Structures for an electrolyser and methods of manufacture

Abstract

There is disclosed structures for an electrolyser, including a porous wall (2020) for an electrode. The porous wall comprises a body, a plurality of flow regions (2045) extending through the body at discrete locations to provide the porous wall with a discontinuous porous structure. The body comprises a plurality of bonded stacked plates, each flow region (2045) being defined by a respective array of flow zones (2049) extending through a respective subset of adjacent plates and overlapping along a thickness direction to cumulatively define the flow region. There is also disclosed a related flow arrangement, electrolyser, and structures for a multi-cell electrolyser.

Description

STRUCTURES FOR AN ELECTROLYSER AND METHODS OF MANUFACTUREFIELD OF INVENTION

[0001] The invention relates to structures for an electrolyser, with disclosure relating to a porous wall for an electrolyser and method of manufacture, a flow arrangement for an electrolyser, an electrolyser, electrolysis installation, methods of manufacture and operation. Related electrolysers may be for performing continuous electrolysis, for example at high pressure and / or temperature (e.g., at supercritical conditions), particularly electrolysis of water and aqueous electrolyte fluids.BACKGROUND OF THE INVENTION

[0002] One use of electrolysis is for the generation of hydrogen for energy storage. Electricity can be used to separate hydrogen and oxygen from water. Stored hydrogen and oxygen can be recombined in a fuel cell to generate electricity. In the meantime, the hydrogen (and oxygen) can be stored and transported. With improving efficiencies of electrolysis and fuel cell technologies, hydrogen energy storage is being proposed as a solution for many energy storage problems, particularly for the storage of energy from renewable energy sources.

[0003] W02022 / 195110 includes disclosure relating to an electrolyser cell configuration in which two porous walls separate respective retention chambers for retaining fluid reaction products of electrolysis from an inlet chamber. The two porous walls can provide respective electrodes of the cell configuration, and inhibit return flow of the fluid reaction products to the inlet chamber. The cell configuration avoids use of polymer electrolyte membranes. WO2022 / 195110 also discloses operation of an electrolyser at high pressure, for example at supercritical conditions, and associated benefits for efficiency of electrolysis.

[0004] Challenges associated with implementation and adoption of electrolysers, for example for hydrogen generation, include the provision of practical and efficient manufacturing techniques suitable for scale-up of production capacity.SUMMARY OF THE INVENTION

[0005] Aspects of the disclosure relate to a porous wall for an electrolyser, a flow arrangement for an electrolyser, an electrolyser, an electrolysis installation, and a structure for an electrolyser, and associated methods (e.g., of manufacture or operation). The disclosure includes the following numbered clauses and intervening statements relating to such aspects.

[0006] Clause 1. A porous wall for an electrode of an electrolyser, the porous wall comprising: a body having an inlet side and an outlet side, wherein the body is elongate along a longitudinal direction, and has a thickness direction from the inlet side to the outlet side; a plurality of flow regions extending through the body at discrete locations to provide the porous wall with a discontinuous porous structure; wherein the body comprises a plurality of bonded stacked plates; wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the plurality of plates, each flow zone configured to permit flow through the respective plate, wherein flow zones of adjacent plates in the flow subset overlap along the thickness direction to cumulatively define the flow region.

[0007] Clause 2. A porous wall according to clause 1, wherein each of the flow regions comprises a porous region; wherein each of the porous regions is defined by a respective array of porous zones extending through a respective subset of adjacent plates of the plurality of plates, wherein porous zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the porous region.

[0008] Clause 3. A porous wall for an electrode of an electrolyser, the porous wall having a discontinuous porous structure, the porous wall comprising: a body having an inlet side and an outlet side, wherein the body is elongate along a longitudinal direction, and has a thickness direction from the inlet side to the outlet side; a plurality of porous regions extending through the body at discrete locations; wherein the body comprises a plurality of bonded stacked plates; wherein each of the porous regions is defined by a respective array of porous zones extending through a respective subset of adjacent plates of the plurality of plates, wherein porous zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the porous region.

[0009] Clause 4. A porous wall according to clause 3, comprising a plurality of flow regions extending through the body at the discrete locations; wherein each of the flow regions comprises a respective porous region; wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the plurality of plates, wherein flow zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the flow region, the array of flow zones comprising the array of porous zones.

[0010] Clause 5. A porous wall according to clause 2 or 4, wherein for a subset of the flow regions, the array of flow zones comprises an array of open zones defining an open region and an array of porous zones comprising the respective porous region.

[0011] When considered in isolation, the inlet side of the body may equally be considered as or otherwise defined as a first side, and the outlet side of the body may be considered as or otherwise defined as a second side.

[0012] The plurality of plates may be stacked in the longitudinal direction. For example, the plurality of plates may be stacked along a stacking direction parallel with the longitudinal direction.

[0013] Clause 6. A porous wall according to any one of clauses 2-5, wherein each porous region defines a respective network of flow paths through the body.

[0014] Clause 7. A porous wall according to any one of clauses 2-6, wherein for at least some of the porous regions, the respective subset of adjacent plates comprises at least three plates. For example, the respective subset of adjacent plates may comprise at least four plates, for example at least five plates.

[0015] Clause 8. A porous wall according to any one of clauses 2-7, wherein a subset of the plurality of porous regions are defined by a common subset of adjacent plates.

[0016] Clause 9. A porous wall according to clause 8, wherein there are a plurality of subsets of the plurality of porous regions, each defined by a respective common subset of adjacent plates and longitudinally offset from each other.

[0017] Clause 10. A porous wall according to clause 8 or 9, wherein the porous wall is annular, and wherein for each subset of the plurality of porous regions, the respective porous regions are angularly distributed around the porous wall.

[0018] Clause 11. A porous wall according to any one of clauses 2-10, wherein for each porous region, the respective subset of adjacent plates comprises plates defined according to a plurality of different patterns of porous zones.

[0019] Clause 12. A porous wall according to clause 11, wherein the plurality of porous zones and / or the plurality of plates are arranged in a repeating sequence of the plurality of different patterns of porous zones.

[0020] Clause 13. A porous wall according to any one of clauses 2-12, wherein the porous wall is annular, and wherein for each porous region, the respective subset of adjacent plates comprises plates defined according to a common pattern of porous zones which is angularly offset for successive plates in the subset to cause the porous zones to overlap and form the porous regions.

[0021] Clause 14. A porous wall according to any one of clauses 2-13, wherein the porous regions each have a porosity of between 0.2-0.9.

[0022] Clause 15. A porous wall according to any one of clauses 2-14, wherein a material composition of the porous regions differs from a material composition of the body; or wherein amaterial composition of the body is the same as the material composition of the respective porous regions.

[0023] Clause 16. A porous wall according to any one of clauses 2-15, wherein each of the porous regions comprise a porous medium.

[0024] Clause 17. A porous wall according to clause 1 or 4, and optionally according to any one of clauses 2 and 5-16.

[0025] Clause 18. A porous wall according to clause 17, wherein for at least some of the flow regions, the respective subset of adjacent plates comprises at least three plates. For example, the respective subset of adjacent plates may comprise at least four plates, for example at least five plates.

[0026] Clause 19. A porous wall according to clause 17 or 18, wherein a subset of the plurality of flow regions are defined by a common subset of adjacent plates.

[0027] Clause 20. A porous wall according to clause 19, wherein there are a plurality of subsets of the plurality of flow regions, each defined by a respective common subset of adjacent plates and longitudinally offset from each other.

[0028] Clause 21. A porous wall according to clause 19 or 20, wherein the porous wall is annular, and wherein for each subset of the plurality of flow regions, the respective porous regions are angularly distributed around the porous wall.

[0029] Clause 22. A porous wall according to any one of clauses 19-21, wherein for each flow region, the respective subset of adjacent plates comprises plates defined according to a plurality of different patterns of flow zones.

[0030] Clause 23. A porous wall according to clause 22, wherein the plurality of flow zones and / or the plurality of plates are arranged in a repeating sequence of the plurality of different patterns of flow zones.

[0031] Clause 24. A porous wall according to any one of clauses 19-23, wherein the porous wall is annular, and wherein for each flow region, the respective subset of adjacent plates comprises plates defined according to a common pattern of flow zones which is angularly offset for successive plates in the subset to cause the flow zones to overlap and form the flow regions.

[0032] Clause 25. A porous wall according to any one of clauses 19-24, wherein each of the flow regions comprise a porous medium.

[0033] Clause 26. A porous wall according to clause 25, wherein a material composition of the porous medium differs from a material composition of the body; or wherein a material composition of the body is the same as the material composition of the respective porous regions.

[0034] Clause 27. A porous wall according to clause 24 or 25, wherein within each flow region, the porous medium defines a respective network of flow paths through the body.

[0035] Clause 28. A porous wall according to any one of clauses 16 and 25-27, wherein the porous medium comprises an electrocatalyst-containing particulate.

[0036] Clause 29. A porous wall according to any one of clauses 1-28, wherein the plurality of bonded stacked plates are diffusion bonded.

[0037] Clause 30. A flow arrangement for an electrolyser, comprising: first and second porous walls corresponding to first and second electrodes of the electrolyser; an inlet chamber disposed between the first and second electrodes of the electrolyser; first and second outlet chambers for retaining respective fluid reaction products of electrolysis, separated from the inlet chamber by the first and second porous walls respectively; wherein one of, or each of, the first and second porous walls is a porous wall having a discontinuous porous structure in accordance with any one of clauses 1-29; wherein for the or each porous wall having the discontinuous porous structure, the inlet side is adjacent to the inlet chamber and the outlet side is adjacent to the respective outlet chamber, and the plurality of porous regions are to permit flow from the inlet chamber to the outlet chamber.

[0038] When provided or defined, any flow region (e.g. the plurality of flow regions) may permit flow from the inlet chamber to the outlet chamber.

[0039] Clause 31. A flow arrangement for an electrolyser, comprising: first and second porous walls corresponding to first and second electrodes of the electrolyser; an inlet chamber disposed between the first and second porous walls and configured to receive a fluid through an inlet; first and second outlet chambers for retaining respective fluid reaction products of electrolysis, separated from the inlet chamber by the first and second porous walls respectively; wherein one of, or each of, the first and second porous walls has a discontinuous porous structure, wherein the or each porous wall having the discontinuous porous structure: comprises a body having an inlet side adjacent to the inlet chamber and an outlet side adjacent to the respective outlet chamber, wherein the body is elongate along a longitudinal direction, and has a thickness direction from the inlet side to the outlet side; comprises a plurality of porous regions extending through the body at discrete locations to permit the fluid to flow from the inlet chamber to the respective outlet chamber; wherein the body comprises a plurality of bonded stacked plates;wherein each of the porous regions is defined by a respective array of porous zones extending through a respective subset of adjacent plates of the plurality of plates, wherein porous zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the porous region.

[0040] When each of the first and second porous walls is a porous wall in accordance with any one of clauses 1-29, it may instead be defined that each of the first and second porous walls is in accordance with any one of clauses 1-30 (ora subset), such that it is unnecessary to define further features of the porous walls by identifying each one as having the discontinuous porous structure. Similarly, the definition of “a discontinuous porous structure” is provided herein as a short-form way to identify a porous wall having a plurality of flow regions or porous regions at discrete locations, such that this short-form definition may be referred to in subsequent statements and enable differentiation from any porous wall which may not have that structure and associated features. This definition may therefore be accordingly unnecessary (and may be removed) when defining a single porous wall or any other apparatus where the or each porous wall being referred to is already defined by the associated features.

[0041] Clause 32. A flow arrangement according to clause 30 or 31, wherein the first and second porous walls are annular, wherein the inlet chamber is an annular inlet chamber, the first outlet chamber is a radially inner outlet chamber and the second outlet chamber is a radially outer outlet chamber.

[0042] It may be that the first outlet chamber is an inner core chamber defined within the first porous wall, and the second outlet chamber is an annular outlet chamber surrounding the second porous wall.

[0043] A flow arrangement as disclosed herein may be configured so that each of the first and second outlet chambers is configured to only receive fluid flow via the respective porous walls. The flow arrangement may be configured so that the inlet chamber is only configured to receive fluid from outside of the flow arrangement through the inlet (e.g. the inlet being a single inlet or opening into the inlet chamber). Accordingly, all flow entering an outlet chamber passes through the flow regions or porous regions of the respective porous wall, and as such the flow regime into the outlet chamber (e.g. flow rate) may be reliably controlled in the design of the flow arrangement by controlling the properties of the flow regions or porous regions. Further, when the porous wall provides an electrode for electrolysis, all flow entering an outlet chamber passes through the electrode (e.g. through an electrocatalytic region of the electrode) rather than bypassing active regions of the electrode. An electrocatalytic region may be interchangeably referred to as an electrocatalytically active region.

[0044] Clause 33. An electrolyser for performing continuous electrolysis of an electrolyte fluid, wherein the electrolyser comprises a flow arrangement according to any one of clauses 30-32 for receiving the electrolyte fluid at the inlet, wherein the first and second porous walls provide first and second electrodes of the electrolyser respectively.

[0045] Clause 34. An electrolyser for performing electrolysis of an electrolyte fluid, wherein the electrolyser comprises a cell, the comprising: an inner electrode defining an inner chamber; an outer electrode; an inlet chamber defined between the inner electrode and the outer electrode; an outer chamber delimited by the outer electrode; wherein the inner electrode and / or the outer electrode comprises a porous wall in accordance with any one of clauses 1-29.

[0046] Clause 35. An electrolyser of clause 34, wherein each of the inner electrode, outer electrode, the inlet chamber and the outer chamber are annular.

[0047] Clause 35. An electrolyser according to any one of clauses 33-35, further comprising a controller, wherein the controller is configured to control flow control equipment to maintain supercritical conditions for the electrolyte fluid at the first and / or second porous walls.

[0048] Clause 36. An electrolyser according to clause 35, wherein the controller is configured to control the flow control equipment to maintain supercritical pressure and temperature conditions for the electrolyte fluid at the first and / or second porous walls of at least 22 MPa pressure and at least 374°C temperature for an aqueous electrolyte fluid.

[0049] A controller as defined herein with respect to an electrolyser may be configured to maintain supercritical conditions for the electrolyte fluid at the first and / or second porous walls by: controlling flow control equipment to maintain a target inlet pressure and a target inlet temperature of electrolyte fluid at the inlet; and / or controlling a current through, and / or a voltage applied between, the first and second electrodes.

[0050] It may be that heating of the electrolyte fluid, for example to a critical temperature corresponding to supercritical conditions for the electrolyte fluid, is provided at the or each respective porous wall (electrode) of the electrolyser.

[0051] The controller may be configured to control the flow control equipment, for example a heater, so that the electrolyte fluid is provided to the inlet at a temperature within 50°C (for example within 30°C or within 20°C) of a critical temperature, for example a critical temperature for an aqueous electrolyte fluid of 374°C.

[0052] The controller may be configured to control flow control equipment, for example a compressor and / or one or more discharge valves associated with the electrolyser, to maintain a target inlet pressure. The target inlet pressure may be at least a critical pressure for the respective electrolyte fluid. For example, the target inlet pressure may be at least 22MPa for an aqueous electrolyte fluid.

[0053] It may be that the controller is configured to control flow control equipment to maintain supercritical conditions for the electrolyte fluid within the inlet chamber and in the first and second outlet chambers.

[0054] It may be that the controller is configured to control the flow control equipment so that the electrolyte fluid is provided to the inlet at supercritical conditions.

[0055] The flow control equipment may comprise a heater configured to heat electrolyte fluid upstream of the inlet chamber. The heater may be part of the electrolyser or may be installed together with it at (or in) an electrolysis installation.

[0056] The flow control equipment may comprise a compressor configured to compress the electrolyte fluid upstream of the inlet chamber. The flow control equipment may be part of the electrolyser or may be installed together with it at (or in) an electrolysis installation.

[0057] Supercritical conditions for the electrolyte fluid may be supercritical pressure and temperature conditions for the electrolyte fluid of at least 22 MPa pressure and at least 374°C temperature for an aqueous electrolyte fluid.

[0058] Supercritical conditions may be between 22 and 27 MPa pressure and between 374°C and 550°C temperature, for example between 374 and 400°C. By maintaining supercritical conditions at the first and / or second porous walls, losses associated with an electrolysis reaction may be reduced by (i) inhibiting formation of bubbles of reaction products on surfaces of the electrodes and / or (ii) increasing the conductivity of an electrolyte fluid for a given electrolyte concentration for a given amount of electrolyte (or vice versa, achieving a suitable conductivity using a relatively lower concentration of electrolyte).

[0059] Although some examples discussed herein relate to operation at supercritical conditions and the appended claims refer to an electrolyser or electrolyser installation in which a controller is configured to maintain supercritical conditions, the disclosure envisages electrolysers and electrolyser installations and methods of operation according as described herein (e.g. according to any combination of features envisaged in the present disclosure) and in which there is no such controller or control to maintain supercritical conditions for the electrolyte fluid.

[0060] It may be that the electrolyser comprises a controller configured to control flow control equipment to provide the electrolyte fluid to the inlet chamber at an inlet temperature of at least 320°C, for example at least 350°C. The inlet temperature may be below a critical temperature for the respective electrolyte fluid, for example a critical temperature of 374°C for an aqueous electrolyte fluid. The inlet temperature may be within 50°C (for example within 30°C or within 20°C) of a critical temperature for the electrolyte fluid. The inlet temperature may be greater than or equal to 320° and less than 374°C, for example 350°C-370°C or 350°C-360°C. It may be that the controller is configured to control the flow control equipment to provide the electrolyte fluid to the inlet chamber at a pressure which is less than or greater than a critical pressure for the respective electrolyte fluid (for example a critical temperature of 22MPafor an aqueous electrolytefluid). It may be that the controller is configured to control the flow equipment to provide the electrolyte fluid to the inlet chamber at a pressure of at least 22MPa.

[0061] It may be that the inlet temperature and inlet pressure are controlled (e.g., by control of the flow control equipment) so that subcritical conditions are maintained throughout the inlet chamber and outlet chambers.

[0062] Clause 37. An electrolyser according to any one of clauses 33-36, wherein for the or each porous wall having the discontinuous porous structure and providing an electrode of the electrolyser: the porous regions each comprise an electrocatalyst and thereby define an electrocatalytic region of the respective electrode for an electrolysis half-reaction.

[0063] The expression “electrocatalyst” as used herein refers to an electrocatalyst (e.g. an electrocatalytically active material) suitable for catalysing a half-reaction of electrolysis of an electrolyte fluid. Provision of such an electrocatalyst is considered to provide an associated electrocatalytic region of the porous wall which is electrocatalytically active (i.e. for the respective half-reaction of electrolysis). The electrolysis reaction may be electrolysis of water or an aqueous (water-based) electrolyte fluid. Accordingly, the electrocatalyst may be an electrocatalyst suitable for catalysing a half-reaction of electrolysis of water.

