, then it is defined as the height above the bottom end (bottom distal end) of the porous capillary spacer.

[0127] The term ‘flow rate’ as used herein, is defined as the mass of liquid per unit time that flows through and within a strip of spacer, including but not limited to a porous capillary spacer, normalised to a 1 cm width and fully imbued with liquid. The flow rate may also be termed the ‘throughput’ of liquid electrolyte inside the spacer. The flow rate within a porous capillary spacer may be induced by the influence of capillarity only. When measured with flow upward, against gravity, from a liquid reservoir at the base, the ‘flow rate’ typically declines with increasing height of the porous capillary spacer. The ‘flow rate’ at a particular ‘height’ is then defined as the flow rate at that height above the surface of a reservoir of liquid at its base into which the porous capillary spacer is dipped, as measured using the technique employed for collecting the measured data in the Applicant’s International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, which are incorporated by reference. If the porous capillary spacer is not dipped into a reservoir of liquid, then it is defined as the ‘flow rate’ at that height above the bottom end (bottom distal end) of the porous capillary spacer.

[0128] A ‘capillary-based’ electro-synthetic or electro-energy cell is an electro-synthetic or electro-energy cell utilizing a porous capillary spacer between the electrodes.

[0129] ‘Diffusion’ is the spontaneous net movement of liquid-phase or gas-phase molecules from a region of higher concentration to a region of lower concentration, with the tendency to equalize the concentrations in both regions.

[0130] ‘Osmosis’ is the spontaneous movement of water molecules from a region of low solute concentration to a region of high solute concentration, typically under circumstances where the solute itself is not as free to move in the opposite direction (e.g. when there is a membrane that is not permeable or poorly permeable to solute between the two regions).

[0131] An electrochemical cell is ‘self-regulating’ when the rate of supply of reactants to and/or the rate of removal of products from the reaction zones at the electrodes, inherently adjusts itself according to, and in response to the rate of the electrochemical reaction. That is, a faster rate of electrochemical reaction spontaneously leads to a faster supply of reactants and removal of products, while a slower electrochemical reaction rate yields a slower supply of reactants and removal of products to/from the reaction zones.

[0132] A surface of a spacer that lies or extends ‘beyond the electrodes’ is defined herein as a surface of a spacer, that is a partial surface area of the total surface area of the spacer, that is not abutted by or overlapped by an electrode and lies or extends outside of the inter-electrode gap of an electro-synthetic or electro-energy cell. That is, the surface of the spacer lies or extends outside of the ‘electrode-spacer-electrode’ assembly of the cell. Reference to a surface of the spacer that extends beyond an electrode may refer to all of the surface of the spacer that extends beyond the electrode, or to part of the surface that extends beyond the electrode.

[0133] A ‘side surface’ of a spacer is defined herein as a surface of a spacer, that forms a side of the spacer, where that side is separated from a second, substantially parallel side only by the thickness of the spacer. That is, to determine the thickness of a spacer, a measurement must be made from one side surface of the spacer to the other, substantially parallel side surface that is separated from it by only the thickness of the spacer. The plane of a side surface is substantially parallel to the overall plane of the spacer. Each side surface may typically have a larger surface area than any other surface on the spacer. That is, the side surfaces of a spacer may typically form a large proportion of the overall surface area of the spacer. Typically, a spacer will have two side surfaces, being a ‘left side surface’ and a ‘right side surface’ on opposite sides of the spacer.

[0134] An ‘end surface’ of a spacer is defined herein as a surface of the spacer that lies on an edge of the spacer and has a plane that is orthogonal (at 90°) to the overall plane of the spacer. An edge surface may typically have a surface area equal to or corresponding to a cross-sectional area of the spacer. An end surface may typically form a tiny proportion of the overall surface area of the spacer. An end surface may generally be the farthest surface at a distal end of the spacer. Typically, a spacer will have an end surface at a distal end positioned between, or joining, a ‘left side surface’ and a ‘right side surface’ of the spacer.

[0135] A ‘side surface’ of a spacer that lies or extends ‘beyond the electrodes’ is defined herein as a partial surface area of a total side surface area of the spacer, that is not abutted by or overlapped by an electrode and lies or extends outside of the inter-electrode gap of an electro- synthetic or electro-energy cell. A ‘side surface’ of a spacer that lies or extends ‘beyond the electrodes’, may in some (but not all) examples be generally (i.e. substantially) vertical with respect to the direction of gravity, or be generally (i.e. substantially) parallel to a surface of an electrode.

[0136] An ‘end surface’ of a spacer that lies or is positioned ‘beyond the electrodes’ is defined herein as a surface of a spacer, that is a partial surface area of the total surface area of the spacer, that is not abutted by or overlapped by an electrode and lies or is positioned outside of the interelectrode gap of an electro- synthetic or electro -energy cell, and that is the farthest surface at a distal end of the spacer. In some (but not all) examples, an ‘end surface’ of a spacer that lies or is positioned ‘beyond the electrodes’ might be generally (i.e. substantially) horizontal with respect to the direction of gravity, or might be generally (i.e. substantially) perpendicular to a surface of an electrode.

[0137] The term ‘transfer’ as used herein is defined to refer to the movement of a liquid from a reservoir to a spacer, or from a spacer to a reservoir, and is defined to include any mode by which the liquid may move in this respect, including but not limited to: drip, drop, flow, pour, run, spray, migrate, or pass.

[0138] The term ‘feed rate’ as used herein is defined to refer to the rate at which liquid is ‘transferred’ between a reservoir and a spacer, as defined above.

[0139] A ‘gas diffusion electrode’ is defined herein as any electrode through which a gas may pass.

[0140] A gas-producing electrode is herein defined as being ‘bubble-free’ if, during operation, no bubbles can be discerned to form on at least a portion of its surface using the human eye, or if it can be demonstrated using analysis that less than 10% of the electrons flowing through the electrode produce gas in the form of gas bubbles at the electrode. The method of analysis involves voltage fluctuation measurements and is described in Figures 4(a)-(c) and associated text in the scientific paper entitled “A High-Performance Capillary-Fed Electrolysis Cell Promises more Cost-Competitive Renewable Hydrogen” in the journal Nature Communications, 2022, Vol. 13, page 1304 (https://doi.org/10.1038/s41467-022-28953-x), and in Figure 5 and associated text in the scientific paper entitled “Bubble detection on the cathode and anode of a high-performing capillary-fed water electrolysis cell“ in the journal Sustainable Energy Fuels, 2023, Vol. 7, page 4450.

[0141] An electrode is defined as being ‘properly wetted’ or ‘saturated’ (i.e. not ‘oversaturated’) with liquid electrolyte when the electrode is substantially or to all-intents-and-purposes or on- average covered with sufficient liquid electrolyte to allow for high energy efficiency during operation (i.e. it is not overwhelmed or over-wetted with liquid electrolyte), which condition may be practically demonstrated by: (i) the electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) the electrode enjoys full access to a gaseous reactant during operation (for an electrode that consumes gas during operation). [0142] An electrode is defined as being “oversaturated” or “over-wetted” with liquid electrolyte when it is substantially or to all-intents-and-purposes or on-average over-wetted or overwhelmed with liquid electrolyte, such that: (i) the electrode produces gas bubbles during operation - i.e. it is not ‘bubble-free’ (for an electrode that produces a gas during operation), or (ii) the electrode has reduced access to a gaseous reactant during operation (for an electrode that consumes gas during operation). An electrode is defined as being “undersaturated” or “under-wetted” with liquid electrolyte when it is substantially or to all-intents-and-purposes or on-average insufficiently wetted or under-wetted and, consequently, unable to operate energy efficiently.

[0143] A ‘reservoir’ is a part of an apparatus in which liquid is held. In the case of electro-energy or electro- synthetic cells of the type described herein, it is a container within which liquid electrolyte is held.

[0144] A ‘reservoir plate’ is a plate-like structure that, when sandwiched tightly against a spacer, forms a reservoir within which liquid electrolyte may be held.

[0145] A ‘reservoir wall’ is a containment structure that forms a liquid-impermeable wall of a reservoir.

[0146] A cell is defined as being ‘over-fed’ if the transfer of liquid electrolyte from a liquid electrolyte reservoir onto a side surface of a spacer, including but not limited to a ‘porous capillary spacer’, that extends beyond the electrodes, is carried out at a higher feed rate of liquid electrolyte than is required to replenish liquid that is removed or consumed in the electrochemical reaction (for example, removed through evaporation, or consumed as a reactant of the electrochemical reaction).

[0147] A ‘narrow gap’ structure is defined as a structure at or near to a surface of a spacer that provides a narrow gap between the surface of the spacer and another structure, wherein liquid is induced to transfer in a more controlled way into the narrow gap and thereby to transfer onto the surface of the spacer, for example onto a side surface of the spacer. Preferably but not exclusively, a narrow gap structure is sufficiently narrow to utilise a capillary action to help control the rate of, and distribute the liquid transferring evenly and uniformly onto a side surface of the spacer.

[0148] A ‘liquid feed structure’ is defined as a cell component that, when placed between a liquid reservoir, such as a liquid electrolyte reservoir, and a surface of a spacer, for example a side surface of the spacer, the spacer including but not limited to a porous capillary spacer, whilst simultaneously being in contact with both, may transfer liquid to or from the reservoir to a side surface of the spacer, including but not limited to a porous capillary spacer.

[0149] A ‘porous capillary liquid feed structure’ is defined as a type of liquid feed structure that comprises a porous material that uses a capillary action to draw in and maintain liquid electrolyte within itself, where the liquid electrolyte is confined within the volume of the porous capillary liquid feed structure and displays a capillary pressure. In general, a porous capillary liquid feed structure must be capable of facilitating a flow rate through it that can sustain the flow rate within a porous capillary spacer with which it is in contact. Preferably, such flow occurs under capillary and/or diffusion and/or osmotic control that is ‘self-regulated’; i.e. is driven by the concentration differentials present between liquid in the porous capillary liquid feed structure/reservoir and liquid at the surface of the porous capillary spacer, at its contact points with the porous capillary liquid feed structure.

[0150] A ‘surface liquid feed structure’ is defined as a type of liquid feed structure that comprises a surface to which a liquid may adhere and along which the liquid may move in response to an external stimulus, for example, a concentration differential between the liquids at two ends of the surface liquid feed structure, or a physical effect, such as a contact angle effect.

[0151] An ‘engineered liquid feed structure’ is defined as a type of liquid feed structure capable of conveying a liquid, that is engineered into a cell, such as a pipe, a conduit, a channel, a tube, a chamber, a trough, or a construction of any type for moving a fluid between the surface of the spacer, for example a side surface of the spacer, the spacer including but not limited to a porous capillary spacer, and the liquid reservoir, such as a liquid electrolyte reservoir (other than a porous capillary liquid feed structure and a surface liquid feed structure, as discussed above). Preferably but not exclusively, liquid is induced to move within the liquid feed structure by one or a combination of the following: gravity, a physical effect, such as, for example, a siphon effect, or an engineering device, such as a pump, an ejector, an evactor, eductor, aspirator, vacuum ejector, venturi, venturi pump, jet pump, exhauster, a compressor, or of a man-made component of any type that is capable of inducing movement in a liquid-phase fluid. Preferably but not exclusively, the feed rate at which liquid transfers between the reservoir and a side surface of the spacer, including but not limited to a porous capillary spacer, is regulated. [0152] ‘Electrode compression’ or ‘electrode clamping force’ or ‘electrode pressure’ herein refers to the pressure with which two electrodes are compressed against opposite sides of an intervening spacer, including but not limited to a porous capillary spacer. Such compression may be delivered by springs or washers on the tie rods compressing the cell or cell stack, or by a spring fitting within the cell.

[0153] The ‘energy efficiency’ of an electro-synthetic cell is herein defined as the net energy present within a single unit output of a chemical product, divided by the net energy consumed by the cell to produce that same unit output of the chemical product, expressed as a percentage. The ‘energy efficiency’ of an electro-energy cell is herein defined as the energy produced by the cell per unit time, divided by the maximum theoretical energy that may be produced by the cell per unit time, expressed as a percentage.

[0154] ‘Top’, ‘above’, ‘bottom’ and ‘below’ as used herein refer to an orientation of the cell or the cell components with respect to the direction of gravity.

Preferred Embodiment Electro-Synthetic or Electro-Energy Cells

[0155] The inventors have surprisingly discovered that electro-synthetic and electro-energy cells, including but not limited to capillary-based electro-synthetic and electro-energy cells such as those depicted in Figures 1-3, may be induced to display improved and/or more sustained operation if liquid electrolyte is continuously or continually transferred from a liquid electrolyte reservoir at the top or side of the cell to a side surface of the spacer, including but not limited to a ‘porous capillary spacer’, that lies or extends beyond the electrodes. The term ‘transfer’ includes any mode by which the liquid may move, including but not limited to: drip, drop, flow, pour, run, spray, migrate, or pass. Such transfer of liquid electrolyte may maintain the spacer hydrated, wetted, or imbued with liquid electrolyte during operation of the cell, thereby avoiding the need to fill one or both of the half-cells with liquid electrolyte, or circulate humidified gases through one or both of their respective half-cells. Preferably but not exclusively, liquid electrolyte is transferred from the liquid electrolyte reservoir onto a side surface of the spacer only, including but not limited to a ‘porous capillary spacer’, and not directly onto the surface of an electrode to thereby avoid oversaturation of the electrode with liquid electrolyte, and provide for high energy efficiency during operation. Preferably but not exclusively, liquid electrolyte is transferred from the liquid electrolyte reservoir onto two side surfaces (i.e. both side surfaces, or the left side surface and the right side surface) of the spacer only, including but not limited to a ‘porous capillary spacer’, and not onto the surface of an electrode.

[0156] Preferably, but not exclusively, such transfer of liquid onto a side surface of a spacer, including but not limited to a ‘porous capillary spacer’, that extends beyond the electrodes, is carried out from a liquid electrolyte reservoir located at the top or sides of the cell in order to utilise gravity, and thereby provide for high throughput of liquid electrolyte (i.e. a high flow rate) within the spacer between the electrodes. Preferably but not exclusively, the flow rate of liquid electrolyte between the electrodes is higher than would have been the case if only an end of the spacer was located within a liquid electrolyte reservoir.

[0157] Preferably, but not exclusively, high throughputs of liquid electrolyte (i.e. high flow rates) of the type described in the paragraphs above and below this paragraph, provide for improved maintenance and uniformity of the liquid electrolyte within the spacer between the electrodes during operation, with an associated improvement in the performance and/or more sustained operation of the electro-synthetic or electro-energy cell. That is, preferably but not exclusively, as well as supplying the required reactants to the electrodes and removing any products, the high flow rate keeps the concentration of the liquid electrolyte within the spacer between the electrodes within a suitably narrow range during operation, thereby avoiding concentration-related changes in the properties of the liquid electrolyte, including but not limited to changes in conductivity, viscosity or density. The concentration of the liquid electrolyte within the spacer between the electrodes, is best kept within suitable ranges, since the properties of the liquid electrolyte change with concentration.

[0158] Preferably, but not exclusively, transfer of liquid from a liquid electrolyte reservoir onto a side surface of a spacer, including but not limited to a ‘porous capillary spacer’, that extends beyond the electrodes, is carried out at a higher feed rate of liquid electrolyte than is required to: (i) replenish liquid that is removed or consumed during the electrochemical reaction (for example, removed through evaporation, or consumed as a reactant of the electrochemical reaction), or (ii) remove excess liquid that is retained or produced during the electrochemical reaction (for example, retained by condensation, or produced as a product of the electrochemical reaction). Preferably, but not exclusively, such higher feed rate than is needed for the electrochemical reaction (i.e. ‘overfeeding’), provides for high throughput of liquid electrolyte (i.e. a high flow rate) within the spacer between the electrodes. Preferably but not exclusively, the flow rate of the liquid electrolyte between the electrodes is higher than it would have been if only an end of the spacer was located within a liquid electrolyte reservoir, including a liquid electrolyte reservoir at the top, sides or bottom of the cell.

[0159] Preferably but not exclusively, ‘over-feed’ rates of the above type are 2-times up to 20- times the feed rate required to: (i) replenish liquid that is removed or consumed in the electrochemical reaction (for example, removed through evaporation, or consumed as a reactant of the electrochemical reaction), or (ii) remove excess liquid that is retained or produced during the electrochemical reaction (for example, retained by condensation, or produced as a product of the electrochemical reaction). The factor of supply rate to consumption and evaporation rate, or to retention and production rate, will depend on the reaction and properties of the electrolyte, but for alkaline electrolysis employing 6 M KOH and operating at 0.5 A/cm² for example, it may be in the order of 5-times the volume flow, which would limit the change in the concentration of the liquid electrolyte between the electrodes during operation, to a few percent. As a further example, if a factor of 2 were used, the concentration of the KOH electrolyte could approximately double between the inlet and the outlet of the cell - which could impact the operation.

[0160] Preferably, but not exclusively, transfer of liquid from a liquid electrolyte reservoir onto a side surface of a spacer, including but not limited to a ‘porous capillary spacer’, that extends beyond the electrodes, is carried out with utilisation of gravity and at a higher feed rate of liquid electrolyte than is required to: (i) replenish liquid that is removed or consumed during the electrochemical reaction (for example, removed through evaporation, or consumed as a reactant of the electrochemical reaction), or (ii) to remove excess liquid that is retained or produced during the electrochemical reaction (for example, retained by condensation, or produced as a product of the electrochemical reaction). Preferably, but not exclusively, such utilisation of gravity and application of an ‘over-feed’ rate that is higher than needed for the electrochemical reaction, provides for a particularly high throughput of liquid electrolyte (i.e. a high flow rate) within the spacer between the electrodes. Preferably but not exclusively, the high throughput of liquid electrolyte (i.e. high flow rate) within the spacer between the electrodes is higher than can be achieved solely through utilisation of gravity or solely with the ‘over-feed’ rate. The inventors consider it likely that the abovementioned particularly high throughput (i.e. high flow rate) within the spacer, including but not limited to a ‘porous capillary spacer’, between the electrodes may derive from the combined effect of gravity coupled with the over-feed rate of liquid electrolyte from the liquid electrolyte reservoir onto the side surface of the spacer. These effects may together induce a surprisingly virtuous, synergistic cycle in which the liquid electrolyte within the spacer is induced to flow faster down the spacer, thereby creating a capacity for the spacer to draw in more liquid electrolyte at its side surfaces.

[0161] A high feed rate of liquid electrolyte from a liquid electrolyte reservoir onto a side surface of a spacer, including but not limited to a ‘porous capillary spacer’, that extends beyond the electrodes, is preferably more than 0.1 g of liquid electrolyte per minute (for a 1 cm wide strip of spacer, which is the normalisation factor) at all locations and heights between the electrodes. In other examples, the feed rate is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute.

[0162] A high throughput of liquid electrolyte (i.e. a high flow rate) within the spacer between the electrodes is preferably more than 0.1 g of liquid electrolyte per minute (for a 1 cm wide strip of spacer, which is the normalisation factor) at all locations and heights between the electrodes. In other examples, the feed rate is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute. Such flow rates are notably higher than the flow rate of more than 0.0014 g per minute at a height of more than 8 cm within a porous capillary spacer that was considered advantageous in electro-energy and electro- synthetic cells of the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606.

[0163] A feature of example cells is that their electrodes are properly wetted and not substantially over- saturated or overwhelmed with liquid electrolyte, including during operation. Example cells that generate gases at one or more of their electrodes may thereby directly produce bulk gases from a liquid electrolyte without visible formation of gas bubbles at the electrode in the electrolyte. Such ‘bubble-free ’ gas generation may provide important benefits over conventional gas-generating cells that produce gas in the form of gas bubbles within a liquid electrolyte. These benefits may include higher energy efficiency, due to an avoidance of the energy needed to form gas bubbles, and the fact that the electrode surfaces may be maintained free of bubbles and available for the electrochemical reaction. In particular, the crevices, cracks and defects on the surface, which are generally the most active catalytic sites, may be maintained free and available for catalysis, whereas they are typically the first place that gas bubbles form and to which they cling the most tenaciously. Bubble coverage of electrode active surfaces may decrease the energy efficiency of gas generating cells because of such impediments. Bubble-free operation of this type may be facilitated by the capillary pressure of the spacer, which may inhibit bubble formation by increasing the already high partial pressures needed to nucleate a gas bubble from a dissolved gas. That is, at the spacer, a nucleating gas bubble would have to not only push itself up, but also push away the liquid in a capillary that is held there with a notable capillary pressure. Example cells that consume gas at one or more electrodes may similarly enjoy improved energy efficiency as the gasconsuming electrodes, being properly wetted and not over- saturated with liquid, may provide for full access to a gaseous reactant during operation.

[0164] Surprisingly, even utilisation of gravity coupled with a high over-feed rate of liquid electrolyte from a reservoir at the top of the cell, onto a side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, which leads, in turn, to a particularly high throughput (i.e. a particularly high flow rate) of liquid electrolyte within the porous capillary spacer between the electrodes, may not cause the electrodes to become substantially over- saturated with liquid electrolyte. That is, even at high flow rates of liquid electrolyte within a spacer, including but not limited to a porous capillary spacer, between the electrodes, the electrodes may be sustainably maintained properly wetted, and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0165] The inventors have found that this may be primarily due to the capillary pressure in the pores of the spacer, including but not limited to a porous capillary spacer. The capillary pressure in the pores of the electrodes may have a lesser effect, including little to no effect. That is, the capillary pressure of the electrode pores, both absolute and relative to the capillary pressure of the porous capillary spacer, may not substantially influence the extent to which the electrodes are wetted in example cells. This property may provide for high energy efficiency despite liquid electrolyte being transferred at high over-feed rates from the liquid electrolyte reservoir to a side surface of the spacer, including but not limited to a porous capillary spacer, that lies beyond the electrodes, during operation. [0166] Accordingly, in one example form, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the capillary pressure in the pores of the spacer, including but not limited to a porous capillary spacer, is sufficient to maintain the electrodes in a properly wetted state, in which they are not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation). In another example, preferably, though not necessarily, the capillary pressure in the pores of the spacer exceeds the hydrostatic pressure of the head of liquid.

