WO2021045614A1

WO2021045614A1 - Compact electrochemical stack using corrugated electrodes

Info

Publication number: WO2021045614A1
Application number: PCT/NL2020/050539
Authority: WO
Inventors: Johannes Wilhelmus HAVERKORT
Original assignee: Technische Universiteit Delft
Priority date: 2019-09-05
Filing date: 2020-09-02
Publication date: 2021-03-11
Also published as: NL2023775B1

Abstract

The present invention is in the field of a system for electrolysis, for a redox flow battery, for a fuel cell, and combinations thereof, and in particular for electrolysis of gas- evolving reactions, such as in the production of water into hydrogen and oxygen, of chlorine, or chlorate, or for an electrochemical process with mass transfer limitations. The system comprising an anode, a cathode and electrolyte and involves an electrical potential, as well as an inlet and outlet.

Description

Compact electrochemical stack using corrugated electrodes

FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION

In an electrolytic cell an electrical potential differ ence may be applied to obtain a direct electric current (DC) from a redox reaction. Without the electrical potential dif ference, the reaction would not occur. The reverse spontane ous reaction takes place in a Galvanic cell like a fuel cell or a battery. A redox flow battery allows both reactions in the same cell. Electrolysis may be important for separation of elements or splitting of molecules, such as ¾ and O2 from ¾0, or for separation from naturally occurring sources. The voltage that is needed for electrolysis to oc cur is called the decomposition potential.

During actual electrolysis a direct electric current is provided through an electrolyte. The current enters in the form of electrons in the cathode where a reduction reaction creates a current carried by ions that travel to the other electrode where an oxidation reaction supplies again elec trons. The electrolyte has the function of carrying an ionic current. The reactants/products may form separate phases or they may be dissolved in the electrolyte in case of a liquid electrolyte. By chemical reactions at the electrodes com pound molecules may be decomposed or molecules/atoms may be combined. Main components in electrolysis are an electro lyte, an electrical current, and electrodes, and in particu lar a cathode and anode. The electrolyte conducts ions ei- ther through a solid or a liquid. An applied voltage pro vides for the thermo-dynamical energy that is necessary for the reaction. In the external circuit the electric current is carried by electrons. Further typically two electrodes are present per electrochemical cell, that are electrical conductors. They provide a physical interface between elec trolyte and the electrical circuit that provides the energy. Electrodes may be made of various materials, such as metals, graphite, and semiconductor material. Typically, in electro- lysers many electrochemical cells are electronically con nected in a stacking or stack in parallel, a monopolar or unipolar configuration, or in series, a bipolar configura tion.

The amount of electrical energy that is added is con sidered to be equal to the change in (thermo-dynamical)

Gibbs free energy of the reaction. Due to losses in a system the required energy is always higher and often much higher, for instance due to a release of heat.

Electrolysis of water produces hydrogen according to 2 H₂0(1) 2 H_{2 (}g) + 0₂(g); E₀ = +1.229 V.

The required cell potential at standard conditions is ³ 1.229 V. It is noted that energy efficiency of water elec trolysis may vary widely. The efficiency of an electrolyser is often defined as the enthalpy contained in the hydrogen, compared to electrical energy provided. Heat/enthalpy values for hydrogen are about 144 MJ/kg. Some reports quote water electrolysis efficiencies between 50% and 70% for alkaline electrolysers; higher efficiencies are available, such as 95% efficiency. Production costs for 1 kg of hydrogen through electrolysis are about €5 in the near term and €2 in the long term.

Only a small fraction of hydrogen gas produced worldwide is generated by electrolysis, and normally used onsite. The generated hydrogen may be used for subsequent reaction, such as for forming ammonia.

A disadvantage with prior art systems is that cheap sys tems tend to be rather large. For instance, an alkaline wa ter electrolyser (with an aqueous electrolyte containing usually potassium hydroxide to make it more conductive) are typically an order more voluminous than the more expensive polymer electrolyte membrane (PEM) electrolysers this can be up to an order of magnitude higher. A reason may be the lower current densities in alkaline electrolysis due to larger Ohmic losses. By Ohms law the losses are proportional to the current density (A/m²) and the distance over which the current travels. The main focus is therefore on making thinner membranes that reduce the distance between the anode and cathode, such as thinner than 0.5 mm thickness.

A way of reducing Ohmic losses may be reducing the cur rent density. However, this directly increases the volume of an electrolyser for a given amount of gas (hydrogen) pro duced thus making the electrolyser more expensive per kg of hydrogen produced per unit of time. An important metric to be improved is therefore the current produced per unit vol ume at a given current density. This is particularly im portant for mobile, space, or distributed ap-plications where volume comes with a premium. An innovation improving this metric has recently been raised in W0018101. A problem with this invention is however the ease of manufacturing.