[0064] The electrocatalyst may comprise (e.g. consist essentially of, consist of, or be) one or more elements selected from: noble metals (i.e. Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, Re), d-block transition metals (i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, R, Os, Ir, Pt, Au, Hg, Rf, Db, S, Rh, Hs, Mt, Ds, Rg, Cn), f-block lanthanides (i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metals (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), platinum group metals (i.e. Ru, Rh, Pd, Os, Ir, Pt), P, S, C and / or combinations thereof. Said one or more elements may be present in elemental form (e.g. as (substantially) pure metals), in mixtures (e.g. alloys), in compounds (e.g. oxides, hydroxides, nitrides, borides, sulfides, phosphides, carbonates and / or organic compounds such as metal-organic frameworks) and / or incorporated into nanomaterials such as nanoparticles, nanotubes (e.g. carbon nanotubes), nanocages (e.g. fullerenes) and / or nanosheets (e.g. graphene).

[0065] The electrocatalyst may comprise (e.g. consist essentially of, consist of or be) Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof.

[0066] The electrocatalyst may comprise (e.g. consist essentially of, consist of or be) Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof.

[0067] The electrocatalyst may comprise (e.g. consist essentially of, consist of or be) Ni, Fe, Co, P, S, and / or combinations thereof.

[0068] The electrocatalyst may comprise (e.g. consist essentially of, consist of or be) Pt, Ir, Pd, Ni, Mo, and / or combinations thereof.

[0069] In some examples, the electrocatalyst comprises (e.g. consists essentially of, consists of or is) Ni (e.g. elemental Ni) or Pt (e.g. elemental Pt).

[0070] In some examples, the electrocatalyst comprises (e.g. consists essentially of, consists of or is) Ni (e.g. elemental Ni).

[0071] In some examples, the electrocatalyst comprises (e.g. consists essentially of, consists of or is) Pt (e.g. elemental Pt).

[0072] The electrocatalyst may be provided in the form of, or may be formed from, an electrocatalyst-containing particulate. Particles of the electrocatalyst-containing particulate may comprise (e.g. consist essentially of, or consist of) the electrocatalyst. The electrocatalystcontaining particulate may comprise (e.g. consist essentially of, or consist of) particles of the electrocatalyst.

[0073] For example, the electrocatalyst-containing particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) one or more elements selected from: noble metals (i.e. Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, Re), d-block transition metals (i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, R, Os, Ir, Pt, Au, Hg, Rf, Db, S, Rh, Hs, Mt, Ds, Rg, Cn), f-block lanthanides (i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metals (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), platinum group metals (i.e. Ru, Rh, Pd, Os, Ir, Pt), P, S, C and / or combinations thereof. Said one or more elements may be present in elemental form (e.g. as (substantially) pure metals), in mixtures (e.g. alloys), in compounds (e.g. oxides, hydroxides, nitrides, borides, sulfides, phosphides, carbonates and / or organic compounds such as metal-organic frameworks) and / or incorporated into nanomaterials such as nanoparticles, nanotubes (e.g. carbon nanotubes), nanocages (e.g. fullerenes) and / or nanosheets (e.g. graphene).

[0074] The electrocatalyst-containing particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof.

[0075] The electrocatalyst-containing particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof.

[0076] The electrocatalyst-containing particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Ni, Fe, Co, P, S, and / or combinations thereof.

[0077] The electrocatalyst-containing particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Pt, Ir, Pd, Ni, Mo, and / or combinations thereof.

[0078] In some examples, the electrocatalyst-containing particulate comprises (e.g. consists essentially of or consists of) particles comprising (e.g. consisting essentially of, or consisting of) Ni (e.g. elemental Ni) or Pt (e.g. elemental Pt).

[0079] In some examples, the electrocatalyst-containing particulate comprises (e.g. consists essentially of or consists of) particles comprising (e.g. consisting essentially of, or consisting of) Ni (e.g. elemental Ni).

[0080] In some examples, the electrocatalyst-containing particulate comprises (e.g. consists essentially of or consists of) particles comprising (e.g. consisting essentially of, or consisting of) Pt (e.g. elemental Pt).

[0081] In some examples, the electrocatalyst-containing particulate is a Ni-containing particulate. The Ni-containing particulate may comprise (e.g. consist essentially of, or consist of) particles of Ni (e.g. elemental Ni) or an Ni-based alloy.

[0082] In some examples, the electrocatalyst-containing particulate is an Ni particulate consisting essentially of particles of Ni.

[0083] It may be that for the or each porous wall having the discontinuous porous structure and providing an electrode of the electrolyser, the respective porous regions each comprise a porous medium formed from an electrocatalyst-containing particulate.

[0084] The porous medium may be formed by consolidating the electrocatalyst-containing particulate. In other words, the respective porous regions may each comprise the electrocatalyst which is provided in the form of a consolidated porous medium.

[0085] The term “consolidating” used herein refers to a process of physically and / or chemically adhering particles of the electrocatalyst-containing particulate to one another to form the porous medium. Consolidation of the electrocatalyst-containing particulate may comprise sintering the electrocatalyst-containing particulate, fusing the electrocatalyst-containing particulate and / or bonding particles of the electrocatalyst-containing particulate to one another by way of a binder and / or a chemical reaction.

[0086] For example, the porous medium may be formed by sintering the electrocatalystcontaining particulate. It will be appreciated that sintering is a process of forming a solid mass ofmaterial from a particulate by application of heat and / or pressure without melting the particulate to the point of liquefaction. During sintering, particles of the particulate may be bonded to one another by diffusion of atoms and / or molecules between neighbouring particles at temperatures below the melting point of the material. Plastic deformation of the particles may also occur.

[0087] Accordingly, the respective porous regions may each comprise the electrocatalyst which is provided in the form of a sintered porous medium.

[0088] The porous medium may be formed by fusing the electrocatalyst-containing particulate. It will be appreciated that fusion is a process involving melting of solid material to liquid. A porous medium may be formed from a particulate by heating the particulate to a temperature at which local melting (for example, melting at particle surfaces) occurs, leading to bonding of adjacent particles, while avoiding total liquefaction of the particulate.

[0089] Accordingly, the respective porous regions may each comprise the electrocatalyst which is provided in the form of a fused porous medium.

[0090] The porous medium may be formed by bonding particles of the electrocatalyst-containing particulate to one another using a binder. The binder may be a polymeric binder such as a thermoplastic binder or a thermosetting binder (e.g. a resin). A thermoplastic binder is a polymeric binder which melts or becomes pliable at elevated temperatures and which solidifies upon cooling. A thermosetting binder (e.g. a resin) is a polymeric binder which hardens irreversibly (i.e. cures) by heating, exposure to radiation and / or exposure to a suitable catalyst.

[0091] The porous medium may be formed by bonding particles of the electrocatalyst-containing particulate to one another by a chemical reaction. For example, a chemical reaction may take place which forms a reaction product which bonds adjacent particles to one another. The chemical reaction may be an oxidation reaction, for example, the growth of an oxide layer at surfaces of the particles, which oxide layer bonds adjacent particles to one another. The chemical reaction may take place at elevated temperatures, for example, on exposure to a suitable (e.g. oxidising) atmosphere.

[0092] Accordingly, the respective porous regions may each comprise the electrocatalyst which is provided in the form of a bonded porous medium.

[0093] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) one or more elements selected from: noble metals (i.e. Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, Re), d-block transition metals (i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, R, Os, Ir, Pt, Au, Hg, Rf, Db, S, Rh, Hs, Mt, Ds, Rg, Cn), f-block lanthanides (i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metals (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), platinumgroup metals (i.e. Ru, Rh, Pd, Os, Ir, Pt), P, S, C and / or combinations thereof. Said one or more elements may be present in elemental form (e.g. as (substantially) pure metals), in mixtures (e.g. alloys), in compounds (e.g. oxides, hydroxides, nitrides, borides, sulfides, phosphides, carbonates and / or organic compounds such as metal-organic frameworks) and / or incorporated into nanomaterials such as nanoparticles, nanotubes (e.g. carbon nanotubes), nanocages (e.g. fullerenes) and / or nanosheets (e.g. graphene).

[0094] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof.

[0095] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof.

[0096] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) Ni, Fe, Co, P, S, and / or combinations thereof.

[0097] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) Pt, Ir, Pd, Ni, Mo, and / or combinations thereof.

[0098] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) Ni (e.g. elemental Ni) or Pt (e.g. elemental Pt).

[0099] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) Ni (e.g. elemental Ni).

[0100] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise (e.g. consist essentially of, or consist of) Pt (e.g. elemental Pt).

[0101] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt. %, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, electrocatalyst. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, electrocatalyst. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. % to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, electrocatalyst.

[0102] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt.%, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, noble metal (i.e. Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, Re), d-block transition metal (i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, R, Os, Ir, Pt, Au, Hg, Rf, Db, S, Rh, Hs, Mt, Ds, Rg, Cn), f-block lanthanide (i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metal (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), platinum group metal (i.e. Ru, Rh, Pd, Os, Ir, Pt), P, S, C and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, noble metal (i.e. Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, Re), d-block transition metal (i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, R, Os, Ir, Pt, Au, Hg, Rf, Db, S, Rh, Hs, Mt, Ds, Rg, Cn), f-block lanthanide (i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metal (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), platinum group metal (i.e. Ru, Rh, Pd, Os, Ir, Pt), P, S, C and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. % to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, noble metal (i.e. Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, Re), d-block transition metal (i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, R, Os, Ir, Pt, Au, Hg, Rf, Db, S, Rh, Hs, Mt, Ds, Rg, Cn), f-block lanthanide (i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metal (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), platinum group metal (i.e. Ru, Rh, Pd, Os, Ir, Pt), P, S, C and / or combinations thereof.

[0103] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt. %, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. %to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof.

[0104] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt. %, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. % to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof.

[0105] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt. %, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, Ni, Fe, Co, P, S, and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, Ni, Fe, Co, P, S, and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. % to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, Ni, Fe, Co, P, S, and / or combinations thereof.

[0106] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt. %, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, Pt, Ir, Pd, Ni, Mo, and / or combinations thereof. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, Pt, Ir, Pd, Ni, Mo, and / or combinations thereof. The (e.g. consolidated,sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. % to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, Pt, Ir, Pd, Ni, Mo, and / or combinations thereof.

[0107] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt. %, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, Ni and / or Pt. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, Ni and / or Pt. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. % to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, Ni and / or Pt.

[0108] The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no less than about 50 wt. %, for example, no less than about 60 wt. %, or no less than about 70 wt. %, or no less than about 80 wt. %, or no less than about 90 wt. %, or no less than about 95 wt. %, or no less than about 99 wt. %, Ni. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise no more than about 100 wt. %, for example, no more than about 99 wt. %, or no more than about 95 wt. %, or no more than about 90 wt. %, Ni. The (e.g. consolidated, sintered, fused and / or bonded) porous medium may comprise from about 50 wt. % to about 100 wt. %, for example, from about 60 wt. % to about 100 wt. %, or from about 70 wt. % to about 100 wt. %, or from about 80 wt. % to about 100 wt. %, or from about 90 wt. % to about 100 wt. %, or from about 95 wt. % to about 100 wt. %, or from about 99 wt. % to about 100 wt. %, Ni.

[0109] Clause 38. An electrolyser according to any one of clauses 37, wherein for the or each porous wall having the discontinuous porous structure: a material composition of the porous regions differs from a material composition of the body; and / or the body comprises a passive region of the respective electrode to inhibit electrolysis.

[0110] Clause 39. An electrolyser according to any one of clauses 37-38, wherein for the or each porous wall having the discontinuous porous structure: the inlet side of the body is defined by a passive region which is configured to be less electrocatalytically active than theelectrocatalytic region; optionally wherein the passive region comprises a passivating coating defining the inlet side of the body to inhibit electrolysis.

[0111] The passive region as defined with respect to any of the statements above may be configured to inhibit a respective half-reaction of electrolysis. By providing the passive region (e.g. as provided by the body as a whole, a core portion or uncoated portion of the body, or at an inlet side of the body - for example by a passivating coating), the respective half-reaction of electrolysis may be inhibited or prevented from occurring on the inlet side of the porous wall, such that the reaction may only take place or may predominantly take place once the electrolyte fluid (and / or respective ions) has passed into one of the porous regions (and / or passed through the porous regions to reach an electrocatalytic region defining the outlet side of the porous wall).

[0112] The passive region (and any passive region as described herein) may be configured to inhibit electrolysis by being less electrocatalytically active than the electrocatalytic region (for the respective half-reaction of electrolysis of the electrolyte fluid). A rate of the respective halfreaction in the passive region (as a whole) may be lower than a rate of the respective half-reaction in the electrocatalytic region (as a whole), and this may make the passive region less electrocatalytically active than the electrocatalytic region. The rate of the respective half-reaction may be: a rate of generation of the respective fluid reaction product (e.g. hydrogen or oxygen depending on the electrode) in the respective region, for example a mass of the fluid reaction product generated per unit time (e.g. g / s of hydrogen); or the current density integrated over an electrolyte interface of the respective region (e.g. in A) - the electrolyte interface being the surface of the respective region configured to contact the electrolyte fluid. The rate for the respective region as used herein is the total rate for the respective region, rather than a specific rate per unit volume, thickness, mass, or surface area (e.g. of the porous wall or of the electrolyte interface of the respective region of the porous wall) etc. The passive region and the electrocatalytic region may be configured so that the rate of the respective half-reaction in the passive region (as a whole) may be lower than a rate of the respective half-reaction in the electrocatalytic region (as a whole). For example, the rate in the passive region may be no more than 50% of the rate in electrocatalytic region, no more than 20%, nor more than 10%, no more than 5% or no more than 1%. The rate in the passive region may be substantially zero.

[0113] It may be that the passive region comprises less of an electrocatalyst (for electrocatalysing the respective half-reaction of electrolysis of the electrolyte fluid) than the electrocatalytic region, for example less of the same electrocatalyst of the electrocatalytic region; and / or any electrocatalyst of the passive region may be less electrocatalytically active for the respective halfreaction than the electrocatalyst of the electrocatalytic region.

[0114] The passive region may comprise less of the electrocatalyst of the electrocatalytic region at an electrolyte interface of the passive region with the electrolyte fluid (i.e. in a surface region of the passive region which contacts the electrolyte fluid in use) than there is at the electrolyte interface of the electrocatalytic region (i.e. in the surface region of the electrocatalytic region). In other words, a material composition of the passive region at the electrolyte interface of the passive region (i.e. in the surface region) may comprise less of the electrocatalyst than a material composition of the electrocatalytic region at the respective electrolyte interface. For example, it may comprise less than 5 wt.% of the electrocatalyst, less than 1 wt.% of the electrocatalyst, of less than 0.1 wt.% of the electrocatalyst. The composition of the passive region at the electrolyte interface may be assessed by reference to a surface region of the passive region adjacent to the electrolyte fluid in use, for example having a thickness of 1 m.

[0115] An electrocatalytic region as referred to herein may have a first composition. A passive region as referred to herein may have a second composition. A nominal electrode for conducting the respective half-reaction of electrolysis of the electrolyte fluid in a nominal cell may have a surface region which is adjacent the electrolyte fluid at an electrolyte interface of the nominal electrode. The surface region may have a thickness of 1 m from the electrolyte interface.

[0116] The first and second compositions may be selected so that, when the surface region of the nominal electrode has the first composition, the overpotential required to reach a current density of 10 mA cm-2 at the nominal electrode in the nominal cell is no more than half, no more than one third, or no more than one fifth of the overpotential required to reach the current density of 10 mA cm-2 at the nominal electrode in the nominal cell when the surface region of the nominal electrode has the second composition, at a nominal pressure and temperature, for example 22.5 MPa and 375°C.

[0117] A respective half-reaction may be inhibited by the passive region being provided as a passivating layer or coating as discussed elsewhere herein.

[0118] Any of the above statements relating to the electrocatalytic region, the passive region, and the properties of those regions as electrocatalytically active or less electrocatalytically active regions may be applied to any of the aspects or statements provided above and below and as discussed in the detailed description.

[0119] When the passive region comprises a passivating coating defining the inlet side of a porous wall, the passivating coating may be a dielectric coating, for example an oxide coating (e.g. an inorganic metal oxide coating), such as silica (SiO2), zinc oxide (ZnO), or zirconia (ZrO2)). All references herein to passivating or providing a passivating coating or providing a dielectric coating or layer may comprise applying a dielectric coating, such as a coating of the examplematerials described in the preceding sentence, or of any material disclosed herein with reference to forming a dielectric coating on a plate. A passivating coating may be provided, for example by CVD (chemical vapour deposition) of a passivating substance, such as Alumina (AI2O3), Zirconia (ZrO2) or Titania (TiO2), or any material disclosed herein with reference to forming a dielectric coating on a plate. Techniques and materials discussed herein for forming a dielectric coating or layer may also be applied for forming a passivating coating.

[0120] By passivating the inlet side of a porous wall, the respective fluid reaction product generated at the electrode may only be generated at locations which are downstream from the inlet chamber (e.g. within the porous regions of the porous or on the outlet side of the porous wall), rather than on the inlet side which delimits the inlet chamber. This may inhibit the respective fluid reaction product being generated in or migrating to the inlet chamber.

[0121] Irrespective of the provision of a passive region, it may be that any fluid reaction product generated within or provided to the outlet chamber (for example by reaction with an electrocatalytic region at or defining the outlet side of the compound porous electrode) is inhibited from flowing back through the porous wall, as this would require the lower-density fluid reaction product to flow against buoyancy forces downwardly through the flow regions or porous regions (which flow may also be against a pressure gradient over the porous wall). This may be referred to as inhibiting return flow by downstream-biased buoyancy effects, since buoyancy forces within the flow regions or porous regions promote downstream flow to the outlet chamber rather than upstream flow to the inlet chamber.

[0122] Clause 40. An electrolysis installation comprising: a source of electrolyte fluid, optionally an aqueous electrolyte fluid; and an electrolyser in accordance with any one of clauses 33-39 for performing continuous electrolysis of the electrolyte fluid.

[0123] A plurality of plates as defined herein may otherwise (e.g., interchangeably) be defined as layers of the body, each layer having an axial extent along a stacking direction of the body (e.g. corresponding to that of a layer or plate before a bonding process). The extent of a layer may be determined by axial locations of junctions where one or more porous zones (or flow zones or open zones) of the respective layer interface and overlap with one or more respective porous zones (or flow zones or open zones) of adjacent layers. That interface may be discontinuous and delimit the axial extent of the respective layer. As discussed elsewhere herein, in variant examples the body may comprise open regions defined by open zones (as opposed to porous regions defined by porous zones).

[0124] An axial extent (e.g., height) of the plates (or layers) may be at least 0.1mm, for example at least 0.15mm, at least 0.2mm, or at least 0.25mm. An axial extent of the plates (or layers) maybe between 0.1mm and 1mm, for example between 0.1mm and 0.6mm, for example between 0.15mm and 0.4mm, for example between 0.15mm and 0.3mm.