[0167] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein electrodes having pores with any capillary pressure, including no capillary pressure, may be employed, provided only that the capillary pressure in the pores of the spacer, including but not limited to a porous capillary spacer, is sufficient to maintain the electrodes in a properly wetted state, in which they are not over-saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0168] In another example form there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the capillary pressure in the pores of the spacer exceeds the hydrostatic pressure of the head of liquid above the pores, thereby ensuring that the liquid electrolyte is substantially confined within the spacer and does not continuously leak out of the spacer to flood the gas volumes. Preferably, though not necessarily, the spacer is a porous capillary spacer. In example embodiments wherein liquid electrolyte is transferred from a liquid electrolyte reservoir at the top or sides of the cell, onto a side surface of the spacer that extends beyond the electrodes, and wherein no part of the spacer is located within the liquid electrolyte reservoir, the head of liquid includes only liquid in and on the surface of the spacer, and not liquid inside the liquid electrolyte reservoir. The lower hydrostatic pressure resulting from the lesser quantity of liquid in the head of liquid, may provide for higher maximum cell heights than can be achieved in cells of the types depicted in Figures 1-3. That is, one outcome of the above features (and the unusually high flow rates described several paragraphs earlier) is that the inventors have found that the maximum height of example electro-synthetic or electro-energy cells as disclosed herein, is not limited in the same way that they were in electro-synthetic and electro-energy cells of the type described in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606.

[0169] Accordingly, in another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the maximum height of the cell is greater than 15 cm. In other examples, the maximum cell height is greater than 18 cm, greater than 20 cm, greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm.

[0170] The inventors have further found that compression of the electrodes against opposite sides of the spacer, including but not limited to a porous capillary spacer, may influence the extent to which the electrodes are wetted in example cells and may be useful in this respect. The effect of compressing the electrodes against opposite sides of the spacer is to release some liquid from the spacer to thereby better wet or properly wet the electrodes.

[0171] Accordingly, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the electrodes are compressed against opposite sides of the spacer, including but not limited to a porous capillary spacer, to thereby maintain the electrodes in a properly wetted state, where they are not over- or under- saturated with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0172] Thus, there are provided example electro -synthetic or electro -energy cells as disclosed herein, wherein the electrodes are compressed against opposite sides of the spacer, including but not limited to a porous capillary spacer, by more than 2 bar. In other examples, the electrodes are compressed against opposite sides of the spacer, including but not limited to a porous capillary spacer, by more than 3 bar, more than 4 bar, more than 5 bar, more than 7 bar, or more than 10 bar.

[0173] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein a clamping force (or clamping pressure) of more than 2 bar is applied to the compress the electrodes against the spacer, including but not limited to a porous capillary spacer, this being preferred to properly wet the electrodes, and avoid those electrodes being oversaturated or overwhelmed with liquid electrolyte. That is, an ‘electrode compression’ or ‘electrode clamping force’ or ‘electrode pressure’ of more than 2 bar is applied in the cell. In other examples, more than 3 bar, more than 4 bar, more than 5 bar, more than 7 bar, or more than 10 bar is applied.

[0174] The inventors have surprisingly also found that, whereas an average pore diameter of more than 2 pm was advantageous in the porous capillary spacers of electro-synthetic and electroenergy cells of the type described in Figures 1-3 and the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, no such limitation applies to the spacers, including but not limited to the porous capillary spacers, of preferred embodiment cells of the present specification. Indeed, spacers, including but not limited to porous capillary spacers, having average pore diameters as small as 0.03 pm were found to sustainably accommodate high over-feed rates of liquid electrolyte from a reservoir at the top of the cell, onto a side surface of the spacer that extended beyond the electrodes, and the accompanying, resulting high flow rates within the spacer between the electrodes. The inventors consider it likely that the abovementioned virtuous and synergistic amplification of the flow rate of the liquid electrolyte within the spacer between the electrodes, overcomes the poor liquid electrolyte mobility in small pored porous capillary spacers reported in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606.

[0175] Moreover, the higher capillary pressures deriving from small average pore diameters may have provided for improved maintenance of the electrodes in a properly wetted state, that was not over-saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0176] Accordingly, in another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the average pore diameter of the spacer, including but not limited to a porous capillary spacer, is larger than 0.03 pm. In other examples, the average pore diameter of the spacer, including but not limited to a porous capillary spacer, is smaller than 400 pm, smaller than 200 pm, smaller than 100 pm, smaller than 50 pm, smaller than 25 pm, smaller than 15 pm, smaller than 8 m, smaller than 5 pm, smaller than 3 pm, smaller than 2 pm, or smaller than 1 pm.

[0177] The inventors have also found that example cells disclosed herein may operate successfully and sustainably when employing a thin spacer, including but not limited to a porous capillary spacer. In further examples forms therefore, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the thickness of the spacer, including but not limited to a porous capillary spacer, is less than 0.2 mm, this advantageously diminishing the impedance of the cell.

[0178] The inventors have further found that example cells disclosed herein may operate successfully and sustainably when combining a thin spacer, including but not limited to a porous capillary spacer, with a high maximum cell height. This stands in contrast with electro-synthetic or electro-energy cells described in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, which cannot operate sustainably when combining a thin porous capillary spacer with a high maximum cell height.

[0179] Accordingly, in still further examples forms, there are provided example electrosynthetic or electro -energy cells as disclosed herein, wherein the thickness of the spacer, including but not limited to a porous capillary spacer, is less than 0.2 mm, and the height of the cell is greater than 20 cm. In other examples, the thickness of the spacer, including but not limited to a porous capillary spacer, is less than 0.2 mm, and the height of the cell is greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm.

[0180] It has also been found that, to achieve highly efficient operation in electro- synthetic or electro-energy cells of the type described herein, the temperature can be increased. This generally increases the conductivity of the electrolyte and also improves the kinetics of the electrochemical reaction at the electrodes. However, in a low-pressure system this can lead to large amounts of evaporation. For example, at 85°C in an alkaline electrolysis cell at atmospheric pressure, the amount of water evaporated during operation may be about the same as the amount consumed by the electrochemical reaction. In fact, approximately one in every three gas molecules exiting the cell may be a water vapour molecule. In terms of concentration control, this doubles the volume of liquid electrolyte that needs to be fed to the cell to replenish the water that is lost, relative to room temperature. Increasing the gas pressure in the cell reduces the amount of evaporation due to the lower volume flow of gas out of the cell, and therefore it is advantageous for an electrosynthetic or electro-energy cell described herein to be pressurised to above atmospheric pressure.

[0181] A capacity to operate more energy efficiently at high pressures is a feature of example cells in which water is a reactant or a product of the electrochemical reaction (for example, water electrolysis cells or hydrogen-oxygen fuel cells). In such preferred embodiment cells, water is dealt with primarily as a liquid-phase reactant or product. As a liquid-phase reactant or product it may migrate to or away from the reaction zones at the electrodes within the liquid electrolyte inside the spacer. Reactant water that is consumed during the electrochemical reaction may then be replenished by adding make-up water to the liquid electrolyte at a location remote from the electrode- spacer-electrode assembly, while product water that is produced during the electrochemical reaction may similarly be removed from the liquid electrolyte at a location remote from the electrode-spacer-electrode assembly. The capacity for water to be efficiently harnessed as a reactant or product is therefore not dependent on the pressure of the gases or the pressure of the cell. By contrast in, for example, conventional hydrogen-oxygen fuel cells, where water is a product of the reaction, such product water must primarily directly leave one or both of the electrodes in the form of water vapour within the gases. However, the capacity of gases to carry water vapour is diminished by high pressure, meaning that the use of high pressures disfavours efficient removal of a product of the electrochemical reaction. Similarly, in conventional water electrolysis cells, higher pressures are well-known to thermodynamically disfavour improved electrochemical performance. However, in preferred embodiment cells, high pressures act to better suppress bubble formation, providing for improved energy efficiency.

[0182] Accordingly, in other example forms, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the pressure of a gas within the cell is greater than atmospheric, greater than 1.1 bara, greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara (where ‘bara’ means bar (absolute), and is distinct from ‘barg’, which means bar (gauge)).

[0183] When operating example electro-synthetic or electro-energy cells as disclosed herein in a pressurised system, the pressures within the two gas compartments that may be present are controlled by an external engineering system, known as the Balance-of-Plant, which typically incorporates an arrangement of valves, tanks, pumps, and other engineering equipment. Variations in the differential gas pressures across the spacer, including but not limited to a porous capillary spacer, between the two gas-containing chambers in the cell, may occur during operation and various startup / shutdown procedures of the electro-synthetic or electro-energy cell. Variations in the differential of the gas pressure across the spacer, including but not limited to a porous capillary spacer, may also be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. To prevent these pressure fluctuations from causing the gas to pass through the spacer, the spacer must have a sufficient bubble point. The ‘bubble point’ of a porous material containing liquid, is defined as the gas pressure required to push the liquid out of the largest capillaries within the porous material, as measured using a gas porometer.

[0184] Accordingly, in example forms, there are provided example electro- synthetic or electroenergy cells as disclosed herein, wherein the spacer, including but not limited to a porous capillary spacer, has a bubble point of more than 50 mbar. In other examples, the bubble point is more than 70 mbar, more than 100 mbar, more than 200 mbar, more than 500 mbar, more than 750 mbar, more than 1 bar, more than 2 bar, or more than 5 bar.

[0185] In further example forms, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the pressure of one gas on one side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than the pressure of another gas on the opposite side of the spacer. In examples, the differential in the pressures between the two gases may occur or may be made to occur during startup, shutdown or normal operation of the cell. For example, the differential in the pressures may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the two gases may be more than 10 mbar. In other examples, the differential in the pressures between the two gases may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

[0186] The area of the side surface of the spacer beyond the electrodes onto which the liquid electrolyte is transferred, may play a role in amplifying the throughput (flow rate) of liquid electrolyte within the spacer, including but not limited to a porous capillary spacer, between the electrodes. [0187] In further example forms, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein a side surface of the spacer that extends beyond the electrodes, and that is outside of the liquid electrolyte reservoir, as defined herein, has a contact area with the liquid electrolyte that is preferably greater than or equal to 1 cm². In other examples, a side surface of the spacer has a contact area with the liquid electrolyte that is greater than or equal to 2 cm², greater than or equal to 3 cm², greater than or equal to 4 cm², or greater than or equal to 5 cm². The ability of the cells to provide a sufficiently large contact area of the side surface of the spacer provides for more rapid and higher volume liquid electrolyte transfer, which is also directed away from the electrodes.

[0188] In various example aspects, embodiments relate to electrochemical cell architectures, particularly zero-gap electrochemical cell architectures with spacers, including but not limited to porous capillary spacers, between the electrodes, wherein the cell is configured to transfer liquid electrolyte from a liquid electrolyte reservoir onto a side surface of the spacer. Preferably but not exclusively, the spacer extends beyond the electrodes and the cell is configured to transfer liquid electrolyte onto a side surface of the spacer that lies or extends beyond the electrodes. Preferably but not exclusively, liquid electrolyte is not transferred from the reservoir directly onto an electrode.

[0189] Accordingly, in other example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the liquid electrolyte contacts the electrodes only after first being transported along the spacer, including but not limited to a porous capillary spacer, from the side surface of the spacer that extends beyond the electrodes, upon which it was transferred from the liquid electrolyte reservoir.

[0190] In some embodiments, an end of the spacer, including but not limited to a porous capillary spacer, that lies or extends beyond the electrodes is located within the liquid electrolyte reservoir, that is an end surface of the spacer is positioned beyond the electrodes, and the end surface of the spacer is positioned within the liquid electrolyte reservoir, whilst the liquid electrolyte reservoir is also configured to transfer liquid electrolyte onto a side surface of the spacer outside of the reservoir. In other embodiments the spacer abuts or is close to the outside of the liquid electrolyte reservoir, with the liquid electrolyte reservoir configured to transfer liquid electrolyte onto a side surface of the spacer abutting or close to the outside of the liquid electrolyte reservoir. In some embodiments, a structure with a small gap may be formed above the side surface of the spacer, termed here a ‘narrow gap’ structure, and this narrow gap structure may facilitate and help control the transfer of the liquid from the liquid electrolyte reservoir to the side surface of the spacer. In still other embodiments, the spacer may be physically separated from the liquid electrolyte reservoir, wherein an intervening structure, termed here a ‘liquid feed structure’, is configured to transfer liquid electrolyte from the liquid electrolyte reservoir to the side surface of the spacer. The liquid electrolyte reservoir may be located at one of, some of, or all of: the top, a first side, a second side, both of the sides, and/or the bottom of the cell, with respect to the direction of gravity.

[0191] In other example forms, there are provided example cells as disclosed herein, wherein the cells are reversible, being electro-synthetic cells when operated in one direction and electroenergy cells when operated in the reverse direction. In one example, the cells are water electrolysis cells that produce hydrogen and oxygen from water when operated as electro-synthetic cells, and hydrogen-oxygen fuel cells that produce electricity when provided with hydrogen and oxygen reactants and operated in the reverse direction as electro-energy cells.

1. General description of preferred embodiment cells

[0192] In a first aspect there is provided an electro-synthetic or electro-energy cell, comprising a liquid electrolyte, a first gas diffusion electrode, a second electrode, and a spacer, including but not limited to a porous capillary spacer. The spacer is positioned at least partially between the first gas diffusion electrode and the second electrode. The cell is configured to transfer the liquid electrolyte from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir. In one example, the cell is configured to continuously or continually allow liquid electrolyte to transfer onto a side surface of the spacer. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto a side surface of the spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer.

[0193] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein liquid electrolyte is transferred from a liquid electrolyte reservoir located at the top or sides of the cell in order to utilise the effect of gravity, and / or wherein the transfer of liquid electrolyte is carried out at a feed rate higher than that required to replenish liquid that is removed or consumed during the electrochemical reaction, or higher than that required to remove excess liquid that is retained or produced during the electrochemical reaction. This referred to herein as ‘over-feeding’ the cell.

[0194] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the transfer of liquid electrolyte is carried out at a high feed rate that is more than 0.1 g of liquid electrolyte per minute (for a 1 cm wide strip of spacer, which is the normalisation factor). In other examples, the feed rate is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute.

[0195] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the transfer of liquid electrolyte is carried out at the abovementioned high feed rate, and the high feed rate produces a high flow rate of more than 0.1 g of liquid electrolyte per minute (for a 1 cm wide strip of spacer, which is the normalisation factor) inside the spacer between the first gas diffusion electrode and the second electrode. In other examples, the flow rate is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute.

[0196] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the abovementioned high flow rate keeps the concentration of the liquid electrolyte within the spacer between the first gas diffusion electrode and the second electrode, in a narrow range during operation of the cell, thereby avoiding concentration-related changes in the properties of the liquid electrolyte, including but not limited to changes in its conductivity, viscosity or density.

[0197] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein liquid electrolyte is transferred at an ‘over-feed’ rate that is 2-times to 20-times the feed rate required to replenish liquid that is removed or consumed during the electrochemical reaction, or required to remove excess liquid that is retained or produced during the electrochemical reaction. [0198] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein even at the abovementioned high feed rates of transfer and high flow rates of liquid electrolyte within the spacer, the first gas diffusion electrode and the second electrode remain properly wetted, and are not over-saturated with liquid electrolyte.

[0199] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the capillary pressure in the pores of the spacer is sufficient to maintain the electrodes properly wetted, and not over-saturated with liquid electrolyte.

[0200] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, containing electrodes with any or no capillary pressure, wherein the capillary pressure in the pores of the spacer is sufficient to maintain the electrodes properly wetted, and not over-saturated with liquid electrolyte.

[0201] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the capillary pressure in the pores of the spacer exceeds the hydrostatic pressure of the head of liquid above the pores, thereby ensuring that the liquid electrolyte is substantially confined within the spacer and does not continuously leak out of the spacer to flood the gas volumes. Preferably, though not necessarily, the spacer is a porous capillary spacer. In example embodiments wherein liquid electrolyte is transferred from a liquid electrolyte reservoir at the top or sides of the cell, onto a side surface of the spacer that extends beyond the electrodes, and wherein no part of the spacer is located within the liquid electrolyte reservoir, the head of liquid includes only liquid in and on the surface of the spacer, and not liquid inside the liquid electrolyte reservoir. Preferably but not exclusively, the lower hydrostatic pressure resulting from the lesser quantity of liquid in the head of liquid, provides for higher maximum cell heights than can be achieved in cells of the types depicted in Figures 1-3.

[0202] Accordingly, in another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the maximum height of the cell is greater than 15 cm. In other examples, the maximum cell height is greater than 18 cm, greater than 20 cm, greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm. [0203] In another example form, preferably though not necessarily, the first gas diffusion electrode and the second electrode are compressed against opposite sides of the spacer, including but not limited to a porous capillary spacer, by more than 2 bar, to thereby help maintain the electrodes properly wetted, and not oversaturated or undersaturated with liquid electrolyte. In other examples, the electrodes are compressed by more than 3 bar, more than 4 bar, more than 5 bar, more than 7 bar, or more than 10 bar.

[0204] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein a clamping force (or clamping pressure) of more than 2 bar is applied to the first gas diffusion electrode and the second electrode to compress them against the spacer, including but not limited to a porous capillary spacer, this being preferred to maintain the first and the second electrode properly wetted, and avoid those electrodes being oversaturated or undersaturated with liquid electrolyte. That is, an ‘electrode compression’ or ‘electrode clamping force’ or ‘electrode pressure’ of more than 2 bar is applied in the cell. In other examples, the clamping pressure is more than 3 bar, more than 4 bar, more than 5 bar, more than 7 bar, or more than 10 bar.

[0205] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the average pore diameter of the spacer, including but not limited to a porous capillary spacer, is larger than 0.03 pm. In other examples, the average pore diameter of the spacer, including but not limited to a porous capillary spacer, is smaller than 400 pm, smaller than 200 pm, smaller than 100 pm, smaller than 50 pm, smaller than 25 pm, smaller than 15 pm, smaller than 8 pm, smaller than 5 pm, smaller than 3 pm, smaller than 2 pm, or smaller than 1 pm.

[0206] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the maximum height of the cell is greater than 15 cm. In other examples, the maximum height of the cell is greater than 18 cm, greater than 20 cm, greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm.

[0207] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the thickness of the spacer, including but not limited to a porous capillary spacer, is less than 0.2 mm, this advantageously diminishing the impedance of the cell. [0208] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the thickness of the spacer, including but not limited to a porous capillary spacer, is less than 0.2 mm, and the height of the cell is greater than 20 cm. In other examples, the thickness of the spacer, including but not limited to a porous capillary spacer, is less than 0.2 mm, and the height of the cell is greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm.

[0209] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein a first gas, of a first gas body, is associated with the first gas diffusion electrode. In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the second electrode is also a gas diffusion electrode, i.e. a second gas diffusion electrode, and a second gas, of a second gas body, is associated with the second gas diffusion electrode. For example, the first gas diffusion electrode is configured to generate or consume the first gas of the first gas body. In a further example, the second gas diffusion electrode is configured to generate or consume the second gas of the second gas body.

[0210] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas or the second gas within the cell is greater than atmospheric pressure. In other examples, the pressure of the first gas or the second gas in the cell is greater than 1.1 bara, greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara (where ‘bara’ means bar (absolute), and is distinct from ‘barg’, which means bar (gauge)).

[0211] In example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the spacer, including but not limited to a porous capillary spacer, has a bubble point of more than 50 mbar. In other examples, the bubble point is more than 70 mbar, more than 100 mbar, more than 200 mbar, more than 500 mbar, more than 750 mbar, more than 1 bar, more than 2 bar, or more than 5 bar.

[0212] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas on one side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater or smaller than the pressure of the second gas on the opposite side of the spacer. In examples, the differential in the pressures between the first gas and the second gas may occur or may be made to occur during startup, shutdown or operation of the cell. For example, the differential in the pressures may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the two gases may be more than 10 mbar. In other examples, the differential in the pressures between the first gas and the second gas may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

[0213] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein a side surface of the spacer that extends beyond the electrodes, and that is outside of the liquid electrolyte reservoir, has a contact area with the liquid electrolyte that is greater than or equal to 1 cm². In other examples, the contact area is greater than or equal to 2 cm², greater than or equal to 3 cm², greater than or equal to 4 cm², or greater than or equal to 5 2 cm .

[0214] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the liquid electrolyte contacts the electrodes only after first being transported along the spacer, including but not limited to a porous capillary spacer, from the side surface of the spacer that extends beyond the electrodes, upon which it was transferred from the liquid electrolyte reservoir.

[0215] It is to be understood that all of the characteristics or benefits described in the paragraphs following the heading above entitled “Preferred Embodiment Electro-Synthetic or Electro-Energy Cells”, may also be present in example preferred embodiment cells of this section 1.

2. First example preferred embodiment cells in which an end of a spacer is positioned within a liquid electrolyte reservoir

[0216] In another aspect there is provided an electro- synthetic or electro-energy cell, comprising a liquid electrolyte, a first gas diffusion electrode, a second electrode, and a spacer, including but not limited to a porous capillary spacer. The spacer is positioned at least partially between the first gas diffusion electrode and the second electrode. The cell is configured to transfer the liquid electrolyte from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir. An end of the spacer, that has an end surface, and that extends beyond the electrodes, is also positioned inside the liquid electrolyte reservoir. The end surface of the spacer is positioned beyond the first gas diffusion electrode and the second electrode, and the end surface of the spacer is positioned within the liquid electrolyte reservoir. In one example, the cell is configured to continuously or continually allow liquid electrolyte to transfer onto a side surface of the spacer. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto the side surface of the spacer that extends beyond the electrodes, including but not limited to a porous capillary spacer.

[0217] Figures 4-6 describe example preferred embodiment cells, wherein an end surface of the spacer is positioned beyond the first gas diffusion electrode and the second electrode, and the end surface of the spacer is positioned within the liquid electrolyte reservoir (which is located at or about the top of the cell, with respect to the direction of gravity). The reservoir is further configured to transfer liquid electrolyte to a side surface of the spacer outside of the reservoir, preferably but not exclusively where the side surface of the spacer extends beyond the electrodes.

[0218] Such an arrangement may maintain or help to maintain the spacer hydrated, wetted, or imbued with liquid electrolyte during operation of the cell, thereby avoiding the need to fill one or both of the half-cells with liquid electrolyte, or recirculate the gases with external humidification. In the case where the spacer is a porous capillary spacer, the inventors have found that such an arrangement may provide for improved operation as described above (in the paragraphs following the heading above entitled “Preferred Embodiment Electro-Synthetic or Electro-Energy Cells” and in section 1).