Various documents recite electrode systems, such as US 2015/292094 A1), WO 2015/085363 A1), US 2012/222954 A1, US 6,254,741 Bl, US2014/284209 A1, US 2015/075977 A1 and WO 2017/170664 A1. In particular JP 5639724 Bl recites an electric water generator capable of suppressing the damage of a diaphragm even if there occurs a wide pressure differ ence between the anode chamber and cathode chamber of an electrolytic tank. The electrolytic water generator com prises an electrolytic tank dividing an electrolytic chamber into which the water to be electrolyzed is made to flow; an anode feeder and a cathode feeder arranged so as to be con fronted each other in the electrolytic chamber; and a dia phragm arranged between the anode feeder and the cathode feeder and dividing the electrolytic chamber into the anode chamber on the side of the anode feeder and the cathode chamber on the side of the cathode feeder. The diaphragm is held by the anode feeder and the cathode feeder. The present invention therefore relates to a system for electrolysis and so on, which solves one or more of the above problems and drawbacks of the prior art, providing re liable results, without jeopardizing functionality and ad vantages.

SUMMARY OF THE INVENTION

The present invention relates to a system comprising a stack, which may be a monopolar or a bipolar stack, such as an electrolysis system, or the reverse Galvanic reaction, a redox flow battery, and a fuel cell, and in particular for generation of gaseous species, such as hydrogen and oxygen, chlorine, chlorate, and fluorine, for generation of lower alcohols, such as methanol, and ethanol, for carboxylic ac ids or ions thereof, such as formic acid and formate, me thane, CO, ethylene, and NH₃, for electrodialysis, for ca pacitive deionization, for desalination, and for generation of metals, as a redox flow battery, and for a fuel cell. It is noted that for the present system, such as for electro- lysers, many electrochemical cells are electronically con nected in a stacking or stacked in parallel, referred to as a monopolar configuration, sometimes referred to as unipo lar, or in series, referred to as a bipolar configuration. The present invention relates to an innovative stack with corrugated (or undulated) electrodes, providing higher cur rents per unit volume (at the same or similar overpotential and typically pressure drop over the flow channels and therefore energy efficiency), such as two times higher than comparable prior art electrolysis systems comprising planar electrodes. In the present system current may flow in two substantially independent (such as perpendicular) directions so that for the same current per unit volume a two times lower current density may be applied and thus a two times lower Ohmic voltage drop may be obtained, compared to in a planar configuration with a similar electrode thickness. An other advantage is that e.g. reactants may be supplied and products, such as gas, may be removed through a centre of an electrode rather than at the back (in zero-gap systems, or in front of in traditional systems with a gap between the electrode and the membrane) and that hydrodynamics are im proved. This avoids a need for separate flow channels (other than just making a hole in the centre of the electrode or joining to corrugated plate electrodes). In the case of gas- evolving reactions, at the same current density, a higher volume fraction of gas is obtained in the flow channels, leading to more buoyant flow and improved bubble removal. Another advantage is the improved strength compared to prior art systems, without the need for additional current collec tors. In prior art systems frequent current collectors are necessary also to avoid bending of opposing electrodes and provide structural integrity. Because of the corrugations inherent in the present design there is frequent contact and strength resulting from the curved surfaces. The current can be collected directly from the electrode at the top, bottom, or sides, or combinations thereof. Metallic electrodes are often sufficiently conductive so that additional internal current collectors are not needed. If needed, the contact points of opposing electrodes are convenient locations for placement thereof, not interfering with the flow inside the flow channels. As a result of the improved strength and lack of need for additional current collectors, significant re ductions in material costs and complexity are obtained. An other important advantage is improved mass transfer from a reactant, e.g. dissolved in the electrolyte, at equal (com parable) pressure drop. In a typical bipolar or monopolar electrolyser, reactants diffuse from the bulk of the flow channel in just one or two directions, respectively. In the present configuration the entire flow channel is surrounded by electrode material so that all, for example four, walls of the flow channel are reactive. This means that a much larger mass transfer rate is obtained at the same pressure drop. This implies that shorter and smaller channels suffice to obtain the same conversion rate. The resulting volume savings facilitate miniaturization of compact electrolysers, redox flow batteries, and fuel cells. Finally, a good pro spect for membrane-less operation is provided, i.e. the pre sent stack may also be operated without a membrane, with a chimney-like action providing effective separation of e.g. gases being produced, such as hydrogen and oxygen. Buoyant rise of the gaseous species allows for easy collection, whereas if a liquid would be produced a pump may be applied.

In the present application the cathodes and anodes are considered mutually interchangeable, as well as species formed as a consequence, i.e. a layout wherein each cathode is replaced by an anode and vice versa also falls under the scope of the present invention. A pair of an anode and a cathode may also be referred to as a "cell" or "electrochem ical cell". Likewise the present stack comprises a number of cells, the number typically being referred to as "n".