[0125] The porous zones (or flow zones or open zones) may each have a characteristic dimension, in a plane normal to the stacking direction of the plates (or layers). The characteristic dimension may be a diameter (e.g. for a substantially circular porous zone), or a largest diameter (e.g. for an ellipse), or other largest dimension of the porous zone within the plane. The characteristic dimension may be between 0.1mm and 1mm, for example between 0.1mm and 0.5mm, between 0.1mm and 0.4mm, or between 0.1mm and 0.3mm

[0126] A porous region (or flow region or open region) extending through the body may have a variable cross-sectional profile along a path from the inlet side to the outlet side, the cross-sectional profile being determined relative to a direction along which the porous region extends through the body. The cross-sectional profile may have necked portions where porous zones of adjacent plates (or layers) overlap. A characteristic dimension of the necked portions, considered in a plane normal to the direction along which the porous region extends through the body, may be between 0.025-0.5mm, for example between 0.05-0.4mm, for example between 0.06-0.3mm, or 0.1-0.25mm.

[0127] The porous zones (or flow zones or open zones) may be formed in the respective plate (or layer) along a direction substantially perpendicular to the plate (or layer) (e.g. the stacking direction), and may have a substantially constant cross-section through the respective plate. Otherwise, the porous zones (or open zones) may be formed in the respective plate (or layer) along a direction inclined with respect to a direction perpendicular to the plate (or layer) (e.g., the stacking direction).

[0128] The body of the or each porous wall may be defined as having an anisotropic porous structure provided by the arrangement of the flow regions (or porous regions) within the body (i.e. by virtue of the flow regions or porous regions being discretely arranged, and being elongate along paths which have a longitudinal component, thereby providing for non-uniform flow through the body as a whole). The porous regions themselves may be defined as having an isotropic structure, for example as provided by a generally uniform distribution of a porous medium. The porous medium may be isotropic in that it is generally uniformly distributed within the confines of the porous region, with only the boundaries of the porous regions providing anisotropy to the porous wall.

[0129] A porous wall, flow arrangement or electrolyser as disclosed herein may be configured for installation in an installed orientation in which, for the or each porous wall having the discontinuous porous structure, the paths along which each of the respective plurality of flow regions or porousregions extend, have an upwards component towards the outlet chamber. Each flow region or porous region may therefore be configured to inhibit a return flow from the respective outlet chamber to the inlet chamber when there is a prevailing buoyancy driven flow through the flow region or porous region having an upward component.

[0130] A porous wall, flow arrangement or electrolyser as disclosed herein may be configured so that, when the longitudinal direction of the or each porous wall having the discontinuous porous structure is vertically upward, each of the respective plurality of flow regions or porous regions extends along a path towards the respective outlet chamber having an upward component. It may be that each flow region or porous region extends along a path through the body defining a path angle relative to the longitudinal direction of between 20°-80°. The path angle may be between 25°-75°, for example between 30°-70°, between 35°-70°, between 40°-70°, for example between 50°-70°.

[0131] The thickness direction may be a direction corresponding to a shortest distance from the inlet side to the outlet side. The thickness direction may be orthogonal to the longitudinal direction of the respective porous wall. In a flow arrangement or electrolyser as disclosed herein, the porous walls may each be elongate with respect to a common longitudinal direction (i.e. they may each be elongate along parallel directions), and may have respective thickness directions orthogonal to the common longitudinal direction.

[0132] The or each porous wall may be axisymmetric about its longitudinal direction, such that the thickness direction at any angular location around the longitudinal direction is a local thickness direction corresponding to a radial direction about the longitudinal direction. When both porous walls are axisymmetric, they may also be coaxial with each other. The longitudinal direction may pass through a centroid of the cross-sections of the or each porous wall.

[0133] Otherwise, the flow arrangement may be implemented with one or more non-axisymmetric porous walls, such as planar porous walls extending linearly along both a lateral direction and a longitudinal direction. The extent of the porous walls along the longitudinal direction may be relatively greater than the extent along the lateral direction, such that it is elongate along the longitudinal direction.

[0134] Porosity as defined herein relates to an open porosity of the respective component or structure. Porosity of a porous wall is a total porosity of the porous wall. As described elsewhere herein, the porosity is to be evaluated over a longitudinal extent of the porous wall which is configured to be porous (e.g. excluding non-porous proximal or distal locations, for example for electrical connections).

[0135] A micro porosity of a porous wall relates only to the porosity of the porous regions of the porous wall. The micro porosity of the porous wall may therefore relate to the porosity of a porous medium located within the porous regions. Micro porosity of the porous medium (for example, if a sample of the porous medium is isolated from the porous wall or manufactured separately), and therefore micro porosity of the porous wall, may be measured directly by mercury porosimetry according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA).

[0136] A macro porosity of the porous wall relates to the porosity of the body of the porous wall considered alone (e.g. with the entirety of the porous regions being considered to be open, that is to say, not containing porous medium). Macro porosity of the porous wall can be calculated by reference to the design and / or measured dimensions of the porous wall (including the dimensions of the open regions). Alternatively, if the flow regions or open regions are not or yet to be filled with porous medium, macro porosity of the porous wall can be measured directly by mercury porosimetry according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA).

[0137] A total porosity of a porous wall can be determined as a product of macro and micro porosity. Alternatively, if the flow regions or open regions of a porous wall already contain porous medium, a total porosity of the porous wall can be measured directly by mercury porosimetry according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA). The micro porosity of the porous wall may also be determined (e.g. without isolating the porous medium from the porous wall) by dividing the measured total porosity of the porous wall by the measured or calculated macro porosity of the porous wall.

[0138] It may be that for the or each porous wall having the discontinuous porous structure, the porous regions each have a porosity (e.g. microporosity) of between 0.2-0.9, for example, between 0.2-0.8, or between 0.3-0.8, or between 0.5-0.8, or between 0.6-0.8, or between 0.3-0.7. The porosity of the porous regions may be determined by mercury porosimetry as described elsewhere herein (e.g., according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA).

[0139] It may be that the or each porous wall having the discontinuous porous structure has a porosity (e.g. total porosity) of between 0.03-0.5, for example, between 0.03-0.3, or between 0.03-0.2, or between 0.05-0.15, or between 0.05-0.1. The porosity of the porous walls may be determined by mercury porosimetry as described elsewhere herein (e.g., according to ASTMstandards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA).

[0140] It may be that the or each porous wall having the discontinuous porous structure has a (e.g. total) porosity of between 1% and 20%, for example between 2% and 20%, or between 3% and 20%, or between 4% and 20%, or between 5% and 20%, or between 6% and 20%, or between 7% and 20%, or between 8% and 20%, or between 9% and 20%, or between 10% and 20%, or between 1% and 19%, or between 2% and 19%, or between 3% and 19%, or between 4% and 19%, or between 5% and 19%, or between 6% and 19%, or between 7% and 19%, or between 8% and 19%, or between 9% and 19%, or between 10% and 19%, or between 1% and 18%, or between 2% and 18%, or between 3% and 18%, or between 4% and 18%, or between 5% and 18%, or between 6% and 18%, or between 7% and 18%, or between 8% and 18%, or between 9% and 18%, or between 10% and 18%, or between 1% and 17%, or between 2% and 17%, or between 3% and 17%, or between 4% and 17%, or between 5% and 17%, or between 6% and 17%, or between 7% and 17%, or between 8% and 17%, or between 9% and 17%, or between 10% and 17%, or between 1% and 16%, or between 2% and 16%, or between 3% and 16%, or between 4% and 16%, or between 5% and 16%, or between 6% and 16%, or between 7% and 16%, or between 8% and 16%, or between 9% and 16%, or between 10% and 16%, or between 1% and 15%, or between 2% and 15%, or between 3% and 15%, or between 4% and 15%, or between 5% and 15%, or between 6% and 15%, or between 7% and 15%, or between 8% and 15%, or between 9% and 15%, or between 10% and 15%, or between 1% and 14%, or between 2% and 14%, or between 3% and 14%, or between 4% and 14%, or between 5% and 14%, or between 6% and 14%, or between 7% and 14%, or between 8% and 14%, or between 9% and 14%, or between 10% and 14%, or between 1% and 13%, or between 2% and 13%, or between 3% and 13%, or between 4% and 13%, or between 5% and 13%, or between 6% and 13%, or between 7% and 13%, or between 8% and 13%, or between 9% and 13%, or between 10% and 13%, or between 1% and 12%, or between 2% and 12%, or between 3% and 12%, or between 4% and 12%, or between 5% and 12%, or between 6% and 12%, or between 7% and 12%, or between 8% and 12%, or between 9% and 12%, or between 10% and 12%, or between 1% and 11%, or between 2% and 11%, or between 3% and 11%, or between 4% and 11%, or between 5% and 11%, or between 6% and 11%, or between 7% and 11%, or between 8% and 11%, or between 9% and 11%, or between 10% and 11%, or between 1% and 10%, or between 2% and 10%, or between 3% and 10%, or between 4% and 10%, or between 5% and 10%, or between 6% and 10%, or between 7% and 10%, or between 8% and 10%, or between 9% and 10%. The porosity of the porous walls may be determined by mercury porosimetry as describedelsewhere herein (e.g., according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA).

[0141] It may be that for the or each porous wall having the discontinuous porous structure, the porous regions each have a median pore diameter, as determined by mercury porosimetry as described elsewhere herein (e.g., according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA), of between about 10 to about 50 pm, for example, about 20 to about 40 pm.

[0142] It may be that the or each porous wall having the discontinuous porous structure has a permeability, as determined by mercury porosimetry as described elsewhere herein (e.g., according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA), of between about 10 to about 400 mdarcy, or between about 10 to about 50 mdarcy, or from about 250 to about 400 mdarcy, or from about 100 to about 200 mdarcy.

[0143] It may be that for the or each porous wall having the discontinuous porous structure, the porous regions each have a characteristic length, as determined by mercury porosimetry as described elsewhere herein (e.g., according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA), of between about 5 to about 60 pm, or between about 5 to about 20 pm, or between about 40 to about 60 pm, or between about 20 to about 50 pm.

[0144] It may be that the or each porous wall having the discontinuous porous structure has a tortuosity, as determined by mercury porosimetry as described elsewhere herein (e.g., according to ASTM standards D4284 and D6761 using an AutoPore V device (available from Micromeritics Instrument Corporation, USA), of between about 10 to about 80, or between about 10 to about 30, or between about 30 to about 50, or between about 50 to 80.

[0145] The body may be configured to prevent fluid flow therethrough, except for flow through the porous regions. The body may be substantially non-porous, for example it may be configured so that there is no flow path through the body except for through the discrete porous regions. The body may have a porosity (open porosity) of 0.

[0146] Clause 41. A method comprising: providing a plurality of plates for stacking in a longitudinal direction for forming a porous wall of an electrolyser, each plate comprising a wall region corresponding to a longitudinal portion of the porous wall; wherein the plurality of plates comprises a flow-through set of plates, wherein for each of the flow-through set of plates the respective wall region comprises one or more flow zones extending through the plate to permit fluid to flow through the respective plate; arranging the plurality of plates in a stack in thelongitudinal direction to form a body for the porous wall that is elongate along the longitudinal direction, and has a thickness direction from a first side to a second side; wherein the plurality of plates are stacked so that a plurality of flow regions are defined extending through the body at discrete locations, to permit fluid to flow from the first side to the second side; wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the flow-through set of plates, wherein flow zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the flow region.

[0147] Clause 42. A method according to clause 41, wherein the plurality of plates is for forming an array of porous walls, each plate comprising a plurality of wall regions each corresponding to a longitudinal portion of a respective porous wall; wherein for each of the flow-through set of plates, each of the respective wall regions comprises one or more flow zones; wherein the plurality of plates is arranged in the stack to form an array of bodies for the respective porous walls, wherein each body is elongate in the longitudinal direction and has a thickness direction from a first side to a second side; wherein the plurality of plates are stacked so that, for each body of the array of bodies, a respective plurality of flow regions are defined; wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the flow-through set of plates, wherein flow zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the flow region.

[0148] Clause 43. A method according to clause 42, wherein each plate of the plurality of plates comprises a support region for supporting the respective plurality of wall regions.

[0149] Clause 44. A method according to any one of clauses 41-43, wherein for each flow region, the respective subset of adjacent plates comprises wall regions defined according to a plurality of different patterns of flow zones; wherein the plurality of the plurality of plates are arranged in a repeating sequence of the plurality of different patterns of flow zones.

[0150] Clause 45. A method according to any one of clauses 41-43, wherein the or each body is annular; and wherein for each flow region, the respective subset of adjacent plates comprises wall regions defined according to a common pattern of flow zones which is angularly offset for successive plates in the subset to cause the flow zones to overlap and form the flow regions.

[0151] Clause 46. A method according to any one of clauses 41-45, comprising bonding the stack of plates to provide the or each body.

[0152] Clause 47. A method according to clause 46, wherein bonding the stack of plates comprises diffusion bonding.

[0153] Clause 48. A method according to clause 45 or 46, further comprising applying an electrocatalyst composition to the or each body so that it flows into the flow regions, thereby providing a corresponding plurality of porous regions of the or each porous wall.

[0154] Clause 49. A method according to any one of clauses 41-48, comprising: applying an electrocatalyst composition to a subset of the flow-through set of plates so that for each wall region of the respective subset of flow-through plates, one or more of the respective flow zones comprises a porous zone; wherein the plurality of plates are arranged in the stack such that for each of the flow regions, the respective array of flow zones extending through the respective subset of adjacent plates comprises one or more porous zones, the flow region thereby comprising a porous region.

[0155] Clause 50. A method according to clause 49, wherein the subset of the flow-through set of plates to which the electrocatalyst composition is applied is a proper subset of the flow-through set of plates; and wherein the plurality of plates are arranged in the stack so that for at least some of the flow regions, the respective array of flow zones extending through the respective subset of adjacent plates comprises one or more porous zones and one or more open zones.

[0156] The one or more open zones may be free of the electrocatalyst composition and / or a porous medium formed from the electrocatalyst composition.

[0157] Clause 51. A method according to clause 50, wherein the plurality of plates are arranged in the stack so that for each of the flow regions, the respective array of flow zones extending through the respective subset of adjacent plates comprises one or more porous zones and one or more open zones.

[0158] Clause 52. A method according to clause 49, wherein the subset of flow-through set of plates to which the electrocatalyst composition is applied comprises the flow-through set of plates, such that when the plurality of plates are arranged in the stack, for each of the flow regions, each of the flow zones of the respective array of flow zones extending through the respective subset of adjacent plates comprises a porous zone.

[0159] Clause 53. A method according to any one of clauses 49-52, comprising applying the electrocatalyst composition to the subset of the flow-through set of plates before arranging the plurality of plates in the stack.

[0160] Clause 54. A method according to clause 53, wherein the electrocatalyst composition is applied to each plate of the subset of the flow-through set of plates individually such that no other plate of the stack is adjacent to the respective plate.

[0161] Clause 55. A method according to clause 53 or 54, wherein the electrocatalyst composition is applied to at least some of the plates of the subset of the flow-through set of plates when the respective plate is received on a jig masking one or more flow zones and / or cut-outs of the plate.

[0162] Clause 56. A method of manufacturing a porous wall having a discontinuous porous structure, for an electrolyser, comprising: providing a plurality of plates in a stack to form a body for the porous wall, wherein the body is elongate along a longitudinal direction, and has a thickness direction from a first side to a second side; wherein the plurality of plates comprises a porous set of plates, each having one or more open zones extending through the respective plate; wherein the plurality of plates are stacked so that a plurality of open regions are defined extending through the body at discrete locations, to permit fluid to flow from the first side to the second side; wherein each of the open regions is defined by a respective array of open zones extending through a respective subset of adjacent plates of the porous set of plates, wherein open zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the open region.

[0163] Clause 57. A method according to clause 56, further comprising applying an electrocatalyst composition to the body so that it flows into the open regions, thereby providing a corresponding plurality of porous regions of the porous wall.

[0164] Clause 58. A method of manufacturing a porous wall having a discontinuous porous structure, for an electrolyser, comprising: providing a porous set of plates, each having one or more open zones extending through the respective plate; applying an electrocatalyst composition to the porous set of plates, so that it flows into the respective open zones, to form porous zones of the respective plates; arranging a plurality of plates including the porous set of plates in a stack to form a body of the porous wall, wherein the body is elongate along a longitudinal direction, and has a thickness direction from a first side to a second side; wherein the plurality of plates are stacked so that a plurality of porous regions are defined extending through the body at discrete locations, to permit fluid to flow from the first side to the second side; wherein each of the porous regions is defined by a respective array of porous zones extending through a respective subset of adjacent plates of the porous set of plates, wherein porous zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the porous region.

[0165] Clause 59. A method according to any one of clauses 48-58, comprising performing a heat treatment operation in which an electrocatalyst component of the electrocatalyst composition forms a porous structure for the respective porous region, whereby each porous region defines a1respective network of flow paths through the body to permit fluid to flow from the first side of the body to the second side of the body.

[0166] Clause 60. A method according to clause 59, further comprising a drying operation to vaporise a component of the electrocatalyst composition, conducted after applying the electrocatalyst composition and before the heat treatment operation.

[0167] The drying operation may be conducted to reduce a mass of the electrocatalyst composition retained on the body by 5-60%, for example 10-60%, 20-60%, 30-60%, or 30-50%. The drying operation may be conducted to reduce a mass of the electrocatalyst composition corresponding to a mass of one or more solvents in the electrocatalyst composition as applied. The drying operation may be carried out at a temperature between 100°C and 300°C, for example between 150°C and 250°C, for example approximately 200°C. The drying operation may be carried out in an oven. The drying operation may be carried out for between 1 and 4 hours, for example between 1 and 3 hours, for example approximately 2 hours.

[0168] It may be that the heat treatment operation comprises heating the flow-through or porous set of plates to a target temperature of between 150-1000°C.

[0169] The target temperature may be between 150-1000°C, for example between 250-800°C, between 300-600°C, between 300-450°C, for example approximately 350°C.

[0170] Alternatively, the target temperature may be between 150-1500°C, for example between 150-1000°C, or between 600-1000°C, or between 800-1000°C, or between 900-1000°C, for example approximately 930°C.

[0171] The heat treatment operation may be a sintering operation in which the electrocatalyst component of the electrocatalyst composition is sintered to form a porous region (e.g. a sintered porous region) at each location of the open regions.

[0172] The heat treatment operation may be a fusing operation in which the electrocatalyst component of the electrocatalyst composition is fused to form a porous region (e.g. a fused porous region) at each location of the open regions.

[0173] The heat treatment operation may be a bonding operation in which electrocatalystcontaining particles (e.g. electrocatalyst particles) of the electrocatalyst composition are bonded to one another to form a porous region (e.g. a bonded porous region) at each location of the open regions. Bonding the particles may comprise bonding the particle by way of a binder (e.g. polymeric binder). Bonding the particles may comprise melting and / or curing the binder (e.g. polymeric binder).

[0174] The heat treatment operation may be a chemical reaction operation in which electrocatalyst-containing particles (e.g. electrocatalyst particles) of the electrocatalystcomposition are bonded to one another by way of a chemical reaction to form a porous region (e.g. a bonded porous region) at each location of the open regions. For example, the chemical reaction operation may comprise forming a reaction product (e.g. oxide) by a chemical reaction, the reaction product bonding electrocatalyst-containing particles (e.g. electrocatalyst particles) to one another.