[0219] Additionally, for example, porous capillary spacers with higher ‘column heights’ and ‘maximum column heights’ may be used during operation of a cell than may otherwise be possible. Moreover, porous capillary spacers may be induced to display higher ‘flow rates’ at higher heights during operation than may otherwise be possible. Such improvements may, thereby, raise or, at least, ameliorate the strict height limitations that may generally apply to capillary-based cells. That is, capillary-based cells with greater height dimensions may be constructed and operated successfully. As noted above, these benefits appear to arise at least in part because, when coupled with high feed rates or over-feed rates, gravity is better utilised to amplify the flow rate of the liquid electrolyte within the porous capillary spacer between the electrodes. [0220] Figure 4 depicts a cross-section of the inner elements of an example cell 201. The cell includes a first gas diffusion electrode 220 and a second electrode 230, separated by a spacer 210, preferably but not exclusively a porous capillary spacer, containing liquid electrolyte 200. A first gas body 225 associated with the first gas diffusion electrode, and a second gas body 235, associated with the second electrode fill the two half-cells. The inter-electrode volume 239 contains the spacer 210, which is filled with liquid electrolyte 200. The direction 250 is shown of ‘in-plane’ movement of liquid-phase reactants in the liquid electrolyte 200 within the porous capillary spacer 210. The first gas diffusion electrode 220 is separated from the second electrode 230 by an average inter-electrode distance 270.

[0221] Cell 201 in Figure 4 differs from cell 10 in Figure 2, for example, in that the slit 245 (i.e. aperture or opening) in barrier wall 255, which can be considered as part of the liquid electrolyte reservoir, in Figure 4 has been modified relative to the slit 145 in barrier wall 155 in Figure 2. The modification has incorporated additional apertures 245a and 245b between the liquid electrolyte reservoir 240 / barrier wall 255 and the spacer 210. This is counter-intuitive as it would have been expected not to allow liquid electrolyte 200 to escape from the liquid electrolyte reservoir 240 through the barrier wall 255. Unexpectedly, the inventors have discovered surprising benefits of creating one or more apertures in the liquid electrolyte reservoir 240 / barrier wall 255 to purposefully allow liquid electrolyte 200 to transfer from the liquid electrolyte reservoir 240 to the side surfaces of the spacer 210 that are outside of the liquid electrolyte reservoir 240. The benefits are described above (in the paragraphs following the heading above entitled “Preferred Embodiment Electro-Synthetic or Electro-Energy Cells”). Liquid electrolyte 200 from the liquid electrolyte reservoir 240 may transfer through the apertures 245a and 245b onto side surface 285a (i.e. left side surface 285a) and side surface 285b (i.e. right side surface 285b), respectively, of the spacer 210 that lie (i.e. are located) outside of the liquid electrolyte reservoir 240. As shown in the magnified inset in Figure 4, side surfaces 285a and 285b also lie or extend, preferably but not exclusively, beyond the first gas diffusion electrode 220 and the second electrode 230 (i.e. the electrodes), respectively. Preferably, no electrode abuts or is near to the spacer 210. That is, side surfaces 285a and 285b of the spacer 210 preferably but not exclusively, lie (i.e. are located) in the region 260 extending beyond the electrodes 220, 230, not in the region 204 that denotes the ‘electrode-spacer-electrode’ assembly. It should be noted that in one example two apertures 245a and 245b are not required, and one aperture only, either aperture 245a or aperture 245b, may be used. The end surface 258 of the spacer 210 is positioned beyond the first gas diffusion electrode 220 and the second electrode 230, and the end surface 258 of the spacer 210 is positioned within the liquid electrolyte reservoir 240.

[0222] Thus, Figure 4 illustrates an electro-synthetic or electro-energy cell 201, comprising a liquid electrolyte 200, a first gas diffusion electrode 220, a second electrode 230, and a spacer 210, for example a porous capillary spacer. The spacer 210 is positioned at least partially between the first gas diffusion electrode 220 and the second electrode 230. The cell 201 is configured to transfer the liquid electrolyte 200 from a liquid electrolyte reservoir 240 onto at least part of a side surface 285a, 285b of the spacer 210 that extends beyond the first gas diffusion electrode 220 and the second electrode 230, and that is outside of the liquid electrolyte reservoir 240. Preferably, cell 201 is configured to transfer the liquid electrolyte 200 from the liquid electrolyte reservoir 240 onto at least part of each of two side surfaces (left side surface 285a and right side surface 285b) of the spacer 210 that extend beyond the first gas diffusion electrode 220 and the second electrode 230, and that are outside of the liquid electrolyte reservoir 240.

[0223] Preferably but not exclusively, during and after transfer of the liquid electrolyte via the aperture(s) to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not oversaturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0224] Additional apertures, similar to apertures 245a and 245b, may be incorporated at multiple locations in liquid electrolyte reservoir 240 / barrier wall 255. An example of this is shown in Figure 5 and Figure 6.

[0225] Figure 5 depicts a ‘reservoir plate’ 275, which is a component that can be used to fabricate a liquid electrolyte reservoir in a cell. Figure 6(a) depicts how two such reservoir plates 275 may be sandwiched in register, on opposite sides of a spacer 210, to thereby create a reservoir at or about the top of a cell. Figure 6(b) depicts a cross-section of such a reservoir, showing the two reservoir plates 275 sandwiched against opposite sides of the spacer 210. [0226] Figure 5 shows features that may be present in a reservoir plate 275. These include a left reservoir wall 276L, a right reservoir wall 276R, and an outer reservoir wall 2760. The outer reservoir wall 2760 is angled off vertical, in order to taper the reservoir down to a barrier wall 245 at the bottom of the reservoir. The barrier wall 245, which will be pressed tightly against the spacer 210, forms one half of a slit that fits tightly against the spacer 210. Protrusions 279 keep the top of the reservoir away from the spacer 210; the surfaces 279a of the protrusions 279 will be pressed tightly against the spacer 210. Liquid may then be added into the top of the reservoir, via the vacancies created by structures 278 between the protrusions 279. To prevent the reservoir from becoming over-full, a weir 277R and associated overflow channel are present on the right-hand side of the reservoir plate 275. The left-hand side of the reservoir plate 275 also contains a larger overflow channel 277L, which serves as pipe to connect the body of gas at the top of the reservoir to the body of gas at the bottom of the reservoir (on the one side of the spacer 210).

[0227] As can be seen in the magnified inset in Figure 5, several apertures 245a (i.e. one or more apertures 245a) have been included along the barrier wall 245 at the bottom of reservoir plate 275. These apertures 245a constitute an example physical embodiment of the apertures 245a and 245b depicted in Figure 4. That is, the cross-section shown in Figure 4 is a cross-section of the cell at the point where the spacer 210 is sandwiched by the apertures 245a in barrier wall 245 in Figure 5.

[0228] Figure 6(b) shows a cross-section of the entire reservoir that is created by sandwiching two reservoir plates 275 tightly against opposite sides of the spacer 210 (Figure 6(a)). As can be seen in the cross-section in Figure 6(b), each reservoir plate 275 contains an outer wall 2760, as well as a barrier wall 245 (which is tightly pressed against the spacer 210). The outer walls 2760 and barrier walls 245 form the reservoir 240 (which contains liquid 200, including the liquid surface 200a). The protrusions 279 have surfaces 279a pressed tightly against the spacer 210.

[0229] At the bottom of the reservoir 240, on either side of spacer 210, is a small gap 246 formed above the surface of the spacer 210, between it and a downwardly jutting wall 275G of the reservoir plates 275. Such gaps, termed herein a ‘narrow gap’ 246 structure, may be employed to help control the rate of, or facilitate a uniform or even transfer of liquid electrolyte 200 from the reservoir 240 to the side surfaces of the spacer 210 outside of the reservoir 240. Preferably but not exclusively, the gap in such narrow gap structures is sufficiently small to utilize a capillary action to help control the rate of transfer, and distribute the liquid electrolyte 200 evenly and uniformly over the side surfaces of the spacer 210 in the vicinity of narrow gaps 246. In the case shown in Figure 6(b), the narrow gap 246 spontaneously accumulates and then spreads out the liquid electrolyte 200 that transfers onto the side surfaces of spacer 210 from the multiplicity of apertures 245a (i.e. one or more spacers 245a), so that the liquid electrolyte 200 is evenly distributed across the full width of the reservoir plates 274. In this way, the narrow gap structure 246 helps ensure uniform and even transfer of liquid electrolyte 200 from the reservoir 240 to the full width of a side surface of the spacer 210 that is below and outside of the reservoir 240.

[0230] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein a first gas, of a first gas body, is associated with the first gas diffusion electrode. In further example forms, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the second electrode is also a gas diffusion electrode, i.e. a second gas diffusion electrode, and a second gas, of a second gas body, is associated with the second electrode. For example, the first gas diffusion electrode is configured to generate or consume the first gas of the first gas body. In a further example, the second gas diffusion electrode is configured to generate or consume the second gas of the second gas body.

[0231] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas or the second gas within the cell is greater than atmospheric pressure. In other examples, the pressure of the first gas or the second gas in the cell is greater than 1.1 bara, greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara (where ‘bara’ means bar (absolute), and is distinct from ‘barg’, which means bar (gauge)).

[0232] In example forms, there are provided example electro -synthetic or electro-energy cells as disclosed herein, wherein the spacer, including but not limited to a porous capillary spacer, has a bubble point of more than 50 mbar. In other examples, the bubble point is more than 70 mbar, more than 100 mbar, more than 200 mbar, more than 500 mbar, more than 750 mbar, more than 1 bar, more than 2 bar, or more than 5 bar.

[0233] In further example forms, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas on one side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than the pressure of the second gas on the opposite side of the spacer. In examples, the differential in the pressures between the first gas and the second gas may occur or may be made to occur during startup, shutdown or operation of the cell. For example, the differential in the pressures may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the first gas and the second gas may be more than 10 mbar. In other examples, the differential in the pressures between the first gas and the second gas may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

[0234] It is to be understood that all of the characteristics and benefits, including the surprising benefits, noted in section 1 and in the paragraphs following the heading above entitled “Preferred Embodiment Electro-Synthetic or Electro-Energy Cells”, also apply to example preferred embodiments of the type described in this section 2.

[0235] It is further to be understood that, while the example described above and in Figures 4-6 specifically involved a porous capillary spacer, other spacers that do not fit the definition of a porous capillary spacers, may alternatively be used.

[0236] It is further to be understood that apertures, such as apertures 245a or 245b, may have many different physical forms and not only the form shown in the magnified inset in Figure 5. All such aperture forms fall within the scope of this specification.

[0237] Moreover, apertures, such as apertures 245a or 245b, may be incorporated at many different locations in a liquid electrolyte reservoir / barrier wall, and in a variety of numbers and densities. All such arrangements of apertures fall within the scope of this specification.

[0238] It is further to be understood that, while Figure 6(a)-(b) depicts the formation of a reservoir at the top of a cell by sandwiching two reservoir plates in register against opposite sides of the spacer, a reservoir may, alternatively, be created by:

- sandwiching a single reservoir plate against one side of the spacer (for example, when the spacer may be capable of providing an acceptably liquid-tight reservoir wall), or - sandwiching a single reservoir plate against one side of the spacer, and sandwiching an equivalently sized reservoir wall in register with it on the other side of the spacer (for example, when the spacer is too porous to be an acceptably liquid-tight reservoir wall).

[0239] Preferably but not exclusively, during operation of the cell, the feed rate of liquid electrolyte transferring between the reservoir and the side surface of the spacer, including but not limited to a porous capillary spacer, is regulated to occur in a controlled, pre-determined manner. Preferably, the flow rate of liquid-phase materials within the spacer is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products.

3. Second example preferred embodiment cells in which liquid electrolyte transfers onto (or from) a side surface of a spacer that abuts or is close to the reservoir

[0240] In another example aspect there is provided an electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein the cell is configured to transfer liquid electrolyte from the liquid electrolyte to a side surface of the spacer that lies beyond the electrodes, and wherein that side surface of the spacer abuts or is close to the outside of the reservoir. The cell is configured to continuously or continually allow liquid electrolyte to transfer onto a side surface of the spacer. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto a side surface of the spacer, including but not limited to a porous capillary spacer, that lies beyond the electrodes.

[0241] In one example, liquid electrolyte continuously or continually transfers out of the reservoir onto the side surface of the spacer, including but not limited to a porous capillary spacer. In another example, liquid electrolyte continuously or continually transfers from a side surface of the spacer, including but not limited to a porous capillary spacer, into the reservoir. Preferably but not exclusively, the transfer of liquid electrolyte is induced by one or a combination of the following: the influence of gravity; or the use of a device or construction that dispenses liquid continuously or continually fed to it, such as a constricted aperture (e.g. a valve), an overflow weir (e.g. a waterfall, a dam, a dike, a levee, a barrier, a cataract, a boom, a wall, or a similar construction over which liquid may pass), or the like; or the use of a pump, an ejector, an evactor, eductor, aspirator, vacuum ejector, venturi, venturi pump, jet pump, exhauster, a compressor, or of a man-made component of any type that is capable of moving a liquid-phase fluid.

[0242] Preferably but not exclusively, during operation of the cell, the feed rate at which liquid electrolyte transfers between the reservoir and the side surface of the spacer, including but not limited to a porous capillary spacer, is regulated to occur in a controlled, pre-determined manner. Preferably, the flow rate of liquid-phase materials within the spacer is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products.

[0243] In another example there is provided an electro-synthetic or electro-energy cell, comprising a liquid electrolyte reservoir for containing a liquid electrolyte, a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir, and a second electrode positioned outside of the liquid electrolyte reservoir. A spacer, including but not limited to a porous capillary spacer, is positioned at least partially between the first gas diffusion electrode and the second electrode, and the spacer, including but not limited to a porous capillary spacer, is positioned outside of the liquid electrolyte reservoir. Preferably, though not necessarily, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto a side surface of the spacer beyond the electrodes, including but not limited to a porous capillary spacer.

[0244] In another example the aperture is an overflow weir. In another example when a height of the liquid electrolyte in the liquid electrolyte reservoir is at a height of the overflow weir, and further liquid electrolyte is added, then the liquid electrolyte transfers onto the side surface of the porous capillary spacer. Optionally, a feed rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the side surface of the spacer, including but not limited to a porous capillary spacer, is regulated by regulating a rate at which the liquid electrolyte is added to the liquid electrolyte reservoir. Optionally, a feed rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the side surface of the porous capillary spacer is regulated by a size of the aperture. Preferably, the liquid electrolyte reservoir is located at, with respect to the direction of gravity: a top of the cell, and/or a side of the cell. Preferably, the first gas diffusion electrode is positioned below the liquid electrolyte reservoir, and the second electrode is positioned below the liquid electrolyte reservoir, with respect to the direction of gravity.

[0245] In another example the aperture is or is associated with a constricted aperture and/or a valve. The aperture is located below a height of the liquid electrolyte in the liquid electrolyte reservoir. Optionally, the constricted aperture and/or the valve regulates the transfer of the liquid electrolyte out of the liquid electrolyte reservoir.

[0246] In another example there are two or more liquid electrolyte reservoirs. Preferably, the two or more liquid electrolyte reservoirs are located at, with respect to the direction of gravity: a top of the cell, and/or a side of the cell.

[0247] In another example the liquid electrolyte transfers from a side surface of the spacer, including but not limited to a porous capillary spacer, into a lower liquid electrolyte reservoir positioned below the first gas diffusion electrode and the second electrode, with respect to the direction of gravity.

[0248] In another example, the cell is configured such that when the liquid electrolyte reservoir contains the liquid electrolyte, the first gas diffusion electrode and the second electrode are separated from the liquid electrolyte in the reservoir. In another example, the cell is configured such that during operation the liquid electrolyte contacts the first gas diffusion electrode and the second electrode only after first being transported via the spacer, including but not limited to a porous capillary spacer.

[0249] In another example the first gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate. In another example the first gas diffusion electrode is configured to generate a first gas to form a first gas body, a first side of the porous capillary spacer is adjacent a first side of the first gas diffusion electrode, a second side of the porous capillary spacer is adjacent a first side of the second electrode, and a second side of the first gas diffusion electrode is adjacent the first gas body.

[0250] In another example the second electrode is a second gas diffusion electrode. In another example the second gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate. In another example the second gas diffusion electrode is configured to generate a second gas to form a second gas body, and a second side of the second gas diffusion electrode is adjacent the second gas body.

[0251] In another example the first gas diffusion electrode and the second electrode are sandwiched against opposite sides of the spacer, including but not limited to a porous capillary spacer. In another example the distance between the first gas diffusion electrode and the second electrode is 0.2 mm or less. In another example an average pore diameter of the spacer when it is a porous capillary spacer is more than 2 pm. In another example a clamping force (or clamping pressure) of more than 2 bar is applied to the first gas diffusion electrode and the second electrode to compress them against the spacer, including but not limited to a porous capillary spacer.

[0252] In preferred examples, the capillary pressure in the pores of the spacer, for example a porous capillary spacer, is sufficient to maintain the electrodes properly wetted and not oversaturated with liquid electrolyte, for example when an electrode is a gas diffusion electrode. This advantageously limits the amount of liquid electrolyte that can enter the electrodes. Thus, how wet the electrodes become can be controlled using the capillary pressure of the spacer (and the compression of the electrodes against opposite sides of the spacer). That is, the electrodes may be maintained properly wetted and not oversaturated with liquid electrolyte. This is used for bubble-free operation of the cell for example in a cell that produces a gas, by preventing bubble formation which occurs if electrodes become over- wetted (oversaturated), which is undesirable as bubble formation reduces efficiency of the cell. This can also be used to facilitate high energy efficiency in a cell with an electrode that consumes gas, as overs aturation of the electrode with liquid electrolyte may block the reactant gas from contact with the electrode surface. Accordingly, preferred example cells are configured to operate without substantially saturating the electrodes with liquid electrolyte.

[0253] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein a first gas, of a first gas body, is associated with the first gas diffusion electrode. In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the second electrode is also a gas diffusion electrode, i.e. a second gas diffusion electrode, and a second gas, of a second gas body, is associated with the second gas diffusion electrode. For example, the first gas diffusion electrode is configured to generate or consume the first gas of the first gas body. In a further example, the second gas diffusion electrode is configured to generate or consume the second gas of the second gas body.

[0254] In an example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas or the second gas within the cell is greater than atmospheric pressure. In other examples, the pressure of the first gas or the second gas in the cell is greater than 1.1 bara, greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara (where ‘bara’ means bar (absolute), and is distinct from ‘barg’, which means bar (gauge)).

[0255] In example forms, there are provided example electro -synthetic or electro-energy cells as disclosed herein, wherein the spacer, including but not limited to a porous capillary spacer, has a bubble point of more than 50 mbar. In other examples, the bubble point is more than 70 mbar, more than 100 mbar, more than 200 mbar, more than 500 mbar, more than 750 mbar, more than 1 bar, more than 2 bar, or more than 5 bar.

[0256] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas on the first side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than or smaller than the pressure of the second gas on the opposite, second side of the spacer. In examples, the differential in the pressures between the first gas and the second gas may occur or may be made to occur during startup, shutdown or operation of the cell. For example, the differential in the pressures between the first gas and the second gas may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the first gas and the second gas may be more than 10 mbar. In other examples, the differential in the pressures between the first gas and the second gas may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

[0257] It is to be understood that all of the preceding paragraphs of this section 3 also apply to the example embodiments described in sections 1 and 2. It is further to be understood that all of the characteristics and benefits, including the surprising benefits, described in sections 1 and 2 and in the paragraphs following the heading above entitled “Preferred Embodiment Electro-Synthetic or Electro-Energy Cells”, also apply to this section 3 and the example embodiments disclosed therein.

[0258] Figure 7 schematically depicts the internal components of an electro- synthetic or electroenergy cell 301 in which liquid electrolyte transfers between a liquid electrolyte reservoir and a side surface of a spacer that abuts or is close to the outside of the reservoir.

[0259] The electro- synthetic and electro-energy cell 301 comprises a spacer 310, including but not limited to a porous capillary spacer, located between a first gas diffusion electrode 320 and a second electrode 330. The spacer 310, including but not limited to a porous capillary spacer, may completely fill the gap 339 between the first gas diffusion electrode 320 and the second electrode 330 (as depicted in Figure 7) or the spacer 310, including but not limited to a porous capillary spacer, may partially fill the gap 339 between the first gas diffusion electrode 320 and the second electrode 330 (as depicted in Figure 8(b) and not shown in Figure 7). The first gas diffusion electrode 320 and the second electrode 330 may be separated by an average distance 370. The first and second electrodes 320 and 330 respectively, may be connected to a power supply or power receiving unit via electrical connections (not shown in Figure 7). The spacer 310, including but not limited to a porous capillary spacer, may extend beyond the ‘electrode-spacer-electrode’ assembly of the cell itself (denoted by 304) into locations beyond the electrodes where it does not have electrodes abutting it or close to it on one or both sides (denoted by 360a-d).

[0260] In the case where the spacer 310 is a porous capillary spacer, the liquid-phase reactants and/or products of the electrochemical reaction may spontaneously undertake ‘in-plane ’ migration in the liquid electrolyte 300, along the length of the inter-electrode spacer 310 to or from the electrodes 320 and 330. The liquid-phase reactants and/or products may do so under capillary and/or diffusion and/or osmotic control, amongst others, which is ‘ self-regulated’ by the concentration differentials present in the liquid electrolyte and at the reaction zones within or about the inside surfaces of electrodes 320 and 330, where they face the spacer 310. That is, during operation of the cell, liquid-phase reactants and/or products of the electrochemical reaction may move within the liquid electrolyte 300 inside the spacer 310, in the directions 350a or 350b to or from the electrodes 320 and 330.

[0261] The first gas diffusion electrode 320 may be configured to generate or consume a first gas that forms a first gas body 325 in contact with electrode 320. The second electrode 330 may be a gas diffusion electrode and may be configured to generate or consume a second gas that forms a second gas body 335 in contact with electrode 330. At the molecular-level, gas-phase materials produced by or consumed by the electrochemical reaction may migrate in an orthogonal (90°) direction to the liquid-phase materials along continuous gas phase pathways that are separate from and do not interfere with the liquid-phase pathways. That is, gaseous molecules or atoms may migrate to I from their respective gas bodies 325 or 335 through the relevant interface/s to or from the reaction zones of the gas diffusion electrode(s) 320 or 330 respectively, i.e. into or out of the reaction zones within or about the inside surfaces of electrodes 320 and 330 respectively, where they face the spacer 310. Such migrations may occur under (gas) capillary and/or diffusion control along continuous gas-phase pathways connecting the reaction zones within or about the inside surfaces of each electrode 320 or 330, where they face the spacer 310, to each gas body 325 or 335, respectively. The movement of gas-phase materials (reactants or products) may therefore also exhibit self-regulation. Because the pathway of migration of each gas does not overlap with, or interfere with that of the other gas, or with the pathway of liquid migration, gas movements may be independently self-regulated, separately to the self-regulation of the liquid movements. That is, the different gas- and liquid-phase reactants and products may each be subject to their own selfregulation, which does not interfere with the movements of the other reactants and products.