The present applicant has also filed a patent applica tion with respect to a further concept (NL2019/050409), which application and the contents thereof are hereby incor porated by reference. Most of the above advantages are simi lar in both concept because of the strong geometrical simi larities. Topologically however the distinct difference is that while in NL2019/050409 typically slender anode and cathode pillars alternate two normal directions in the pre sent concept diagonally such electrodes are electronically and mechanically connected into a single electrode that is thin in only one instead of two directions. The resulting electrodes with the same volume saving advantages as these electrode arrays can therefore be constructed out of corru gated or undulated plate-like materials as in conventional plate-and-frame designs. This has the distinct advantage of ease of manufacturing as well as improved strength compared to both the slender structures of NL2019/050409 as well as the flat plate electrodes of conventional designs. The pre sent invention is also subject of a scientific publication entitled "Compact monopolar electrochemical cell design us ing checkerboard electrode arrays or corrugated electrodes" which publication and the contents thereof are hereby incor porated by reference.

The present stack design typically comprises corrugated shaped electrodes, which may be undulated, wavy, or other wise shaped. Typically, two or more anodes are present and two or more cathodes, preferably [3-m] anodes (wherein m may be up to 2²⁰), and preferably [3-n] cathodes (wherein n may be up to 2²⁰). The cathodes and anodes are typically alter nating, that is a cathode is in at least one and typically two direction (s) adjacent to two anodes, and vice versa. A material, typically a fluid material, in between said at least one cathode and at least one anode comprises an elec trolyte and is suited for transfer of electrolyte species typically being ions, or precursors thereof, such as a solu tion comprising a polar solvent, such as water. For perform ing electrolysis, or the reverse Galvanic reaction, the at least one anode and at least one cathode are at least partly in fluidic contact the material. This contact may be direct or indirect, i.e. a further medium may be provided in be tween an electrode and fluid material. For performing the electrolysis also an electrical potential/power supplier, typically of a direct current type (DC), is provided. For a Galvanic cell connection to a load or a transformer is pro vided. As electrolyte and dissolved or dispersed reactants and products may need to be replenished, removed, or re freshed, or re-supplied, such in a continuous mode, in a semi-continuous mode, in a batch-wise mode, an inlet and an outlet are provided, as well as an optional outlet for gase ous species, typically one outlet per gaseous species. Each set of anodes may form a row of vertical anolyte channels, and each set of cathodes may form a row of vertical catho- lyte channels, vertical taken along a height of the respec tive anode/cathode. These channels may be made by subtrac tive manufacturing from a relatively thick undulated or cor rugated shaped sheet material or from connecting two or more relatively thin corrugated sheet materials. These connec tions may be force by external compression or physical join ing like through welding, brazing, soldering, sintering, riveting, or alternative permanent or non-permanent joining methods. It was found that with relatively thin metal elec trodes it is possible to do without additional current col lectors, even at higher current densities. The present elec trodes may be in the form of a porous metallic materials with sufficient structural rigidity, such as expanded meshes, perforated plates, metal foams, and sintered partic ulate electrodes. Woven and non-woven metallic fibers like metal paper, felts, wool, or gauze, may also be used but may need additional support to provide the required structural integrity. As all, for example four, sides of the vertical flow channels are electrodes, and hence the current is in an equal number of directions, the present design consumes at least 1.5 to 3.3 times less volume compared to conventional type configurations producing a same amount of product.

Since fluid flow paths or channels of prior art designs are never empty, but typically filled with additional material for current collection or strength, these values can be con sidered a lower limit to the potential volume-savings, typi cally being a factor 2-4. For mass-transfer-limited electro- lysers, fuel cells, and flow-batteries, the volume savings compared to prior art systems, easily increase to a factor three or more. This will additionally result in significant savings in material costs.

The present stack comprises at least one anode, prefera bly at least two anodes, wherein each anode is corrugated at at least one side thereof, preferably at two opposite sides thereof, at least one cathode, preferably at least two cath odes, wherein each cathode is corrugated at at least one side thereof, preferably at two opposite sides thereof, wherein corrugations, each individually, have at least one pitch p and a least one depth d, respectively, wherein the at least one anode is interlocked with the at least one cathode, preferably wherein all cathodes and anodes are in terlocked, that is become engaged such that parallel motion of any part, e.g. an anode, is restrained by another part, e.g. one or two adjacent cathodes. There may be one pitch and one depth, or a multitude of pitches and depths, alt hough a more regular corrugation is preferred e.g. in terms of production.

The present system further involves an electrical volt age, and the at least one anode and at least one cathode are substantially surrounded by the solution. Thereby the present invention provides a solution to one or more of the above-mentioned problems and drawbacks.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a system according to claim 1.

In an exemplary embodiment of the present system an an ode flow channel and/or cathode flow channel is surrounded by electrode material, preferably such that all walls of the flow channel comprise electrode material.