[0175] The heat treatment operation may comprise a ramp phase in which the temperature ramps to the target temperature. In the ramp phase a ramp rate may be between 0.5 and 5°C per minute, for example between 0.5°C and 2°C per minute, such as approximately 1 °C per minute. The heat treatment operation may comprise a holding phase in which the temperature is maintained at the target temperature. The holding phase may be between 30 and 300 minutes, for example between 30 and 90 minutes, such as approximately 60 minutes.

[0176] The heat treatment operation may be a two-stage heat treatment operation comprising heating the body or the flow-through or porous set of plates to a first target temperature of between 150-500°C and then to a second target temperature of between 500-1000°C. The first target temperature may be between 200-500°C, for example between 250-450°C, or between 300-500°C, for example approximately 300C°C or approximately 350°C. The second target temperature may be between 600-1000°C, for example between 700-1000°C, or between 800-1000°C, or between 900-1000°C, or between 900-950°C, for example approximately 930°C. The first stage of the heat treatment operation may comprise holding the body or the flow-through or porous set of plates at the first target temperature for 2-10 hours, for example 4-8 hours, for example approximately 6 hours. The second stage of the heat treatment operation may comprise holding the body or the flow-through or porous set of plates at the second target temperature for between 30 and 300 minutes, for example between 30 and 90 minutes, such as approximately 60 minutes.

[0177] The first stage may be carried out to pyrolyze or burn off non-electrocatalyst components of the electrocatalyst composition such as binder components of the electrocatalyst composition. The first stage may therefore be carried out in an oxidising atmosphere. The first stage of the heat treatment operation may therefore be considered to be a pyrolysis operation.

[0178] The second stage may be carried out to consolidate (e.g. sinter) electrocatalyst-containing particles (e.g. electrocatalyst particles) to one another. The second stage may therefore be carried out in an inert (or reducing) atmosphere such as an argon atmosphere or a nitrogen / hydrogen atmosphere. The second stage of the heat treatment operation may therefore be considered to be a consolidating (e.g. sintering) operation.

[0179] The second stage of the heat treatment operation may be conducted at the same time as, comprise or be another heat treatment operation, such as a post-weld heat treatment operation (e.g. a stress-relief heat treatment operation).

[0180] Clause 61. A method according to clause 59 or 60, wherein the heat treatment operation comprises heating the subset of flow-through plates to which the electrocatalyst composition is applied to a target temperature of between 150-1000°C.

[0181] Clause 62. A method according to any one of clauses 48-61, wherein the electrocatalyst composition has a viscosity of from about 1 Pa.s to about 30 Pa.s when applied.

[0182] The electrocatalyst composition may have a (i.e. dynamic) viscosity no less than about 1 Pa s, for example, no less than about 2 Pa s, or no less than about 4 Pa s, or no less than about 5 Pa s, or no less than about 6 Pa s, or no less than about 8 Pa s, or no less than about 10 Pa s, or no less than about 12 Pa s, or no less than about 14 Pa s, or no less than about 16 Pa s, or no less than about 18 Pa s, or no less than about 20 Pa s, or no less than about 21 Pa s, or no less than about 22 Pa s, or no less than about 23 Pa s, or no less than about 24 Pa s, or no less than about 25 Pa s. The electrocatalyst composition may have a (i.e. dynamic) viscosity no greater than about 30 Pa s, for example, no greater than about 28 Pa s, or no greater than about 26 Pa s, or no greater than about 25 Pa s, or no greater than about 24 Pa s, or no greater than about 23 Pa s, or no greater than about 22 Pa s, or no greater than about 21 Pa s, or no greater than about 20 Pa s, or no greater than about 19 Pa s, or no greater than about 18 Pa s, or no greater than about 17 Pa s, or no greater than about 16 Pa s, or no greater than about 14 Pa s, or no greater than about 12 Pa s, or no greater than about 10 Pa s, or no greater than about 8 Pa s. The electrocatalyst composition may have a (i.e. dynamic) viscosity from about 1 Pa s to about 30 Pa s, for example, from about 1 Pa s to about 28 Pa s, or from about 1 Pa s to about 26 Pa s, or from about 1 Pa s to about 25 Pa s, or from about 1 Pa s to about 24 Pa s, or from about 1 Pa s to about 23 Pa s, or from about 1 Pa s to about 22 Pa s, or from about 1 Pa s to about 21 Pa s, or from about 1 Pa s to about 20 Pa s, or from about 1 Pa s to about 18 Pa s, or from about 1 Pa s to about 16 Pa s, or from about 1 Pa s to about 14 Pa s, or from about 1 Pa s to about 12 Pa s, or from about 1 Pa s to about 10 Pa s, or from about 1 Pa s to about 8 Pa s, or from about 2 Pa s to about 30 Pa s, or from about 2 Pa s to about 28 Pa s, or from about 2 Pa s to about 26 Pa s, or from about 2 Pa s to about 25 Pa s, or from about 2 Pa s to about 24 Pa s, or from about 2 Pa s to about 23 Pa s, or from about 2 Pa s to about 22 Pa s, or from about 2 Pa s to about 21 Pa s, or from about 2 Pa s to about 20 Pa s, or from about 2 Pa s to about 18 Pa s, or from about 2 Pa s to about 16 Pa s, or from about 2 Pa s to about 14 Pa s, or from about 2 Pa s to about 12 Pa s, or from about 2 Pa s to about 10 Pa s, or from about 2 Pa s to about 8Pa s, or from about 4 Pa s to about 30 Pa s, or from about 4 Pa s to about 28 Pa s, or from about 4 Pa s to about 26 Pa s, or from about 4 Pa s to about 25 Pa s, or from about 4 Pa s to about 24 Pa s, or from about 4 Pa s to about 23 Pa s, or from about 4 Pa s to about 22 Pa s, or from about 4 Pa s to about 21 Pa s, or from about 4 Pa s to about 20 Pa s, or from about 4 Pa s to about 18 Pa s, or from about 4 Pa s to about 16 Pa s, or from about 4 Pa s to about 14 Pa s, or from about 4 Pa s to about 12 Pa s, or from about 4 Pa s to about 10 Pa s, or from about 4 Pa s to about 8 Pa s, or from about 5 Pa s to about 30 Pa s, or from about 5 Pa s to about 28 Pa s, or from about 5 Pa s to about 26 Pa s, or from about 5 Pa s to about 25 Pa s, or from about 5 Pa s to about 24 Pa s, or from about 5 Pa s to about 23 Pa s, or from about 5 Pa s to about 22 Pa s, or from about 5 Pa s to about 21 Pa s, or from about 5 Pa s to about 20 Pa s, or from about 5 Pa s to about 18 Pa s, or from about 5 Pa s to about 16 Pa s, or from about 5 Pa s to about 14 Pa s, or from about 5 Pa s to about 12 Pa s, or from about 5 Pa s to about 10 Pa s, or from about 5 Pa s to about 8 Pa s, or from about 6 Pa s to about 30 Pa s, or from about 6 Pa s to about 28 Pa s, or from about 6 Pa s to about 26 Pa s, or from about 6 Pa s to about 25 Pa s, or from about 6 Pa s to about 24 Pa s, or from about 6 Pa s to about 23 Pa s, or from about 6 Pa s to about 22 Pa s, or from about 6 Pa s to about 21 Pa s, or from about 6 Pa s to about 20 Pa s, or from about 6 Pa s to about 18 Pa s, or from about 6 Pa s to about 16 Pa s, or from about 6 Pa s to about 14 Pa s, or from about 6 Pa s to about 12 Pa s, or from about 6 Pa s to about 10 Pa s, or from about 6 Pa s to about 8 Pa s, or from about 8 Pa s to about 30 Pa s, or from about 8 Pa s to about 28 Pa s, or from about 8 Pa s to about 26 Pa s, or from about 8 Pa s to about 25 Pa s, or from about 8 Pa s to about 24 Pa s, or from about 8 Pa s to about 23 Pa s, or from about 8 Pa s to about 22 Pa s, or from about 8 Pa s to about 21 Pa s, or from about 8 Pa s to about 20 Pa s, or from about 8 Pa s to about 18 Pa s, or from about 8 Pa s to about 16 Pa s, or from about 8 Pa s to about 14 Pa s, or from about 8 Pa s to about 12 Pa s, or from about 8 Pa s to about 10 Pa s, or from about 8 Pa s to about 8 Pa s, or from about 10 Pa s to about 30 Pa s, or from about 10 Pa s to about 28 Pa s, or from about 20 Pa s to about 26 Pa s, or from about 10 Pa s to about 25 Pa s, or from about 10 Pa s to about 24 Pa s, or from about 10 Pa s to about 23 Pa s, or from about 10 Pa s to about 22 Pa s, or from about 10 Pa s to about 21 Pa s, or from about 10 Pa s to about 20 Pa s, or from about 10 Pa s to about 18 Pa s, or from about 10 Pa s to about 16 Pa s, or from about 10 Pa s to about 14 Pa s, or from about 10 Pa s to about 12 Pa s, or from about 12 Pa s to about 30 Pa s, or from about 14 Pa s to about 30 Pa s, or from about 16 Pa s to about 30 Pa s, or from about 18 Pa s to about 30 Pa s, or from about 20 Pa s to about 30 Pa s, or from about 21 Pa s to about 30 Pa s, or from about 22 Pa s to about 30 Pa s, or from about 23 Pa s to about 30 Pa s, or from about 24 Pa s to about 30 Pa s, or from about 25 Pa s to about 30 Pa s, or from about 16 Pa s to about25 Pa s, or from about 18 Pa s to about 25 Pa s, or from about 20 Pa s to about 25 Pa s, or from about 16 Pa s to about 23 Pa s, or from about 18 Pa s to about 23 Pa s, or from about 20 Pa s to about 23 Pa s, or from about 16 Pa s to about 20 Pa s, or from about 18 Pa s to about 20 Pa s. The (i.e. dynamic) viscosity of the electrocatalyst composition may be measured at 25 °C, for example, according to ISO 3104:2020.

[0183] It may be that the electrocatalyst composition comprises a mixture of an electrocatalyst and liquid when applied (e.g. to the body or flow-through set or porous set of plates).

[0184] The electrocatalyst composition is a composition which comprises (e.g. consists essentially of, consists of, or is) an electrocatalyst for the respective half-reaction of electrolysis. For example, the electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a mixture of the electrocatalyst for the respective half-reaction of electrolysis and liquid.

[0185] The electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a slurry comprising the electrocatalyst for the respective half-reaction of electrolysis and liquid.

[0186] The electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a suspension of the electrocatalyst for the respective half-reaction of electrolysis in liquid.

[0187] The electrocatalyst may be provided in the mixture in the form of a particulate.

[0188] The electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a colloidal suspension (e.g. of the particulate in liquid). For example, the electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a sol (i.e. a solid-in-liquid colloidal suspension), a conductive ink (i.e. a suspension of electrically conductive electrocatalyst particles in liquid), or a paste (i.e. a solid-in-liquid suspension having a sufficiently high solids contents that the suspension behaves as a solid in response to low applied stresses) comprising the electrocatalyst for the respective half-reaction of electrolysis.

[0189] The electrocatalyst may be any suitable electrocatalyst described herein.

[0190] Particle size properties of the electrocatalyst particulate may be measured in a well-known manner by a laser scattering technique (e.g. standard ISO 13320-1). In this technique, the size of particles in powders, suspensions and emulsions is measured using the diffraction of a laser beam, based on an application of Mie theory. A machine, for example available from Microtrac MRB, provides measurements and a plot of the cumulative percentage by volume of particles having a size, referred to in the art as the ‘equivalent spherical diameter’ (e.s.d), less than given e.s.d values. The mean particle size d50 is the value determined in this way of the particle e.s.d at which there are 50% by volume of the particles which have an equivalent spherical diameter less than that d50 value. The d99 value is the value determined in the same way of the particlee.s.d. at which there is 99% by volume of the particles which have an equivalent spherical diameter less than the d99 value.

[0191] The electrocatalyst particulate may have a d50 no less than about 100 nm, for example, no less than about 500 nm, or no less than about 1 pm, or no less than about 4 pm, or no less than about 5 pm, or no less than about 8 pm, or no less than about 10 pm. The electrocatalyst particulate may have a d50 no more than about 100 pm, for example, no more than about 75 pm, or no more than about 50 pm, or no more than about 25 pm, or no more than about 20 pm. The electrocatalyst particulate may have a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 750 nm to about 100 pm, or from about 1 pm to about 100 pm, or from about 10 pm to about 100 pm, or from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 750 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 50 pm, or from about 500 nm to about 20 pm, or from about 750 nm to about 20 pm, or from about 1 pm to about 20 pm, or from about 10 pm to about 20 pm, or from about 500 nm to about 50 pm, or from about 750 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 50 pm, or from about 500 nm to about 25 pm, or from about 750 nm to about 25 pm, or from about 1 pm to about 25 pm, or from about 10 pm to about 25 pm, or from about 500 nm to about 20 pm, or from about 750 nm to about 20 pm, or from about 1 pm to about 20 pm, or from about 10 pm to about 20 pm, or from about 500 nm to about 15 pm, or from about 750 nm to about 15 pm, or from about 1 pm to about 15 pm, or from about 10 pm to about 15 pm.

[0192] The electrocatalyst particulate may have a d99 no less than about 1 pm, for example, no less than about 10 pm, or no less than about 20 pm, or no less than about 30 pm, or no less than about 35 pm. The electrocatalyst particulate may have a d99 no more than about 150 pm, for example, no more than about 100 pm, or no more than about 75 pm, or no more than about 50 pm, or no more than about 45 pm, or no more than about 40 pm. The electrocatalyst particulate may have a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 45 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 150 pm, or from about 10 pm to about 100 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 50 pm, or from about 10 pm to about 45 pm, or from about 10 pm to about 40 pm, or from about 20 pm to about 150 pm, or from about 20 pm to about 100 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 20 pm to about 45 pm, or from about 20 pm to about 40 pm, or from about 30 pm to about 150 pm, or from about 30 pm to about 100 pm, or from about 30 pm to about 75pm, or from about 30 pm to about 50 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0193] Smaller particle sizes, as evidenced by lower values of d50 and / or d99, may facilitate better penetration of the electrocatalyst composition into open regions.

[0194] For example, the electrocatalyst particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) one or more elements selected from: noble metals (i.e. Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, Re), d-block transition metals (i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, R, Os, Ir, Pt, Au, Hg, Rf, Db, S, Rh, Hs, Mt, Ds, Rg, Cn), f-block lanthanides (i.e. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metals (i.e. Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), platinum group metals (i.e. Ru, Rh, Pd, Os, Ir, Pt), P, S, C and / or combinations thereof; wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0195] The electrocatalyst particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof, wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm, or from about 8 pm to about 16 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0196] The electrocatalyst particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof, wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0197] The electrocatalyst particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Ni, Fe, Co, P, S, and / or combinations thereof, wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm, or from about 4 pm to about 10 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0198] The electrocatalyst particulate may comprise (e.g. consist essentially of, or consist of) particles comprising (e.g. consisting essentially of, or consisting of) Pt, Ir, Pd, Ni, Mo, and / or combinations thereof, wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0199] In some examples, the electrocatalyst particulate comprises (e.g. consists essentially of or consists of) particles comprising (e.g. consisting essentially of, or consisting of) Ni (e.g. elemental Ni) or Pt (e.g. elemental Pt), wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0200] In some examples, the electrocatalyst particulate comprises (e.g. consists essentially of or consists of) particles comprising (e.g. consisting essentially of, or consisting of) Ni (e.g. elemental Ni), wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0201] In some examples, the electrocatalyst particulate comprises (e.g. consists essentially of or consists of) particles comprising (e.g. consisting essentially of, or consisting of) Pt (e.g. elemental Pt), wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0202] In some examples, the electrocatalyst particulate is a Ni-containing particulate, wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, or from about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm. The Ni-containing particulate may comprise (e.g. consist essentially of, or consist of) particles of Ni (e.g. elemental Ni) or an Ni-based alloy.

[0203] In some examples, the electrocatalyst-containing particulate is an Ni particulate consisting essentially of particles of Ni, wherein the electrocatalyst particulate has: a d50 from about 100 nm to about 100 pm, for example, from about 500 nm to about 100 pm, or from about 500 nm to about 50 pm, or from about 1 pm to about 50 pm, or from about 1 pm to about 25 pm; and a d99 from about 1 pm to about 150 pm, for example, from about 1 pm to about 75 pm, or from about 1 pm to about 50 pm, or from about 10 pm to about 75 pm, or from about 10 pm to about 75 pm, orfrom about 20 pm to about 75 pm, or from about 20 pm to about 50 pm, or from about 30 pm to about 75 pm, or from about 30 pm to about 45 pm, or from about 30 pm to about 40 pm.

[0204] The electrocatalyst-containing particulate may have any suitable particle shape (i.e. morphology), such as (e.g. substantially) spherical, spheroidal, acicular or needle-like, fibrous, platy, flake-like, etc. In some examples, the electrocatalyst-containing particulate has a flake-like particle shape. In some examples, the electrocatalyst-containing particulate comprises (e.g. consists essentially or, or consists of) flakes of electrocatalyst, for example, flakes of metal or metal alloy (such as flakes of Ni or Ni alloy).

[0205] A suitable liquid may be selected based on the nature of the electrocatalyst particulate, the dimensions of the open regions, and / or manufacturing constraints such as heating temperatures.

[0206] The liquid may be polar or non-polar.

[0207] The liquid may be aqueous (e.g. water-based). That is to say, the liquid may comprise (e.g. consist essentially of, consist of, or be) water.

[0208] The liquid may be organic. The liquid may comprise (e.g. consist essentially of, consist of, or be) one or more organic species, e.g., hydrocarbons.

[0209] The liquid may comprise (e.g. consist essentially of, consist of, or be) one or more alcohols, esters, acetates, acetate esters, ether acetates, and / or acids.

[0210] The liquid may comprise (e.g. consist essentially of, consist of, or be) one or more solvents, e.g., one or more polar solvents or one or more non-polar solvents, for example, one or more organic solvents.

[0211] In some examples, the liquid comprises (e.g. consists essentially of, consists of, or is) a non-polar ester (e.g. a non-polar ester solvent).

[0212] In some examples, the liquid comprises (e.g. consists essentially of, consists of, or is) a reaction product of a carboxylic acid and an alcohol, for example, wherein the alcohol comprises an alkoxyalcohol. In some examples, the liquid comprises (e.g. consists essentially of, consists of, or is) an acetate ester or an ether acetate. In some examples, the liquid comprises (e.g. consists essentially of, consists of, or is) 2-butoxyethyl acetate.

[0213] The electrocatalyst composition may comprise a binder, for example, a polymeric binder. The polymeric binder may be a thermoplastic binder or a thermosetting binder (e.g. a resin). A thermoplastic binder is a polymeric binder which melts or becomes pliable at elevated temperatures and which solidifies upon cooling. A thermosetting binder (e.g. a resin) is a polymeric binder which hardens irreversibly (i.e. cures) by heating, exposure to radiation and / or exposure to a suitable catalyst. The binder may be dispersed or dissolved in the liquid.

[0214] The electrocatalyst composition may comprise one or more additives such as viscosity or rheology modifiers, tackifiers, plasticizers, pigments, etc. For example, the electrocatalyst composition may comprise carbon black.

