WO2022006640A1

WO2022006640A1 - Electrolysis cell and method of use

Info

Publication number: WO2022006640A1
Application number: PCT/AU2021/050740
Authority: WO
Inventors: Bartlomiej Piotr KOLODZIEJCZYK
Original assignee: Fortescue Future Industries Pty Ltd
Priority date: 2020-07-10
Filing date: 2021-07-09
Publication date: 2022-01-13
Also published as: AU2021304546A1

Abstract

A method for hydrogen and/or oxygen generation from water in a solid/semi-solid state, using a hydrogel membrane. The method may include the steps of evaporating water to produce a water vapour, and subsequently separating hydrogen and oxygen from the evaporated water. An apparatus for hydrogen and/or oxygen generation from water in a solid/semi-solid state, using a hydrogel membrane. The apparatus may include a pair of electrodes separated by a membrane, with the membrane being hydrated with water such that the membrane forms a source of hydrogen and oxygen.

Description

ELECTROLYSIS CELL AND METHOD OF USE

FIELD OF THE INVENTION

The invention relates to an electrolysis cell and a method of use of the electrolysis cell. More particularly, but not exclusively, the invention relates to a method and apparatus for the generation of hydrogen and/or oxygen from water with improved conversion efficiency.

Broadly, the invention relates to the field of electrochemistry, particularly, electrolysis. In one form, the invention relates to an electrolytic method for gas production. In another form, there is provided an electrolytic device for use in gas synthesis. In one particular aspect, the present invention is suitable for use in water splitting.

It will be convenient to hereinafter describe a non-limiting aspect of the invention in relation to splitting to produce hydrogen and oxygen, however, it should be appreciated that the broadest scope of the present invention is not limited to that use and may be used for production of other compounds such as, but not limited to, ammonia with chemical formula MB, which can be produced from atmospheric nitrogen N2 and hydrogen ¾ contained in water.

BACKGROUND TO THE INVENTION

Typically, existing water electrolysis (water splitting) processes rely on an electrochemical phenomena where two electrodes immersed in water, often with the addition of salts to increase electrical conductivity, are separated by a membrane. Upon supply of electric charge, electrodes (an anode and a cathode) attract hydrogen and oxygen atoms in the water, effectively breaking bonds and allowing for separation of these two gases.

The overall reaction of water splitting, 2H2O 2¾ + O2 produces oxygen and hydrogen gases as end products. These gases need to be kept separate for later individual use and to avoid production of a flammable and potentially explosive gas mixture. The electrolyser used for water splitting through the means of electrolysis has previously been proposed and typically comprises two electrodes separated by a membrane and immersed in water. Salts may be added to the water to increase electrical conductivity. Passage of an electric current across the electrodes causes water to be reduced by the supply of electrons from the cathode and hydrogen gas is formed. A corresponding oxidation reaction occurs at the anode to generate gaseous oxygen.

A number of electrolyser types have been manufactured and used commercially to date. However, those devices typically rely on the concept of using an aqueous medium as a source of hydrogen and oxygen. Two main types of electrolysers have been broadly used in the past, alkaline electrolysers which typically include an electrolyte in the form of a gel and proton exchange membrane (PEM) electrolysers. In recent years, the idea of using solid oxide electrolysers where the membrane is based on oxide (ceramic) materials has been explored. Solid oxide electrolysers allow for high-temperature operation increasing the reaction kinetics and reaction rate. However, all three concepts utilize water in liquid form as a source of hydrogen and oxygen. Membrane electrode assemblies (MEAs) typically have a multi-layered structure comprising the PEM, a current collecting electrode and an electro-catalyst layer on each side.

In traditional electrolysers (both alkaline and PEM), the reaction occurs at a so-called three-phase boundary (sometimes also referred to as a “triple phase boundary” or “TPB” as an alternative) where catalyst, electrolyte and generated gas meet, forming solid - liquid - gas phase. In the preferred example of the present invention, the reaction occurs at a two- phase boundary because the electrolyte is in a solid state (hydrogel) forming a solid - solid - gas boundary.

More recently, new types of gas-to-gas reactors have been developed, an example of which is described in International patent publication WO2016/148637 entitled “Electrolysis System”. The concept relies on evaporating water and subsequent separation of hydrogen and oxygen. This concept overcomes a number of limitations associated with traditional water-based electrolysers. In particular the concept has the advantage that no gas bubbles are formed on the electrode, a phenomenon which over time reduces the active surface of the electrode and effectively decreases the conversion efficiency.

It has been previously proposed by the National Aeronautics and Space Administration to provide a water-vapour electrolysis cell which uses a phosphoric acid electrolyte such that when the cell is operated on recirculated cabin air, dehumidification and generation of oxygen occur simultaneously so as to be suitable for integration in a cabin air-conditioning system. However, the focus of this cell was on the suitability for an air- conditioning system and the applicant has identified that such a cell would not be suitable for the efficient generation of hydrogen.