[0262] During operation of the cell, liquid-phase reactants and/or products of the electrochemical reaction may need to be replenished from (if they are consumed in the electrochemical reaction) or removed to (if they are produced in the electrochemical reaction) the liquid electrolyte in a liquid electrolyte reservoir (e.g. liquid electrolyte reservoirs 340a, 340b, 340c and 340d).

[0263] The inventors have surprisingly found that, even at high required liquid flow rates within the spacer to sustain the electrochemical reaction, this may be continually or continuously achieved over indefinite time periods, by transferring liquid electrolyte via an aperture (e.g. apertures 346a or 346b) in a reservoir (e.g. reservoirs 340a or 340b, respectively) onto an abutting or nearby side surface (e.g. side surface 385a (i.e. left side surface 385a) or side surface 385b (i.e. right side surface 385a), respectively) of the spacer 310, beyond the electrodes 320, 330 (in region 360a or 360b, respectively) (i.e. outside of the electrode-spacer-electrode assembly region of the cell 304), or by transferring liquid electrolyte 300 into a reservoir (e.g. reservoir 340d) from a side surface (e.g. side surface 385d) of the spacer 310 beyond the electrodes 320, 330 (e.g. in region 360d) (outside of the region of the cell 304), wherein the spacer 310 includes but is not limited to a porous capillary spacer.

[0264] The inventors have further found that the liquid electrolyte 300 may be transferred in a controlled and directed manner onto or off one or more of the side surfaces of spacer 310 by utilising a ‘narrow gap’ (e.g. narrow gaps 346a, 346b, or 346d) between the reservoir and the abutting or nearby side surface (e.g. side surface 385a, 385b, or 385d, respectively) of the spacer 310 beyond the electrodes (in region 360a, 360b, or 360d, respectively), wherein the spacer 310 includes but is not limited to a porous capillary spacer. A key benefit of using such a narrow gap is that it may avoid any transfer of liquid electrolyte 300 onto or off the electrodes 320 or 330, which may induce over-wetting or oversaturation of the electrodes, with an associated loss of energy efficiency in the electrochemical reaction

[0265] Further details of the liquid transfers described above are provided in the example embodiments a-d below.

[0266] In another example there is provided a stack of electro- synthetic or electro-energy cells, comprising: a first electro-synthetic or electro -energy cell; and a second electro-synthetic or electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell. Each electro-synthetic or electro-energy cell comprises a liquid electrolyte reservoir for containing a liquid electrolyte, a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir, a second electrode positioned outside of the liquid electrolyte reservoir, and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode. The spacer, including but not limited to a porous capillary spacer, is positioned outside of the liquid electrolyte reservoir with a side surface of the spacer that extends beyond the electrodes, abutting or close to the reservoir. Preferably, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto such a side surface of the spacer, including but not limited to a porous capillary spacer. Preferably, the first electro-synthetic or electro-energy cell is a cell according to any cell as described herein, and the second electro-synthetic or electro -energy cell is a cell according to any cell as described herein. The liquid electrolyte reservoir may be provided as a distinct liquid electrolyte reservoir for each cell, or the liquid electrolyte reservoir may be provided as a common liquid electrolyte reservoir for supplying liquid electrolyte to both the first cell and the second cell. [0267] In another example there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction. The cell comprises a liquid electrolyte reservoir for containing a liquid electrolyte, a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir, and a second electrode positioned outside of the liquid electrolyte reservoir. A spacer, including but not limited to a porous capillary spacer, is positioned at least partially between the first gas diffusion electrode and the second electrode, and the spacer, including but not limited to a porous capillary spacer, is positioned outside of the liquid electrolyte reservoir, with a side surface of the spacer that extends beyond the electrodes, abutting or close to the reservoir. Preferably, the liquid electrolyte reservoir includes an aperture. The method includes the steps of allowing the liquid electrolyte to transfer from the aperture of the liquid electrolyte reservoir onto a side surface of the spacer beyond the electrodes, including but not limited to a porous capillary spacer, then transporting the liquid electrolyte via the spacer, including but not limited to a porous capillary spacer, to the first gas diffusion electrode and the second electrode. A voltage is applied or generated across the first gas diffusion electrode and the second electrode.

[0268] Optionally, when an aperture in a liquid electrolyte reservoir comprises an overflow weir, and the height of the liquid electrolyte in the liquid electrolyte reservoir is at a height of the overflow weir, and further liquid electrolyte is added, then the liquid electrolyte transfers onto the side surface of the spacer, including but not limited to a porous capillary spacer. Optionally, a feed rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the side surface of the spacer, including but not limited to a porous capillary spacer, is regulated by regulating a rate at which the liquid electrolyte is added to the liquid electrolyte reservoir. Optionally, a feed rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the side surface of the spacer, including but not limited to a porous capillary spacer, is regulated by a size of the aperture.

Liquid Electrolyte Transfer, Example Embodiment A:

[0269] Figure 7 depicts multiple but not all-inclusive examples in which liquid electrolyte transfers between the side surface of a spacer 310 that lies beyond the electrodes, including but not limited to a porous capillary spacer, and an abutting or nearby liquid electrolyte reservoir 340a-d. That is, different aspects shown in Figure 7 can be separately implemented in different examples, or combinations of different aspects shown in Figure 7 can be implemented in other examples. [0270] An example mode of operation of such a cell is depicted in Figure 7, which shows a liquid electrolyte reservoir 340a, which has an aperture 382a that provides an outlet in the form of an overflow weir (i.e. a waterfall, a dam, a dike, a levee, a barrier, a cataract, a boom, a wall, or a similar construction over which liquid may pass). When the reservoir 340a is full of liquid electrolyte and further liquid electrolyte is added as shown by addition of further liquid electrolyte 341a, then the liquid level in the reservoir 340a may rise, causing liquid electrolyte to pass over the weir to transfer onto the side surface 385a of a spacer 310, including but not limited to a porous capillary spacer. The feed rate at which liquid electrolyte transfers from the reservoir 340a to the side surface 385a of the spacer 310, including but not limited to a porous capillary spacer, may be regulated by regulating the rate at which further liquid electrolyte 341a is added to the reservoir 340a. That is, the supply of liquid electrolyte to the reservoir 340a may be controlled to thereby ensure that the rate of transfer of, in this case, liquid-phase reactants within the liquid electrolyte 300, from the reservoir 340a to the side surface 385a of the spacer 310, including but not limited to a porous capillary spacer, is sufficiently rapid to ensure that the electrochemical reaction is maintained and not starved of reactants. Preferably, the first gas diffusion electrode is positioned below the liquid electrolyte reservoir, and the second electrode is also positioned below the liquid electrolyte reservoir, with respect to the direction of gravity. When a height of the liquid electrolyte in the liquid electrolyte reservoir 340a is at a height of the aperture 382a, i.e. overflow weir, and further liquid electrolyte 341a is added, then the liquid electrolyte transfers onto the side surface 385a of the spacer 310.

[0271] Preferably but not exclusively, during and after transfer of the liquid electrolyte to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0272] The liquid electrolyte may be transferred from the reservoir 340a to the side surface 385a of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by maintaining a ‘narrow gap’ 346a between the outside of the reservoir 340a and the abutting or nearby side surface 385a of the spacer 310 beyond the electrodes (in region 360a). Such a narrow gap may ensure that all of the liquid electrolyte transfers onto the side surface 385a of the spacer 310, and that none of it transfers directly onto the electrodes 320 or 330. If small enough, narrow gap 346a may harness a capillary action to transfer liquid electrolyte to side surface 385a. A key benefit of employing such a narrow gap 346a is that it may avoid direct transfer of liquid electrolyte from the reservoir 340a to the electrodes 320 or 330, which may cause them to become oversaturated with liquid electrolyte.

[0273] It is to be understood that, in place of the overflow weir 382a, a variety of other devices or constructions that are designed to dispense liquid when liquid is continuously or continually fed to them, such as a constricted aperture, may be used.

Liquid Electrolyte Transfer, Example Embodiment B :

[0274] A different example mode of operation of such a cell is shown by liquid electrolyte reservoir 340b, which has an aperture 382b that forms an outlet below the liquid level. The outlet may be in the form of a valve that regulates the transfer of liquid electrolyte through the aperture 382b and out of the reservoir 340b. When the outlet 382b is open, liquid may transfer out of the reservoir 340b and onto the side surface 385b of a spacer 310, including but not limited to a porous capillary spacer, wherein the side surface 385b of the spacer 310 extends beyond the electrodes and abuts or is near to the outside of the electrolyte reservoir 340b. The feed rate at which liquid electrolyte transfers from the reservoir 340b to the side surface 385b of the spacer 310, including but not limited to a porous capillary spacer, may be regulated by regulating the size of the aperture 382b or by regulating the opening or closing of the valve that incorporates 382b. That is, the transfer of the liquid electrolyte may be controlled to thereby ensure that the rate of transfer of, in this case, liquid-phase reactants in the liquid electrolyte 300, from the reservoir 340b to the side surface 385b of the spacer 310, including but not limited to a porous capillary spacer, is sufficiently rapid to ensure that the electrochemical reaction is maintained and not starved of reactants.

[0275] Preferably but not exclusively, during and after transfer of the liquid electrolyte to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0276] The reservoir 340b may, preferably but not exclusively, include a jutting wall 347b that creates a ‘narrow gap’ 346b above the abutting or nearby side surface 385b of the spacer 310 beyond the electrodes (in region 360b). The liquid electrolyte may be transferred from the reservoir 340b to the side surface 385b of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by transferring it into the ‘narrow gap’ 346b. Such a narrow gap may ensure that all of the liquid electrolyte transfers onto the side surface 385b of the spacer 310, and that none of it transfers directly onto the electrodes 320 or 330. If small enough, narrow gap 346b may harness a capillary action to transfer liquid electrolyte to side surface 385b. A key benefit of employing such a narrow gap 346b is that it may avoid direct transfer of liquid electrolyte from the reservoir 340b to the electrodes 320 or 330.

[0277] It is to be understood that, in place of the aperture 382b or valve, a variety of other devices or constructions that are designed to dispense liquid, may be used.

Liquid Electrolyte Transfer, Example Embodiment C:

[0278] A third example mode of operation of such a cell is shown by liquid electrolyte reservoir 340c having an aspirator pipe 383c that draws liquid through an aspirator 384c to a nozzle 386c, which produces a spray of droplets that fall upon a side surface 385c of a spacer 310, including but not limited to a porous capillary spacer, that extends beyond the electrodes (in region 360c) and abuts or is nearby to the nozzle 386c. The feed rate at which liquid electrolyte transfers from the reservoir 340c to the side surface 385c of the spacer 310, including but not limited to a porous capillary spacer, may be regulated by regulating the aspirator 383c or the nozzle 386c. That is, the transfer of liquid electrolyte may be controlled to thereby ensure that the rate of transfer of, in this case, liquid-phase reactants in the liquid electrolyte 300, from the reservoir 340c to the side surface 385c of the spacer 310, including but not limited to a porous capillary spacer, is sufficiently rapid to ensure that the electrochemical reaction is maintained and not starved of reactants.

[0279] Preferably but not exclusively, during and after transfer of the liquid electrolyte to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0280] The nozzle 386c may, preferably but not exclusively, include jutting enclosure walls 347c that have the effect of creating a ‘narrow gap’ 346c above the abutting or nearby side surface 385c of the spacer 310 beyond the electrodes (in region 360c). The liquid electrolyte may be transferred from the reservoir 340c to the side surface 385c of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by transferring it via the ‘narrow gap’ 346c. Such a narrow gap may ensure that all of the liquid electrolyte transfers onto the side surface 385c of the spacer 310, and that none of it transfers directly from the reservoir 340c onto the electrodes 320 or 330. If small enough, narrow gap 346c may harness a capillary action to transfer liquid electrolyte to side surface 385c. A key advantage of employing such a narrow gap 346c is that it may avoid direct transfer of liquid electrolyte from the reservoir 340c to the electrodes 320 or 330.

[0281] An advantage of using such an aspirator and nozzle is that liquid electrolyte may be transferred to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes regardless of whether that side surface is above or below the reservoir.

[0282] It is to be understood that, in place of the aspirator 384c and nozzle 386c, a variety of other engineering components, such as an ejector, an evactor, eductor, aspirator, vacuum ejector, venturi, venturi pump, jet pump, exhauster, a compressor, or a man-made component of any type that is capable of inducing movement in a liquid-phase fluid, may be used.

Liquid Electrolyte Transfer, Example Embodiment D:

[0283] A further example mode of operation of such a cell is shown by liquid electrolyte reservoir 340d, which contains an aperture 382d that transfers liquid electrolyte to a reservoir 340d from a side surface 385d of a spacer 310, including but not limited to a porous capillary spacer, that extends beyond the electrodes (in region 360d) and abuts or is nearby to the reservoir 340d. The aperture 382d may be a valve. The feed rate at which liquid electrolyte transfers from side - 11 - surface 385d of the spacer 310, including but not limited to a porous capillary spacer, may be regulated by regulating the size of the aperture 382d or the valve 382d. That is, the transfer of liquid electrolyte may be controlled to thereby ensure that the rate of transfer of, for example, liquid-phase products from the side surface 385d of the porous capillary spacer 310 to the reservoir 340d is sufficiently rapid to ensure that the electrochemical reaction is maintained and not overwhelmed by products.

[0284] Preferably but not exclusively, during and after transfer of the liquid electrolyte from the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0285] The reservoir 340d may, preferably but not exclusively, include a jutting wall 347d that creates a ‘narrow gap’ 346d above the abutting or nearby side surface 385d of the spacer 310 beyond the electrodes (in region 360d). The liquid electrolyte may be transferred to the reservoir 340d from the side surface 385d of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by transferring it via the ‘narrow gap’ 346d. Such a narrow gap may ensure that all of the liquid electrolyte transfers off the side surface 385d of the spacer 310, and that none of it transfers onto the electrodes 320 or 330. If small enough, narrow gap 346d may harness a capillary action to transfer liquid electrolyte from side surface 385b. A key benefit of employing such a narrow gap 346d is that it may avoid direct transfer of liquid electrolyte from side surface 385d to the electrodes 320 or 330.

[0286] It is to be understood that, whereas Figure 7 depict different types of example embodiment cells, the examples provided above may be used in any and all preferred embodiment cells described in this specification. It is also to be understood that, while Figure 7 depicts different liquid electrolyte reservoir locations and arrangements within the cell, and different liquid electrolyte transfer arrangements, the locations or groupings of the arrangements, and the methods of liquid transfer in Figure 7 are for illustrative convenience only. Any combination, or individual use, of the arrangements shown in Figure 7 can be applied in different cell configurations. Moreover, other liquid transfer arrangements based on but not explicitly described in Figure 7 fall within the scope of this specification. For example, the narrow gap arrangements shown here may be constructed so as to transfer liquid from or to reservoirs that are not abutting or nearby.

[0287] As a result of regulated or unregulated liquid transfer of the type described above, liquidphase reactants may be replenished to the cell by adding fresh liquid-phase reactants to the reservoir, or liquid-phase products may be removed from the cell by removing them from the reservoir.

4. Third example preferred embodiment cells with a ‘liquid feed structure’ between the reservoir and a side surface of the spacer

[0288] It is to be understood that all of the characteristics and benefits, including the surprising benefits, described in sections 1, 2, and 3, and in the paragraphs following the heading above entitled “Preferred Embodiment Electro-Synthetic or Electro -Energy Cells”, also apply to this section 4 and all example embodiments disclosed therein.

[0289] The inventors have discovered that a spacer, including but not limited to a porous capillary spacer, need not be in direct contact with the liquid electrolyte in a liquid electrolyte reservoir (e.g. immersed in the liquid electrolyte in the reservoir) for such electro- synthetic or electro-energy cells, including capillary-based electro- synthetic and electro-energy cells, to operate: (i) continually or continuously over indefinite periods of time, with (ii) inherent and high energy efficiency, while (iii) consuming reactants and generating products that are too voluminous to be accommodated within the cell, and that (iv) need to be supplied to or removed from an external storage by supply/removal systems.

[0290] Instead, the spacer, including but not limited to a porous capillary spacer, that lies beyond the electrodes, may be physically separate from and not in direct contact with a liquid electrolyte reservoir located elsewhere in the cell. In such embodiments, the cell architecture may allow liquid electrolyte to transfer between the liquid electrolyte reservoir and a side surface of a spacer that lies beyond the electrodes, including but not limited to a porous capillary spacer, despite them being physically separated in the cell. The liquid electrolyte reservoir may be located at one of, some of, or all of: the top, the sides, and/or the bottom of the cell. [0291] In one example aspect there is provided an electro-synthetic or electro-energy cell, comprising: a first gas diffusion electrode; a second electrode; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein an intermediate "liquid feed structure ’ is located between the spacer, including but not limited to a porous capillary spacer, and a physically separate liquid electrolyte reservoir.

[0292] Preferably, liquid electrolyte transfers along the intermediate liquid feed structure between the liquid electrolyte reservoir and a side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes. Preferably, the liquid feed structure is separate and distinct from the spacer, including but not limited to a porous capillary spacer. Preferably but not exclusively, the liquid feed structure is in direct contact with the liquid electrolyte reservoir (e.g. immersed in the liquid electrolyte in the reservoir) at one or more locations. Preferably but not exclusively, the liquid feed structure is also in direct contact with a side surface of the spacer, including but not limited to a porous capillary spacer, at one or more locations of the spacer where it extends beyond the electrodes. Preferably but not exclusively, during operation, liquid transfer along or within the liquid feed structure is "regulated’-, that is, liquid transfer occurs in a pre-determined and controlled manner. Preferably but not exclusively, liquid transfer along or within the liquid feed structure is "self-regulated’-, that is, liquid transfer occurs spontaneously in response to concentration differentials between liquid in the liquid feed structure / reservoir, and liquid at the side surface of the spacer, including but not limited to a porous capillary spacer, where it extends beyond the electrodes and contacts with the porous capillary liquid feed structure.

[0293] In another example there is provided an electro-synthetic or electro-energy cell that comprises a liquid electrolyte reservoir for containing a liquid electrolyte, a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir, and a second electrode positioned outside of the liquid electrolyte reservoir. A spacer, including but not limited to a porous capillary spacer, is positioned at least partially between the first gas diffusion electrode and the second electrode, and the spacer, including but not limited to a porous capillary spacer, extends beyond the electrodes and is positioned outside of the liquid electrolyte reservoir. An intermediate liquid feed structure is located at least partially between the spacer, including but not limited to a porous capillary spacer, and the liquid electrolyte reservoir, and the liquid electrolyte is transferred between the liquid electrolyte reservoir and the side surface of the spacer, including but not limited to a porous capillary spacer, by the intermediate liquid feed structure.

[0294] In another example, the spacer, including but not limited to a porous capillary spacer, does not directly contact the liquid electrolyte that is within the liquid electrolyte reservoir. In another example, the intermediate liquid feed structure is separate and distinct from the spacer, including but not limited to a porous capillary spacer. In another example, the intermediate liquid feed structure is in direct contact with the liquid electrolyte that is within the liquid electrolyte reservoir. In another example, the intermediate liquid feed structure is in direct contact with a side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes. In another example, the spacer, including but not limited to a porous capillary spacer, is spaced apart from the liquid electrolyte reservoir. In another example, the intermediate liquid feed structure is a porous capillary liquid feed structure. In another example, the liquid electrolyte reservoir has a width substantially equal to a width of the cell and is positioned across the top of the cell. In another example, the porous capillary liquid feed structure is sheet-like and has one edge / one end dipped into the liquid electrolyte reservoir.

[0295] In another example, the porous capillary liquid feed structure spontaneously draws in and maintains a volume of the liquid electrolyte within the porous capillary liquid feed structure by capillary action. In another example, the liquid electrolyte transfers within the porous capillary liquid feed structure under the influence of capillary and/or diffusion and/or osmotic control. In another example, the intermediate liquid feed structure is a surface liquid feed structure. Preferably, the liquid electrolyte transfers along a surface of the surface liquid feed structure. In another example, the intermediate liquid feed structure is a pipe, a conduit, a channel, a tube, a chamber, or a trough.

[0296] Preferably, the cell is configured such that during operation, the liquid electrolyte contacts the first gas diffusion electrode and the second electrode only after first transferring from the liquid electrolyte reservoir via the intermediate liquid feed structure and then via the spacer, including but not limited to a porous capillary spacer. In one example, the spacer, including but not limited to a porous capillary spacer, is made of one or more non-conductive materials. That is, the spacer, including but not limited to a porous capillary spacer, of itself is non-conductive. Preferably, transfer of the liquid electrolyte along or within the intermediate liquid feed structure is self-regulated. [0297] Figure 8(a)-(b) schematically depict the key internal components of electro- synthetic or electro-energy cells 401 having some or all of the above characteristics, including but not limited to a capillary-based electro- synthetic and electro-energy cell, incorporating a liquid feed structure.

[0298] The electro- synthetic and electro-energy cell 401 comprises a spacer 410, including but not limited to a porous capillary spacer, located between a first gas diffusion electrode 420 and a second electrode 430. The spacer 410, including but not limited to a porous capillary spacer, may completely fill the gap 439 between the first gas diffusion electrode 420 and the second electrode 430 (as depicted in Figure 8(a)). Alternatively, the spacer 410, including but not limited to a porous capillary spacer, may partially fill the gap 439 between the first gas diffusion electrode 420 and the second electrode 430 (as depicted in Figure 8(b)), with the remaining volumes in the gap 439 that lie within region 404, occupied by other spacers or spacer materials that are not shown in Figure 8(b) for clarity. The first gas diffusion electrode 420 and the second electrode 430 may be separated by an average distance 470. The first and second electrodes 420 and 430 respectively, may be connected to a power supply or power receiving unit via electrical cables (not shown in Figure 8). The spacer 410, including but not limited to a porous capillary spacer, may extend beyond the region of the cell itself (denoted by region 404) into locations beyond the electrodes, where it does not have electrodes abutting it on one or both sides (denoted by regions 460a-d). Preferably but not exclusively, the first gas diffusion electrode 420 and the second electrode 430 are sandwiched against opposite sides of the spacer 410, including but not limited to a porous capillary spacer.