[0215] A suitable electrocatalyst composition may be conductive ink 116-25 available from Creative Materials Inc (of Massachusetts, USA). The viscosity of the conductive ink 116-25 may be adjusted as required by dilution with solvent 112-19, solvent 102-03, or solvent 113-12, also available from Creative Materials Inc (of Massachusetts, USA).

[0216] The plurality of plates, the flow-through set of plates and the plurality of flow regions and flow zones defined by respective plates may have any of the features defined with respect to the corresponding elements of clauses 1-40 (e.g., the corresponding plurality of plates, the porous set of plates which correspond to the flow-through set of plates, the plurality of porous regions which correspond to the plurality of flow regions, and the corresponding flow zones (which may be porous zones).

[0217] Clause 63. A method in accordance with clause 42 and optionally any of clauses 43-62, wherein the plurality of plates is a first plurality of plates arranged in a first stack for forming an array of outer porous walls of the electrolyser, the comprising: providing a second plurality of plates in a second stack for forming an array of inner porous walls of the electrolyser; wherein for each of the first and second plurality of plates: each plate comprises a plurality of wall regions each corresponding to a longitudinal portion of a respective porous wall; the plurality of plates comprises a flow-through set of plates, wherein for each of the flow-through set of plates the respective wall region comprises one or more flow zones extending through the plate to permit fluid to flow through the respective plate; the method comprises arranging the plurality of plates in a respective stack in the longitudinal direction to form an array of bodies for the respective porous walls, wherein each body is elongate along the longitudinal direction and has a thickness direction from a first side to a second side; wherein the plurality of plates are stacked so that, for each body of the array of bodies a respective plurality of flow regions are defined; and wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the flow-through set of plates, wherein flow zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the flow region.

[0218] A method according to clause 63 may comprise the features of any of clauses 42-62 as applied to the second plurality of plates. Such features are defined in clauses 42-62 in relation to a plurality of plates (the first plurality of plates), and the disclosure extends to such features as applied to the second plurality of plates.

[0219] A method in accordance with any of clauses 41-63 and any method of forming a structure by bonding stacked plates as disclosed herein may comprise removing material from a plurality of precursor plates to form the plates, including any flow-through or porous set of plates, each having the one or more respective open zones. The removal of material may be performed by any suitable process. Example processes include by a laser drilling process, by a chemical etching process, by a spark erosion electrical discharge machining (SE-EDM) process, or by an electron beam drilling (E-beam) process. A suitable process may be selected according to known trade-offs. Some processes may only be applicable to remove material along a direction normal to the plate, which leads to a stepped profile of the porous region (or open region), with junctions between the respective layers. Nevertheless, even in such implementations the flow region or porous region (or open region) retains a continuously open cross-section along its extent when the respective flow zones or porous zones (or open zones) are configured to overlap, thereby permitting fluid to flow through the respective flow region or porous region (or open region) from one side to the other.

[0220] Clause 64. A method according to clause 41 and optionally any of clauses 42-62, wherein the stack of plates provides an outer electrode stack of plates, each plate further comprising: a shell region comprising an array of cut-outs in a first pattern; wherein the plurality of wall regions are arranged in the first pattern, each wall region disposed within a respective cutout of the shell region and spaced apart from the shell region by a gap; wherein each wall region is structurally connected to the shell region by one or more support tabs; the method further comprising: diffusion bonding the outer electrode stack of plates, stacked in the longitudinal direction, to provide an outer electrode structure having a longitudinal extent, comprising: an array of outer electrodes in the first pattern, each corresponding to a stacked set of the wall regions of the outer electrode stack; an array of outer chambers in the first pattern, each defined between a shell corresponding to a stacked set of the shell regions of the outer electrode stack, and a respective outer electrode; wherein each outer electrode is structurally connected to the shell by a plurality of the support tabs.

[0221] Accordingly, the array of outer electrodes corresponds to the array of porous walls.

[0222] Clause 65. A method of manufacturing a structure for an electrolyser, comprising: providing an outer electrode stack of plates by a method in accordance with clause 41 and optionally any of clauses 42-62, wherein each plate of the outer electrode stack of plates comprises: a shell region comprising an array of cut-outs in a first pattern; wherein the plurality of wall regions are arranged in the first pattern, each wall region disposed within a respective cutout of the shell region and spaced apart from the shell region by a gap; wherein each wall regionis structurally connected to the shell region by one or more support tabs; diffusion bonding the outer electrode stack of plates, stacked in the longitudinal direction, to provide an outer electrode structure having a longitudinal extent, comprising: an array of outer electrodes in the first pattern, each corresponding to a stacked set of the wall regions of the outer electrode stack; an array of outer chambers in the first pattern, each defined between a shell corresponding to a stacked set of the shell regions of the outer electrode stack, and a respective outer electrode; wherein each outer electrode is structurally connected to the shell by a plurality of the support tabs.

[0223] Accordingly, the array of outer electrodes corresponds to the array of porous walls.

[0224] Clause 66. A method of manufacturing a structure for an electrolyser, comprising: providing an outer electrode stack of plates, each plate comprising: a shell region comprising an array of cut-outs in a first pattern; and a plurality of wall regions in the first pattern, each wall region disposed within a respective cut-out of the shell region and spaced apart from the shell region by a gap; wherein each wall region is structurally connected to the shell region by one or more support tabs; diffusion bonding the outer electrode stack of plates, stacked in a longitudinal direction, to provide an outer electrode structure having a longitudinal extent, comprising: an array of outer electrodes in the first pattern, each corresponding to a stacked set of the wall regions of the outer electrode stack; an array of outer chambers in the first pattern, each defined between a shell corresponding to a stacked set of the shell regions of the outer electrode stack, and a respective outer electrode; wherein each outer electrode is structurally connected to the shell by a plurality of the support tabs.

[0225] Clause 67. A method according to any of clauses 64-66, wherein each of the outer electrodes are annular, and each of the outer chambers are annular.

[0226] Correspondingly, it may be that outer boundaries of the cut-outs defined by the shell regions are cylindrical.

[0227] It may be that the outer electrode structure forms part of a compound outer structure when the support tabs are removed, such that the array of outer electrodes remains in fixed registration with the shell when the support tabs are removed over the longitudinal extent of the outer electrode structure.

[0228] Clause 68. A method according to any of clauses 64-67, further comprising removing the support tabs between the array of outer electrodes and the shell, to structurally separate the outer electrodes and the shell over the longitudinal extent of the outer electrode structure.

[0229] Clause 69. A method according to any one of clauses 64-68, comprising: providing a shell support stack of plates, stacked in the longitudinal direction and diffusion bonded to cooperatively define a shell support structure comprising: an array of outer electrode extensionsin the first pattern, each configured to extend a respective outer electrode of the outer electrode structure; a shell extension configured to extend the shell of the outer electrode structure; an array of outer chamber extensions in the first pattern, each defined between the shell extension and a respective outer electrode extension; wherein each outer electrode extension is structurally connected to the shell extension by one or more support tabs extending through the respective outer chamber extension; wherein the outer electrode structure and the shell support structure are bonded in a compound outer structure.

[0230] It may be that each of the outer electrode extensions are annular. It may be that each of the outer chamber extensions are annular.

[0231] Clause 70. A method according to clause 68 and according to clause 69, wherein the support tabs of the shell support structure are retained when the support tabs of the outer electrode structure are removed, to maintain the outer electrodes in fixed registration with respect to the shell.

[0232] Clause 71. A method according to clause 69 or 70, wherein the support tabs of the outer electrode structure belong to a first outer set and the support tabs of the shell support structure belong to a second outer set; wherein, when projected along the longitudinal direction onto a reference plane normal to the longitudinal direction, positions of the support tabs of the first outer set do not overlap with positions of the support tabs of the second outer set.

[0233] Clause 72. A method according to any one of clauses 68-71 , wherein each support tab of the outer electrode structure is removed by a cutting process using a cutting element extending through the respective outer chamber along the longitudinal axis; optionally wherein the cutting process is wire electrical discharge machining.

[0234] It may be that the support tabs of the outer electrode structure are cut at an interface with the respective outer electrodes, and cut (e.g., subsequently) at an interface with the shell.

[0235] Clause 73. A method according to any one of clauses 69-72, wherein the outer electrode stack and the shell support stack are diffusion bonded together in a common stack to provide the outer electrode structure and the shell support structure in the compound outer structure.

[0236] Multiple stacks of plates being diffusion bonded together as defined herein is intended to refer to a common diffusion bonding process bonding the cumulative stack.

[0237] Otherwise, it may be that the outer electrode stack is diffusion bonded to provide the outer electrode structure separately from the shell support stack being diffusion bonded to provide the shell support structure, and the structures may be bonded by a separate process to form thecompound outer structure. For example, the separate process may be a further diffusion bonding process, or any suitable bonding process, for example vacuum brazing.

[0238] Clause 74. A method according to any one of clauses 69-73, wherein the plates of the shell support stack comprise a dielectric material configured to inhibit electrical electronic conduction between the outer electrodes and the shell extension.

[0239] Accordingly, the shell support stack inhibits electrical electronic conduction between the outer electrodes and the shell of the outer electrode structure, after removal of the support tabs of the outer electrode structure.

[0240] Clause 75. The method of clause 74, wherein the dielectric material comprises a ceramic material, for example silicon carbide or a ceramic metal oxide.

[0241] The dielectric material may comprise (e.g., consist essential of, or consist of), for example, zirconia, alumina, a composite of zirconia and alumina (e.g., ZTA - zirconia toughened alumina), magnesium aluminate, aluminium silicate, silicon carbide, silicon nitride, and fused silica; or may comprise a dielectric oxide of aluminium, yttrium, cerium, titanium, and zirconium (e.g., formed by anodization of a metal surface of a plate).

[0242] Clause 76. A method according to any one of clauses 64-75, comprising: providing an outer electrode connector set of plates, each plate comprising: a connector shell region comprising an array of cutouts in the first pattern, wherein the connector shell region is provided with a dielectric coating over a conductive layer; a plurality of connector wall regions in the first pattern, each wall region disposed within a respective cut-out of the connector shell region and spaced apart from the connector shell region by a gap; wherein the connector shell region is structurally connected to a subset of the connector wall regions by one or more respective electrical connection tabs to electrically couple the respective wall regions to the conductive layer; diffusion bonding the outer electrode connector set of plates in a stack to provide an outer electrode connector structure comprising: an array of outer electrode connector extensions in the first pattern, each configured to extend a respective outer electrode of the outer electrode structure; a connector shell extension configured to extend the shell of the outer electrode structure; wherein the connector shell extension comprises a plurality of conductive layers electronically isolated from each other by dielectric layers, each conductive layer electrically coupled to a subset of the outer electrode connector extensions by one or more respective electrical connection tabs, for electrical communication with a respective subset of the outer electrodes.

[0243] The outer electrode connector set of plates may be diffusion bonded in an outer electrode connector stack to provide the outer electrode connector structure.

[0244] Clause 77. A method according to clause 76, wherein each conductive layer is electrically coupled to a single outer electrode connector extension by one or more respective electrical connection tabs, for electrical communication with a respective single outer electrode.

[0245] Clause 78. A method according to clause 76 or 77, wherein for each plate of the outer electrode connector set of plates, each wall region is structurally connected to the connector shell region by one or more connector support tabs, whereby in the outer electrode connector structure each outer electrode connector extension is structurally connected to the connector shell extension by a respective set of connector support tabs; wherein the method comprises removing the connector support tabs between the array of outer electrode connector extensions and the shell extension.

[0246] Clause 79. A method according to clause 78, wherein, when projected along the longitudinal direction onto a reference plane normal to the longitudinal direction, positions of the connector support tabs of the outer electrode connector structure do not overlap with positions of the electrical connection tabs of the outer electrode connector structure.

[0247] Clause 80. A method according to clause 79 when appendant to clause 71, wherein when projected along the longitudinal direction onto a reference plane normal to the longitudinal direction, positions of the connector support tabs correspond to positions of the support tabs of the first outer set.

[0248] Accordingly, the connector support tabs and the support tabs of the first outer set may be removed in a common removal process, without removing the electrical connection tabs.

[0249] Clause 81. A method according to any one of clauses 78-80, wherein each connector support tab of the outer electrode connector structure is removed by a cutting process using a cutting element extending through the respective outer chamber extension along the longitudinal axis; optionally wherein the cutting process is wire electrical discharge machining.

[0250] It may be that the connector support tabs are cut at an interface with the respective outer electrode connector extensions, and cut (e.g., subsequently) at an interface with the shell extension.

[0251] Clause 82. A method according to any one of clauses 76-81, wherein the outer electrode stack and the outer electrode connector set of plates are diffusion bonded together in a common stack to provide the outer electrode structure and the outer electrode connector structure in a compound outer structure.

[0252] Multiple stacks of plates being diffusion bonded together as defined herein is intended to refer to a common diffusion bonding process bonding the cumulative stack.

[0253] Otherwise, it may be that the outer electrode stack is diffusion bonded to provide the outer electrode structure separately from the outer electrode connector set of plates being diffusion bonded to provide the outer electrode connector structure, and the structures may be bonded by a separate process to form the compound outer structure. For example, the separate process may be a further diffusion bonding process, or any suitable bonding process, for example vacuum brazing.

[0254] Clause 83. A method according to any one of clauses 64 to 82, comprising: providing an outer outlet manifold stack of plates, stacked in the longitudinal direction and bonded to cooperatively define an outer outlet manifold structure comprising an embedded outlet manifold to convey a fluid from the array of outer chambers to an outlet port.

[0255] The outer outlet manifold stack of plates may be diffusion bonded to define the outer outlet manifold structure.

[0256] It may be that the outer outlet manifold stack of plates is provided in addition to the outer electrode stack of plates, and in addition to any shell support stack of plates and outer connector stack of plates, such that the outer outlet manifold structure is provided in a longitudinal layer of the structure adjacent to the corresponding structures (i.e. , the outer electrode structure, or the shell support structure or the outer electrode connector structure). In this event the outer outlet manifold may be in fluid communication with the array of outer chambers by providing manifold inlets at an end of the respective outer chambers (or any associated outer chamber extension), for example. Otherwise, the outer outlet manifold may be in fluid communication with the array of outer chambers by a structure adjacent to the outer outlet manifold structure providing an outer supply manifold for fluid communication with the outer outlet manifold. For example, the outer electrode structure and / or any shell support structure and / or any outer electrode connector structure may define an embedded supply manifold to convey a fluid from the array of outer chambers to the outer outlet manifold.

[0257] The outer outlet manifold may extend along the longitudinal direction to a longitudinal position beyond the longitudinal extent of the outer electrode stack, and optionally beyond a longitudinal extent of any outer electrode extension or electrical connection element coupled to the outer electrodes of the outer electrode stack.

[0258] It may be that the outer outlet manifold structure delimits a longitudinal extent of the array of outer outlet chambers or any outer chamber extension, as arranged in the first pattern.

[0259] Clause 84. A method according to clause 83, wherein the outer outlet manifold structure defines an array of inner electrode openings in the first pattern, each configured toreceive an inner electrode to extend through the outer outlet manifold structure and along the longitudinal extent of the outer electrode stack.

[0260] It may be that the inner electrodes are annular, each defining a core chamber radially within.

[0261] Clause 85. A method of manufacturing a structure for an electrolyser, comprising: providing an outer electrode stack of plates, stacked in a longitudinal direction and diffusion bonded to cooperatively define an outer electrode structure comprising an array of outer electrodes arranged in a first pattern; optionally wherein the outer electrode stack of plates are provided by a method in accordance with clause 41 and optionally any of clauses 42-62.

[0262] Clause 86. A method according to any one of the clauses 64-85, comprising: providing an array of inner electrodes, each inner electrode defining an inner chamber; assembling the array of inner electrodes and the outer electrode structure so that each of the inner electrodes is received within a cavity defined by a respective outer electrode and separated from the respective outer electrode by a gap; whereby the outer electrode structure and the array of inner electrodes cooperatively define an array of cells, each cell comprising: an outer chamber of the array of outer chambers; an outer electrode of the array of outer electrodes; an inner electrode of the array of inner electrodes; an inlet chamber defined between the outer electrode and the inner electrode; and the inner chamber defined by the inner electrode.

[0263] Clause 87. A method according to clause 86, comprising providing an inner electrode stack of plates, stacked in the longitudinal direction and diffusion bonded to cooperatively define the array of inner electrodes.

[0264] Clause 88. A method according to clause 87, wherein the inner electrode stack of plates is provided by a method in accordance with clause 42 and optionally any of clauses 43-62, the array of inner electrodes corresponding to the array of porous walls.

[0265] Clause 89. A method in accordance with clause 63 and in accordance with clause 87, wherein: the first plurality of plates provides the outer electrode stack of plates, the array of outer porous walls corresponding to the array of outer electrodes; and the second plurality of plates provides the inner electrode stack of plates, the array of inner porous walls corresponding to the array of inner electrodes.

[0266] It may be that the array of inner electrodes is provided as part of a compound inner structure comprising the array of inner electrodes extending from an inner electrode support structure. The array of inner electrodes and the inner electrode support structure may be formed together (e.g., by diffusion bonding together corresponding stacks of plates), or may be initiallyformed separately and then bonded, for example by a further diffusion bonding process, or any suitable bonding process, for example vacuum brazing.

[0267] Clause 90. A method according to any one of clauses 87-89, wherein the inner electrode stack of plates comprises a subset of one or more plates that define an array of end caps, each delimiting one end of a respective inner chamber defined by a respective inner electrode.

[0268] It may be that the end cap is provided at a first end of each inner electrode opposing a second end that connects to any inner electrode support structure. The first end may correspond to an inlet end of the respective cell, and the second end may correspond to an outlet end of the respective cell.

[0269] Clause 91. A method according to any one of clauses 87-90, comprising providing an inner electrode support stack of plates, stacked in the longitudinal direction and diffusion bonded to provide an inner electrode support structure; wherein the inner electrode stack and the inner electrode support stack are diffusion bonded together in a common stack to provide the inner electrode structure and the inner electrode support structure as a compound inner structure comprising the array of inner electrodes extending from the inner electrode support structure.

[0270] Multiple stacks of plates being diffusion bonded together as defined herein is intended to refer to a common diffusion bonding process bonding the cumulative stack.

[0271] Clause 92. A method according to any one of clauses 87-91, comprising: providing an inner electrode connector stack of plates, each plate comprising: a connector shell region comprising an array of cutouts in the first pattern, wherein the connector shell region is provided with a dielectric coating over a conductive layer; a plurality of connector wall regions in the first pattern, each wall region disposed with a respective cut-out of the connector shell region and spaced apart from the connector shell region by a gap; wherein the connector shell region is structurally connected to a subset of the connector wall regions by one or more respective electrical connection tabs to electrically couple the respective wall regions to the conductive layer; bonding the inner electrode connector set of plates in a stack to provide an inner electrode connector structure comprising: an array of inner electrode connector extensions in the first pattern, each configured to extend a respective inner electrode of the inner electrode structure; a connector shell corresponding to a stacked set of the connector shell regions; wherein the connector shell comprises a plurality of conductive layers electronically isolated from each other by dielectric layers, each conductive layer electrically coupled to a subset of the inner electrode connector extensions by one or more respective electrical connection tabs, for electrical communication with a respective subset of the inner electrodes.