The applicant has determined that it would be advantageous for there to be provided an improved method and apparatus for electrolysis which at least alleviates one or more disadvantages of existing electrolysis systems.

SUMMARY OF INVENTION

In accordance with one aspect of the present invention, there is provided a method for hydrogen and/or oxygen generation from water in a solid/semi-solid state, using a hydrogel membrane. Although it is appreciated that both hydrogen and oxygen are necessarily produced in the electrolysis of water, the actual goal of the process when used may be specific to the generation of hydrogen or the generation of oxygen.

In accordance with another aspect of the present invention, there is provided a method of generating hydrogen and/or oxygen, the method including the steps of evaporating water to produce a water vapour, and subsequently separating hydrogen and oxygen from the evaporated water.

Preferably, the method includes the step of using a membrane.

Preferably, the method includes the step of producing a hydrogen-rich medium, providing an electrolyser cell having at least one channel, and passing said hydrogen-rich medium through said channel. In accordance with another aspect of the present invention, there is provided an apparatus for hydrogen and/or oxygen generation from water in a solid/semi-solid state, using a hydrogel membrane.

The apparatus may be in the form of a cell, and the cells may be stacked.

Preferably, the apparatus includes a pair of electrodes separated by the hydrogel membrane.

In a preferred form, the membrane is a polymeric membrane with high water-content.

In accordance with another aspect of the present invention, there is provided an apparatus for hydrogen and/or oxygen generation from water, wherein the apparatus includes a pair of electrodes separated by a membrane, and the membrane is hydrated with water such that the membrane forms a source of hydrogen and oxygen.

In accordance with yet another aspect of the present invention, there is provided a method of generating hydrogen and/or oxygen using an apparatus as described above, wherein the method includes the step of hydrating the membrane to maintain water content in the membrane during electrolysis.

Preferably, the step of hydrating the membrane is achieved with water influx into the membrane equivalent to an amount of water used to generate hydrogen and oxygen. By way of explanation, this hydration step may utilise a so-called water management system which is an existing component of PEM fuel cells (a reverse reaction to electrolysis). In a PEM fuel cell, once hydrogen and oxygen are combined to produce electricity and water, this produced water needs to be removed from the system otherwise a PEM membrane in the form of a Nafion (a brand name for a sulfonated tetrafluoroethylene based fluoropolymer- copolymer discovered in the late 1960s by Walther Grot of DuPont) membrane will get “flooded” and will lose efficiency. Conversely, the Nafion membrane cannot be allowed to become dry because its efficiency would drop in that event. A water management system ensures that the Nafion membrane stays hydrated. Nafion includes a Teflon backbone polymer with functional groups. It does not inhale water like hydrogel but forms two distinct and separated phases with it. In hydrogel, the polymeric core and water captured in it form one phase material. Also, in hydrogel, unlike Nafion, a high water content is preferred.

In a preferred form, the step of hydrating the membrane is achieved by calculating the amount of water used based on one or more parameters including temperature, input voltage, input current, and/or hydrogen flow output.

Preferably, the step of hydrating is achieved by circulating liquid water through the cell.

In one example, the step of hydrating is achieved by introducing water to the membrane in the gaseous phase. In accordance with yet another aspect of the present invention, there is provided an electrolytic cell having an electric circuit comprising an anode and a cathode separated by a hydrogel membrane.

Preferably, the hydrogel membrane forms the electrolyte for the electrolysis.

In accordance with another aspect of the present invention, there is provided an electrolytic cell having an electric circuit comprising an anode and a cathode separated by a hydrogel membrane, wherein the membrane acts as an electrolyte, the membrane includes a hydrophilic polymer, and water absorbed by the polymer is electrolysed when an electric current passes through the electric circuit.

In accordance with another aspect of the present invention, there is provided a method of electrolysing water comprising: locating a hydrophilic polymer membrane between an anode and a cathode of an electric circuit, absorbing water into the hydrophilic polymer membrane, and passing an electric current through the electric circuit such that the water in the hydrophilic polymer membrane is reduced to hydrogen at the cathode and oxygen at the anode. In accordance with another aspect of the present invention, there is provided a solid/semi-solid membrane electrolyser and method of electrolysis for gas synthesis.

Examples of the invention may seek to improve the efficiency of electrolytic reactions used for synthesis.

In one aspect, there is provided an electrolytic cell having an electric circuit comprising an anode and a cathode separated by a hydrogel membrane. The hydrogel membrane may form the electrolyte for the electrolysis.

In another aspect, there is provided an electrolytic cell having an electric circuit comprising an anode and a cathode separated by a hydrogel membrane, wherein the membrane, acting as an electrolyte, comprises a hydrophilic polymer, and water absorbed by the polymer is electrolysed when an electric current passes through the electric circuit.

In another aspect, there is provided a method of electrolysing water comprising the steps of: locating a hydrophilic polymer membrane between an anode and a cathode of an electric circuit, absorbing water into the hydrophilic polymer membrane, and passing an electric current through the electric circuit such that the water in the hydrophilic polymer membrane is reduced to hydrogen at the cathode and oxygen at the anode.