[0299] In the case where the spacer 410 is a porous capillary spacer, the liquid-phase reactants and/or products may undertake ‘in-plane ’ migration in the liquid electrolyte 400 inside spacer 410, along the length of spacer 410, to or from the electrodes 420 and 430. The liquid-phase reactants and/or products may do so under capillary and/or diffusion and/or osmotic control, amongst others, which is ‘ self -regulated’ by the concentration differentials present in the liquid electrolyte and at the reaction zones at or about the inside surfaces of the electrodes 420 and 430, where they face the spacer 410. During operation of the cell, liquid -phase reactants and/or products of the electrochemical reaction may spontaneously move within the liquid 400 inside the spacer 410, including but not limited to a porous capillary spacer, in the directions 450a or 450b to or from the electrodes 420 and 430. [0300] The first gas diffusion electrode 420 may be configured to generate or consume a first gas that forms a first gas body 425 in contact with first electrode 420. The second electrode 430 may be a gas diffusion electrode and may be configured to generate or consume a second gas that forms a second gas body 435 in contact with second electrode 430. At the molecular-level, gasphase materials produced by or consumed by the electrochemical reaction may migrate in an orthogonal (90°) direction to the movement of the liquid-phase materials, along continuous gas phase pathways that are separate from and do not interfere with the liquid-phase pathways. That is, gaseous molecules or atoms may migrate to or from their respective gas bodies 425 or 435 through the relevant interface/s to or from the gas diffusion electrode(s) 420 or 430 respectively, i.e. into or out of the reaction zones at or about the inside faces of electrodes 420 and 430 respectively, where they face the spacer 410. Such migrations may occur under (gas) capillary and/or diffusion control along continuous gas-phase pathways connecting each electrode 420 or 430 to each gas body 425 or 435, respectively. The movement of gas-phase materials (reactants or products) may therefore also exhibit self-regulation. Because the pathway of migration of each gas does not overlap with, or interfere with that of the other gas, or with the pathway of liquid migration, gas movements may be independently self -regulated, separately to the self-regulation of the liquid movements. That is, the different gas- and liquid-phase reactants and products may each be subject to their own self-regulation, which does not interfere with the movements of the other reactants and products.

[0301] In further example forms, there are provided example electro- synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas on the first side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than or smaller than the pressure of the second gas on the opposite, second side of the spacer. In examples, the differential in the pressures between the first gas and the second gas may occur or may be made to occur during startup, shutdown or normal operation of the cell. For example, the differential in the pressures between the first gas and the second gas may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the first gas and the second gas may be more than 10 mbar. In other examples, the differential in the pressures between the first gas and the second gas may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar. [0302] During operation of the cell, liquid-phase reactants and/or products of the electrochemical reaction may need to be replenished from (if they are consumed in the electrochemical reaction) or removed to (if they are produced in the electrochemical reaction) the liquid electrolyte in a liquid electrolyte reservoir 440.

[0303] The inventors have surprisingly found that, even at high required liquid flow rates within the spacer, this may be continually or continuously achieved over indefinite time periods, by transferring liquid to or from a side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes (e.g. in regions 460a-h) and lies outside of the region of the cell 404. Surprisingly, even at very high feed rates of liquid electrolyte onto or off of a side surface of a spacer that extends beyond the electrodes, the electrodes can be maintained properly wetted, and over-saturation or overwhelming of the electrodes with liquid electrolyte may be avoided, which condition may be practically demonstrated by: (i) an electrode being ‘bubble- free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0304] Figure 8(a)-(b) depicts multiple but not all-inclusive examples of liquid feed structures 480a-h located between a spacer 410, including but not limited to a porous capillary spacer, and a physically separate liquid electrolyte reservoir 440a-h, respectively. That is, different aspects shown in Figure 8(a)-(b) can be separately implemented in different examples, or combinations of different aspects shown in Figure 8(a)-(b) can be implemented in other examples.

- Use of a ‘Porous Capillary Liquid Feed Structure’

[0305] In a first example, the intermediate liquid feed structure is a ‘ porous capillary liquid feed structure ’ that spontaneously draws in and maintains a volume of the liquid electrolyte within it by a capillary action. Preferably, liquid moves within the porous capillary liquid feed structure under the influence of capillary and/or diffusion and/or osmotic control, amongst others, in the same way that liquid may move within a porous capillary spacer. Preferably, during operation of the cell, at the molecular-level, liquid-phase materials produced by or consumed by the electrochemical reaction spontaneously undertake ‘in-plane ’ migration along the length of the porous capillary liquid feed structure to or from the spacer, including but not limited to a porous capillary spacer. Preferably, this migration occurs under capillary and/or diffusion and/or osmotic control that is "self-regulated’ by the concentration differentials present between liquid in the porous capillary liquid feed structure and in the reservoir, and liquid at the side surface of the spacer, including but not limited to a porous capillary spacer, at its contact points with the porous capillary liquid feed structure.

[0306] Preferably, the rate of migration of liquid-phase materials along the porous capillary liquid feed structure to or from the side surface of the porous capillary spacer is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products. (The factors that determine the rate at which liquid may migrate in a porous capillary material and their use in the selection of a suitable porous capillary material are taught in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606, and are not repeated here).

Liquid Feed Structure Example Embodiment A:

[0307] The operation of such a cell is depicted in Figure 8(a), which shows a porous capillary liquid feed structure 480a, known as a ‘siphon membrane’, one end of the porous capillary liquid feed structure 480a is immersed in the liquid electrolyte within a liquid electrolyte reservoir 440a, while the other end is pressed tight up against a side surface 485a of the spacer 410, including but not limited to a porous capillary spacer, that lies beyond the electrodes (in region 460a). Liquid electrolyte may move within the porous capillary liquid feed structure 480a under the influence of capillary and/or diffusion and/or osmotic control, as well as, possibly, a siphon effect, amongst others, in response to concentration differentials between liquid electrolyte in the porous capillary liquid feed structure 480a and reservoir 440a, and liquid electrolyte at the contact points of side surface 485a of the spacer 410 with the porous capillary liquid feed structure 480a, wherein the spacer 410 may be, but is not limited, to a porous capillary spacer. Through this driving force, the rate of transfer of liquid-phase reactants and/or products in the liquid electrolyte 400, along the liquid feed structure, to or from the side surface 485a of the spacer 410, including but not limited to a porous capillary spacer, may be sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products. Preferably, the spacer 410, including but not limited to a porous capillary spacer, does not directly contact liquid electrolyte that is within the liquid electrolyte reservoir 440a. Preferably, the spacer 410, including but not limited to a porous capillary spacer, is spaced apart from, and/or does not directly contact, and/or is not positioned within, the liquid electrolyte reservoir 440a. Preferably, liquid electrolyte is transferred between the liquid electrolyte reservoir 440a and the spacer 410, including but not limited to a porous capillary spacer, which may be to a side surface of the spacer 410, including but not limited to a porous capillary spacer, by the intermediate liquid feed structure 480a. Preferably but not exclusively, liquid electrolyte in the capillary feed structure 480a is only transferred to the side surface 485a of the spacer 410, and is not transferred directly onto an electrode 420 or 430. Preferably but not exclusively, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation)

Liquid Feed Structure Example Embodiment B :

[0308] Figure 8(b) depicts an alternative embodiment of a cell utilizing a porous capillary liquid feed structure. In this case, one end of porous capillary liquid feed structure 480b penetrates the bottom of and is located in a liquid electrolyte reservoir 440b and thereby contacts the liquid electrolyte in liquid electrolyte reservoir 440b, while the other end is pressed tight up against a side surface 485b of the spacer 410, including but not limited to a porous capillary spacer, that extends beyond the electrodes (in region 460b). Liquid may transfer through the porous capillary liquid feed structure 480b under the influence of capillary and/or diffusion and/or osmotic control, as well as possibly gravity, amongst others, in response to concentration differentials between liquid in the porous capillary liquid feed structure 480b and reservoir 440b, and liquid at the side surface 485b of the spacer 410, including but not limited to a porous capillary spacer, at its contact points 485b with the porous capillary liquid feed structure 480b beyond the electrodes (in region 460b). Through this driving force, the rate of transfer of liquid-phase reactants and/or products in the liquid electrolyte 400, along the liquid feed structure, to or from the side surface of the spacer 410, including but not limited to a porous capillary spacer, may be sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products. Preferably but not exclusively, liquid electrolyte in the capillary feed structure 480b is only transferred to the side surface 485b and is not transferred directly from the capillary feed structure 480b onto an electrode 420 or 430. [0309] Preferably but not exclusively, during and after transfer of the liquid electrolyte to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0310] It is to be understood that the slit 445b at the bottom of the reservoir 440b, through which the porous capillary liquid feed structure 480b passes, may incorporate additional apertures of the types discussed in Section 2 and depicted in Figures 4-6 above.

Liquid Feed Structure Example Embodiment C:

[0311] Figure 8(b) depicts another alternative embodiment of a cell with a porous capillary liquid feed structure. In this case, the porous capillary liquid feed structure is a porous, hydrophilic block of material 480c (e.g. a porous hydrophilic, polymer block) within which a pipe 440c exists (going into and out of the page in Figure 8(b)). The pipe is filled with liquid 400 that is circulated through the structure (in the direction going into and out of the page in Figure 8(b)), thereby turning the pipe into a reservoir 440c. Liquid may migrate from the reservoir 440c, through the porous, hydrophilic block 480c that comprises the porous capillary liquid feed structure to a side surface 485c of the spacer 410, including but not limited to a porous capillary spacer, that extends beyond the electrodes (in region 460c). Liquid may move within the porous capillary liquid feed structure 480c in response to concentration differentials between liquid in the porous capillary liquid feed structure 480c and reservoir 440c, and liquid at the side surface 485c of the spacer 410, including but not limited to a porous capillary spacer, at its contact points 485c with the surface liquid feed structure 480c, that lie beyond the electrodes (in region 460c). Through this driving force, the rate of transfer of liquid-phase reactants and/or products in the liquid electrolyte 400, along the liquid feed structure, to or from the side surface 485c of the spacer 410, including but not limited to a porous capillary spacer, may be sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products. Preferably but not exclusively, liquid electrolyte in the capillary feed structure 480c is only transferred to the side surface 485c and is not transferred directly from the capillary feed structure 480c onto an electrode 420 or 430. [0312] Preferably but not exclusively, during and after transfer of the liquid electrolyte to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0313] It is to be understood that, whereas Figure 8(a) and Figure 8(b) depict different types of example embodiment cells, the example arrangements may be used in any and all embodiment cells.

[0314] As a result of self-regulated migrations of the type described above, liquid-phase reactants may be replenished to the cell by adding fresh liquid-phase reactants to the reservoir, and liquid-phase products may be removed from the cell by removing them from the reservoir.

- Use of a ‘Surface Liquid Feed Structure’

[0315] In another example, the intermediate liquid feed structure is a "surface liquid feed structure ’ that transfers liquid electrolyte between the side surface of a spacer 410, including but not limited to a porous capillary spacer, and a liquid electrolyte reservoir by a different physical effect to those mentioned above. Surface liquid feed structures harness effects including but not limited to a surface tension effect, a contact angle effect, a hydrophilic-hydrophobic effect, or a similar effect in which liquid electrolyte transfers on the surface of a liquid feed structure. Preferably but not exclusively, liquid electrolyte is spontaneously induced to move along the surface of the liquid feed structure by the effect in operation. Preferably but not exclusively, this migration is ‘ self -regulated’ by the concentration differentials present between liquid electrolyte on the surface of the surface liquid feed structure and the reservoir, and liquid electrolyte at the side surface of the spacer, including but not limited to a porous capillary spacer, at its contact points with the surface liquid feed structure beyond the electrodes. Optionally, the transfer of liquid electrolyte along the surface liquid feed structure is "regulated’ by texturing, modifying, or hydrophobic-hydrophilic engineering of its surface. Preferably, the rate of migration of liquidphase materials along the surface liquid feed structure to or from the side surface of the spacer, including but not limited to a porous capillary spacer, is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products.

Liquid Feed Structure Example Embodiment D:

[0316] The operation of such a cell is depicted in Figure 8(a), which shows a surface liquid feed structure 480d, known as a ‘surface siphon’, whose one end is immersed in the liquid electrolyte within a liquid electrolyte reservoir 440d, while the other end is held against or very close to a side surface 485d of the spacer 410, including but not limited to a porous capillary spacer, beyond the electrodes (in region 460d). Liquid electrolyte may transfer along the surface of the surface liquid feed structure 480d under the influence of a physical effect of the type described above, amongst others, in response to concentration differentials between liquid electrolyte in the surface liquid feed structure 480d and reservoir 440d, and liquid electrolyte at the side surface 485d of the spacer 410, including but not limited to a porous capillary spacer, at its contact points 485d with the surface liquid feed structure 480d beyond the electrodes. Through this driving force, the feed rate of transfer of liquid-phase reactants and/or products within the liquid electrolyte 400, along the liquid feed structure, to or from the side surface of the spacer 410, including but not limited to a porous capillary spacer, may be sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products. Preferably but not exclusively, liquid electrolyte in the surface feed structure 480d is transferred only to side surface 485d and is not transferred directly from the surface feed structure 480d onto an electrode 420 or 430.

[0317] It is to be understood that, whereas Figure 8(a) depicts an example embodiment cell, the example involving surface liquid feed structures of the types 485d may be used in any and all embodiment cells.

[0318] As a result of self-regulated or regulated migrations of the type described above, liquidphase reactants may be replenished to the cell by adding fresh liquid-phase reactants to the reservoir, and liquid-phase products may be removed from the cell by removing them from the reservoir.

Use of an ‘Engineered Liquid Feed Structure’ [0319] In a third example, the intermediate liquid feed structure is an ‘ engineered liquid feed structure ’ such as a pipe, a conduit, a channel, a tube, a chamber, a trough, or a construction of any type for conveying a liquid electrolyte between the side surface of the spacer, including but not limited to a porous capillary spacer, and the liquid electrolyte reservoir (other than a porous capillary liquid feed structure and a surface liquid feed structure, as discussed above). Preferably but not exclusively, liquid is induced to move within the engineered liquid feed structure by one or a combination of the following: the influence of gravity; the influence of a physical effect, such as, for example, a siphon effect; the influence of an engineering device, such as a pump, an ejector, an evactor, eductor, aspirator, vacuum ejector, venturi, venturi pump, jet pump, exhauster, a compressor, or of a man-made component of any type that is capable of inducing movement in a liquid-phase fluid.

[0320] Preferably but not exclusively, during operation of the cell, the feed rate at which liquid electrolyte transfers between the reservoir and the side surface of the spacer, including but not limited to a porous capillary spacer, is regulated to occur in a controlled, pre-determined manner. Optionally, the movement of liquid electrolyte along the engineered liquid feed structure is unregulated. Preferably, the flow rate of the liquid-phase materials along the engineered liquid feed structure to or from the side surface of the spacer, including but not limited to a porous capillary spacer, is sufficiently rapid that the electrochemical reaction is maintained and not starved of reactants or overwhelmed by products.

Liquid Feed Structure Example Embodiment E:

[0321] The operation of such a cell is depicted in Figure 8(a), which shows an engineered liquid feed structure comprising a pipe 480e, that lies between a liquid electrolyte reservoir 440e and a side surface 485e of the spacer 410, including but not limited to a porous capillary spacer, that lies beyond the electrodes (in region 460e). The pipe 480e utilises gravity to transfer liquid electrolyte from the liquid electrolyte reservoir 440e to the side surface 485e of the spacer 210, including but not limited to a porous capillary spacer. The feed rate at which liquid electrolyte transfers from reservoir 440e to side surface 485e of the spacer 410, including but not limited to a porous capillary spacer, may be regulated by a valve 486e in the pipe. That is, the transfer of liquid electrolyte via the liquid feed structure may be controlled to thereby ensure that the rate of movement of, in this case, liquid-phase reactants within the liquid electrolyte 400, along the liquid feed structure, to the side surface 485e of the spacer 410, including but not limited to a porous capillary spacer, is sufficiently rapid to ensure that the electrochemical reaction is maintained and not starved of reactants. Preferably but not exclusively, liquid electrolyte is transferred only from reservoir 440e to side surface 485e and is not transferred directly from the reservoir 440e onto an electrode 420 or 430.

[0322] Preferably but not exclusively, during and after transfer of the liquid electrolyte to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0323] The reservoir 440e may, preferably but not exclusively, include a jutting wall 447e that creates a ‘narrow gap’ 446e above the abutting or nearby side surface 485e of the spacer 410 beyond the electrodes (in region 460e). The liquid electrolyte may be transferred from the reservoir 440e to the side surface 485e of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by transferring it via the ‘narrow gap’ 446e. Such a narrow gap may ensure that all of the liquid electrolyte transfers to the side surface 485e of the spacer 410, and that none of it transfers onto the electrodes 420 or 430. If small enough, narrow gap 446e may harness a capillary action to transfer liquid electrolyte to side surface 485e. A benefit of employing such a narrow gap 446e is that it may avoid direct transfer of liquid electrolyte from reservoir 440e and pipe 480e onto the electrodes 320 or 330.

Liquid Feed Structure Example Embodiment F:

[0324] A different mode of operation of such a cell is also depicted in Figure 8(a), which shows an engineered liquid feed structure comprising a pipe 480f, that lies between a liquid electrolyte reservoir 440f and a side surface 485f of the spacer 410, including but not limited to a porous capillary spacer 410, that extends beyond the electrodes (in region 460f). The pipe 480f utilises gravity to transfer liquid electrolyte from the side surface 485f of the spacer 410, including but not limited to a porous capillary spacer, to the liquid electrolyte reservoir 440f. The feed rate at which liquid electrolyte transfers to the reservoir 440f from the side surface 485f of the spacer 410, including but not limited to a porous capillary spacer, may be regulated by a valve 486f in the pipe. That is, the transfer of liquid electrolyte via the engineered liquid feed structure may be controlled to thereby ensure that the rate of movement of, in this case, liquid-phase products in the liquid electrolyte, out of the spacer 410, including but not limited to a porous capillary spacer, along the liquid feed structure to reservoir 440f is sufficiently rapid to ensure that the electrochemical reaction is maintained and not overwhelmed with products.

[0325] Preferably but not exclusively, during and after transfer of the liquid electrolyte between the reservoir and the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over-saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0326] The reservoir 440f may, preferably but not exclusively, include a jutting wall 447f that creates a ‘narrow gap’ 446f above the abutting or nearby side surface 485f of the spacer 410 beyond the electrodes (in region 460f). The liquid electrolyte may be transferred to the reservoir 440f from the side surface 485f of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by transferring it via the ‘narrow gap’ 446f. Such a narrow gap may ensure that all of the liquid electrolyte transfers off the side surface 485f of the spacer 410 into the pipe 480f and then into reservoir 440f, and that none transfers onto the electrodes 420 or 430. If small enough, narrow gap 446f may harness a capillary action to transfer liquid electrolyte from side surface 485f to pipe 480f for transfer to reservoir 440f. A benefit of employing such a narrow gap 446f is that it may avoid direct transfer of liquid electrolyte from side surface 485f to the electrodes 320 or 330.

Liquid Feed Structure Example Embodiment G:

[0327] Another example of such a cell is depicted in Figure 8(b), which shows an engineered liquid feed structure comprising a pipe 480g, that lies between a liquid electrolyte reservoir 440g and a side surface 485g of the spacer 410, including but not limited to a porous capillary spacer, beyond the electrodes (in region 460g). The pipe 480g utilises a pump 486g to pump liquid electrolyte from the side surface 485g of the spacer 410, including but not limited to a porous capillary spacer, to the liquid electrolyte reservoir 440g. The feed rate at which liquid electrolyte transfers to the reservoir 440g from the side surface 485f of the spacer 410, including but not limited to a porous capillary spacer, may be regulated by the pump 486g in the pipe 480g. That is, the transfer of liquid electrolyte via the engineered liquid feed structure may be controlled to thereby ensure that the rate of movement of, in this case, liquid-phase products in the liquid electrolyte, out of the spacer 410, including but not limited to a porous capillary spacer, along the engineered liquid feed structure 480g to reservoir 440g is sufficiently rapid to ensure that the electrochemical reaction is maintained and not overwhelmed with products.

[0328] Preferably but not exclusively, during and after transfer of the liquid electrolyte between the reservoir and the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over-saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0329] The reservoir 440g may, preferably but not exclusively, include a jutting wall 447g that creates a ‘narrow gap’ 446g above the abutting or nearby side surface 485g of the spacer 410 beyond the electrodes (in region 460g). The liquid electrolyte may be transferred to the reservoir 440g from the side surface 485g of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by transferring it via the ‘narrow gap’ 446g. Such a narrow gap structure may ensure that all of the liquid electrolyte transfers off the side surface 485g of the spacer 410 into the pipe 480g and thence into reservoir 440g, and that none transfers onto the electrodes 420 or 430. If small enough, narrow gap 446g may harness a capillary action to transfer liquid electrolyte from side surface 485g to pipe 480g for transfer to reservoir 440g. A benefit of employing such a narrow gap 446fg is that it may avoid direct transfer of liquid electrolyte from side surface 485g to the electrodes 320 or 330.

Liquid Feed Structure Example Embodiment H:

[0330] A still further mode of operation of such a cell is depicted in Figure 8(b), which shows an engineered liquid feed structure comprising a pipe 480h, that lies between a liquid electrolyte reservoir 440h and a side surface 485h of the spacer 410, including but not limited to a porous capillary spacer, that extends beyond the electrodes (in region 460h). The pipe 480h utilises a pump 486h to pump liquid electrolyte from the liquid electrolyte reservoir 440h to the side surface 485h of the spacer 410, including but not limited to a porous capillary spacer. The feed rate at which liquid electrolyte transfers from the reservoir 440h to the side surface 485f of the spacer 410, including but not limited to a porous capillary spacer, may be regulated by the pump 486h in the pipe 480h. By this means, the transfer of liquid electrolyte via the liquid feed structure may be controlled to thereby ensure that the rate of movement of, in this case, liquid-phase reactants within the liquid electrolyte, along the liquid feed structure 480h to the side surface 485h of the spacer 410, including but not limited to a porous capillary spacer, is sufficiently rapid to ensure that the electrochemical reaction is maintained and not starved of reactants. Preferably but not exclusively, liquid electrolyte is transferred only from reservoir 440h to side surface 485h and is not transferred directly from the reservoir 440h onto an electrode 420 or 430.