In an exemplary embodiment the present system, which may be considered a bipolar variant, comprises n anodes and n cathodes, wherein n is an odd number, wherein an i^th anode and an i^th cathode are interlocked, wherein i£n, wherein each adjacent i^th anode and an i^th cathode has an inter changed cathode and anode with respect to the i-l^th anode and an i-l^th cathode, wherein an outer (first or n^th) anode comprises an electrical connection for a first side of the electrical voltage/power supplier, respectively, and wherein an outer (first or n^th) cathode comprises an electrical con nection for a second side of the electrical voltage/power supplier, wherein, for all but the outer anode and the outer cathode, an i^th anode is in electrical connection with an i- 1^th cathode, and thus an i^th cathode is in electrical connec tion with an i+l^th anode, or vice versa, e.g. for a mirror- imaged configuration. For a electrolytic cell the cathode is typically connected to a negative side, whereas for a gal vanic cell it is connected to the positive side, the anode being connected to the opposite polarity thereof. Said con figuration provides a higher voltage and lower current, re sulting in lower losses in the system. As a consequence con ducting elements can be made thinner, both internally and externally. Also in view of voltage a smaller transformer can be used in that an available power voltage is closer in size to the voltage used for said configuration. A smaller capex is the result. In an exemplary embodiment of the present system adja cent electrodes, typically of the same polarity, are elec trically separated, such as by an electrical insulator.

In an exemplary embodiment of the present system the stack is a monopolar stack. In such a stack cells are con nected in parallel.

In an exemplary embodiment the present system may com prise a separator, such as a membrane between, a set of op posing anodes and a set of opposing cathodes. The membrane is found to improve the performance of the system. The sepa rator may also be a diaphragm, a microporous separator, or a combination of the above.

In an exemplary embodiment of the present system a dis tance between the at least one anode and the a least one cathode may be smaller than 0.5 times an average corrugation depth, preferably smaller than 0.1 times an average corruga tion depth. Preferably each anode and adjacent cathode are at such a distance. As such the anodes and cathodes are well interlocked.

In an exemplary embodiment of the present system each anode may comprise anolyte fluid paths.

In an exemplary embodiment of the present system each cathode may comprise catholyte fluid paths.

As such electrolytes and/or solution may flow relatively free.

In an exemplary embodiment of the present system anode corrugations at either side may have the same depth, and wherein corrugation pitches at either side may have the same phase or a phase shifted by p.

In an exemplary embodiment of the present system cath ode corrugations at either side may have the same depth, and wherein corrugation pitches at either side may have the same phase or a phase shifted by p.

In an exemplary embodiment of the present system the corrugations of an anode side facing corrugations of an op posite cathode side have the same phase or preferably a phase shifted by p. As such the anodes and cathodes can be well interlocked. Thus, the present invention provides a large variation of different shaped anodes and cathodes, varying in types of corrugations, depths of corrugations, pitch of corrugations, and combinations thereof.

In an exemplary embodiment of the present system an an ode may be formed out of two corrugated plates, preferably two corrugated plates in electrical (and typically also physical and mechanical) contact with one and another.

In an exemplary embodiment of the present system a cath ode may be formed out of two corrugated plates, preferably two corrugated plates in electrical (and typically also physical and mechanical) contact with one and another.

In an exemplary embodiment of the present system at least one anode may be formed out of one single part.

In an exemplary embodiment of the present system at least one cathode may be formed out of one single part.

As such using plate-like materials the electrodes can be manufactures with ease.

In an exemplary embodiment of the present system at least one anode may have a corrugation with an anode pitch, and at least one cathode may have a corrugation with a cath ode pitch, wherein the anode pitch may be equal to the cath ode pitch, and wherein in one dimension the phase of the an ode pitch may be p plus the cathode pitch. As such these at least one anode and at least one cathode are well inter locked.

In an exemplary embodiment of the present system the an ode corrugation pitch is preferably from 0.1-100 mm, and wherein the cathode corrugation pitch is preferably from 0.1-100 mm, and wherein the maximum anode corrugation depth is preferably from 0.1-100 mm, and wherein the maximum cath ode corrugation depth is preferably from 0.1-100 mm.

In an exemplary embodiment of the present system at least one anode may be at least one plate.

In an exemplary embodiment of the present system at least one cathode may be at least one plate.

In an exemplary embodiment of the present system at least one anode may be a porous material. In an exemplary embodiment of the present system at least one cathode may be a porous material.

In an exemplary embodiment of the present system pores may have a diameter of 1 nm-10 mm, preferably 3 nm-lmm, more preferably 10 nm-0.1 mm, such as 100 nm-0.01 mm.

In an exemplary embodiment of the present system pores may have a heterogeneous size, e.g. a sigma of smaller than 50% of an average width.

In an exemplary embodiment of the present system a pore density may be 1-10²¹ pores/cm³, preferably 10-10²⁰ pores/cm³, more preferably 10⁴-10¹⁹ pores/cm³, even more preferably 10⁶- 10¹⁸ pores/cm³, such as 10¹⁰-10¹⁶ pores/cm³.

In an exemplary embodiment of the present system a po rosity (volume open/volume solid) may be from 0.1-0.99, preferably 0.5-0.9. The porosity can be measured in various ways, such as by using a water evaporation method and calcu lating accordingly (pore volume = (weight of saturated sam ple - weight of dried sample)/density of water).

In an exemplary embodiment of the present system the at least one anode and/or at least one cathode provide vertical fluid paths.