Preferably, the gas produced at the electrodes diffuses out of the cell via the polymer membrane, separating the gas from the reaction at the electrode. Preferably, the gas is separated without gas bubble formation on the electrode surface. Avoiding bubble formation permits reactions such as water splitting to be achieved with a low over-potential, thereby contributing to the efficiency of the electrolytic cell.

Accordingly, the present invention relates to a novel method for hydrogen and oxygen generation from water in the solid/semi-solid state. Similarly, to traditional water splitting systems, the current design relies on a two-electrode setup separated by the water- rich membrane (with high water-content). The water content in the polymeric membrane can be as high as 90% water by weight, but potentially other similar membranes can be used with a water content of 98% and above. The separation membrane being a source of hydrogen and oxygen itself is a new concept which has not been explored before. While the water content in the membrane changes during the process, it is necessary to keep the membrane hydrated at all times because dehydration may affect the chemical and mechanical properties of the membrane gradually wearing it off, or even breaking. As such, it is important to make sure that the water influx into the membrane is equivalent to the amount of water that was used to generate hydrogen and oxygen.

The water management system can be operated in a number of ways to ensure constant hydration of the membrane at a certain level. One of which is a simple mathematical model that allows calculating the amount of water used based on parameters such as temperature, input voltage, input current, or hydrogen flow output. The hydration of the membrane can be done by, but is not limited to, circulating liquid water through the cell or by introducing water to the membrane in the gaseous phase (water vapour). The single cells can be stacked together just like in traditional electrolysis systems in order to make the device more compact and to increase the power and hydrogen generation capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described, by way of non-limiting example, with reference to the accompanying drawings in which:

Figure 1 shows the cell and stack assembly in accordance with an example of the present invention;

Figure 2 shows an example hydrogel gas separation membrane;

Figure 3 shows the stack of electrolytic cells with flow explanation; and

Figure 4 shows a graph depicting experimental measurement results of output power consumption versus percentage of rated power capacity. DETAILED DESCRIPTION

With reference to Figures 1 to 4, there is shown an example improved electrolytic cell apparatus having a special gas separation membrane in the form of a hydrogel membrane. Advantageously, the applicant has determined that the provision of the hydrogel membrane may result in an improved efficiency and lower system maintenance. More specifically, Figure 1 shows on the left-hand side an expanded view depicting each of the components which together form an electrolytic cell 10. To the right-hand-side of the expanded view there is shown a single, fully assembled electrolytic cell 10 for generating hydrogen and/or oxygen from water in a solid/semi-solid state, using a hydrogel membrane 12. The single assembled electrolytic cell 10 has holes 14 which are used for the delivery of water vapour. Below the fully assembled electrolytic cell 10 is shown a stack of electrolytic cells, expanded to show each of the components in perspective view. At the far right-hand side of Figure 10 is shown in perspective view an example of a multiple (10) stacked cell assembly. Accordingly, the cell 10 is suitable for use in a method of generating hydrogen and/or oxygen, the method including the steps of evaporating water to produce a water vapour, and subsequently separating hydrogen and oxygen from the evaporated water.

As noted above, Figure 1 also shows the cell 10 in an exploded view depicting the separate components of the cell 10. In particular, the cell includes a gasket 16, a cathode 18 which may be in the form of a nickel mesh electrode (catalyst), the polymer membrane in the form of hydrogel membrane 12, an anode 20 which may be in the form of a nickel mesh electrode (catalyst), a frame, an aluminium corrugated plate 24, and a stainless steel corrugated mesh 26. The frame 22 provides support, while water enters the cell 10 from the left (in the direction that is towards the gasket 16 side of the cell 10) and hydrogen exits the cell 10 to the right (in the direction that is away from the stainless steel corrugated mesh 26). Accordingly, in this way, the cell 10 includes a pair of electrodes 18, 20 separated by the hydrogel membrane 12. Nickel mesh can also be replaced with nickel foam, which provides a more expensive solution but results in higher active surface area and improved performance. In addition, the catalyst (nickel nanoparticles, or nickel-iron nanoparticles, or other nanoparticles) can be deposited on the membrane surface with a prior conductive layer deposited on the membrane for electrical conductivity purpose. In certain cases, density of sputtered catalyst nanoparticles and their conductivity allows omission of the requirement for an additional conductive layer.

The nickel mesh electrode (catalyst) 18 / polymer membrane 12 / nickel mesh electrode (catalyst) 20 / aluminium corrugated plate 24 / stainless steel corrugated mesh 26 form a separate electrically conductive assembly cell following the sequence as described. The stainless steel corrugated mesh 26 in one electrochemical cell is in close contact with the nickel mesh electrode (catalyst) 18 in the subsequent cell allowing for electric charge to pass through the system. All electrochemical cells are connected in series. The electric charge passes from one copper current collector though all subsequent cells in the system to the copper current collector at the other end of the stack at the same time facilitating the electrolysis reaction. Importantly, this novel construction with the hydrogel membrane leads to increased efficiency and results in superior performance when using a nickel catalyst, as compared to the performance of an electrolyser using platinum (considered the best water splitting catalyst).