[0272] The inner electrode connector set of plates may be diffusion bonded in an inner electrode connector stack to provide the inner electrode connector structure.

[0273] Clause 93. A method according to clause 92, wherein each conductive layer is electrically coupled to a single inner electrode connector extension by one or more respective electrical connection tabs, for electrical communication with a respective single inner electrode.

[0274] Clause 94. A method according to clause 92 or 93, wherein for each plate of the inner electrode connector set of plates, each wall region is structurally connected to the connector shell region by one or more connector support tabs, whereby in the inner electrode connector structure each inner electrode connector extension is structurally connected to the connector shell by a respective set of connector support tabs.

[0275] Clause 95. A method according to clause 94, wherein, when projected along the longitudinal direction onto a reference plane normal to the longitudinal direction, positions of the connector support tabs of the inner electrode connector structure do not overlap with positions of the electrical connection tabs of the inner electrode connector structure.

[0276] Clause 96. A method according to any one of clauses 94-95, wherein each connector support tab of the inner electrode connector structure is removed by a cutting process using a cutting element extending into a respective cavity between the connector shell and the inner electrode connector extension along the longitudinal axis; optionally wherein the cutting process is wire electrical discharge machining.

[0277] It may be that the connector support tabs are cut at an interface with the respective inner electrode connector extensions, and cut (e.g., subsequently) at an interface with the connector shell.

[0278] Clause 97. A method according to any one of clauses 92-96, wherein the inner electrode stack of plates and the inner electrode connector set of plates are diffusion bonded together in a common stack to provide the inner electrode structure and the inner electrode connector structure in a compound outer structure.

[0279] Otherwise, it may be that the inner electrode stack is diffusion bonded to provide the inner electrode structure separately from the inner electrode connector set of plates being diffusion bonded to provide the inner electrode connector structure, and the structures may be bonded by a separate process to form the compound outer structure. For example, the separate process may be a further diffusion bonding process, or any suitable bonding process, for example vacuum brazing.

[0280] Clause 98. A method according to any one of clauses 87-87, wherein each plate of the inner electrode stack of plates comprises: an intermediate shell region comprising an array of cut-outs in the first pattern; and a plurality of wall regions in the first pattern, each wall region disposed within a respective cut-out of the shell region and spaced apart from the shell region by a gap, each wall region corresponding to a slice of an inner electrode; wherein each wall region is structurally connected to the intermediate shell region by one or more intermediate support tabs; whereby the array of inner electrodes is provided as part of an intermediate inner electrode structure comprising the array of inner electrodes each structurally connected to an intermediate shell by a plurality of the intermediate support tabs; the method further comprising: removing the intermediate support tabs between the intermediate shell and the array of inner electrodes of the intermediate inner electrode structure to separate the intermediate shell from the array of inner electrodes.

[0281] It may be that the intermediate support tabs of the intermediate inner electrode structure are removed by a cutting process using a cutting element extending through a gap extending along the longitudinal direction between the intermediate shell and the respective inner electrode in the intermediate inner electrode structure. The cutting process may be wire electrical discharge machining. It may be that the intermediate support tabs are cut at an interface with the respective inner electrodes, and cut (e.g., subsequently) at an interface with the intermediate shell.

[0282] When the array of inner electrodes is provided as a part of a compound inner structure as described herein, for example together with an inner electrode support structure and / or an inner electrode connector structure, it may be that the intermediate inner electrode structure forms part of the compound inner structure, with the intermediate shell of the intermediate inner electrode structure being removed from the compound inner structure following removal of the intermediate support tabs.

[0283] Clause 99. A method according to clause 98, wherein the support tabs of the intermediate inner electrode structure are removed by a cutting process using a cutting element extending through a gap extending along the longitudinal axis between: the intermediate shell and the respective inner electrode in the intermediate inner electrode structure.

[0284] Clause 100. A method according to clause 95 and also according to clause 99, wherein, when projected along the longitudinal direction onto a reference plane normal to the longitudinal direction, positions of the intermediate support tabs of the intermediate inner electrode structure do not overlap with positions of the electrical connection tabs of the inner electrode connector structure; optionally wherein positions of the intermediate support tabs overlap with positions of the connector support tabs for simultaneous cutting.

[0285] The cutting process may be wire electrical discharge machining. It may be that the intermediate support tabs and / or connector support tabs are cut at an interface with the respectiveinner electrodes or inner electrode extensions, and cut (e.g., subsequently) at an interface with the connector shell or intermediate shell.

[0286] Clause 101. A method according to any one of clauses 87 to 100, comprising: providing an inner outlet manifold stack of plates, stacked in the longitudinal direction and bonded to cooperatively define an inner manifold structure comprising an embedded inner outlet manifold to convey a fluid from an array of the inner chambers defined by the inner electrodes.

[0287] The inner outlet manifold stack of plates may be diffusion bonded to define the inner outlet manifold structure.

[0288] It may be that the inner outlet manifold structure is provided in addition to an any inner electrode connector structure and / or any inner electrode support structure, with the inner chambers defined by the inner electrodes extending through the inner electrode connector structure (when provided) and / the inner electrode support structure (when provided), for communication with the inner outlet manifold structure.

[0289] Clause 102. A method according to any one of clauses 86-101, comprising: providing an inlet stack of plates, stacked in the longitudinal direction and bonded to cooperatively define an inlet structure for the electrolyser comprising: an array of inlet plenums in the first pattern; a inlet manifold configured to convey a fluid to the array of inlet plenums; wherein each inlet plenum is configured to discharge the fluid into a respective inlet chamber.

[0290] Clause 103. A method according to clause 97, wherein the inlet structure further defines an array of flow straighteners each disposed between an inlet plenum and a respective inlet chamber.

[0291] Clause 104. A method according to any one of clauses 86-103, comprising: assembling an outer structure comprising at least the outer electrode structure with an inner structure comprising at least the array of inner electrodes in a joining process to provide an integral assembly within which the array of cells is defined; wherein the integral assembly is configured to electrically electronically isolate each outer electrode from the respective inner electrode.

[0292] Clause 105. A method according to clause 104, wherein assembling the outer structure with the inner structure includes providing a dielectric seal arrangement therebetween; optionally wherein the dielectric seal arrangement is provided around portions of the inner electrodes extending longitudinally beyond the respective outer electrodes, optionally longitudinally beyond the outer structure.

[0293] The dielectric seal arrangement may be configured to provide a fluid seal to prevent escape of fluid from the array of inlet chambers.

[0294] Clause 106. A method according to clause 104 or 105, wherein before assembly with the inner structure, the outer structure is a compound outer structure comprising the outer electrode structure and one or more of: an outer electrode support structure configured to structurally connect the shell of the outer electrode structure and the array of outer electrodes; an outer electrode connector structure configured to provide an electrical pathway to each outer electrode for coupling to a circuit; an outer outlet manifold structure comprising an embedded outlet manifold to convey a fluid from the array of outer chambers to an outlet port; optionally wherein stacks of plates defining the respective structures are diffusion bonded together in a common diffusion bonding process.

[0295] The outer electrode support structure may be provided by a method as described above in statements relating to an outer electrode support structure, and may include any of the features defined above in statements relating to an outer electrode support structure.

[0296] The outer electrode connector structure may be provided by a method as described above in statements relating to an outer electrode connector structure, and may include any of the features defined above in statements relating to an outer electrode connector structure.

[0297] The outer outlet manifold structure may be provided by a method as described above in statements relating to an outer outlet manifold structure, and may include any of the features defined above in statements relating to an outer outlet manifold structure.

[0298] Clause 107. A method according to any one of clauses 104-106, wherein before assembly with the outer structure, the inner structure is a compound inner structure comprising the array of inner electrodes and one or more of: an inner electrode support structure from which the array of inner electrodes extend; an inner electrode connector structure configured to provide an electrical pathway to each inner electrode for coupling to a circuit; an inner outlet manifold structure comprising an embedded outlet manifold to convey a fluid from the array of inner chambers to an outlet port; optionally wherein stacks of plates defining the respective structures for the compound inner structure are diffusion bonded together in a common diffusion bonding process.

[0299] The inner electrode support structure may be provided by a method as described above in statements relating to an inner electrode support structure, and may include any of the features defined above in statements relating to an inner electrode support structure.

[0300] The inner electrode connector structure may be provided by a method as described above in statements relating to an inner electrode connector structure, and may include any of the features defined above in statements relating to an inner electrode connector structure.

[0301] The inner outlet manifold structure may be provided by a method as described above in statements relating to an inner outlet manifold structure, and may include any of the features defined above in statements relating to an inner outlet manifold structure.

[0302] Clause 108. A method according to any one of clauses 104 to 107, wherein the outer structure and the inner structure are further assembled with an inlet structure in the joining process, the inlet structure defining an inlet manifold for fluid communication with each inlet chamber of the array of cells.

[0303] The joining process may be a common joining process to join the outer structure, inner structure and inlet structure (e.g. as opposed to sequential joining processes).

[0304] Clause 109. A method according to clause 108, wherein the joining process comprises vacuum brazing.

[0305] Clause 110. A method according to any one of clauses 105-109, comprising electrically coupling the array of outer electrodes and the array of inner electrodes in a series arrangement whereby each cell of the array of cells is connected in series.

[0306] It may be that pairs of outer electrodes and inner electrodes are electrically coupled using electrical connectors outside of the integral assembly.

[0307] Clause 111. A method according to any one of clauses 105-110, comprising providing the integral assembly within a pressure vessel.

[0308] Clause 112. A method according to clause 111, further comprising charging the pressure vessel to a vessel pressure higher than an operating pressure for the electrolyser.

[0309] Clause 113. A structure for an electrolyser, comprising an array of electrodes arranged in a first pattern and extending along a longitudinal direction.

[0310] Clause 114. A structure for an electrolyser, comprising: an array of electrodes arranged in a first pattern, each comprising a porous wall in accordance with any one of clauses 1-29.

[0311] Clause 115. A structure for an electrolyser according to clause 113 or 114, comprising a plurality of longitudinally-adjacent structures, including an electrode structure comprising the array of electrodes, and one or more of: a support structure configured to support the array of electrodes; a connector structure configured to define a plurality of electrode connection paths, each electrode connection path extending to a respective subset of the electrodes of the array; an outlet manifold structure comprising an embedded outlet manifold to convey a fluid from an array of chambers, each associated with an outlet side of a respective electrode.

[0312] The longitudinally-adjacent structures may be bonded together, for example by diffusion bonding. Each of the longitudinally adjacent structures may be formed of a plurality of bonded stacked plates, for example as diffusion bonded together.

[0313] Clause 116. A structure according to clause 115, comprising the connector structure configured to define a plurality of electrode connection paths, each electrode connection path extending to a respective subset of the electrodes of the array; wherein the connector structure defines a layered arrangement of electrode connection paths, each electrically electronically isolated from the other by intervening layers of a dielectric material.

[0314] The dielectric material may be a dielectric material as described elsewhere herein (e.g., a ceramic dielectric material, for example silicon carbide or a ceramic metal oxide). Example dielectric materials and coatings, and related application techniques, are described elsewhere herein.

[0315] Clause 117. A structure according to clause 115 or 116, comprising the support structure configured to support the array of electrodes; wherein the support structure comprises a dielectric material to electrically electronically isolate the support structure from the array of electrodes.

[0316] Example dielectric materials and coatings, and related application techniques, are described elsewhere herein. The dielectric material may be a dielectric material as described elsewhere herein (e.g., a ceramic dielectric material, for example silicon carbide or a ceramic metal oxide).

[0317] Clause 118. A structure according to any of clauses 113-117, comprising a shell structure defining an array of cavities in the first pattern, wherein each cavity receives a respective electrode of the array of electrodes.

[0318] Clause 119. A structure according to clause 118, wherein a support structure provides a structural connection between the shell structure and the array of electrodes; optionally wherein the structure is configured to electrically electronically isolate the shell structure from the array of electrodes.

[0319] Clause 120. A structure according to any of clauses 113-119, wherein there are two arrays of electrodes including an array of outer electrodes and an array of inner electrodes; wherein the structure comprises an outer structure comprising the array of outer electrodes, and an inner structure comprising the array of inner electrodes; wherein the outer structure and the inner structure cooperatively define an array of cells in the first pattern, each cell comprising: an inner electrode of the array of inner electrodes, defining an inner chamber; an outer electrode of the array of outer chambers, the inner electrode received within the outer electrode; an inlet chamber defined between the inner electrode and the outer electrode; and an outer chamber delimited by the outer electrode.

[0320] One or both of the arrays of electrodes (i.e., the array of outer electrodes and the array of inner electrodes) may have any of the features defined above with reference to clauses 113-119. One or both of the inner structure and the outer structure may have any of the features defined above with reference to clauses 113-119. The support structure may be as defined above in in clause 117.

[0321] Clause 121. A structure according to clause 120, further comprising an isolation arrangement disposed between the array of inner electrodes and the outer structure, configured to electrically electronically isolate the outer structure from the array of inner electrodes; optionally wherein the isolation arrangement is configured to provide a fluid seal between the inner structure and the outer structure.

[0322] The isolation arrangement may comprise any of the example dielectric materials as discussed elsewhere herein.

[0323] Clause 122. A structure according to clause 120 or 121, further comprising an inlet structure longitudinally adjacent to the outer chamber, defining an array of inlets in the first pattern for providing a fluid to the inlet chambers of the respective cells, and an embedded inlet manifold configured to provide fluid from a manifold inlet to the array of inlets.

[0324] Clause 123. A structure according to any one of clauses 120-123, wherein the outer structure, inner structure, and optionally any inlet structure, are bonded together to provide an integral body.

[0325] Clause 124. A structure according to any one of clauses 120-123, wherein the outer structure, inner structure, and optionally any inlet structure, are each formed as a bonded stack of plates.

[0326] Clause 125. A structure according to any one of clauses 120-124, wherein the outer structure and the inner structure are assembled so that the array of inner electrodes are received in the array of outer electrodes; wherein the array of inner electrodes extends longitudinally beyond the array of outer electrodes to an inner electrode support structure; wherein the outer structure comprises one or more of: an outer electrode support structure an outer electrode connector structure at a longitudinal position between the array of outer electrodes and the inner electrode support structure.

[0327] Clause 126. A structure according to any one of clauses 120-125, wherein the array of outer electrodes and the array of inner electrodes are connected in series by a set of electrical connections; optionally wherein the set of electrical connections extend out of an assembly of the outer structure and the inner structure.

[0328] Clause 127. A structure according to any one of clauses 120-126, comprising a pressure vessel configured to house an assembly of the outer structure and the inner structure within a pressurized environment.

[0329] References herein to performing continuous electrolysis refer to performance of electrolysis as an electrolyte fluid flows through the electrolyser - for example a continuous or replenishing flow of electrolyte fluid for a continuing electrolysis reaction.

[0330] The expression “subset” as used herein in relation to another set or plurality of elements (which may be referred to as a superset) may be a “proper subset” of the superset (i.e., containing fewer elements than the superset), or may be equal to the superset (i.e., containing all elements of the superset).

[0331] The controller(s) described herein may comprise a processor. The controller and / or the processor may comprise any suitable circuity to cause performance of the methods described herein and as illustrated in the drawings. The controller or processor may comprise: at least one application specific integrated circuit (ASIC); and / or at least one field programmable gate array (FPGA); and / or single or multi-processor architectures; and / or sequential (Von Neumann) / parallel architectures; and / or at least one programmable logic controllers (PLCs); and / or at least one microprocessor; and / or at least one microcontroller; and / or a central processing unit (CPU), to perform the methods and or stated functions for which the controller or processor is configured.

[0332] The controller may comprise or the processor may comprise or be in communication with one or more memories that store that data described herein, and / or that store machine readable instructions (e.g. software) for performing the processes and functions described herein (e.g. determinations of parameters and execution of control routines).

[0333] The memory may be any suitable non-transitory computer readable storage medium, data storage device or devices, and may comprise a hard disk and / or solid state memory (such as flash memory). In some examples, the computer readable instructions may be transferred to the memory via a wireless signal or via a wired signal. The memory may be permanent nonremovable memory, or may be removable memory (such as a universal serial bus (USB) flash drive). The memory may store a computer program comprising computer readable instructions that, when read by a processor or controller, causes performance of the methods described herein, and / or as illustrated in the Figures. The computer program may be software or firmware, or be a combination of software and firmware.

[0334] Except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except wheremutually exclusive, any feature described herein may be applied to any aspect and / or combined with any other feature described herein.BRIEF DESCRIPTION OF DRAWINGS

[0335] Aspects of the disclosure including an invention as claimed are described, by way of example only, with reference to the accompanying drawings, in which:

[0336] Figure 1a shows a cross-sectional view of an example flow arrangement for an electrolyser;

[0337] Figures 1 b-1f show cross-sectional views of example configurations of a porous wall for the flow arrangement;

[0338] Figures 2a-2c show cross-sectional views of further example configurations of a porous wall, comprising a passive region;

[0339] Figure 3a is a flow diagram of a method of manufacturing a porous wall;

[0340] Figure 3b schematically illustrates applicators for an electrocatalyst composition;

[0341] Figures 4a-4d show SEM (scanning electron microscopy) images of a side of the porous wall at various levels of magnification

[0342] Figure 4e is an image of a cross section of an example porous wall;

[0343] Figures 5a-5c schematically show portions of example stacked porous walls

[0344] Figures 6 and 7 schematically show example patterns of porous zones or flow zones for a stacked porous wall;

[0345] Figures 8 and 9 are flow diagrams of example methods of manufacturing a stacked porous wall;

[0346] Figure 10 schematically shows example an electrolysis installation comprising an electrolyser according to Figure 1a;

[0347] Figure 11 shows a cross-sectional view of an example multi-cell electrolyser;

[0348] Figure 12 schematically shows arrangements of longitudinally-adjacent structures of an example electrolyser;

[0349] Figure 13 shows a plate for a stack for forming an electrolyser;

[0350] Figures14a and 14b show cross-sectional views of example stacks of plates for a structure for an electrolyser;

[0351] Figure 15a schematically shows a normal view of plates for an electrode connector structure, and Figure 15b shows a partial cutaway perspective view of plates for an electrode connector structure;

[0352] Figures 16a and 16b show exploded and assembled views of plates for an example electrode connector structure.

[0353] Figure 17a and 17b show perspective views of porous walls within a structure for a multicell electrolyser (17a) and in isolation (17b);

[0354] Figures 18a-18d show exploded and assembled views of structures for an electrolyser;

[0355] Figures 19 and 20 show cutaway perspective views of an outer structure and an inner structure for an electrolyser at progressive longitudinal positions;

[0356] Figure 21 schematically shows an example electrolyser;

[0357] Figures 22 and 23 are flow diagrams of example methods of manufacture; and

[0358] Figures 24 and 25 are full and partial perspective views of an applicator jig.DETAILED DESCRIPTION OF THE INVENTION

[0359] Figure 1a schematically shows an example flow arrangement 100 for an electrolyser having first and second porous walls. Figures 1b to 1d show example configurations of the porous walls.