[0331] Preferably but not exclusively, during and after transfer of the liquid electrolyte to the side surface of the spacer, including but not limited to a porous capillary spacer, that extends beyond the electrodes, the electrodes are maintained properly wetted and not over- saturated or overwhelmed with liquid electrolyte, which condition may be practically demonstrated by: (i) an electrode being ‘bubble-free’ during operation (for an electrode that produces a gas during operation), or (ii) an electrode enjoying full access to a gaseous reactant during operation (for an electrode that consumes gas during operation).

[0332] The reservoir 440h may, preferably but not exclusively, include a jutting wall 447h that creates a ‘narrow gap’ 446h above the abutting or nearby side surface 485h of the spacer 410 beyond the electrodes (in region 460h). The liquid electrolyte may be transferred from the pipe 480h to the side surface 485h of the spacer 310, including but not limited to a porous capillary spacer, in a controlled and directed manner by transferring it via the ‘narrow gap’ 446h. Such a narrow gap structure may ensure that all of the liquid electrolyte transfers to the side surface 485h of the spacer 410, and that none of it transfers from the pipe 480h onto the electrodes 420 or 430. If small enough, narrow gap 446h may harness a capillary action to transfer liquid electrolyte to side surface 485h. A benefit of employing such a narrow gap 446h is that it may avoid direct transfer of liquid electrolyte from reservoir 440h and pipe 480h onto the electrodes 320 or 330. [0333] It is to be understood that, whereas Figure 8(a) and Figure 8(b) depict different types of example embodiment cells, the examples involving engineered liquid feed structures may be used in any and all embodiment cells.

[0334] It is further to be understood that, in place of a valve or a pump, a variety of other engineering components, such as an ejector, an evactor, eductor, aspirator, vacuum ejector, venturi, venturi pump, jet pump, exhauster, a compressor, or a man-made component of any type that is capable of inducing movement in a liquid-phase fluid, may be used. A physical effect such as but not limited to a siphon effect, applied via a pipe, a conduit, a channel, a tube, a chamber, or a construction of any type for conveying a fluid, may also be used.

[0335] As a result of regulated or unregulated migrations of the type described above, liquidphase reactants may be replenished to the cell by adding fresh liquid-phase reactants to the reservoir, or liquid-phase products may be removed from the cell by removing them from the reservoir.

[0336] It is further to be understood that Figure 8(a) and Figure 8(b) depict different liquid electrolyte reservoir locations and arrangements and different liquid electrolyte transfer arrangements, and the positions or groupings of the arrangements in Figure 8(a) and Figure 8(b) are for illustrative convenience. Any combination, or individual use, of the arrangements shown in Figure 8(a) and Figure 8(b) can be applied in different cell configurations.

Examples of cell architectures that may be realised using ‘liquid feed structures’ in electrochemical cells

[0337] Figure 9A(a)-(b) and Figure 9B(c)-(d) depicts practical examples of an electrochemical cell in which a liquid feed structure may be employed.

[0338] Figure 9A(a) shows a polymer frame 4090 to which a spacer 4010, including but not limited to a porous capillary spacer, is attached and sealed by thermal, platen or ultrasonic welding along the seam 4095. Spacers may routinely need to be sealed around their edges to a frame, for example a polymer frame, in industrial electro -energy or electro-synthetic cells. This may be required, for example, to prevent the first gas body (e.g. first gas body 425 in Figure 8) from contacting and mixing with the second gas body (e.g. second gas body 435 in Figure 8). In some electro-energy or electro-synthetic cells, for example water electrolysis cells or hydrogen-oxygen fuel cells, such mixing of the gas bodies may constitute a safety hazard.

[0339] The problem that may then arise, particularly but not exclusively in the case where the spacer 4010 is a porous capillary spacer, is that the process of sealing the spacer 4010 to the frame may typically cause the spacer 4010 to be compressed into a non-porous, solid-state material at the seam 4095, thereby losing its capacity, at that location, to transport liquid within it. That is, for the case where the spacer 4010 is a porous capillary spacer, the porous capillary spacer may lose its capacity to harness capillary and/or diffusion and/or osmotic effects, amongst others, to induce liquid movement within it at its sealed edges.

[0340] Accordingly, depending on the specific cell architecture employed, it may not be possible to immerse one end of the porous capillary spacer 4010 in a liquid electrolyte reservoir. That is, because all ends of the porous capillary spacer 4010 are securely bound in a non-porous, solid- state form to the frame, it may not be possible or simple to immerse one end of the porous capillary spacer in a liquid electrolyte reservoir. For example, it may be challenging to fabricate a cell architecture wherein the liquid electrolyte reservoir is at the top of the cell and wherein a top edge of the porous capillary spacer 4010 is positioned within it. It may, similarly, be challenging to have a liquid electrolyte reservoir on the sides of the cell. In such a case, it may be necessary to use a liquid feed structure.

[0341] Figure 9A(b) depicts in cross-section, one way in which a reservoir at the top of a cell may be realised using a liquid feed structure. A porous capillary liquid feed structure 4080 has one end immersed in the liquid electrolyte within a liquid electrolyte reservoir 4040, while the other end is pressed up against the spacer 4010, including but not limited to a porous capillary spacer, with which it makes contact at interface 4085.

[0342] Figure 9B(c) partially depicts the resulting cell architecture, showing the polymer frame 4090 welded along seam 4095 to the spacer 4010, including but not limited to a porous capillary spacer. A liquid electrolyte reservoir 4040, which is the full width of the cell, is arrayed across the top of the cell. That is, the liquid electrolyte reservoir has a width substantially equal to the width of the cell and is positioned across the top of the cell. A sheet-like porous capillary liquid feed structure 4080 has one edge dipped into the reservoir 4040, while the other edge is bent over to locate it up against the spacer 4010, including but not limited to a porous capillary spacer, with which it forms an interface 4085. The porous capillary liquid feed structure 4080 may be termed a ’siphon membrane’. This is because it may harness a siphon effect in addition to the capillary and/or diffusion and/or osmotic effects, amongst others, that normally induce liquid electrolyte to move within a porous capillary structure 4080. Liquid electrolyte may move in such a porous capillary liquid feed structure 4080 in response to concentration differentials between liquid electrolyte in the porous capillary liquid feed structure 4080 and reservoir 4040, and liquid electrolyte at the side surface 4085 of the spacer 4010, including but not limited to a porous capillary spacer, at its contact interface 4085 with the porous capillary liquid feed structure 4080.

[0343] A ‘side-reservoir’ cell architecture is also possible using such a porous capillary liquid feed structure. Figure 9B(d) depicts the key elements of such a cell. A spacer 4010, including but not limited to a porous capillary spacer, is attached and sealed by thermal, platen or ultrasonic welding along the seam 4095 to a frame 4090. One edge of a sheet-like porous capillary liquid feed structure 4080 penetrates into and is rolled up within a cylindrical liquid electrolyte reservoir 4040 that is the full height of the cell (see smaller inset in Figure 9B(d)). Its other edge passes over the seal 4095 and is then pressed tightly against the side surface 4085 of the spacer 4010, including but not limited to a porous capillary spacer, forming an interface 4085 with it.

[0344] Preferably, the rate of migration of liquid-phase materials in liquid electrolyte along such liquid feed structures to or from the side surface of the spacer, including but not limited to a porous capillary spacer, is sufficiently rapid that the electrochemical reaction in the cell is maintained and not starved of reactants or overwhelmed by products. Preferably, the material of the porous capillary liquid feed structure 4080 is selected to allow sufficiently rapid transport of liquid-phase materials, according to the principles described in the Applicant's International Patent Publication Nos. W02022056603, W02022056604, W02022056605, and W02022056606 (and not repeated here).

[0345] It is to be understood that top- and side -reservoir cell architectures may also be achieved using surface liquid feed structures or engineered liquid feed structures. The principles described above may be involved in such architectures. It is further to be understood that liquid feed structures may be used to create architectures involving reservoirs around some or all of the peripheries; i.e. top- side-, and/or bottom-reservoir configurations.

5. Other Preferred Conditions and Embodiments

[0346] In one example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the porosity of the spacer is more than 60%, this being preferred for low impedance and high rates of flow of liquid electrolyte, including within but not limited to, porous capillary spacers and porous capillary flow structures. In other examples, the porosity of the spacer is more than 70%, more than 80%, or more than 90%.

[0347] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein, when the spacer is filled with liquid electrolyte, it has an ionic resistance of less than 140 mO cm² at room temperature.

[0348] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the liquid electrolyte comprises a hydroxide salt and has a pH of at least 10.

[0349] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the first gas diffusion electrode and the second electrode each have a side with a geometric surface area of greater than or equal to 10 cm².

[0350] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the first gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

[0351] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the second electrode is also a gas diffusion electrode and the second gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

[0352] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the pressure of the first gas on the first side of the spacer within the cell, including but not limited to a porous capillary spacer, is greater than or smaller than the pressure of the second gas on the opposite, second side of the spacer. In examples, the differential in the pressures between the first gas and the second gas may occur or be made to occur during startup, shutdown or normal operation of the cell. For example, the differential in the pressures between the first gas and the second gas may be deliberately applied to keep the electrodes properly wetted, as described in Figure 3 and associated text. In examples, the differential in the pressures between the first gas and the second gas may be more than 10 mbar. In other examples, the differential in the pressures between the first gas and the second gas may be more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

[0353] In another example form, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the movement of liquid electrolyte with the cell is self-regulated.

[0354] In further example forms, there are provided example electro-synthetic or electro-energy cells as disclosed herein, wherein the average distance between the first gas diffusion electrode and the second electrode is 0.2 mm or less, this being preferred for energy efficient operation. That is, the average inter-electrode distance between the electrodes is 0.2 mm or less.

[0355] In a further example aspect, there is provided an electro-synthetic water electrolysis cell, comprising: a first gas diffusion electrode configured to generate a first gas and be in direct contact with a first gas body comprising the first gas; a second electrode; and a porous capillary spacer configured to be filled with a liquid electrolyte and positioned at least partially between the first gas diffusion electrode and the second electrode; wherein an average pore diameter of the porous capillary spacer is more than 0.03 pm, and I or less than 400 pm, and wherein a side surface of the porous capillary spacer is in contact with a liquid feed structure that contacts the reservoir.

[0356] In a further example aspect there is provided an electro-synthetic water electrolysis cell, comprising: a first gas diffusion electrode configured to generate a first gas and be in direct contact with a first gas body comprising the first gas; a second electrode; and a porous capillary spacer configured to be filled with a liquid electrolyte and positioned at least partially between the first gas diffusion electrode and the second electrode; wherein an average pore diameter of the porous capillary spacer is more than 0.03 pm, and / or less than 400 pm, and wherein liquid electrolyte that continuously or continually transfers out of the reservoir will contact a side surface of the porous capillary spacer. [0357] In another example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell is an example cell as disclosed herein, and the method comprises applying a voltage across the first gas diffusion electrode and the second electrode, or generating a voltage across the first gas diffusion electrode and the second electrode.

[0358] In another example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, the electro -synthetic or electroenergy cell comprising: a reservoir containing a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the spacer, including but not limited to a porous capillary spacer, is in contact with a liquid feed structure that contacts the reservoir. The method comprising the steps of: contacting the first gas diffusion electrode and the second electrode with the liquid electrolyte; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

[0359] In another example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, the electro -synthetic or electroenergy cell comprising: a reservoir containing a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer, including but not limited to a porous capillary spacer, positioned at least partially between the first gas diffusion electrode and the second electrode, wherein liquid electrolyte that continuously or continually transfers out of the reservoir will contact a side surface of the spacer, including but not limited to a porous capillary spacer.

[0360] In another example aspect, there are provided example cells as disclosed herein, wherein the cells are reversible, being electro-synthetic cells when operated in one direction and electroenergy cells when operated in the reverse direction. In one example, the cells are water electrolysis cells that produce hydrogen and oxygen from water when operated as electro-synthetic cells, and hydrogen-oxygen fuel cells that produce electricity when provided with hydrogen and oxygen reactants and operated in the reverse direction as electro-energy cells.

6. Examples [0361] Example embodiment water electrolysis cells and fuel cells employing a ‘top-reservoir’ architecture were fabricated.

Example cells employing a porous capillary spacer between the electrodes

[0362] Figure 10 depicts the overall fabrication process used for these cells. In the first step, a polymer frame 590 had a porous capillary spacer 510 thermally, platen or ultrasonically welded to it, producing the assembly 591. The porous capillary spacer 510 was a polyether sulfone microfiltration membrane with an average pore diameter of 8 pm supplied by Sterlitech Corporation (Auburn, Washington, USA). The polymer frame was machined, or injection moulded. The polymer used for the frame was Udel P-1700 supplied by Solvay (Neder-Over- Heembeek, Brussels, Belgium).

[0363] Within assembly 591, the porous capillary spacer 510 was sealed all along its outer periphery to the frame 590, forming a seam similar to seam 4095 in Figure 9A(a) all along the outer periphery of the porous capillary spacer 510.

[0364] A reservoir of the type depicted in Figures 5-6 or Figure 9B(c), was positioned at the top of the cell (not shown in Figure 10 for clarity).

[0365] An anode electrode and a cathode electrode were then prepared following the directions provided in Example 6 in the Applicant's International Patent Publication No. W02022056603. The electrodes were the same shape as the porous capillary spacer 510, but they were 2-20 mm shorter at each periphery than the porous capillary spacer 510.

[0366] The resulting metallic anode was then attached to a metallic anode bipolar plate and metallic porous transport layer as described in the Applicant's International Patent Application W 02023193057, which is hereby incorporated by reference, to form the metal-to-metal joined assembly 592. The cathode was similarly attached to a metallic cathode bipolar plate and metallic porous transport layer to form the metal-to-metal joined assembly 593. The anode bipolar plate had the overall shape shown in 592, while the cathode bipolar plate had the overall shape depicted in 593. [0367] Cell 501 was then formed when the anode metallic bipolar plate (part of metal-to-metal joined assembly 592) and the cathode metallic bipolar plate (part of metal-to-metal joined assembly 593) were securely attached and sealed by polymer-to-metal joins (e.g. polymer-to-metal welding) to the uncovered, exposed polymer surfaces at the top, bottom and around the sides of the cell frame 590, on both sides, that is on the front and the back of the cell frame 590 respectively, as taught in the Applicant's International Patent Application WO2023193057.

[0368] In an example aspect there is provided a method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell is an example cell as disclosed herein, and the method comprises applying a voltage across the first gas diffusion electrode and the second electrode, or generating a voltage across the first gas diffusion electrode and the second electrode.

[0369] Figure 11 schematically depicts the operation of cell 501. Figure 11(a) shows the polymeric cell frame 590 with porous capillary spacer 510 affixed to it, i.e. assembly 591, as seen from the anode side. A liquid electrolyte 500 (aqueous 6 M KOH) was introduced into header 520 of assembly 591.

[0370] Figure 11(b) shows that the liquid electrolyte 500 moves from header 520 through restrictor 525 to dripper 530, where the stream of liquid electrolyte is broken into droplets by dripper 530, which droplets are received in and fall through drip chamber 535. The liquid management techniques, as well as the terms ‘restrictor’, ‘dripper’, and ‘drip chamber’, are described in the Applicant's International Patent Application WO2023193055, which is hereby incorporated by reference.

[0371] A ‘dripper’, such as dripper 530, is a device that reliably and dependably, if not unfailingly, over long periods of time of continuous or continual operation, breaks a liquid stream passing through it into a continuous, consistent, uniform and / or regular stream of drops, droplets, slugs, or other portions of liquid electrolyte, with gas gaps, for example air gaps, between them. Preferably, the gas gaps, for example air gaps, constitute electrically non-conducting voids, i.e. non-conducting gas voids, that, effectively, break the electrical conductivity of an incoming stream of liquid electrolyte that is otherwise electrically conductive along the incoming stream. That is, where the liquid passing through a dripper is an electrically conductive electrolyte, preferably, the liquid electrolyte body on one side of a dripper is not in electrically conductive contact with the liquid electrolyte body of the other side of the dripper due to the dripper reliably and dependably, if not unfailingly, breaking the liquid stream passing through it into a continuous, consistent, uniform and / or regular stream of drops, droplets, slugs, or other portions of liquid electrolyte, with gas gaps, for example air gaps, between them.

[0372] As noted in the Applicant's International Patent Application WO2023193055, the use of drippers on the liquid electrolyte inlet and outlet of a cell may be used to avoid ‘shunt’ currents (also called ‘by-pass’ currents or ‘leakage’ currents) that may occur between cells when multiple cells are stacked into cell stacks (as described below). That is, the presence and use of drippers on the liquid electrolyte inlet and outlet of a cell may make the cell immune to shunt currents.

[0373] The droplets of liquid electrolyte fall into reservoir 540, which is positioned across the top of the cell, as depicted in Figures 5-6 or Figure 9B(c). The reservoir fills with liquid electrolyte and then transfers liquid to the porous capillary spacer 510. The transfer rate may typically, but not exclusively, be at least double, but up to 20 times, the rate at which the cell requires replenishment water (for example, in the case where the cell consumes water as a reactant). This results in a flow in direction 541 of liquid electrolyte within the porous capillary spacer 510 as shown by the arrows.

[0374] The mode by which reservoir 540 transfers liquid to the porous capillary spacer 510 may occur in several ways, depending on how the reservoir is configured. Some of these non-limiting alternative configurations are described in the paragraphs that follow. It is to be understood that many different possible configurations may be employed in this respect, including ones that are not described below. All such configurations, without limitation, fall within the scope of this specification.

[0375] In a first configuration, one edge of the porous capillary spacer 510 passes through the bottom of reservoir 540, which forms a slit (of the type 245 depicted in Figures 4-6) on either side of the porous capillary spacer 510, at the bottom of reservoir 540. Above the slit, the porous capillary spacer 510 is immersed in the liquid electrolyte inside liquid electrolyte reservoir 540. Liquid electrolyte is transferred into the porous capillary spacer 510 inside the reservoir 540, and may then flow downward in direction 541 as shown by the arrows, within the porous capillary spacer 510. Additionally, apertures of the type 245a depicted in Figures 4-6, may be present in the slit and these apertures may transfer liquid electrolyte onto the side surfaces of the porous capillary spacer 510 immediately below the reservoir 540, as described in Section 2 and Figures 4-6. Such liquid electrolyte may also flow downward in direction 541 and into and within the porous capillary spacer 510, as shown by the arrows.

[0376] In a second, alternative configuration, a porous capillary liquid feed structure (this being, for example, a separate sheet of a polyether sulfone microfiltration membrane with an average pore diameter of 8 pm) is placed with its one edge in the liquid electrolyte reservoir and the other edge bent over and placed tight up against the side surface of the porous capillary spacer 510, where it extends beyond the electrodes, as depicted in Figure 9B(c). The porous capillary liquid feed structure draws liquid electrolyte out of the liquid electrolyte reservoir and transfers the liquid electrolyte to the side surfaces of the porous capillary spacer 510, thereby inducing the flow in direction 541 of liquid electrolyte within the porous capillary spacer 510 shown by the arrows.

[0377] In a third alternative configuration, one edge of a porous capillary liquid feed structure (this also being, for example, a separate sheet of a polyether sulfone microfiltration membrane with an average pore diameter of 8 pm) penetrates the bottom of reservoir 540, through a slit (of the type 245 in Figures 4-6 or 445b in Figure 8(b)) at the bottom of reservoir 540, and is immersed in the liquid electrolyte inside liquid electrolyte reservoir 540. The opposite edge of the porous capillary liquid feed structure is placed tight up against the side surface of the porous capillary spacer 510, where it extends beyond the electrodes (in the manner described in Liquid Feed Structure Example Embodiment A of section 4 and depicted by 440b, 480b, and 485b in Figure 8(b)). The porous capillary liquid feed structure transfers liquid electrolyte from the liquid electrolyte reservoir 540 to the side surfaces of the porous capillary spacer 510, thereby inducing the flow in direction 541 within the porous capillary spacer 510 shown by the arrows.

[0378] In a fourth alternative configuration, reservoir 540 has 4-10 equally spaced pipes attached to it, each of which contains a valve or comprises a constriction, through which liquid 500 may be transferred from the bottom of reservoir 540 to the side surfaces of porous capillary spacer 510, where it extends beyond the electrodes (in the manner described in Liquid Feed Structure Example Embodiment E of section 4 and depicted by 440e, 486e, and 480e in Figure 8(a)). The transferred liquid electrolyte induces the flow in direction 541 within the porous capillary spacer 510 shown by the arrows. The valves may regulate the rate at which liquid electrolyte 500 transfers to the porous capillary spacer 510. [0379] In a fifth alternative configuration, reservoir 540 has 4-10 equally spaced pipes attached to it, each of which contains a small pump or pumping actuator, through which liquid electrolyte 500 may be transferred from the top of liquid electrolyte reservoir 540 to the side surfaces of porous capillary spacer 510, where it extends beyond the electrodes (in the manner described in Liquid Feed Structure Example Embodiment H of section 4 and depicted by 440h, 480h, 485h, and 486h in Figure 8(b)). The transferred liquid electrolyte induces the flow in direction 541 within the porous capillary spacer 510 shown by the arrows. The pumps or pumping actuators may regulate the rate at which liquid electrolyte 500 transfers to the porous capillary spacer 510.

[0380] In a sixth alternative configuration, reservoir 540 has 4-10 equally spaced apertures in it, each of which serves as an overflow weir. As the liquid electrolyte reservoir is continuously or continually filled by dripper 530, excess liquid electrolyte passes out of the apertures and transfers onto the side surface of the porous capillary spacer 510, where it extends beyond the electrodes (in the manner described in Liquid Electrolyte Transfer Example Embodiment A of section 3 and depicted by 340a, 341a, 382a, and 385a in Figure 7). The transferred liquid electrolyte induces the flow in direction 541 within the porous capillary spacer 510 shown by the arrows. The rate at which dripper 530 supplies liquid electrolyte to liquid electrolyte reservoir 540 may regulate the transfer rate of liquid electrolyte 500 to the porous capillary spacer 510. Thus, in this example the cell includes dripper 530 which breaks the liquid electrolyte into droplets before being transported into the liquid electrolyte reservoir 540.