Where water vapour is used instead of liquid water to replenish water in the hydrogel used to generate hydrogen and oxygen, an evaporator is used, which is also developed by the applicant. Because of the three-dimensional modular design with multiple vertical cells, each supplying large amounts of water vapour, it is possible to achieve nearly ten times more water vapour than what would normally be achieved from the same area. Advantageously, an integrated evaporation system enables water purification. As such, even sea water can be used directly (although this would require higher maintenance and salt removal). Most electrolysers require very pure water otherwise impurities will reduce the lifetime of the system. Impurities can also block pores in the membranes and reduce the active electrode surface. Further, impurities in feedwater can get into hydrogen/oxygen output streams. PEM electrolysers require ultrapure deionized water, whereas alkaline electrolysers can work with lower purity water grade. More specifically, Figure 1 illustrates on the left-hand-side the electrolytic cell 10 expanded to show each of the components. This view shows a printed and cured gasket 16 approximately 0.1 mm thick. The polymer membrane 12 is located between two mesh electrodes 18, 20 comprising a nickel catalyst. A polymer, preferably polypropylene, frame 22 separates the electrodes 18, 20 from a stamped aluminium corrugated plate 24 that facilitates oxygen and water vapour flow in the electrolytic cell 10. The plate 24 is adjacent a stamped stainless steel corrugated mesh 26 that also facilitates oxygen and water vapour flow. The frame 22 serves as a support and provides a means for assembly. The small holes/channels 14 on both sides of the frame 22 allow for water vapour to enter and for excess water vapour plus oxygen generated on the anode (open anode cell) side to leave the system. Both aluminium plate 24 and stainless steel mesh 26 also close the entire system electrically and allow for the charge to flow through from one copper collector to the other, at the same time facilitating the reaction. The applicant has also investigated the effect of using stainless steel instead of aluminium for the corrugated plate and what effect it will have on the system and its performance. This creates the possibility of using cheaper stainless steel for the stamped corrugated plate.

Figure 1 shows a stack 28 of 10 electrolytic cells. The stack 28 is further explained in Figure 3 which illustrates the concept of an open anode cell. Normally, the water vapour inlet side of the cell is at the bottom. By putting one electrolyser stack on top of another, the excess water vapour leaving one stack enters the other stack and is used there. The arrow 30 depicts the water vapour inlet from an evaporation unit, the arrow 32 depicts the flow of excess water vapour mixed with generated oxygen gas. The arrows 34 depict inlet and outlet holes on both sides of each cell 10 (open anode cell concept).

Figure 1 also illustrates the stack 28 of electrolytic cells expanded to show each of the components in perspective view. Fasteners 36, in the non-limiting example as M10 screws, pass through the edges of all elements at their edges to ensure proper sealing of the stack 28. Two thick stainless steel end plates 38, 40 are located at both ends of the stack 28 and may be used to collect gas - particularly hydrogen gas - generated during the electrolytic process. The end plates 38, 40 are present to compress the cells and the entire stack. The end plates 38, 40 must be thick to distribute the pressure - generated by tightened screws - evenly, otherwise there could be potentially a gas (hydrogen) leak. The fasteners 36 are tightened so as to ensure that pressure evenly distributes across the stack 28. Individual electrolytic cells 10 are located between the end plates 38, 40. Plastic pipes 42 are also located at the edges of the electrolytic cells 10 to insulate the fasteners 36 from the electrodes and other metal components of the stack 28.

The small holes 14 on the sides of the stack 28 are used to deliver water or water vapour to the membranes 12 (that is, the membrane 12 of each cell 10) to keep them hydrated. The water may, for example, be pumped or supplied in a passive manner from a reservoir or by any other method known in the art. The holes 14 may also be used for removal of gas, and, in particular, oxygen generated during the electrolytic process. This functionality is important to the operation of the system. It also allows the system to be much simpler and cheaper since it obviates the need for additional channels to remove oxygen in each of the cells. These channels are free-flowing and no additional pump or other means are required to force the oxygen flow and remove it from the system.

Figure 2 illustrates the hydrogel membrane 12 assembled in the electrolysis cells shown in Figure 1.