[0360] The flow arrangement 100 comprises an inlet chamber 102 which in this example is an annular chamber 102 having a central longitudinal direction A, and is elongate along the longitudinal direction A. The inlet chamber 102 is configured to receive an annular inlet flow at an annular inlet 101. In this example, various structures are axisymmetric with respect to the longitudinal direction A, which may be referred to as a longitudinal direction A of the flow arrangement.

[0361] The flow arrangement 100 further comprises first and second outlet chambers 130, 140 which are separated from the inlet chamber by the first and second porous walls 110, 120 respectively. In this example, the first outlet chamber 130 is an inner central chamber radially within and surrounded by the inlet chamber 102, and the second outlet chamber 140 is an outer annular chamber radially outside of and surrounding the inlet chamber 102. Each of the first and second outlet chambers are concentric with and elongate along the longitudinal direction A.

[0362] The flow arrangement is generally elongate and has a proximal end (or inlet end) corresponding to the inlet 101 which is to receive a fluid flow, and a distal end (or outlet end) corresponding to outlets for discharging flow (to be described). Various components of the flow arrangement (and of related apparatus such as an electrolyser) may be described with reference to their proximal and distal ends (or interchangeably at the inlet and outlet ends) according to the same frame of reference.

[0363] The inlet chamber 102 is open at its proximal end at the inlet 101 , and is closed at its distal end 104. Accordingly, the flow arrangement 10 is configured so that the only inlet to the inletchamber 102 is the inlet 101, and the only routes for flow out of the inlet chamber 102 is via one or both of the porous walls 110, 120.

[0364] The first outlet chamber 130 is closed at a proximal end and defines a first outlet 132 at or towards its distal end. The first outlet chamber 130 may extend beyond a longitudinal extent of the first porous wall 110 (or beyond a longitudinal extent of the first porous wall 110 which is configured to provide flow to the first outlet chamber), as schematically shown with extension lines in Figure 1. The first outlet chamber 130 is configured to only receive flow via the first porous wall 110, and to only discharge flow through the first outlet 132.

[0365] While the first outlet chamber 130 is shown as cylindrical in this example, it may have any other suitable configuration, for example it may be annular or conical, or non-axisymmetric as further described below.

[0366] The second outlet chamber 140 is closed at a proximal end and defines a second outlet 142 at or towards its distal end. The second outlet chamber 140 may extend beyond a longitudinal extent of the second porous wall 120 (or beyond a longitudinal extent of the second porous wall which is configured to provide flow to the second outlet chamber), as schematically shown with extension lines in Figure 1.

[0367] While the second outlet chamber 140 is shown as annular in this example, it may have any other suitable configuration, for example having a non-cylindrical radially-outer wall, or a non-axisymmetric configuration as described below.

[0368] The example flow arrangement 10 further comprises an inlet flow distributor 150 configured to provide an annular flow of fluid to the annular inlet 101 of the inlet chamber 102. In this example, the flow distributor 150 has a diverging conical profile configured to direct the fluid around a flow diverter 152, but in other examples any suitable configuration may be adopted. The flow distributor has a port 154 for coupling to a source of fluid. In variant examples, the flow distributor 150 may take any suitable shape or configuration, for example it may have cylindrical outer walls and there may be a conical flow diverter within the flow distributor to direct flow towards the annular inlet 101.

[0369] The first and second porous walls 110, 120 are each elongate along a respective longitudinal direction, which in this example is the longitudinal direction A of the flow arrangement 100. The first and second porous walls 110, 120 each have a thickness direction from an inlet side adjacent to the inlet chamber 102 and an outlet side adjacent to the respective outlet chamber 130, 140.

[0370] An example of flow through the flow arrangement will now be described. A fluid (for example an electrolyte fluid) is received from a fluid source (e.g. a source of an electrolyte fluid)at the port 154 and flows through the flow distributor 150 to the inlet 101 to the inlet chamber 102. The inlet chamber 102 has no flow outlets other than through the porous walls 110, 120. In use, branch flows from the inlet chamber 102 to the respective outlet chambers 130, 140 become established, each branch flow passing through a respective porous wall 110, 120. Each outlet chamber 130, 140 only has a single inlet in the form of the respective porous wall 110, 120, and has an outlet 132, 142 (e.g. a single outlet). Accordingly, in each outlet chamber flow passes from the respective porous wall 110, 120 along the outlet chamber in a generally longitudinal direction, and is discharged at the outlet.

[0371] Further features regarding mechanisms for inhibiting reverse flows through the porous walls (i.e. from an outlet chamber 130, 140 to the inlet chamber 102) are discussed below. An example use of the flow arrangement in an electrolyser is discussed below, following discussion relating to an electrolysis reaction.

[0372] As shown in Figure 1b, in a first example, the first and second porous walls 110, 120 each have an isotropic porous configuration, being formed of an isotropic porous medium having a porosity to permit fluid to flow therethrough, from the inlet side to the outlet side. The expression “porosity” as used herein refers to an open porosity of a component (e.g. the volume fraction that is open for fluid flow therethrough). A suitable test or procedure for determining a porosity is described elsewhere herein. By way of example, Figure 1b shows the example of flow through the first porous wall 110 from the inlet chamber 102 to the first outlet chamber 130, but is equally applicable and representative of flow through the second porous wall 120 from the inlet chamber 102 to the second outlet chamber 140.

[0373] As used herein, the expression “isotropic porous medium” relates to a porous medium in which the porosity does not significantly vary by an order of magnitude according to the direction of measurement. The porosity may locally vary, for example it may be defined by a structure of fused granular or particulate elements having a distribution of characteristic dimensions and defining open spaces between them, but without a directional configuration as to their arrangement which significantly biases flow in a particular direction (e.g., by an order of magnitude) within the medium.

[0374] In isolation (e.g. when not provided in a flow arrangement which may bias flow in a particular direction), the isotropic porous wall is configured to permit flow in any direction therethrough. Accordingly, the local direction of flow at any point in the isotropic porous wall is determined by local pressure gradients, and the relative flow resistance offered by different routes through a network of flow paths defined by the isotropic porous wall.

[0375] In the example flow arrangement 100, fluid is caused to flow across (i.e. , through) each porous wall 110, 120 by virtue of a pressure difference between the fluid in the inlet chamber 102 and the fluid in a respective outlet chamber 130, 140. The pressure difference acts to drive flow through the porous wall 110, 120 and this may generally be along the thickness direction 112, since the resistance offered by any particular path through a porous medium is a function of the length of the path, and the thickness direction 112 provides the shortest distance between the inlet and outlet sides of the porous wall. However, at each point along the isotropic porous wall, a particular local route taken through the network of flow paths may depend on local variations in the porosity, such that there are local routes through the isotropic porous wall which are tortuous, as shown by example routes 113.

[0376] As shown in Figure 1c, in a second example, the first and second porous walls 110, 120 each have an anisotropic porous configuration provided by a plurality of inclined channels 114 which extend through the respective wall from the inlet side to the outlet side. For the purposes of illustration, only the first porous wall 110 is shown, but the following description applies equally to both porous walls 110, 120. Each of the channels 114 is elongate along a path which is inclined with respect to both the longitudinal direction A and the thickness direction 112 of the respective porous wall, such that flow along the channels from the inlet chamber 102 to the respective outlet chamber has a longitudinal component.

[0377] As used herein, the expression “longitudinal component” refers to a component of a path being along the longitudinal direction A (i.e. parallel with it and of the same sign / direction). In the examples described herein, the longitudinal direction extends from the proximal end of the flow arrangement to the distal end, and so a definition that a path along which something is elongate has a longitudinal component requires that the path has a positive longitudinal component in the proximal to distal direction. As shown in Figure 1c, in this example the longitudinal direction A corresponds to a vertically upward direction, and each of the porous walls 112, 122 is inclined so that flow passing therethrough from the inlet chamber 102 to the respective outlet chamber 130, 140 flows along a path 115 having an upward component.

[0378] The expression “channel” as used herein relates to an open path for flow which is free of obstruction, delimited by bounding walls of the channel.

[0379] As shown in Figure 1d, in a third example, the firstand second porous walls 110, 120 each have a discontinuous porous structure, by which each porous wall comprises a body 116 and a plurality of porous regions 117 extending through the body from the inlet side of the body (adjacent to the inlet chamber) to an outlet side of the body (adjacent to the respective outlet chamber). For the purposes of illustration, only the first porous wall 110 is shown, but the following descriptionapplies equally to both porous walls 110, 120. Similarly, a flow arrangement may be implemented in which only one of the porous walls has a discontinuous porous structure as described herein.

[0380] The body 116 defines the overall profile of the porous wall 110, 120, being elongate along the longitudinal direction A, and having a thickness direction 112 from the inlet side to the outlet side.

[0381] The plurality of porous regions 117 extend through the body 116 at discrete locations to permit fluid to flow from the inlet chamber 102 to the respective outlet chamber 130, 140. Each porous region 117 defines a respective network of flow paths through the body (such that there is a plurality of discrete networks of flow paths through the body). In this example, each porous region 117 is elongate along a path through the body having a longitudinal component (which may be referred to herein as an “inclined discontinuous porous structure”). However, it is also envisaged that the porous regions may extend along a path through the body which does not have a longitudinal component (e.g. is orthogonal to the longitudinal direction).

[0382] Each porous region 117 is defined by a porous medium (i.e. a medium having open porosity). As in the example of Figure 1 b, a local route through the network of flow paths provided by a particular porous region 117 may be tortuous, and may depend on variations in the local porosity and the relative resistance to flow offered by different routes. Example tortuous routes are indicated by arrows 113’.

[0383] Although the third example porous wall 110 of Figure 1d is shown with the porous regions 117 extending throughout the full extent of the body along the thickness direction, in variant implementations the porous regions 117 may have an extent along the thickness direction which is less than the thickness of the body.

[0384] A fourth example is shown in Figure 1e, which is similar to the third example of Figure 1d but differs in the form of the porous regions owing to a method of manufacture from a plurality of stacked plates (as will be described separately below). In the fourth example of Figure 1e, the first and second porous walls 110, 120 each have a discontinuous porous structure, by which each porous wall comprises a body 116 and a plurality of porous regions 118 extending through the body from the inlet side (adjacent to the inlet chamber) to an outlet side of the body (adjacent to the respective outlet chamber). For the purposes of illustration, only the first porous wall 110 is shown, but the following description applies equally to both porous walls 110, 120. Similarly, a flow arrangement may be implemented in which only one of the porous walls has a discontinuous porous structure as described herein.

[0385] The description of the body 116 with respect to the third example of Figure 1 c also applies to the body 116 of the fourth example. The description of the porous regions 117 of the thirdexample of Figure 1d also applies to the description of the porous regions 118 of the fourth example, except for as follows.

[0386] In this example, each porous region 118 is substantially elongate along a path through the body having a longitudinal component (which may be referred to herein as an ’’inclined discontinuous porous structure”. However, it is also envisaged that the porous regions may extend along a path through the body which does not have a longitudinal component (e.g., is orthogonal to the longitudinal direction). For example, in an annular porous wall, a porous region may extend radially (e.g., through the thickness direction without necessarily extending along the longitudinal direction.

[0387] Each porous region 118 is defined by an array of staggered porous zones along the thickness direction corresponding to respective plates that are stacked to form the body. As such, the porous region 118 has a staggered profile along the thickness and longitudinal directions, as shown in Figure 1e.

[0388] As in the third example of Figure 1d, each porous region 118 is defined by a porous medium (i.e. a medium having open porosity), and a local route through the network of flow paths provided by a particular porous region 118 may be tortuous, with an example route indicated by the arrow 113’.

[0389] A fifth example is shown in Figure 1f, which differs from the fourth example of Figure 1e only in the extent of the porous region. In Figure 1f, the porous regions 119 have an extent along the thickness direction which is less than the thickness of the body (as also envisaged above regarding the third example of Figure 1d). Accordingly, the porous wall 110, 120 of the fifth example comprises a plurality of flow regions 119 which extend throughout the full extent of the body along the thickness direction, and each flow region 119 comprises a porous region 118 which occupies less than the full extent of the thickness direction. While the example of Figure 1f shows the porous region 118 located towards one side (e.g., the inlet side), the porous region 118 may be located anywhere along the flow region. When the porous region 118 extends throughout the full extent of the body along the thickness direction, the flow region 119 and the porous region are coterminous.

[0390] Any of the flow arrangements described above are suitable for implementing in an electrolyser, with each porous wall corresponding to (e.g. providing) a respective electrode of the electrolyser. The present disclosure envisages that two porous walls of the same flow arrangement may have any combination of the configurations described above with respect to Figures 1 b-1 f. It may be that at least one of the porous walls has a discontinuous porous structure in accordance with the examples of Figure 1d or 1e). When such a flow arrangement isimplemented in an electrolyser, fluid reaction products such as hydrogen or oxygen may be generated at respective electrodes defined by the porous walls.

[0391] By separating the inlet chamber 102 and the outlet chambers 130, 140 with respective porous walls 110, 120 as disclosed herein, each porous wall serves to (e.g. is configured to) inhibit a return flow of a respective fluid reaction product through the respective porous wall towards the inlet chamber, without relying on an ion exchange membrane. Such a return flow may also be described as a reverse flow herein. The porous walls are porous to permit fluid to flow therethrough, and also permit ion exchange in either direction to enable respective half-reactions of electrolysis. Accordingly, a flow arrangement as disclosed herein may be implemented in an electrolyser without use of an ion exchange membrane between respective electrodes, such as a polymer-electrolyte membrane, PEM.

[0392] By permitting fluid flow (e.g. of an electrolyte fluid) between the inlet chamber 102 and an outlet chamber 130, 140, the respective porous wall 110, 120 places the inlet chamber and the respective outlet chamber in fluid communication with each other, such that the pressures in the respective chambers are linked. As compared with arrangements which prevent fluid communication between such chambers, this may prevent an excessive pressure difference becoming established over any intervening wall / electrode / membrane, which may deform or otherwise damage such a wall / electrode / membrane and the integrity of the associated electrolyser. Such a risk of damage may be more pronounced when operating at high pressure, such as high pressure for operation at supercritical conditions (i.e. temperature and pressure at or above the supercritical point for the respective fluid). Accordingly, the provision of a porous wall to separate each outlet chamber from the inlet chamber may protect or improve the structural integrity of an electrolyser, particularly for high pressure operation.

[0393] The provision of a porous wall 110, 120 between the inlet chamber 102 and each outlet chamber 130, 140 provides a flow restriction to flow therethrough, such that fluid flow through the wall is associated with a pressure drop being established over the porous wall. A pressure drop and a flow rate of a fluid through a component are related to each other, and may also be dependent on properties of the component (e.g. its flow factor KV - which may be considered a constant) and properties of the fluid (e.g. the specific gravity SG). A pressure drop over the porous wall inhibits a return flow of a respective fluid reaction product through the porous wall towards the inlet chamber, because such flow would be against the pressure gradient over the wall.

[0394] An additional mechanism to inhibiting return flow may be provided when the flow arrangement comprises one or more porous walls in accordance with the second to fifth examples (described above with respect to Figures 1c -1f respectively).

[0395] In particular, in such arrangements, there may be a prevailing buoyancy-driven flow towards the or each outlet chamber. The buoyancy-driven flow may be biased to flow upwards owing to the relatively lower density of fluid reaction products. Accordingly, when an inclined channel 114 (second example), a porous region 117, 118 (third and fourth examples) or a flow region 119 comprising a porous region 118 (fifth example) is elongate along a path having an upward component, a return flow therethrough may be against the direction of a prevailing buoyancy-driven flow, and therefore inhibited.

[0396] By way of example, in an electrolysis reaction involving an aqueous electrolyte fluid, the fluid reaction products (oxygen and hydrogen) have a lower density that water (or any suitable electrolyte fluid), such that buoyancy forces on those fluid reaction products will tend to drive those fluid reaction products upward. When the respective reaction takes place within the inclined channels 114 of a porous wall having inclined channels (the second example of Figure 1c) or within the porous regions 117, 118 of a porous wall having an inclined discontinuous porous structure (the third to fifth examples of Figures 1 d-1 f), or when the reaction products are otherwise provided at such locations, the buoyancy forces acting owing to the lower density of the respective fluid reaction product may drive the flow upward and thereby along the respective inclined channel 114, porous region 117, 118 or flow region 119 towards the respective outlet chamber.

[0397] By providing the flow arrangement 100 with a porous wall according to any of the third to fifth examples (of Figures 1d - 1f), flow effects relating to (i) flow rate and (ii) reverse flow may depend on respective properties of the porous region. Firstly, a flow rate through the or each porous wall may be at least partly determined by properties of the porous regions 117, 118 other than the orientation of the path along which it extends, such as the porosity, cross-sectional area or diameter, and the length of the porous region. Such properties may be referred to herein as properties of the porous region 117, 118 relating to flow rate.

[0398] Secondly, by providing the porous regions 117, 118 or flow regions 119 so that they are elongate along a path having a longitudinal component (e.g. a vertical component in use) and therefore at an angle relative to the longitudinal direction, the routes through each respective network of flow paths are effectively constrained to extend along a path having a longitudinal component (e.g. within boundaries of the porous region which are oriented at an angle relative to the longitudinal direction). The porous regions 117, 118 or flow regions 119 may be configured so that a majority and optionally all (each and every) routes through the network of flow paths have a longitudinal component (e.g. irrespective of whether the route has a tortuous pathway through the porous region 117, 118 having local upward and / or downward components, it may have a net positive longitudinal component corresponding to the longitudinal direction of therespective porous wall). Accordingly, without having to specifically configure each flow path of the porous region to provide such a longitudinal component, this can nevertheless be achieved for the majority or optionally all (each and every) route through the porous region. Accordingly, a return flow through the porous region or flow region is inhibited as it would be against the direction of the prevailing buoyancy-driven flow. For example, each porous region 117, 118 or flow region 119 may be configured so that, with respect to the longitudinal position, an end of the porous region 117, 118 or flow region 119 at the outlet side is longitudinally spaced apart an end of the porous region 117 at the inlet side, with no overlapping longitudinal extend of the ends.

[0399] The flow effect of inhibiting a reverse-flow owing to buoyancy effects is related to properties of the paths along which the porous regions extend, for example the angle of the path relative to the longitudinal direction.

[0400] The porous medium of the porous regions 117, 118 may be formed or provided without control as to a directional orientation of the porous medium, and as such it may that the porous medium itself has a structure or porosity which does not significantly vary by an order of magnitude according to the direction of measurement. Within the boundaries of each porous region 117, 118 the porous medium may be substantially isotropically arranged, or may not be isotropic. In either case, it is considered that the porous medium of each porous region 117, 118 itself is not provided for the purpose of providing a directional bias itself, and instead it is considered that the profile or path of the porous region or flow region itself provides anisotropy to the porous wall, for example to provide any buoyancy-related effect for inhibiting a reverse flow.