In an exemplary embodiment of the present system a cross section of one period (pitch) of the at least one anode and at least one cathode fluid paths may be independently se lected from square, rectangular, circular, ellipsoidal, mul- tigonal, such as pentagonal, hexagonal, octagonal, and com binations thereof. This may relate to an approximate cross- section. As such a large freedom of design is provided by the present system.

In an exemplary embodiment of the present system verti cal channels of opposing cathodes and of opposing anodes in at least one diagonal direction alternate, preferably in at least two diagonal directions (see e.g. figures).

In an exemplary embodiment of the present system at least one electrode comprises a metal, such as made of said metal or coated with said metal, such as Pt, Ir, Ni, Cu, Zn, Ru, Ti, Fe, such as NiFe/NiO, graphite, a semiconductor, ox ides, or combinations thereof. The Electrode material may be provided on a support.

In an exemplary embodiment of the present system a height h_c of the at least one cathode is 0.1-1.0 times a length l_c thereof. In an exemplary embodiment of the present system and/or wherein a height h_a of the at least one anode is 0.1-1.0 times a length l_a thereof.

In an exemplary embodiment of the present system a width of the at least one anode is 0.1-5 cm.

In an exemplary embodiment of the present system a width of the at least one cathode is 0.1-5 cm.

In an exemplary embodiment of the present system a height of the cathode may be at least 1 mm, such as at least one cm.

In an exemplary embodiment of the present system a height of the anode is at least 1 mm, such as at least one cm.

In an exemplary embodiment of the present system an electrode may comprise at least one of a top electrical cur rent collector, a bottom electrical current collector, and a side electrical current collector, typically parallel to the height of the electrodes. The current collector provides an improved conductance and may increase a current applied to the electrodes.

In an exemplary embodiment of the present system the so lution may be an aqueous solution, an ionic liquid, or a melt.

In an exemplary embodiment of the present system the so- lution may comprise anions and cations, preferably selected from at least one of Li⁺, Rb⁺, K⁺, Cs⁺, Ba²⁺, Sr²⁺, Ca²⁺, Na⁺, Mg²⁺, SO4²-, HCC>3, and Oth, preferably K⁺ and Ofh for water electrolysis and preferably HC03 and K⁺ for CO2 electroly sis. In an exemplary embodiment of the present system may comprise 2-2²⁰ cathodes and 2-2²⁰ anodes, preferably 4-2¹⁵ cathodes and 4-2¹⁵ anodes, more preferably 10-2¹² cathodes and 10-2¹² anodes, even more preferably 16-2¹⁰ cathodes and 16-2¹⁰ anodes, such as 32-2⁹ cathodes and 32-2⁹ anodes, wherein the array comprises at least one symmetry axis, such as a two-fold axis, a three-fold axis, and a four-fold axis.

In an exemplary embodiment the present system may be for electrolysers, such as electrolysis of water, for a redox flow battery, for a fuel cell, and combinations thereof. The voltage supplier in operation may provide a potential dif ference over the electrodes of about 1.23-2.2V, such as 1.48-2 V, and optionally providing an overpotential.

In an exemplary embodiment of the present system the solution and/or electrolyte flow in a horizontal direction and/or in a vertical direction, respectively, that is in two perpendicular directions

In an exemplary embodiment of the present system the height of the at least one cathode may be substantially equal to the height of the at least one anode, i.e. both are of equal height or almost equal height.

In an exemplary embodiment of the present system the width of the at least one cathode may be substantially equal to the width of the at least one anode, i.e. an array of electrodes appears to substantially regular in one direction of a top view.

In an exemplary embodiment of the present system the length of the at least one cathode may substantially equal to the length of the at least one anode, i.e. an array of electrodes appears to substantially regular in one direction of a top view. Each individual electrode may be structured as indicated.

In an exemplary embodiment the present system may com prise at least one component selected form a storage vessel, a cleaner, a purifier, a separator, a compressor, and a drier, such as for replenishing or for storage of gases be ing produced.

In an exemplary embodiment of the present system at least one electrode may be hollow. In addition, thereto also a fluid material may be provided at both an inside and an outside of the electrode. Therewith both an internal and an external surface, as well as the surface in the preferred pores and channels, may be used for electrolysis.

In an exemplary embodiment of the present system at least one membrane (M) may be provided in between at least one cathode and at least one anode, preferably in between any cathode and any neighboring anode. The membrane prefera bly may have a thickness of 0.001-0.1 cm, such as 0.01-0.05 cm.

In an exemplary embodiment of the present system at least one electrode may have a wall thickness of 0.1-3 mm, such as 0.2-1 mm, whereas a thickness of the electrode may be up to 100 mm.

In an exemplary embodiment of the present system at least one electrode may be obtained by corrugating.

In an exemplary embodiment of the present system at least one cathode and at least one anode may be separated by a porous diaphragm, or a separator, or a membrane, such as a polymer electrolyte membrane, a cation exchange membrane, an anion exchange membrane, or a bipolar membrane, and are thus chemically separated from one and another.