[0381] In a seventh alternative configuration, reservoir 540 has 4-10 equally spaced apertures at its bottom, each of which comprises a valve whose aperture may be adjusted. Liquid electrolyte passes out of the apertures and transfers onto the side surface of the porous capillary spacer 510, where it extends beyond the electrodes (in the manner described in Liquid Electrolyte Transfer Example Embodiment B of section 3 and depicted by 340b, 382b, and 385b in Figure 7). The transferred liquid electrolyte induces the flow in direction 541 within the porous capillary spacer 510 shown by the arrows. The rate at which liquid electrolyte is transferred to the porous capillary spacer 510 may be regulated by the aperture size of the valves.

[0382] It will be appreciated that, depending on the rate at which dripper 530 supplies liquid electrolyte to the liquid electrolyte reservoir 540, in some of the above configurations the reservoir 540 may be supplied with an excess of liquid. In such cases, liquid electrolyte reservoir 540 may be configured to have an overflow weir 545 at its one end (see, for example, conduit 277R in Figure 5), over which excess liquid electrolyte 500 may drain, to thereby maintain a fixed liquid level within the liquid electrolyte reservoir 540.

[0383] The flow in direction 541 of liquid within porous capillary spacer 510, shown by the arrows, provides the conditions needed for the water electrolysis or fuel cell reaction to occur. Accordingly, the dashed line 551 in Figure 11(c) depicts the flow of anode gas to or from the anode gas header 550. In the case of a water electrolysis cell, the anode gas is produced by the anode in the cell and flows out of the cell via anode gas header 550. In the case of a fuel cell, anode gas is consumed by the anode in the cell and flows into the cell via anode gas header 550.

[0384] That is, in a water electrolysis cell, the anode produces oxygen gas while the cathode produces hydrogen gas. The oxygen gas produced by the anode passes out of the cell via header 550, with the gas moving in the upward direction 551 shown by the arrow. Hydrogen gas will be produced on the back side of the assembly 591 and will flow out of the cell via another header.

[0385] In a fuel cell by contrast, the anode consumes hydrogen gas, while the cathode consumes oxygen gas. The hydrogen gas consumed by the anode flows into the cell via header 550, with the gas moving in the downward direction 551 shown by the arrow. Oxygen gas will be consumed on the back side of the assembly 591 and will flow into the cell via another header.

[0386] Figure 11(d) depicts what happens when the liquid flowing down the porous capillary spacer 510 in the direction 541 shown by the arrows reaches the bottom of the cell. Such liquid electrolyte flows into a lower liquid electrolyte reservoir 560 in the manner described in Liquid Elecrolyte Transfer Example Embodiment D of section 3 and depicted by 340d, 382d, and 385d in Figure 7. The lower liquid electrolyte reservoir may have 4-10 equally spaced apertures at its top to receive the liquid electrolyte.

[0387] The lower liquid electrolyte reservoir 560 has a channel 565 that connects it to a second dripper 570. A suction force provided by the outlet header 590 induces liquid electrolyte from liquid electrolyte reservoir 560 to flow up channel 565 and into the dripper 570, from where its flow is broken into droplets in the drip chamber 575, as shown in Figure 11(e).

[0388] In cases where the top liquid electrolyte reservoir 540 has an overflow weir 545 at its one end, over which excess liquid electrolyte 500 may drain, the excess liquid electrolyte may flow down channel 546 into dripper 570, as depicted in Figure 11(d). Such liquid electrolyte, along with liquid electrolyte drawn up from the lower liquid electrolyte reservoir 560, exit the cell via dripper 570 and outlet header 590.

[0389] As noted above and in the Applicant's International Patent Application WO2023193055, the purpose of the two drippers 530 (inlet) and 570 (outlet) are to electrically isolate the liquid electrolyte in the cell from the liquid electrolyte in other adjacent or nearby cells, by breaking any conduction pathways via the conductive liquid electrolyte passing into or out of the cell. That is, the creation of gas gaps between the droplets in the drip chambers 535 and 575 avoids electrical conduction between adjacent or nearby cells via the liquid electrolyte, e.g. 6 M KOH electrolyte. This, in turn, avoids ‘shunt currents’ (also called bypass currents or leakage currents) that may occur when multiple cells of this type are stacked into filter-press -type cell stacks.

[0390] Thus, the liquid electrolyte reservoir 540 is in fluid communication with a dripper 530. The dripper 530 is positioned in-line in a liquid electrolyte inlet section. The dripper 570 is positioned in-line in a liquid electrolyte outlet section. The drippers 530, 570 break the liquid electrolyte into drops. The drops are received in and fall through drip chamber 535 positioned below the dripper. The liquid electrolyte on one side of each of the drippers 530, 570 is electrically isolated from the liquid electrolyte on the other side of each of the drippers 530, 570.

- Example cells employing a different type of spacer between the electrodes

[0391] A similar cell to that described above was produced wherein the spacer 510 was a X37- 50 anion exchange membrane (AEM) spacer from Dioxide Materials (Boca Raton, Florida, USA) imbued with 1 M aqueous KOH electrolyte. The cell employed 1 M aqueous KOH as a conductive liquid electrolyte. The anion exchange membrane spacer was soaked in the liquid electrolyte for several days prior to use and following its attachment to the cell frame 590. The attachment of the anion exchange membrane spacer to the cell frame may be made using a separate polymeric frame, which mechanically clamped and sealed the peripheries of the anion exchange membrane spacer to the cell frame 590. The cell may be operated as described above. More of the liquid electrolyte appeared to flow on the surface of the AEM spacer 510 in the directions 541 and not within the spacer 510, as occurred with the porous capillary spacer of the previous example. This was likely because of the non-porous nature of the AEM spacer.

[0392] Cells of types similar to the above may also be constructed using Nafion membrane spacers, including but not limited to, Nafion 115 or Nafion 117. In such cases, the liquid electrolyte transferred onto the side surface of the Nafion spacer 510, where it extended beyond the electrodes, was de-ionized water or a weakly acidic aqueous solution. More of the liquid electrolyte also appeared to flow on the surface of the Nafion spacer 510 in the directions 541 and not within the spacer 510, as occurred with the porous capillary spacer of the previous example. This was likely because of the non-porous nature of the Nafion membrane.

[0393] Even in cases where some or more of the liquid appeared to flow on the surface of the spacer, the electrodes could be maintained properly wetted and not oversaturated or overwhelmed with liquid electrolyte.

7. Electrochemical cell stacks

[0394] In another example aspect there is provided a stack of electro-synthetic or electro-energy cells, comprising: a first electro -synthetic or electro-energy cell; and a second electro-synthetic or electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell; wherein each electro -synthetic or electro -energy cell is an example cell as disclosed herein.

[0395] Figure 12 depicts how cells of the type disclosed herein may be stacked into filter-press type ‘cell stacks’. Multiple cells 501 are stacked one after the other as shown at 601 or 660 in Figure 12, between two conductive, metallic endplates 610 and 620. Tie rods 630 are passed through common apertures in the cells within the stacked cells 601 to thereby ensure that all cells in the stack have the same orientation and all headers line up to form internal pipes within the stack. Bolts and washers 640 and 650 are screwed onto the tie rods 630 to thereby create the final cell stack 660. Liquid electrolyte is then passed into and through the stack via the appropriate liquid headers, while gases are either collected from or passed into the stack via the gas headers. An electrical current is then passed through the stack by connecting one endplate 610 to the positive terminal and the other endplate 620 to the negative terminal of an electrical power supply or electrical power receiving device. The electrical current is transmitted from one cell to the next via the contact between their bipolar plates in the stack. No electrical current flows between cells via the liquid electrolyte headers, as the inlet and outlet dripper in each cell isolate each cell from the next in this respect (as described in the Applicant’ International Patent Application WO2023193055).

[0396] In another example aspect there is provided a method of operating a stack of electrosynthetic or electro-energy cells to perform an electrochemical reaction, wherein the stack of electro-synthetic or electro-energy cells is a stack of example electro-synthetic or electro-energy cells as disclosed herein, and the method comprises applying a voltage across the first gas diffusion electrode and the second electrode in each stack of electro -synthetic or electro-energy cells, or generating a voltage across the first gas diffusion electrode and the second electrode in each stack of electro-synthetic or electro-energy cells.

8. Combinations of Features

[0397] According to various non-limiting example embodiments, the following points disclose combinations of features that provide various example cells, multi-cell stacks, systems and/or example methods of operation.

1. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode.

2. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to transfer the liquid electrolyte from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir.

3. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; a spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the spacer is positioned outside of the liquid electrolyte reservoir.

4. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; a spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the spacer is positioned outside of the liquid electrolyte reservoir; and an intermediate liquid feed structure, located at least partially between the side surface of the spacer and the liquid electrolyte reservoir, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir to at least part of the side surface of the spacer by the intermediate liquid feed structure.

5. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a porous capillary spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the porous capillary spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the porous capillary spacer is positioned outside of the liquid electrolyte reservoir; wherein, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto at least part of the side surface of the porous capillary spacer.

6. The cell of any one or more of the preceding points, wherein an end surface of the spacer is positioned beyond the first gas diffusion electrode and the second electrode, and the end surface of the spacer is positioned within the liquid electrolyte reservoir.

7. The cell of any one or more of the preceding points, wherein the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer.

8. The cell of any one or more of the preceding points, wherein a pressure of a gas within the cell is greater than atmospheric pressure.

9. The cell of any one or more of the preceding points, wherein a pressure of a gas within the cell is greater than 1.1 bara.

10. The cell of any one or more of the preceding points, wherein a pressure of a gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

11. The cell of any one or more of the preceding points, wherein the first gas diffusion electrode and the second electrode are compressed against the spacer by more than 2 bar.

12. The cell of any one or more of the preceding points, wherein the first gas diffusion electrode and the second electrode are compressed against the spacer by more than 3 bar, more than 4 bar, more than 5 bar, more than 7 bar, or more than 10 bar.

13. The cell of any one or more of the preceding points, wherein an average pore diameter of the spacer is larger than 0.03 pm.

14. The cell of any one or more of the preceding points, wherein an average pore diameter of the spacer is smaller than 400 pm. - I l l -

15. The cell of any one or more of the preceding points, wherein an average pore diameter of the spacer is more than 0.03 pm and less than 400 pm.

16. The cell of any one or more of the preceding points, wherein an average pore diameter of the spacer is smaller than 200 pm, smaller than 100 pm, smaller than 50 pm, smaller than 25 pm, smaller than 15 pm, smaller than 8 pm, smaller than 5 pm, smaller than 3 pm, smaller than 2 pm, or smaller than 1 pm.

17. The cell of any one or more of the preceding points, wherein a height of the cell is greater than 15 cm.

18. The cell of any one or more of the preceding points, wherein a height of the cell is greater than 18 cm, greater than 20 cm, greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm.

19. The cell of any one or more of the preceding points, wherein the spacer has a thickness of less than 0.2 mm.

20. The cell of any one or more of the preceding points, wherein the spacer has a thickness of less than 0.2 mm and a height of the cell is greater than 20 cm.

21. The cell of any one or more of the preceding points , wherein the sp acer has a bubble point of more than 50 mbar.

22 The cell of any one or more of the preceding points, wherein the spacer has a bubble point of more than 70 mbar, more than 100 mbar, more than 200 mbar, more than 500 mbar, more than 750 mbar, more than 1 bar, more than 2 bar, or more than 5 bar.

23. The cell of any one or more of the preceding points, wherein a capillary pressure in the pores of the spacer is greater than a capillary pressure in the pores of the first gas diffusion electrode. 24. The cell of any one or more of the preceding points, wherein the cell operates without substantially saturating the first gas diffusion electrode and the second electrode with the liquid electrolyte.

25. The cell of any one or more of the preceding points, wherein during operation the first gas diffusion electrode and the second electrode are not over-saturated with the liquid electrolyte.

26. The cell of any one or more of the preceding points, wherein the side surface of the spacer has a contact area with the liquid electrolyte that is greater than or equal to 1 cm².

27. The cell of any one or more of the preceding points, wherein the side surface of the spacer has a contact area with the liquid electrolyte that is greater than or equal to 2 cm², greater than or equal to 3 cm², greater than or equal to 4 cm², or greater than or equal to 5 cm².

28. The cell of any one or more of the preceding points, wherein during operation the transfer of the liquid electrolyte from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer utilises gravity.

29. The cell of any one or more of the preceding points, wherein during operation the liquid electrolyte is transferred from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer at a feed rate greater than that required to replenish the liquid electrolyte that is removed or consumed during the electrochemical reaction, or greater than that required to remove excess liquid that is retained or produced during the electrochemical reaction.

30. The cell of any one or more of the preceding points, wherein during operation the transfer of the liquid electrolyte is at a feed rate that is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer.

31. The cell of any one or more of the preceding points, wherein during operation a flow rate of the liquid electrolyte is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer, inside the spacer between the first gas diffusion electrode and the second electrode. 32. The cell of any one or more of the preceding points, wherein the spacer is a porous capillary spacer.

33. The cell of any one or more of the preceding points, wherein the spacer does not directly contact the liquid electrolyte that is within the liquid electrolyte reservoir.

34. The cell of any one or more of the preceding points, wherein the liquid electrolyte reservoir is located at, with respect to the direction of gravity: a top of the cell, and/or a side of the cell.

35. The cell of any one or more of the preceding points, wherein the first gas diffusion electrode is positioned below the liquid electrolyte reservoir, and the second electrode is positioned below the liquid electrolyte reservoir, with respect to the direction of gravity.

36. The cell of any one or more of the preceding points, wherein the first gas diffusion electrode is positioned below the side surface of the spacer, and the second electrode is positioned below the side surface of the spacer, with respect to the direction of gravity.

37. The cell of any one or more of the preceding points, wherein the aperture is an overflow weir.

38. The cell of any one or more of the preceding points, wherein the aperture is located below a height of the liquid electrolyte in the liquid electrolyte reservoir.

39. The cell of any one or more of the preceding points, wherein the aperture is or is associated with a constricted aperture and/or a valve.

40. The cell of any one or more of the preceding points, wherein the constricted aperture and/or the valve regulates the transfer of the liquid electrolyte out of the liquid electrolyte reservoir.

41. The cell of any one or more of the preceding points, wherein there are two or more liquid electrolyte reservoirs. 42. The cell of any one or more of the preceding points, wherein the two or more liquid electrolyte reservoirs are located at, with respect to the direction of gravity: a top of the cell, and/or a side of the cell.

43. The cell of any one or more of the preceding points, wherein the liquid electrolyte transfers from the at least part of the side surface of the spacer into a lower liquid electrolyte reservoir positioned below the first gas diffusion electrode and the second electrode, with respect to the direction of gravity.

44. The cell of any one or more of the preceding points, wherein the at least part of the side surface of the spacer abuts or is close to the liquid electrolyte reservoir.

45. The cell of any one or more of the preceding points, configured such that during operation the liquid electrolyte contacts the first gas diffusion electrode and the second electrode only after first being transported via the spacer.

46. The cell of any one or more of the preceding points, wherein the first gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

47. The cell of any one or more of the preceding points, wherein the first gas diffusion electrode is configured to generate or consume a first gas of a first gas body, a first side of the spacer is adjacent a first side of the first gas diffusion electrode, a second side of the spacer is adjacent a first side of the second electrode, and a second side of the first gas diffusion electrode is adjacent the first gas body.

48. The cell of any one or more of the preceding points, wherein a pressure of the first gas within the cell is greater than atmospheric pressure.

49. The cell of any one or more of the preceding points, wherein a pressure of the first gas within the cell is greater than 1.1 bara. 50. The cell of any one or more of the preceding points, wherein a pressure of the first gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

51. The cell of any one or more of the preceding points, wherein the second electrode is a second gas diffusion electrode.

52. The cell of any one or more of the preceding points, wherein the second gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

53. The cell of any one or more of the preceding points, wherein the second gas diffusion electrode is configured to generate or consume a second gas of a second gas body, and a second side of the second gas diffusion electrode is adjacent the second gas body.

54. The cell of any one or more of the preceding points, wherein a pressure of the second gas within the cell is greater than atmospheric pressure.

55. The cell of any one or more of the preceding points, wherein a pressure of the second gas within the cell is greater than 1.1 bara.

56. The cell of any one or more of the preceding points, wherein a pressure of the second gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

57. The cell of any one or more of the preceding points, wherein the pressure of the first gas is greater or smaller than the pressure of the second gas.

58. The cell of any one or more of the preceding points, wherein a differential in the pressures between the first gas and the second gas is more than 10 mbar, more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

59. The cell of any one or more of the preceding points, wherein the first gas diffusion electrode and the second electrode are sandwiched against opposite sides of the spacer. 60. The cell of any one or more of the preceding points, wherein the distance between the first gas diffusion electrode and the second electrode is 0.2 mm or less.

61. The cell of any one or more of the preceding points, wherein the transfer of the liquid electrolyte involves the liquid electrolyte to flow, run, pour, migrate, pass, drop, drip, or spray from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer.

62. The cell of any one or more of the preceding points, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir onto at least part of each of two side surfaces of the spacer that extend beyond the first gas diffusion electrode and the second electrode, and that are outside of the liquid electrolyte reservoir.

63. The cell of any one or more of the preceding points, further including a dripper which breaks the liquid electrolyte into droplets before being supplied to the liquid electrolyte reservoir.

64. The cell of any one or more of the preceding points, wherein the cell is a reversible cell.

65. The cell of any one or more of the preceding points, wherein the cell is a water electrolysis cell.

66. The cell of any one or more of the preceding points , wherein the cell is a hydrogen-oxygen fuel cell.

67. The cell of any one or more of the preceding points, further including an intermediate liquid feed structure, located at least partially between the side surface of the spacer and the liquid electrolyte reservoir, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir to at least part of the side surface of the spacer by the intermediate liquid feed structure.

68. The cell of any one or more of the preceding points, wherein the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto at least part of the side surface of the porous capillary spacer. 69. The cell of any one or more of the preceding points, wherein the spacer does not directly contact the liquid electrolyte that is within the liquid electrolyte reservoir.

70. The cell of any one or more of the preceding points, wherein the intermediate liquid feed structure is separate and distinct from the spacer.

71. The cell of any one or more of the preceding points, wherein the intermediate liquid feed structure is in direct contact with the liquid electrolyte that is within the liquid electrolyte reservoir.

72. The cell of any one or more of the preceding points, wherein the intermediate liquid feed structure is in direct contact with the side surface of the spacer.

73. The cell of any one or more of the preceding points, wherein the spacer is spaced apart from the liquid electrolyte reservoir.

74. The cell of any one or more of the preceding points, wherein the intermediate liquid feed structure is a porous capillary liquid feed structure.

75. The cell of any one or more of the preceding points, wherein the liquid electrolyte reservoir has a width substantially equal to a width of the cell and is positioned across a top of the cell, with respect to the direction of gravity.

76. The cell of any one or more of the preceding points, wherein the porous capillary liquid feed structure is sheet-like and has one edge dipped into the liquid electrolyte reservoir.

77. The cell of any one or more of the preceding points, wherein the porous capillary liquid feed structure spontaneously draws in and maintains a volume of the liquid electrolyte within the porous capillary liquid feed structure by capillary action.

78. The cell of any one or more of the preceding points, wherein the liquid electrolyte moves within the porous capillary liquid feed structure under the influence of capillary and/or diffusion and/or osmotic control. 79. The cell of any one or more of the preceding points, wherein the intermediate liquid feed structure is a surface liquid feed structure.

80. The cell of any one or more of the preceding points, wherein the liquid electrolyte moves along a surface of the surface liquid feed structure.

81. The cell of any one or more of the preceding points, wherein the intermediate liquid feed structure is a pipe, a conduit, a channel, a tube, a chamber, or a trough.

82. The cell of any one or more of the preceding points, configured such that during operation the liquid electrolyte contacts the first gas diffusion electrode and the second electrode only after first being transported from the liquid electrolyte reservoir by the intermediate liquid feed structure and then by the spacer.

83. The cell of any one or more of the preceding points, wherein movement of the liquid electrolyte along or within the intermediate liquid feed structure is self-regulated.

84. A stack of electro-synthetic or electro -energy cells, comprising: a first electro-synthetic or electro -energy cell; and a second electro-synthetic or electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell; wherein each electro-synthetic or electro-energy cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode.

85. A stack of electro-synthetic or electro -energy cells, comprising: a first electro-synthetic or electro -energy cell; and a second electro-synthetic or electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell; wherein each electro-synthetic or electro-energy cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to allow the liquid electrolyte to transfer from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir.

86. A stack of cells, wherein the first electro -synthetic or electro -energy cell is a cell according to the cell of any one or more of the preceding points, and the second electro- synthetic or electro-energy cell is a cell according to the cell of any one or more of the preceding points.

87. A method of operating an electro- synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; the method including the steps of: transporting the liquid electrolyte via the spacer to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

88. A method of operating an electro- synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; the method including the steps of: allowing the liquid electrolyte to transfer from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir; transporting the liquid electrolyte via the spacer to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

89. A method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte reservoir for containing a liquid electrolyte, wherein the liquid electrolyte reservoir includes an aperture; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a porous capillary spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the porous capillary spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the porous capillary spacer is positioned outside of the liquid electrolyte reservoir; the method including the steps of: allowing the liquid electrolyte to transfer from the liquid electrolyte reservoir via the aperture onto at least part of the side surface of the porous capillary spacer; transporting the liquid electrolyte via the porous capillary spacer to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

90. The method of any one or more of the preceding points, wherein an end of the spacer extends beyond the first gas diffusion electrode and the second electrode, the end of the spacer positioned within the liquid electrolyte reservoir.

91. The method of any one or more of the preceding points, wherein the spacer is positioned outside of the liquid electrolyte reservoir. 92. The method of any one or more of the preceding points, further including the liquid electrolyte reservoir having an aperture to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer.

93. The method of any one or more of the preceding points, wherein the aperture is an overflow weir and when a height of the liquid electrolyte in the liquid electrolyte reservoir is at a height of the overflow weir, and further liquid electrolyte is added, then the liquid electrolyte transfers onto the at least part of the side surface of the spacer.