The membrane 12 may be in the form of a polymeric membrane, specifically a hydrogel membrane, with high water-content. The membrane 12 may be hydrated with water such that the membrane forms a source of hydrogen and oxygen to the electrolytic process. The membrane 12 may be hydrated to maintain water content in the membrane 12 during electrolysis. In particular, this may be achieved with water influx into the membrane equivalent to an amount of water used to generate hydrogen and oxygen. In one example, the hydration of the membrane 12 is achieved by calculating the amount of water used based on one or more parameters including temperature, input voltage, input current, and/or hydrogen flow output, and by circulating liquid water through the cell 10 accordingly. Alternatively, the hydration may be achieved by introducing water to the membrane 12 in the gaseous phase. The hydrogel membrane 12 may form the electrolyte for the electrolysis process. More specifically, the membrane 12 may act as an electrolyte, the membrane 12 including a hydrophilic polymer, and water absorbed by the polymer being electrolysed when an electric current passing through the electric circuit. In this way, an example of the invention provides a method of electrolysing water including a first step of locating a hydrophilic polymer membrane between an anode and a cathode of an electric circuit, a second step of absorbing water into the hydrophilic polymer membrane, and a third step of passing an electric current through the electric circuit such that the water in the hydrophilic polymer membrane is reduced to hydrogen at the cathode and oxygen at the anode.

Owing to the nature of the hydrogel membrane, in the example of the invention as described above, this provides a solid/semi-solid membrane electrolyser and a method of electrolysis for gas synthesis. Examples of the invention may seek to improve the efficiency of electrolytic reactions used for synthesis.

In one example of the invention, the gas produced at the electrodes diffuses out of the cell 10 via the polymer membrane 12, separating the gas from the reaction at the electrode. Ideally, the gas is separated without gas bubble formation on the electrode. Avoiding bubble formation permits reactions such as water splitting to be achieved with a low over-potential, thereby contributing to the efficiency of the electrolytic cell 10.

Advantageously, hydrophilic hydrogel is used as a solid/semi-solid membrane and electrolyte in one. It allows separation of produced gases and, at the same time, being a source of water to generate hydrogen and oxygen. Water in the hydrogel is replenished either by supplying liquid water through the electrolyser channels or by supplying water vapour through special inlet holes on the side of the electrolyser cells 10. The opposite side of each of the cells have similar holes to remove the excess water vapour as well as produced oxygen. In the applicant’s arrangement, the anode side where oxygen is produced is referred to as the “open cell” which allows oxygen to be easily removed. This simplifies the entire system as well as all the processes. Although there has been some discussion previously of water vapour electrolysis, the applicant has identified that it would be beneficial to actually have water vapour as a means of water delivery to a membrane, with the reaction occurring at a two-phase boundary (solid- solid-gas) instead of a three phase boundary (solid-gas-liquid) as in traditional electrolysers.

Turning to Figure 4, there is shown experimental results for five measurements of how power consumption changes according to percentage of electrolyser’s rated power capacity. A 12-kW system (100-cell stack) has a power consumption of 3.5 to 4.4 kWh/Nm³ FF depending on the operation mode, and applied power, as well as energy consumption of auxiliary systems, processes, i.e., control system pumps, etc.

As can be seen in the exploded view of Figure 1, each cell 10 of the example depicted includes a printed and cured gasket 16 (0.1 mm in thickness in the non-limiting example depicted/described), a cathode in the form of a nickel mesh electrode (catalyst) 18, a special gas separation membrane manufactured in-house 12, an anode in the form of a nickel mesh electrode (catalyst) 20, a polypropylene frame 22, a second printed and cured gasket 44 (thickness 0.1 mm), a stamped aluminium corrugated plate to facilitate oxygen and water vapour flow 24, and a stamped stainless steel corrugated mesh to facilitate oxygen and water vapour flow 26. These components are pressed together as a single cell assembly as shown by reference numeral 10 in Figure 1.

In turn, the single cell assemblies 10 are combined and stacked together into a stack 28 as shown in exploded view in Figure 1 and as an assembly on the far right-hand- side of Figure 1. The components of the stack 28 of 10 cells includes two tube fittings/hydrogen outlets 46, a thick stainless steel end plate 38 to ensure equal pressure distribution by screws and to collect produced hydrogen gas, two rubber insulators 48 separating end plates from current collectors, two copper current collectors 50 at each end, single cell assemblies 10 (as shown above), plastic pipes 42 to separate fasteners (screws) from electrodes and other metal components of the stack 28, (20 x M10 screws in the non-limiting example depicted/described) 36 to ensure proper sealing of the stack 28 (screws can be larger if needed), and a second stainless steel end plate 40. Further information on the membrane and on hydrogels is provided below.

Hydrophilic Polymer Membrane

The hydrophilic polymer membrane can absorb a large proportion of water rapidly and has a robust physical structure. Preferably, the hydrophilic polymer membrane is a hydrogel, a macromolecular polymer gel which can hydrogen-bond molecules of water within interstices located throughout a network of cross-linked polymer chains. The water content in the polymer membrane can be as high as 98 wt% of the polymer, but typically the water content is at least 90 wt%. The electrolytic splitting is effectively carried out in a hydrogel environment.

Hydrophilic polymers typically include charged functional groups. In a preferred embodiment, the hydrophilic polymer of the present invention is chosen from the group comprising acrylic acid, acrylamide, maleic anhydride, polyacrylic acid, polyacrylamide, polyvinyl alcohol polymers and copolymers thereof. The membrane may comprise one or more polymers. The main composition of the membrane is a copolymer of poly(sodium acrylate-co-acrylamide) with some other ingredients to reinforce the mechanical strength or tune the hydrophilicity.