In an exemplary embodiment of the present system at least one anode may be in electrical connection to a common anode plate.

In an exemplary embodiment of the present system at least one cathode may be in electrical connection to a com mon cathode plate.

In an exemplary embodiment of the present system a cath ode or a group of cathodes may be in electrical connection to a first common cathode plate and an anode or a group of anodes may be in electrical connection to a first common an ode plate, and so on, wherein the first common cathode plate may be electrically connected in series or in parallel to the first common anode plate, which in turn may be connected to a second common cathode plate, and so on.

In an exemplary embodiment of the present system in the array anodes and cathodes may be alternating.

In an exemplary embodiment of the present system pores may have a heterogeneous size, that is very small sized pores may be present, such as of 1-100 nm, slightly larger size pores may be present, such as of 0.1-100 pm, and rela tively large pores may be present, such as of 100 pm-l mm. Therewith gas transport and liquid transport can be con trolled well, and a pore size can be adapted to specific species, such as gas species, such as ¾ and O2, allowing one species to pass, and to block another.

In an exemplary embodiment of the present system a dis tance between an anode and neighboring cathode may be 0.001- 5 cm, preferably 0.01-0.3 cm. depending on design and fur ther boundary conditions the distance may vary and may be adapted.

In an exemplary embodiment the present system may com prise at least one of sealing side covers, a support, such as supporting pillars, a first gas outlet for a first gase ous species, such as ¾, a second gas outlet for a second gaseous species, such as O2, a pump, and a fluid material chamber.

The one or more of the above examples and embodiments may be combined, falling within the scope of the invention.

EXAMPLES

The below relates to examples, which are not limiting in nature, showing the benefits of the invention.

Electrodes were produced as shown in fig. 4b which are found to have similar advantages as the present invention. The reactions studied were

4H₂0 + 4e > 2H₂0 + 40H Ec = -0.826V

40H -> +0₂ + 2¾0 + 4e Ea = 0.404V

The performance of the electrode has been measured in the range of 1.48 to 3.0 V, with minimal step size of the used power source being 0.1 V.

The electrolyte used is KOH dissolved in water. Experi ments have been done for 0.1 M, 1 M and 3 M KOH. The mate rial used for the electrode is 316-L stainless steel, which was used for the 3-D print. The material contains about 10 % Nickel (Fe0.9Nio.i) and is used as a cathode material. The material choice for the 3D printed plastic parts is Acrylo nitrile Butadiene Styrene (ABS), in view of its strength and that it does not react with high concentrations KOH. The electrode wall thickness was 2 mm. The porosity of the material was about 50 percent. The current density ex pected was about 2000 A/m². The pores/channels in this printed structure have a diameter of around 250 pm, which is found sufficient for the bubbles to escape in view of sizes of the gas bubbles in electrolysis. These channels are set under an angle of 45 degrees. Hollow electrodes, reminiscent of chimneys, are designed to be able to remove gas with an almost zero gap between the electrodes and the membrane. The chimney width and length were about 4 mm. For a good compar ison a 2 mm gap behind each electrode in the conventional configuration was provided for the removal of bubbles.

The anode plate is connected to 18 electrodes and the cathode plate is connected to 17 electrodes. This system has 58 surfaces of 8x20 mm, which oppose an electrode of oppo site polarity. The 0.5 mm thick membrane (Zirfon Perl, Agfa) is folded in the 0.7 mm gap between the anodes and the cath odes to separate the oxygen gas and hydrogen gas.

For every step in potential, a waiting time of 2 minutes is used in order to have the reaction reach an equilibrium state. The chimneys from the array electrodes produced clouds of bubbles above the electrode. This was most visible on chimneys from the cathode. For every emerging oxygen mol ecule, 2 hydrogen molecules are produced, which explains the difference in chimney activity.

The main result is shown in Figures 5 and 6. Figure 5 shows that the required overpotential to obtain a certain current per unit external electrode area is similar between the conventional and array configurations. This is expected since similar electrodes and membrane are used. Figure 6 shows a roughly 50% increase in current per unit volume at the same potential compared to the conventional configura tion. This is related to the roughly 1.5 times higher sur face area per unit volume of the array electrolyser. When upscaling to more anodes and cathodes, this factor can be shown to approach approximately 2 for the used dimensions.

The invention is further detailed by the accompanying figures, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

FIGURES

The invention although described in detailed explanatory context may be best understood in conjunction with the ac companying figures.

Fig. 1 shows a conventional alkaline water electrolysis set-up.

Fig. 2 shows a traditional (left) and zero gap cell (right) layout.

Fig. 3a and 3c show a prior art layout and fig. 3b and 3d a schematic layout of recent improvements.

Also figs. 4a-l show schematic layouts of the present invention .

Figs. 5 and 6 show advantages of the present invention based on a comparison between current densities of a prior art system and the recent design, which are considered to provide similar advantages.

Fig. 7 shows a layout of the present system with cells connected in series.