94. The method of any one or more of the preceding points, wherein a rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the at least part of the side surface of the spacer is regulated by regulating a rate at which the liquid electrolyte is added to the liquid electrolyte reservoir.

95. The method of any one or more of the preceding points, wherein a rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the at least part of the side surface of the spacer is regulated by a size of the aperture.

96. The method of any one or more of the preceding points, wherein during operation the first gas diffusion electrode is configured to generate or consume a first gas of a first gas body.

97. The method of any one or more of the preceding points, wherein a pressure of the first gas within the cell is greater than atmospheric pressure.

98. The method of any one or more of the preceding points, wherein a pressure of the first gas within the cell is greater than 1.1 bara.

99. The method of any one or more of the preceding points, wherein a pressure of the first gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

100. The method of any one or more of the preceding points, wherein the second electrode is a second gas diffusion electrode and during operation the second gas diffusion electrode is configured to generate or consume a second gas of a second gas body. 101. The method of any one or more of the preceding points, wherein a pressure of the second gas within the cell is greater than atmospheric pressure.

102. The method of any one or more of the preceding points, wherein a pressure of the second gas within the cell is greater than 1. 1 bara.

103. The method of any one or more of the preceding points, wherein a pressure of the second gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

104. The method of any one or more of the preceding points, wherein the pressure of the first gas is greater than or smaller the pressure of the second gas.

105. The method of any one or more of the preceding points, wherein a differential in the pressures between the first gas and the second gas is more than 10 mbar, more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

106. The method of any one or more of the preceding points, wherein the transfer of the liquid electrolyte from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer utilises gravity.

107. The method of any one or more of the preceding points, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer at a feed rate greater than that required to replenish the liquid electrolyte that is removed or consumed during the electrochemical reaction.

108. The method of any one or more of the preceding points, wherein the transfer of the liquid electrolyte is at a feed rate that is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer.

109. The method of any one or more of the preceding points, wherein the transfer of the liquid electrolyte is at a feed rate that is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute, of liquid electrolyte per minute, normalised for a 1 cm wide spacer.

110. The method of any one or more of the preceding points, wherein a flow rate of the liquid electrolyte is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer, within the spacer between the first gas diffusion electrode and the second electrode.

111. The method of any one or more of the preceding points, wherein a flow rate of the liquid electrolyte is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute, of liquid electrolyte per minute, normalised for a 1 cm wide spacer, within the spacer between the first gas diffusion electrode and the second electrode.

112. The method of any one or more of the preceding points, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir onto at least part of each of two side surfaces of the spacer that extend beyond the first gas diffusion electrode and the second electrode, and that are outside of the liquid electrolyte reservoir.

113. The method of any one or more of the preceding points, wherein the cell is a reversible cell.

114. The method of any one or more of the preceding points, wherein the cell is a water electrolysis cell.

115. The method of any one or more of the preceding points, wherein the cell is a hydrogenoxygen fuel cell.

116. The cell, stack of cells, or method of any one or more of the preceding points, wherein the porosity of the spacer is more than 60%, more than 70%, more than 80%, or more than 90%. 117. The cell, stack of cells, or method of any one or more of the preceding points, wherein, when the spacer is filled with liquid electrolyte, the spacer has an ionic resistance of less than 140 m cm² at room temperature.

118. The cell, stack of cells, or method of any one or more of the preceding points, wherein the liquid electrolyte comprises a hydroxide salt and has a pH of at least 10.

[0398] Although preferred embodiments have been described in detail, it is to be understood that many modifications, changes, substitutions or alterations will be apparent to those skilled in the art without departing from the scope of the present invention.

[0399] Embodiments and modes of operation may be said to broadly involve the parts, elements and features referred to or indicated herein, individually or collectively, in any or all combinations of two or more of the parts, elements or features, and wherein specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0400] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

The Claims.

1. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to transfer the liquid electrolyte from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir.

2. The cell of claim 1, wherein an end surface of the spacer is positioned beyond the first gas diffusion electrode and the second electrode, and the end surface of the spacer is positioned within the liquid electrolyte reservoir.

3. The cell of either claim 1 or 2, wherein the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer.

4. The cell of any one of claims 1 to 3, wherein a pressure of a gas within the cell is greater than atmospheric pressure.

5. The cell of any one of claims 1 to 3, wherein a pressure of a gas within the cell is greater than 1.1 bara.

6. The cell of any one of claims 1 to 3, wherein a pressure of a gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

7. The cell of any one of claims 1 to 6, wherein the first gas diffusion electrode and the second electrode are compressed against the spacer by more than 2 bar.

8. The cell of any one of claims 1 to 6, wherein the first gas diffusion electrode and the second electrode are compressed against the spacer by more than 3 bar, more than 4 bar, more than 5 bar, more than 7 bar, or more than 10 bar.

9. The cell of any one of claims 1 to 8, wherein an average pore diameter of the spacer is larger than 0.03 pm.

10. The cell of any one of claims 1 to 8, wherein an average pore diameter of the spacer is smaller than 400 pm.

11. The cell of any one of claims 1 to 8, wherein an average pore diameter of the spacer is more than 0.03 pm and less than 400 pm.

12. The cell of any one of claims 1 to 8, wherein an average pore diameter of the spacer is smaller than 200 pm, smaller than 100 pm, smaller than 50 pm, smaller than 25 pm, smaller than 15 pm, smaller than 8 pm, smaller than 5 pm, smaller than 3 pm, smaller than 2 pm, or smaller than 1 pm.

13. The cell of any one of claims 1 to 12, wherein a height of the cell is greater than 15 cm.

14. The cell of any one of claims 1 to 12, wherein a height of the cell is greater than 18 cm, greater than 20 cm, greater than 22 cm, greater than 24 cm, greater than 25 cm, greater than 30 cm, greater than 40 cm, greater than 50 cm, or greater than 100 cm.

15. The cell of any one of claims 1 to 14, wherein the spacer has a thickness of less than 0.2 mm.

16. The cell of any one of claims 1 to 14, wherein the spacer has a thickness of less than 0.2 mm and a height of the cell is greater than 20 cm.

17. The cell of any one of claims 1 to 16, wherein the spacer has a bubble point of more than 50 mbar.

18. The cell of any one of claims 1 to 16, wherein the spacer has a bubble point of more than 70 mbar, more than 100 mbar, more than 200 mbar, more than 500 mbar, more than 750 mbar, more than 1 bar, more than 2 bar, or more than 5 bar.

19. The cell of any one of claims 1 to 18, wherein a capillary pressure in the pores of the spacer is greater than a capillary pressure in the pores of the first gas diffusion electrode.

20. The cell of any one of claims 1 to 19, wherein the cell operates without substantially saturating the first gas diffusion electrode and the second electrode with the liquid electrolyte.

21. The cell of any one of claims 1 to 19, wherein during operation the first gas diffusion electrode and the second electrode are not over- saturated with the liquid electrolyte.

22. The cell of any one of claims 1 to 21, wherein the side surface of the spacer has a contact area with the liquid electrolyte that is greater than or equal to 1 cm².

23. The cell of any one of claims 1 to 21, wherein the side surface of the spacer has a contact area with the liquid electrolyte that is greater than or equal to 2 cm², greater than or equal to 3 cm², greater than or equal to 4 cm², or greater than or equal to 5 cm².

24. The cell of any one of claims 1 to 23, wherein, during operation, the transfer of the liquid electrolyte from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer utilises gravity.

25. The cell of any one of claims 1 to 24, wherein during operation the liquid electrolyte is transferred from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer at a feed rate greater than that required to replenish the liquid electrolyte that is removed or consumed during the electrochemical reaction, or greater than that required to remove excess liquid that is retained or produced during the electrochemical reaction.

26. The cell of any one of claims 1 to 25, wherein during operation the transfer of the liquid electrolyte is at a feed rate that is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer.

27. The cell of any one of claims 1 to 26, wherein during operation a flow rate of the liquid electrolyte is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer, inside the spacer between the first gas diffusion electrode and the second electrode.

28. The cell of any one of claims 1 to 27, wherein the spacer is a porous capillary spacer.

29. The cell of claim 1, wherein the spacer does not directly contact the liquid electrolyte that is within the liquid electrolyte reservoir.

30. The cell of any one of claims 1 to 29, wherein the liquid electrolyte reservoir is located at, with respect to the direction of gravity: a top of the cell, and/or a side of the cell.

31. The cell of any one of claims 1 to 30, wherein the first gas diffusion electrode is positioned below the liquid electrolyte reservoir, and the second electrode is positioned below the liquid electrolyte reservoir, with respect to the direction of gravity.

32. The cell of any one of claims 1 to 31, wherein the first gas diffusion electrode is positioned below the side surface of the spacer, and the second electrode is positioned below the side surface of the spacer, with respect to the direction of gravity.

33. The cell of claim 3, wherein the aperture is an overflow weir.

34. The cell of claim 3, wherein the aperture is located below a height of the liquid electrolyte in the liquid electrolyte reservoir.

35. The cell of claim 3, wherein the aperture is or is associated with a constricted aperture and/or a valve.

36. The cell of claim 35, wherein the constricted aperture and/or the valve regulates the transfer of the liquid electrolyte out of the liquid electrolyte reservoir.

37. The cell of any one of claims 1 to 36, wherein there are two or more liquid electrolyte reservoirs.

38. The cell of claim 37, wherein the two or more liquid electrolyte reservoirs are located at, with respect to the direction of gravity: a top of the cell, and/or a side of the cell.

39. The cell of any one of claims 1 to 38, wherein the liquid electrolyte transfers from the at least part of the side surface of the spacer into a lower liquid electrolyte reservoir positioned below the first gas diffusion electrode and the second electrode, with respect to the direction of gravity.

40. The cell of any one of claims 1 to 39, wherein the at least part of the side surface of the spacer abuts or is close to the liquid electrolyte reservoir.

41. The cell of any one of claims 1 to 40, configured such that during operation the liquid electrolyte contacts the first gas diffusion electrode and the second electrode only after first being transported via the spacer.

42. The cell of any one of claims 1 to 41, wherein the first gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

43. The cell of any one of claims 1 to 42, wherein the first gas diffusion electrode is configured to generate or consume a first gas of a first gas body, a first side of the spacer is adjacent a first side of the first gas diffusion electrode, a second side of the spacer is adjacent a first side of the second electrode, and a second side of the first gas diffusion electrode is adjacent the first gas body.

44. The cell of claim 43, wherein a pressure of the first gas within the cell is greater than atmospheric pressure.

45. The cell of claim 43, wherein a pressure of the first gas within the cell is greater than 1.1 bara.

46. The cell of claim 43, wherein a pressure of the first gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

47. The cell of any one of claims 1 to 46, wherein the second electrode is a second gas diffusion electrode.

48. The cell of claim 47, wherein the second gas diffusion electrode includes a metallic mesh, a metallic foam and/or a metallic perforated plate.

49. The cell of claim 47 or 48, wherein the second gas diffusion electrode is configured to generate or consume a second gas of a second gas body, and a second side of the second gas diffusion electrode is adjacent the second gas body.

50. The cell of claim 49, wherein a pressure of the second gas within the cell is greater than atmospheric pressure.

51. The cell of claim 49, wherein a pressure of the second gas within the cell is greater than

1.1 bara.

52. The cell of claim 49, wherein a pressure of the second gas within the cell is greater than

1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

53. The cell of any one of claims 43 to 46, and, any one of claims 49 to 52, wherein the pressure of the first gas is greater than or smaller than the pressure of the second gas.

54. The cell of claim 53, wherein a differential in the pressures between the first gas and the second gas is more than 10 mbar, more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

55. The cell of any one of claims 1 to 54, wherein the first gas diffusion electrode and the second electrode are sandwiched against opposite sides of the spacer.

56. The cell of any one of claims 1 to 55, wherein the distance between the first gas diffusion electrode and the second electrode is 0.2 mm or less.

57. The cell of any one of claims 1 to 56, wherein the transfer of the liquid electrolyte involves the liquid electrolyte to flow, run, pour, migrate, pass, drop, drip, or spray from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer.

58. The cell of any one of claims 1 to 57, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir onto at least part of each of two side surfaces of the spacer that extend beyond the first gas diffusion electrode and the second electrode, and that are outside of the liquid electrolyte reservoir.

59. The cell of any one of claims 1 to 58, further including a dripper which breaks the liquid electrolyte into droplets before being supplied to the liquid electrolyte reservoir.

60. The cell of any one of claims 1 to 59, wherein the cell is a reversible cell.

61. The cell of any one of claims 1 to 60, wherein the cell is a water electrolysis cell.

62. The cell of any one of claims 1 to 60, wherein the cell is a hydrogen-oxygen fuel cell.

63. A stack of electro-synthetic or electro -energy cells, comprising: a first electro-synthetic or electro -energy cell; and a second electro-synthetic or electro-energy cell electrically connected to the first electro-synthetic or electro-energy cell; wherein each electro-synthetic or electro-energy cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; wherein, the cell is configured to allow the liquid electrolyte to transfer from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir.

64. The stack of cells of claim 63, wherein the first electro-synthetic or electro-energy cell is a cell according to any one of claims 1 to 62, and the second electro-synthetic or electro-energy cell is a cell according to any one of claims 1 to 62.

65. A method of operating an electro- synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte; a first gas diffusion electrode; a second electrode; and a spacer positioned at least partially between the first gas diffusion electrode and the second electrode; the method including the steps of: allowing the liquid electrolyte to transfer from a liquid electrolyte reservoir onto at least part of a side surface of the spacer that extends beyond the first gas diffusion electrode and the second electrode, and that is outside of the liquid electrolyte reservoir; transporting the liquid electrolyte via the spacer to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

66. The method of claim 65, wherein an end of the spacer extends beyond the first gas diffusion electrode and the second electrode, the end of the spacer positioned within the liquid electrolyte reservoir.

67. The method of claim 65, wherein the spacer is positioned outside of the liquid electrolyte reservoir.

68. The method of any one of claims 65 to 67, further including the liquid electrolyte reservoir having an aperture to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer.

69. The method of claim 68, wherein the aperture is an overflow weir and when a height of the liquid electrolyte in the liquid electrolyte reservoir is at a height of the overflow weir, and further liquid electrolyte is added, then the liquid electrolyte transfers onto the at least part of the side surface of the spacer.

70. The method of claim 68, wherein a rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the at least part of the side surface of the spacer is regulated by regulating a rate at which the liquid electrolyte is added to the liquid electrolyte reservoir.

71. The method of claim 68, wherein a rate at which the liquid electrolyte transfers from the liquid electrolyte reservoir to the at least part of the side surface of the spacer is regulated by a size of the aperture.

72. The method of any one of claims 65 to 71 , wherein during operation the first gas diffusion electrode is configured to generate or consume a first gas of a first gas body.

73. The method of claim 72, wherein a pressure of the first gas within the cell is greater than atmospheric pressure.

74. The method of claim 72, wherein a pressure of the first gas within the cell is greater than

1.1 bara.

75. The method of claim 72, wherein a pressure of the first gas within the cell is greater than

76. The method of any one of claims 65 to 75, wherein the second electrode is a second gas diffusion electrode and during operation the second gas diffusion electrode is configured to generate or consume a second gas of a second gas body.

77. The method of claim 76, wherein a pressure of the second gas within the cell is greater than atmospheric pressure.

78. The method of claim 76, wherein a pressure of the second gas within the cell is greater than 1.1 bara.

79. The method of claim 76, wherein a pressure of the second gas within the cell is greater than 1.2 bara, greater than 1.3 bara, greater than 1.5 bara, greater than 2 bara, greater than 3 bara, greater than 5 bara, or greater than 10 bara.

80. The method of any one of claims 72 to 75, and, any one of claims 76 to 79, wherein the pressure of the first gas is greater than or smaller than the pressure of the second gas.

81. The method of claim 80, wherein a differential in the pressures between the first gas and the second gas is more than 10 mbar, more than 20 mbar, more than 30 mbar, more than 50 mbar, more than 75 mbar, more than 100 mbar, more than 200 mbar, more than 300 mbar, or more than 500 mbar.

82. The method of any one of claims 65 to 81, wherein the transfer of the liquid electrolyte from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer utilises gravity.

83. The method of any one of claims 65 to 82, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir onto the at least part of the side surface of the spacer at a feed rate greater than that required to replenish the liquid electrolyte that is removed or consumed during the electrochemical reaction.

84. The method of any one of claims 65 to 82, wherein the transfer of the liquid electrolyte is at a feed rate that is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer.

85. The method of any one of claims 65 to 82, wherein the transfer of the liquid electrolyte is at a feed rate that is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute, of liquid electrolyte per minute, normalised for a 1 cm wide spacer.

86. The method of any one of claims 65 to 85, wherein a flow rate of the liquid electrolyte is more than 0.1 g of liquid electrolyte per minute, normalised for a 1 cm wide spacer, within the spacer between the first gas diffusion electrode and the second electrode.

87. The method of any one of claims 65 to 85, wherein a flow rate of the liquid electrolyte is more than 0.2 g per minute, more than 0.3 g per minute, more than 0.4 g per minute, more than 0.5 g per minute, more than 0.8 g per minute, more than 1 g per minute, more than 2 g per minute, more than 3 g per minute, more than 4 g per minute, more than 5 g per minute, or more than 10 g per minute, of liquid electrolyte per minute, normalised for a 1 cm wide spacer, within the spacer between the first gas diffusion electrode and the second electrode.

88. The method of any one of claims 65 to 87, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir onto at least part of each of two side surfaces of the spacer that extend beyond the first gas diffusion electrode and the second electrode, and that are outside of the liquid electrolyte reservoir.

89. The method of any one of claims 65 to 88, wherein the cell is a reversible cell.

90. The method of any one of claims 65 to 89, wherein the cell is a water electrolysis cell.

91. The method of any one of claims 65 to 89, wherein the cell is a hydrogen-oxygen fuel cell.

92. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; a spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the spacer is positioned outside of the liquid electrolyte reservoir; and an intermediate liquid feed structure, located at least partially between the side surface of the spacer and the liquid electrolyte reservoir, wherein the liquid electrolyte is transferred from the liquid electrolyte reservoir to at least part of the side surface of the spacer by the intermediate liquid feed structure.

93. The cell of claim 92, wherein the spacer does not directly contact the liquid electrolyte that is within the liquid electrolyte reservoir.

94. The cell of claim 92 or 93, wherein the intermediate liquid feed structure is separate and distinct from the spacer.

95. The cell of any one of claims 92 to 94, wherein the intermediate liquid feed structure is in direct contact with the liquid electrolyte that is within the liquid electrolyte reservoir.

96. The cell of any one of claims 92 to 95, wherein the intermediate liquid feed structure is in direct contact with the side surface of the spacer.

97. The cell of any one of claims 92 to 96, wherein the spacer is spaced apart from the liquid electrolyte reservoir.

98. The cell of any one of claims 92 to 97, wherein the intermediate liquid feed structure is a porous capillary liquid feed structure.

99. The cell of any one of claims 92 to 98, wherein the liquid electrolyte reservoir has a width substantially equal to a width of the cell and is positioned across a top of the cell, with respect to the direction of gravity.

100. The cell of claim 98, wherein the porous capillary liquid feed structure is sheet-like and has one edge dipped into the liquid electrolyte reservoir.

101. The cell of claim 98, wherein the porous capillary liquid feed structure spontaneously draws in and maintains a volume of the liquid electrolyte within the porous capillary liquid feed structure by capillary action.

102. The cell of claim 98, wherein the liquid electrolyte moves within the porous capillary liquid feed structure under the influence of capillary and/or diffusion and/or osmotic control.

103. The cell of any one of claims 92 to 97, wherein the intermediate liquid feed structure is a surface liquid feed structure.

104. The cell of claim 103, wherein the liquid electrolyte moves along a surface of the surface liquid feed structure.

105. The cell of any one of claims 92 to 97, wherein the intermediate liquid feed structure is a pipe, a conduit, a channel, a tube, a chamber, or a trough.

106. The cell of any one of claims 92 to 105, configured such that during operation the liquid electrolyte contacts the first gas diffusion electrode and the second electrode only after first being transported from the liquid electrolyte reservoir by the intermediate liquid feed structure and then by the spacer.

107. The cell of any one of claims 92 to 106, wherein movement of the liquid electrolyte along or within the intermediate liquid feed structure is self-regulated.

108. An electro-synthetic or electro-energy cell, comprising: a liquid electrolyte reservoir for containing a liquid electrolyte; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a porous capillary spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the porous capillary spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the porous capillary spacer is positioned outside of the liquid electrolyte reservoir; wherein, the liquid electrolyte reservoir includes an aperture configured to allow the liquid electrolyte to transfer from the liquid electrolyte reservoir onto at least part of the side surface of the porous capillary spacer.

109. A method of operating an electro-synthetic or electro-energy cell to perform an electrochemical reaction, wherein the cell comprises: a liquid electrolyte reservoir for containing a liquid electrolyte, wherein the liquid electrolyte reservoir includes an aperture; a first gas diffusion electrode positioned outside of the liquid electrolyte reservoir; a second electrode positioned outside of the liquid electrolyte reservoir; and a porous capillary spacer positioned at least partially between the first gas diffusion electrode and the second electrode, wherein a side surface of the porous capillary spacer extends beyond the first gas diffusion electrode and the second electrode, and wherein the porous capillary spacer is positioned outside of the liquid electrolyte reservoir; the method including the steps of: allowing the liquid electrolyte to transfer from the liquid electrolyte reservoir via the aperture onto at least part of the side surface of the porous capillary spacer; transporting the liquid electrolyte via the porous capillary spacer to the first gas diffusion electrode and the second electrode; and applying or generating a voltage across the first gas diffusion electrode and the second electrode.

110. The cell of any one of claims 1 to 62 or 92 to 108, the stack of cells of any one of claims 63 to 64, or the method of any one of claims 65 to 91 or 109, wherein the porosity of the spacer is more than 60%, more than 70%, more than 80%, or more than 90%.

111. The cell of any one of claims 1 to 62 or 92 to 108, the stack of cells of any one of claims 63 to 64, or the method of any one of claims 65 to 91 or 109, wherein, when the spacer is filled with liquid electrolyte, the spacer has an ionic resistance of less than 140 m cm² at room temperature.

112. The cell of any one of claims 1 to 62 or 92 to 108, the stack of cells of any one of claims 63 to 64, or the method of any one of claims 65 to 91 or 109, wherein the liquid electrolyte comprises a hydroxide salt and has a pH of at least 10.