During electrolysis, water in the polymer membrane is converted into hydrogen and oxygen and it will be necessary to compensate for the water loss. The polymer membrane must be adequately hydrated at all times during electrolysis because dehydration can adversely affect the chemical and mechanical properties of the membrane, potentially causing the membrane to break or wear off. As such, water influx into the membrane preferably balances the amount of water converted into hydrogen and oxygen.

A number of water management strategies can be used to ensure constant hydration of the polymer membrane at a desired level. In a preferred embodiment, the desired level of water can be calculated by a simple mathematical model based on parameters such as temperature, voltage and current of the electric circuit, or hydrogen flow output. In a preferred embodiment, the membrane is hydrated by circulating liquid water through the cell or by introducing water vapour to the polymer membrane. Other suitable hydration methods may also be used. For example, patent publication EP2463407A entitled "Electrolysis method and electrolysis cells" in the name of Astrium GmbH describes pumping water into microchannels in a hydrophobic membrane. Patent publication US2014224668A1 entitled "Method for operating an electrolytic cell" in the name of Astrium GmbH describes a hydrophobic membrane for electrolytic water splitting, the membrane being supplied with liquid water in a passive manner from a reservoir without using a pump. Water from the reservoir may pass by capillary effect via at least one cavity structure in the membrane.

As will be apparent to a person skilled in the art, an electrolytic system may comprise a plurality of connected electrolytic cells, each cell being in accordance with the present invention. Each electrolytic cell may have separate or common water feeds. In particular, single electrolytic cells of the present invention can be stacked in a manner well known in the prior art to increase the power capacity or hydrogen generation.

The polymer membrane can be made by any convenient means known in the art for constructing membranes, such as polymer moulding or phase inversion technique. Polymer moulding is appropriate for small scale and prototype applications, whereas the phase inversion technique may be used with a support layer so that the entire process can be automated. In a preferred embodiment the polymer precursor in liquid/semi-liquid form is injected into customized stainless steel or ceramic moulds. The polymer is then subjected to a predetermined process at desired temperatures, pressures and cycle times.

The electrolytic cell of the present invention may additionally comprise a model catalyst associated with the hydrophilic polymer membrane. The catalyst may be deposited upon the porous membrane.

Generally, precious metals such as platinum, gold or palladium are used for water splitting. However, the electrolytic cell and method of the present invention may be used in association with less expensive and non-precious catalysts, such as nickel and manganese- based catalysts. The present invention may include incorporation of different catalysts and different chemistries, and may be used for production of compounds other than hydrogen and oxygen. This could include, for example, ammonia (from water and atmospheric nitrogen) or methane, methanol or ethanol from water and carbon dioxide. The applicant foresees that it may also be possible to utilise substances having longer carbon chains.

Hydrogels

It appears there is no prior application of hydrophilic hydrogel membranes for water splitting reaction. There are, however, some reports where hydrogel was used in batteries and fuel cells but for electrolytes rather than as membranes.

In contrast, the applicant’s system achieves solid/semi-solid state water splitting, since hydrogels can be considered to be solid or semi-solid materials due to their solid rather than liquid behaviour.

The applicant has determined that hydrogel materials are of benefit for electrolysis because their structures consist of a cross-linked network of polymer chains having interstitial spaces filled with solvent water. Hydrogels are thus both wet and soft, making them ideal candidates for electrolyte materials in flexible energy storage devices, and rechargeable batteries.

Hydrogel is as a gel in which the swelling agent is water. The network component of a hydrogel is usually a cross-linked polymer network. More specifically, a hydrogel is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. A three-dimensional solid results from the hydrophilic polymer chains being held together by cross-links. The structural integrity of the hydrogel network does not dissolve from the high concentration of water because of the inherent cross-links. Hydrogels are highly absorbent (they can contain over 90% - or even 98% - water) natural or synthetic polymeric networks. Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water content. As responsive "smart materials," hydrogels can encapsulate chemical systems which upon stimulation by external factors such as a change of pH may cause specific compounds such as glucose to be liberated to the environment, in most cases by a gel-sol transition to the liquid state. Chemomechanical polymers are mostly also hydrogels, which upon stimulation change their volume and can serve as actuators or sensors.

A hydrogel usually consists of water soluble polymers (long molecular chains of repeating units) that are “cross-linked” / attached to each other forming a three-dimensional network. This network traps a large volume of water, resulting in a solid/semi-solid material consisting of mostly water.

Particular hydrogels tested for water splitting

Various hydrogels have been tested for their usefulness in the method of water splitting according to the present invention. Hydrogels that have been tested include cross- linked polymers based on acrylic acid, acrylamide, maleic anhydride, polyacrylic acid, polyacrylamide, polyvinyl alcohol polymers and copolymers thereof.