DETAILED DESCRIPTION OF THE FIGURES

In the figures:

A Anode

C Cathode d outer dimension cathode and/or anode d2 inner dimension cathode and/or anode d_m distance cathode-anode d_p depth corrugation e electrode

E electrolyte h_a height anode h_c height cathode i electrical insulator M membrane p pitch corrugation w_a width anode w_c width cathode

The figures have been detailed throughout the descrip tion. Fig. 1 shows a conventional (Zeng, K., and Zhang, D.

(2010)) alkaline water electrolysis set-up.

Fig. 2 shows a traditional (left) and zero (right) gap cell layout (Phillips, R., & Dunnill, C. W. (2016)).

Fig. 3a and 3c show a prior art layout, fig. 3b the re- cent improvement of NL2019/050409, and fig. 3d a layout of the present invention. In fig. 3d a corrugated electrode and membrane configuration showing geometrical equivalence with the electrode array of Fig. 3b tilted by p/4 rad. The topological change of connecting neighbouring electrodes of equal polarity greatly simplifies manufactur ing while also allowing current collection from the sides.

At the vertices between different flow channels additional current collectors can be placed or additional space for flow created. The flow direction is normal to the pa- per/screen. To enhance mass transfer inside thick porous electrodes, flowing one or both electrolyte streams in the horizontal direction, or under an angle with the vertical, may however also be considered. Finally, various shapes other than square flow channels can be created, including hexagonal and smoothly undulated channels.

Fig. 4a shows a top view of an interlocked stack of two cathodes, one anode, and membranes in between. The corruga tion has a pitch p and a depth d_p. Anode and cathodes are shifted in phase along the horizontal axis by p, as depicted by the arrow.

Figs. 4b-4i show alternative layouts, with curved elec trodes (fig. 4b), with curved and diamond shaped electrodes (fig. 4c), with solid or porous electrodes (fig. 4d), with partly solid or porous and partly hollow porous electrodes (fig. 4e), with elongated channels (fig. 4f), with elongated diamond shaped electrodes (4g), less preferred two-coincid- ing sinusoidal shapes (fig. 4h), and with vertically elon gated more diamond shaped electrodes (4i). Fig. 4j shows a stacked layout(not showing the corruga tions) with dimensions h_a (height anode), h_c (height cath ode), w_a (width anode) and w_c (width cathode).

Figs. 4k-l show possible fluid flow paths. Note that the flow may be combinations thereof. For example, electrolyte flowing up through anodic flow channels while flowing down through cathodic flow channels.

Fig. 5 shows a comparison between current densities (A per m² of external electrode area) of a prior art system and the geometrically similar configuration of the NL2019/050409 system with a 3 M KOH.

Fig. 6 shows a comparison between volumetric current densities (A per m³ of total electrolyser volume) of a prior art system and the NL2019/050409 system with a 3 M KOH.

Fig. 7 shows a layout of the present system with cells connected in series. Therein alternating cells of anodes and cathodes, optionally comprising a membrane in between, are stacked with cells of cathodes and anodes in the reversed order, or vice versa. Each anode therein is connected to a cathode of a "previous" and adjacent cell, whereas the first anode and last cathode are connected with the respective sides of the power source, or vice versa. In view of said configuration typically an odd number of cells is provided. The opposing cathodes, and likewise anodes, are preferably separated physically from one and another, such as by a sep arator, preferably an electrical insulator. It is preferred to use a separator at each individual corrugation. It is also preferred to have small separators such that a volume between opposing anodes and likewise opposing cathodes re mains substantially open for fluid flow.

Claims

1. System comprising a stack, the stack comprising at least two anodes, wherein each anode is corrugated at least one side thereof, preferably at two opposite sides thereof, at least two cathodes, wherein each cathode is corru gated at at least one side thereof, preferably at two oppo site sides thereof, wherein corrugations have at least one pitch and at least one depth, respectively, wherein the at least one anode is interlocked with the at least one cathode, preferably wherein all cathodes and anodes are interlocked, a solution in between said at least one cathode and at least one anode, the solution being electrically conducting and comprising an electrolyte, an electrical voltage/power supplier, and wherein the at least one anode and at least one cathode are substantially surrounded by the solution.

2. System according to claim 1, wherein an anode flow chan nel and/or cathode flow channel is surrounded by electrode material, preferably such that all walls of the flow channel comprise electrode material.

3. System according to claim 1 or 2, comprising n anodes and n cathodes, wherein n is an odd number, wherein an i^th anode and an i^th cathode are interlocked, wherein i£n, wherein each adjacent i^th anode and an i^th cathode has an in terchanged cathode and anode with respect to the i-l^th anode and an i-l^th cathode, wherein an outer anode comprises an electrical connection for a first side of the electrical voltage/power supplier, respectively, and wherein an outer cathode comprises an electrical connection for a second side of the electrical voltage/power supplier, wherein, for all but the outer anode and the outer cathode, an i^th anode is in electrical connection with an i-l^th cath ode, or vice versa.

4. System according to any of claims 1-3, wherein adjacent electrodes are electrically separated, such as by an elec trical insulator.