The best performing hydrogels were found to be based on cross-linked poly(potassium acrylate-co-acrylamide), followed by poly(sodium acrylate-co-acrylamide), both cross-linked using N,N-Methylenebisacrylamide (a cross-linking agent used during the formation of polymers such as polyacrylamide).

Other tested hydrogels include biopolymer-based hydrogels such as alginate, carrageenan and xanthan gum, as well as their potassium and sodium salt compounds, i.e., potassium alginate, sodium carrageenan, etc. Both carrageenan and xanthan gum are natural polysaccharides produced by red and purple seaweeds, and bacterial fermentation, respectively. Glutaraldehyde, sodium sulfate, and potassium sulfate have been used as cross-linking agents.

Alginic acid is a polysaccharide distributed widely in the cell walls of brown algae that is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Hydrogels of sodium alginate and potassium alginate have been tested for hydrogen generation. The presence of metal ions enhances ionic conductivity of the hydrogel membrane.

Some other tested hydrogels include commercially available products like AmGel hydrogels (AG900 Series and AG2500 Series) by Axelgaard Manufacturing Co., Ltd.

Other hydrogels might be suitable as well, however their practical applicability for this particular application (water splitting and hydrogen generation) have to be evaluated.

Examples and Variations

In a preferred example, the electrolytic cell 10 and method of the present invention is used for synthesis. In another preferred example, the cell 10 forms part of a fuel cell or a fuel cell system. For example, the electrolysis cell 10 may produce hydrogen through water splitting, then hydrogen is stored in a storage tank, and fuel cells use hydrogen to power a car or other appliances.

The electrolytic cell 10 and method of the present invention may be used for water splitting to synthesise hydrogen and oxygen, but it will be readily apparent to a person skilled in the art that other gases could be synthesised by adjusting the catalyst and/or chemistry of the process. For example, ammonia could be synthesised.

The applicant has conducted initial work on methanol production using the same setup but with a different catalyst. Other reactions (such as using carbon dioxide to form formic acid, carbon monoxide or formaldehyde; or halide oxidation to halide gas; or hydrogen peroxide oxidation to oxygen gas; or nitrite reduction to nitrous oxide gas or ammonia gas) could possibly be achieved with the current setup and the same or similar hydrogel membrane 12, although the catalyst would most likely have to be changed for each of the reactions, as nickel may not be suitable or the most efficient catalyst to facilitate each of those reactions. The applicant also foresees that to produce ammonia, it is more efficient and industrially more feasible to have two units (a two-step reaction process) where the first unit generates hydrogen from water and supplies this hydrogen to the second similar unit (with different catalyst) to combine it electrochemically with nitrogen. Using a two-step reaction process may be preferable and more efficient than using one system where water and nitrogen are supplied to generate ammonia in single step.

In essence, examples of the present invention stem from the realization that the separation membrane of an electrolytic cell, in addition to separating gasses, may also be a source of reactant. For example, the membrane that separates oxygen and hydrogen formed during electrochemical splitting of water may also be the source of water for the electrochemical splitting.

Advantages

Advantages provided by examples of the present invention may include the following:

• overcoming the bubble gas formation that is often present in water-based electrolysis. Where gas bubbles (hydrogen and oxygen) build up on the electrode, these effectively reduce the conversion efficiency;

• the process allows for superior power conversion (balance of plant power conversion), in some cases, as low as 3.5 kWh/Nm³ of hydrogen, which translates to the conversion efficiency of about 85.6%;

• low system maintenance;

• compact design;

• simplified structure and assembly processes, allowing for the use of inexpensive materials and manufacturing processes, effectively reducing the system cost;

• allows for the use of inexpensive and non-precious catalysts whilst at the same time achieving superior efficiencies;

• excellent hydrogen purity (up to 99.999%);

• in some instances, possible use of any water feedstock, including tap water, rainwater or even seawater; • no electrolyte requirement, water is replenished in the membrane;

• small footprint and scalability;

• no cooling requirement, the system uses waste heat to further reduce activation losses and increase the conversion efficiency; and

• the invention relies on electrochemical principles, hence the ability for quick turn on and off, as well as quick ramp up and ramp down.

Accordingly, it will be understood from the foregoing that the invention provides a novel type of electrolyser / gas reactor, where input gas or gases are electrochemically converted into other gases (products). One example would be water vapour being converted into hydrogen and oxygen. In another instance, hydrogen and nitrogen are electrochemically converted into ammonia, whereas in the third instance, conversion of carbon dioxide and hydrogen is also possible. Catalysts and chemistries of this invention can be tailored to achieve specific outcomes or products. The developed gas reactor can work at room temperatures and temperatures of 100°C or above. The system utilizes a novel approach whereby hydrogel with water content of up to 95 wt% is used as a gas separation membrane, and also, in the case of water splitting, to generate hydrogen, the hydrogel is used as a source of water feedstock.

Inventive elements include:

• the overall system design;

• high-temperature operation;

• solid/semi-solid water splitting principle with water supplied from a novel hydrogel membrane;

• the use of water vapour instead of liquid water;

• novel water treatment and water management system;

• unique hydrogel membrane with water contents of up to 95 wt% as a source of the feedstock for water splitting; and

• novel cell design (an open anode concept), which allows for water feedstock delivery and efficient removal of oxygen from the system. The concept relies on the evaporation of water and the consequent separation of hydrogen and oxygen. This solution allows overcoming a number of limitations that are present in traditional water-based electrolysers, namely no gas bubble formation is present on the electrodes which would otherwise over time reduce the active surface of the electrode and effectively decrease the conversion efficiency. The applicant determined that dealing with water vapour proved to be much easier than dealing with liquid water, especially when forcing the hydrogen-rich medium through very narrow channels present in the electrolyser cells.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments. 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 that 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.

Claims

Hll CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method for hydrogen and/or oxygen generation from water in a solid/semi solid state, using a hydrogel membrane.

2. A method of generating hydrogen and/or oxygen as claimed in claim 1, the method including the steps of evaporating water to produce a water vapour, and subsequently separating hydrogen and oxygen from the evaporated water.

3. A method for hydrogen and/or oxygen generation including the step of separating hydrogen and oxygen from water with a reaction at a two-phase boundary.

4. An apparatus for hydrogen and/or oxygen generation from water, the apparatus including a membrane, and a pair of electrodes separated by the membrane, wherein the apparatus separates hydrogen and oxygen from the water with a reaction at a two-phase boundary.

5. A method for hydrogen and/or oxygen generation including the step of separating hydrogen and oxygen from water with a reaction at a solid— solid/semi-solid— gas boundary.

6. An apparatus for hydrogen and/or oxygen generation from water, the apparatus including a membrane, and a pair of electrodes separated by the membrane, wherein the apparatus separates hydrogen and oxygen from the water with a reaction at a solid— solid/semi-solid— gas boundary.

7. An apparatus as claimed in claim 6, wherein the catalyst is solid, the electrolyte is solid/semi-solid and the hydrogen and/or oxygen is/are produced in gaseous form.

8. A method of generating hydrogen and/or oxygen, the method including the steps of evaporating water to produce a water vapour, and subsequently separating hydrogen and oxygen from the evaporated water.

9. A method as claimed in claim 8, including the step of using a membrane.

10. A method as claimed in claim 8 or claim 9, wherein the method includes the step of producing a hydrogen-rich medium, providing an electrolyser cell having at least one channel, and passing said hydrogen-rich medium through said channel.

11. An apparatus for hydrogen and/or oxygen generation from water in a solid/semi solid state, using a hydrogel membrane.

12. An apparatus as claimed in claim 11, wherein the apparatus includes a pair of electrodes separated by the hydrogel membrane.

13. An apparatus as claimed in claim 11 or claim 12, wherein the membrane is a polymeric membrane with high water-content.

14. An apparatus for hydrogen and/or oxygen generation from water, wherein the apparatus includes a pair of electrodes separated by a membrane, and the membrane is hydrated with water such that the membrane forms a source of hydrogen and oxygen.

15. A method of generating hydrogen and/or oxygen using an apparatus as claimed in claim 14, wherein the method includes the step of hydrating the membrane to maintain water content in the membrane during electrolysis.

16. A method of generating hydrogen and/or oxygen as claimed in claim 15, wherein the step of hydrating the membrane is achieved with water influx into the membrane equivalent to an amount of water used to generate hydrogen and oxygen.

17. A method of generating hydrogen and/or oxygen as claimed in claim 15 or claim 16, wherein the step of hydrating the membrane is achieved by calculating the amount of water used based on one or more parameters including temperature, input voltage, input current, and/or hydrogen flow output.

18. A method of generating hydrogen and/or oxygen as claimed in any one of claims 15 to 17, wherein the step of hydrating is achieved by circulating liquid water through the cell.

19. A method of generating hydrogen and/or oxygen as claimed in any one of claims 15 to 18, wherein the step of hydrating is achieved by introducing water to the membrane in the gaseous phase.

20. An electrolytic cell having an electric circuit comprising an anode and a cathode separated by a hydrogel membrane.

21. An electrolytic cell as claimed in claim 20, wherein the hydrogel membrane forms the electrolyte for the electrolysis.

22. An electrolytic cell having an electric circuit comprising an anode and a cathode separated by a hydrogel membrane, wherein the membrane acts as an electrolyte, the membrane includes a hydrophilic polymer, and water absorbed by the polymer is electrolysed when an electric current passes through the electric circuit.

23. A method of electrolysing water comprising: locating a hydrophilic polymer membrane between an anode and a cathode of an electric circuit, absorbing water into the hydrophilic polymer membrane, and passing an electric current through the electric circuit such that the water in the hydrophilic polymer membrane is reduced to hydrogen at the cathode and oxygen at the anode.