5. System according to claim 1 or 2, wherein the stack is a monopolar stack.

6. System according to any of claims 1-5, comprising at least one separator, such as a membrane, between at least one anode and at least one adjacent cathode.

7. System according to any of claims 1-6, wherein a distance between the at least one anode and the at least one cathode is smaller than 0.5 times an average corrugation depth, preferably smaller than 0.1 times an average corrugation depth, preferably for each anode and adjacent cathode.

8. System according to any of claims 1-7, wherein each anode comprises anolyte fluid paths, and/or wherein each cathode comprises catholyte fluid paths.

9. System according to any of claims 1-8, wherein anode cor rugations at either side have the same depth, and wherein corrugation pitches at either side have the same phase or a phase shifted by p, and/or wherein cathode corrugations at either side have the same depth, and wherein corrugation pitches at either side have the same phase or a phase shifted by p, and/or wherein the corrugations of an anode side facing corrugations of an opposite cathode side have the same phase or a phase shifted by p.

10. System according to any of claims 1-9, wherein at least one anode is formed out of two corrugated plates, preferably two corrugated plates in electrical contact with one and an other, and/or wherein at least one cathode is formed out of two corrugated plates, preferably two corrugated plates in electrical contact with one and another, and/or wherein at least one anode is formed out of one single part, and/or wherein at least one cathode is formed out of one single part.

11. System according to any of claims 1-10, wherein at least one anode has a corrugation with an anode pitch, and at least one cathode has a corrugation with a cathode pitch, wherein the anode pitch is equal to the cathode pitch, and wherein in one dimension the phase of the anode pitch is p plus the phase of the cathode pitch, wherein the anode corrugation pitch is preferably from 0.1- 100 mm, and wherein the cathode corrugation pitch is prefer ably from 0.1-100 mm, and wherein the maximum anode corruga tion depth is preferably from 0.1-100 mm, and wherein the maximum cathode corrugation depth is preferably from 0.1-100 mm.

12. System according to any of claims 1-11, wherein at least one anode is at least one plate, and/or wherein at least one cathode is at least one plate, and/or wherein at least one anode is a porous material, and/or wherein at least one cathode is a porous material, preferably with pores with a diameter of 1 nm-10 mm, and/or wherein the pores have a het erogeneous size, and/or wherein a pore density is 1-10²¹ pores/cm³, and/or wherein a porosity (volume open/volume solid) is from 0.1-0.99, preferably 0.5-0.9, and combina tions thereof.

13. System according to any of claims 1-12, wherein the at least one anode and/or at least one cathode provide vertical fluid paths with a cross-section geometry selected from square, rectangular, ellipsoidal, circular, hexagonal, mul- tigonal, and combinations thereof, and/or wherein a/the po rous material of at least one anode and/or at least one cathode provide horizontal fluid paths, and/or wherein a/the porous material of at least one anode and/or at least one cathode provide diagonal fluid paths.

14. System according to any of claims 1-13, wherein vertical channels of opposing cathodes and of opposing anodes in at least one diagonal direction alternate.

15. System according to any of claims 1-14, wherein at least one electrode is made from a metal, a carbon comprising ma terial, such as graphite, a semiconductor, a porous mate rial, such as an expanded mesh, a metal foam, and a sintered particulate structure, a perforated material, a non-woven fibrous material, a woven or embroidered fibrous material, or combinations thereof.

16. System according to any of claims 1-15, wherein a height h_c of the at least one cathode is 0.1-1.0 times a length l_c thereof, and/or wherein a height h_a of the at least one anode is 0.1-1.0 times a length l_a thereof.

17. System according to any of claims 1-16, wherein the so lution is an aqueous solution or a melt.

18. System according to any of claims 1-17, wherein the so lution comprises anions and cations.

19. System according to any of claims 1-18, comprising 2-2¹⁴ cathodes and 2-2¹⁴ anodes, wherein the array preferably com prises a two-fold axis.

20. System according to any of claims 1-19, for electrolys- ers, such as electrolysis of water, for a redox flow bat tery, for a fuel cell, and combinations thereof.

21. System according to any of claims 1-20, wherein the so lution and/or electrolyte flow in a horizontal direction and/or in a vertical direction, respectively.

22. System according to any of claims 1-21, wherein the height of the at least one cathode is substantially equal to the height of the at least one anode, and/or wherein the width of the at least one cathode is substantially equal to the width of the at least one anode, and/or wherein the length of the at least one cathode is substantially equal to the length of the at least one anode, each individually.

23. System according to any of claims 1-22, comprising at least one component selected form a storage vessel, a cleaner, a purifier, a separator, a compressor, and a drier.

24. System according to any of claims 1-23, wherein at least one electrode has a thickness of 0.1-3 mm.

25. System according to any of claims 1-24, comprising at least one of a top electrical current collector, a bottom electrical current collector, and a side electrical current collector.

26. System according to any of claims 1-25, wherein at least one electrode is obtained by corrugating, and preferably welded, such as spot-welded.