[0401] In variants of any of the above examples, a flow arrangement as described above may not be axisymmetric. For example, a flow arrangement may comprise a rectilinear duct partitioned by porous walls into side-by-side inlet and outlet chambers (i.e. with a central inlet chambers and two outer outlet chambers).

[0402] Although the example flow arrangement of Figures 1a schematically shows first and second outlets 132, 142 at distal ends of the first and second outlet chambers, it will be appreciated that outlets from the outlet chambers may be provided at any suitable location. Nevertheless, the outlets may generally be longitudinally separated from the portion of the outlet chamber which receives flow through the respective porous wall.

[0403] An electrolyser may comprise a flow arrangement 100 as described above with reference to Figure 1a, with one or both of the porous walls 110, 120 having a configuration as described above with reference to any of Figures 1 b-1f, or a configuration as described below with reference to any of Figures 2a-2c. In such an electrolyser, each of the porous walls 110, 120 may provide a respective electrode for the electrolyser - i.e., an anode or a cathode. A configuration of anelectrolyser comprising the example flow arrangement 100 substantially corresponds to the configuration of the flow arrangement as described above, and as such Figure 1a is considered to show a configuration of an electrolyser 100.

[0404] While the description above primarily relates to the flow effects in the flow arrangement, the following further description of the electrolyser 100 of Figure 1a is provided in relation to the functionality and configuration of the porous walls 110, 120 as electrodes, with particular reference to any electrocatalytic regions and / or passive regions of the electrodes (to be described with reference to Figures 2a-2c).

[0405] It will be appreciated that the electrolyser 100 may be provided with further components in addition to those shown in Figure 1a, for example electrical connections (also known as electrical feed-throughs) to the electrodes provided by the porous walls.

[0406] Each of the porous walls 110, 120 may have an electrocatalytic region comprising an electrocatalyst for a respective half-reaction of electrolysis. In use, respective fluid reaction products of the electrolysis reaction are generated at the electrocatalytic regions. For example, in electrolysis of an aqueous electrolyte fluid to generate hydrogen and oxygen, hydrogen is generated at an electrocatalytic region of the cathode, and oxygen is generated at an electrocatalytic region of the anode. A wide range of materials are suitable as electrocatalysts, and a particular choice of electrocatalyst may depend on a selected electrolyte fluid. Example electrocatalysts and electrolyte fluids are discussed elsewhere herein.

[0407] The following disclosure relates to example configurations of the porous walls 110, 120 as described above to provide respective electrocatalytic regions and / or passive regions. The following disclosure refers to Figures 1 b-1d and Figures 2a-2c, which each show a first porous wall 110. However, it will be appreciated that the following disclosure is equally applicable to the second porous wall 120.

[0408] Figures 2a-2c show a sixth-eighth example configurations of the porous wall which correspond to the third to fifth examples of Figures 1d-1f respectively, but which differ in the provision of a passive region 202 on the inlet side of the porous wall adjacent to the inlet chamber 102. As discussed elsewhere herein, a passive region is configured to inhibit a respective halfreaction of electrolysis. The passive region may inhibit the respective half-reaction of electrolysis by virtue of being less electrocatalytically active than the electrocatalytic region for the respective half-reaction of electrolysis reaction, as described elsewhere herein.

[0409] The provision of a passive region (which may be formed by a passivating coating) defining the inlet side of the porous wall has the effect that the respective half-reaction of electrolysis is inhibited from occurring within the inlet chamber 102. Accordingly, the respective-half reaction ofelectrolysis may primarily occur when electrolyte fluid has passed through the passive region to reach the electrocatalytic region, thereby generating a respective fluid reaction product downstream of the passive region, with respect to a direction of flow through the respective porous wall. As discussed above, the porous walls disclosed herein have the effect of inhibiting a reverse flow of fluid reaction products, and as such the fluid reaction products are inhibited from flowing upstream to return to the inlet chamber 102. The body may define a passive region of the porous wall as discussed herein, for example the body may comprise (e.g. consist of) a material which is not electrocatalytically active for the respective half-reaction of electrolysis, or is less electrocatalytically active than the electrocatalytic region, such as a body of stainless steel 316 or titanium (e.g. to be coated with an electrocatalytic coating for example comprising nickel or platinum).

[0410] Example methods for applying a passivating coating include a submersion-based technique (e.g. dip coating), which may be suitable to apply before formation of the any channels through a body (where provided) in order to prevent the passivating coating flowing into the channels. However, for other techniques, such as CVD (chemical vapour deposition), it may be that a depletion effect associated with deposition of the passivating coating is such that there is only a limited penetration of the passivating coating onto walls of pre-formed channels, such that application after forming of the channels may be suitable (or after formation of any precursors to a porous region of the body, for example an open region through the body prior to application of a porous medium (e.g., electrocatalyst composition) to form the porous regions).

[0411] When a porous wall 110 (whether as anode or cathode) has a discontinuous porous structure according to the third to fifth examples of Figures 1 d-1f, an electrocatalytic region may be defined by (i) the porous regions 117, 118 (e.g. only) or (ii) the body 116 and the porous regions 117, 118. In the first alternative, the body may have a first material composition and may define a passive region of the porous wall (e.g. may comprise (e.g. consist essentially, consist of, or be) stainless steel 316 or titanium), whereas the porous regions 117, 118 may have a second material composition including an electrocatalyst for the respective half-reaction of electrolysis (e.g. nickel or platinum, with further suitable electrocatalysts described elsewhere herein), and thereby define an electrocatalytic region of the porous wall. An example method for forming the porous regions 117 with a different material composition is described below with reference to Figure 3a, and further example methods for forming the porous regions 118 with a different material composition is described below with reference to Figures 8-9 .

[0412] In the second alternative, the body may have a second material composition also including an electrocatalyst for the respective half-reaction of electrolysis, as discussed above.

[0413] Figures 2a-2c show sixth to eighth example configurations of the porous wall which corresponds to the third to fifth examples of Figure 1d-1f, but which differ in the provision of a passive region 202 on the inlet side of the porous wall adjacent to the inlet chamber 102. The passive region 202 may be provided as a passivating coating as described elsewhere herein, and may be applied before or after formation of the porous regions 117, 118 as described above. As noted above, example methods for forming a porous wall having a discontinuous porous structure are described below, and such methods describe formation of the passive region (which may comprise a passivating coating).

[0414]

[0415] To further illustrate the flow paths and locations of electrolysis reactions in an electrolyser 100 having the flow arrangement of Figure 1a and one or more porous walls according to any of the fourth to eighth examples of Figures 1d-2c, an example of use will now be described. The example of use will be described with reference to electrolysis with an electrolyte fluid which is a water-based (aqueous) electrolyte fluid (e.g. electrolyte solution), at supercritical conditions for flow through the respective electrodes, for example at pressure of 22.5 MPa and an inlet temperature of 375°C, although as discussed elsewhere herein, operation below supercritical conditions is also envisaged.

[0416] At supercritical conditions, a fluid behaves such that it does not have distinct liquid and gas phases. Supercritical electrolyte fluids may be advantageous for use in electrolysis, as compared with subcritical electrolyte fluids. In particular, supercritical fluids are completely miscible with each other, such that mixtures of fluids form a single phase with no phase boundary or surface tension between them. Therefore, when the reaction products are supercritical rather than gaseous as they are generated (e.g. by having a lower critical temperature and pressure than the electrolyte fluid, or the temperature and pressure otherwise being higher than the respective critical point), those reaction products are completely miscible with the electrolyte fluid. Accordingly, bubbles of reaction products do not accumulate on the surfaces of the electrodes. Such accumulation may otherwise inhibit the reaction by preventing local interaction between the electrolyte fluid and the electrode.

[0417] Further, it is known that a conductivity of an electrolyte fluid tends to be higher at elevated temperature and pressure (see for example the paper "High Pressure Electrolyte Conductivity of the Homogeneous, Fluid Water-Sodium Hydroxide System to 400°C and 3000bar", A. Eberz and E.U. Franck, Ber. Bunsenges. Phys. Chem. 99, 1091-1103 (1995) No. 9, in particular Table 2). Without wishing to be bound by theory, it is thought that a dissociation constant and conductivity of water increases as temperature and pressure rises. Further, a conductivity of an electrolyte oran electrolyte fluid (e.g. an electrolyte solution) is a function of pressure and temperature, with increasing conductivity being observed as pressure and temperature rise towards the critical point. Within the supercritical range (i.e. in the range of pressure and temperature conditions in which the temperature is at least the critical temperature for the fluid, and the pressure is at least the critical pressure for the fluid), conductivity may decrease with rising temperature at constant pressure. However, conductivity may increase within the supercritical range when pressure is increased. Accordingly, a concentration of electrolyte within an electrolyte solution may be reduced by operating at relatively high temperatures and pressures. The supercritical range is an example of relatively high pressure and temperature conditions, and it is considered that operation in the supercritical range may provide a relatively higher conductivity of an electrolyte fluid as compared with operation within the subcritical range at temperatures and pressures significantly below the critical temperature and critical pressure. By operating at conditions such that the conductivity of an electrolyte fluid is higher, ohmic losses associated with the electrolyte may be reduced, or otherwise a different electrolyte that is associated with reduced ohmic losses may be used, while still providing a suitable conductivity.

[0418] By way of example only, a suitable electrolyte fluid for use with the example electrolyser 100 described above is an aqueous electrolyte solution comprising NaOH as electrolyte (with further suitable electrolyte fluids being disclosed elsewhere herein). As stated above, conductivity of an electrolyte fluid tends to increase with temperature and pressure

[0419] To illustrate the above trend of conductivity increasing with pressure and temperature, reference can be made to the Eberz and Franck paper referred to above, according to which at 0.1 MPa and 25 °C an electrolyte composed of NaOH with a concentration of 17 wt% exhibits a conductivity of 0.4 S cm-1 whereas at 30 MPa and 400 °C, the electrolyte exhibits a conductivity of 1.3 S cm-1. It is estimated that, for a 0.5 M NaOH solution the conductivity at 22.5 MPa and 375 °C would be approximately 150-200 mS cm-1, whereas at 0.1 MPa and 25°C the conductivity may be approximately 100 mS cm-1.

[0420] As an example of a suitable electrolyte fluid for use with the example electrolyser 100, the electrolyte fluid may comprise an aqueous solution comprising NaOH at a concentration of 0.5 M NaOH.

[0421] In this example, the first porous wall 110 is configured as a cathode (for hydrogen generation) and the second porous wall is configured as an anode (for oxygen generation), (by virtue of respective electrical configuration of the electrolyser), but in other examples this may be inverted.

[0422] As discussed above with respect to the general flow paths through the flow arrangement 100 of Figure 1a, when the electrolyte fluid is provided to the inlet chamber 102 via the inlet 101, branch flows through the respective porous walls (electrodes) 110, 120 to the respective outlet chambers 130, 140 become established.

[0423] As the flow passes through an electrocatalytic region of each porous wall, a respective half-reaction of electrolysis is conducted. In particular, the electrolyte fluid undergoes a reduction reaction as it passes through the electrocatalytic region of the first porous wall 110 (cathode) to generate a fluid reaction product which in this example is supercritical hydrogen, and the electrolyte fluid undergoes an oxidation reaction at the second porous wall 120 (anode) to generate a fluid reaction product which in this example is supercritical oxygen. Ions are transferred between the anode and cathode, for example by electromotive force. In this particular example, hydroxide ions (OH-) are transferred through the electrolyte fluid to the anode for generation of a fluid reaction product (oxygen) at the anode (along with transferring electrons to the anode).

[0424] In this example, the pressure and temperature conditions of the electrolyser are controlled such that both the electrolyte fluid and the respective fluid reaction products are in a supercritical state at the porous walls. As such, the fluid reaction products are considered to be completely miscible with the electrolyte fluid within the porous walls with no interface (e.g. bubble interface) forming therebetween, as discussed above.

[0425] When the electrocatalytic region of a respective porous wall does not define the inlet side of a respective porous wall, the respective half-reaction of electrolysis does not tend to take place at the inlet side of the porous wall and so the respective fluid reaction product does not tend to be generated within the inlet chamber.

[0426] For the example porous walls of Figures 1d-2c, each having a discontinuous porous structure as discussed herein, the electrocatalytic region may not define the inlet side of the porous wall by virtue of the electrocatalytic region being limited to the porous regions 117, 118 and the body 116 defining a passive region of the porous wall, and / or by virtue of there being a passive region defining the inlet side as in the sixth to eighth examples of Figures 2a-2c.

[0427] Accordingly, when the porous walls are in accordance with any of the third to eighth examples of Figures 1d-2c, the respective half-reactions of electrolysis do not tend to occur in the inlet chamber, but instead occur as the flow passes through the porous wall itself, and in particular through the electrocatalytic region. The location of the respective half-reaction of electrolysis is therefore downstream of the inlet chamber, with respect to the direction of the branch flows of fluid from the inlet chamber to the outlet chambers as described above.

[0428] For each of the example configurations of the porous walls described herein, a reverse flow of fluid reaction products generated within the porous wall is inhibited by virtue of being against a pressure gradient acting through the wall. This effect may be stronger with increasing pressure difference acting over the respective porous wall. The fluid reaction products are effectively entrained in a pressure-driven flow through the respective porous wall, which limits or mitigates migration or diffusion of the respective fluid reaction product in the reverse direction.

[0429] When the porous wall has an anisotropic configuration according to the third to eighth examples (e.g., with an inclined discontinuous porous structure having porous regions 117, 118), the flow paths through the porous wall (e.g. a majority or all of them) may be effectively constrained to have a longitudinal component, which in this example corresponds to a vertically upward component. Accordingly, buoyancy forces are considered to influence the flow as discussed above. The fluid reaction products each have a lower density than the electrolyte fluid, and therefore tend to establish a buoyancy driven flow through the respective porous wall and outlet chamber by which the flow preferentially flows upward. A reverse flow of the fluid reaction products is inhibited by virtue of the buoyancy effect, because flow along the reverse direction toward the inlet chamber would require the fluid reaction product to move against the prevailing buoyancy-driven flow, to flow downwards towards the inlet chamber.

[0430] In use at the supercritical conditions described above (22.5 MPa and 375 °C), the thermoneutral voltage for electrolysis is approximately 1 ,3V, which corresponds to 35.62 kWH per kg of hydrogen reaction product that is generated. This is 110% of the higher heating value of hydrogen (39.4 kWh per kg), and 93.5% of the lower heating value of hydrogen (33.3 kWh), and so is representative of efficient electrolysis. To maintain the electrolysis reaction at these conditions, the ohmic losses of the electrolyser should be no more than 0.120 V. In this example, the ohmic losses of the electrolyser (associated with ion exchange through the example electrolyte fluid of 0.5 M NaOH, having a predicted conductivity of about 150 mS cm-1) is approximately 0.11 V when the electrode spacing is 1mm, whereas ohmic losses associated with bubble formation at the electrodes is eliminated owing to operation at supercritical conditions. The electrode spacing may be less than 1mm, for example 0.5mm or between 0.5mm and 1mm. Suitable electrocatalysts may be determined by the skilled person and are discussed elsewhere herein, but merely as an example suitable electrocatalysts may comprise nickel or a nickel alloy at the anode (which may be the first electrode), and nickel, a nickel alloy or platinum for the cathode (which may be the second electrode).

[0431] The ohmic losses are a function of the electrolyte conductivity and the electrode spacing. For example, if the electrodes are spaced apart by 3mm then it may be that a higher electrolyte conductivity is required, such as 2000 mS cm-1.

[0432] While example supercritical conditions have been discussed above, the conditions may be varied. For example, supercritical operation of the electrolyser may correspond to operation so that the pressure of the electrolyte fluid is between 22 MPa and 27 MPa at the porous walls for an aqueous electrolyte fluid, and so that the temperature of the electrolyte fluid is at least 374°C at the porous walls for an aqueous electrolyte fluid, for example between 374-550°C or 374-400°C.

[0433] It may generally be desirable to operate to achieve lower temperatures and pressures towards the critical point at the porous walls, which may minimise energy resources to pressurise and to heat the electrolyte fluid. Ohmic losses may be lower at higher temperatures and pressures, but it is thought that efficiency advantages to be gained at elevated temperature and pressure conditions may be offset by the additional energy required to heat and / or pressurise the electrolyte fluid, unless such additional energy is available as surplus energy (e.g. as excess heat from a heating source that would otherwise be discharged without thermal recovery).

[0434] Although the above discussion focusses on examples in which each porous wall 110, 120 provides an electrocatalytic region to react with an electrolyte fluid as it passes through the respective porous wall for a respective half-reaction of electrolysis, the disclosure envisages implementations of the flow arrangement 100 in an electrolyser in which an electrode and / or an electrocatalytic region of a porous wall is only provided in an outlet chamber associated with a porous wall. For example, an electrode may be disposed in an outlet chamber and separated from the respective porous wall, or an electrocatalytic region may be disposed only on the outlet side of a respective porous wall to form an electrode. In such arrangements, the electrolyser is configured so that the respective half-reaction of electrolysis takes place in the outlet chamber (e.g. only).

[0435] By inhibiting reverse flows of the fluid reaction products, for example by any of the mechanisms described above, the inventors have found that the electrodes (e.g. porous walls) can be arranged with a relatively low separation gap between them (and without use of a membrane), which reduces ohmic losses in the electrolyser.

[0436] In particular, by inhibiting reverse flows, a flow through a porous walls as described herein may be substantially one-way, even if the area of the porous wall is relatively large for a given amount of flow (i.e. even when the flow rate per unit area through the porous wall is relatively low), as compared with previously-considered arrangements.

[0437] Consequently the separation gap between the electrodes can be made relatively slender, as the size of the electrodes can be relatively large compared to a cross-sectional area and / or separation gap defined by the inlet chamber.

[0438] In the particular example of the electrolyser 100 of Figure 1a, the co-extensive elongate extent of the electrodes is 100 mm, whereas the average shortest distance of separation is approximately 0.7mm, resulting in a ratio of approximately 140.

[0439] Figure 3a is a flow diagram of a method of manufacturing a porous wall for an electrolyser having a discontinuous porous structure, for example a porous wall according to the third example of Figure 1 d, or according to the fourth example of Figure 2a. The porous wall comprises a body and a plurality of porous regions. The method will be described by way of example with reference to the fourth example porous wall of Figure 2a (using reference numerals associated with Figure 2a).

[0440] In block 302, a body 116 for the porous wall is provided. In this example, the body 116 has a material composition corresponding to an electrocatalytic region of the porous wall, but in variant examples the body may have a material composition corresponding to passive region of the porous wall.

[0441] The body may have a shape and size corresponding to shape of the porous wall to be manufactured. It may be machined to conform to the shape and size. The dimensions of the porous wall may correspond to the example dimensions provided for (either of) the inner and outer electrode as specified in Table 2 below.

[0442] In this example, the body comprises (e.g. consists of) nickel or a nickel alloy. In this particular example, the body consists of a nickel-chromium alloy (in particular an Inconel® alloy, Inconel® 600).

[0443] In a variant example in which the body has a material composition corresponding to a passive region of the porous wall, the material composition of the body may be such that the body is less electrocatalytically active than the porous regions according to any definition herein, and as such the body may form a passive region of the porous wall once manufactured. For example, the body may have a material comprising (e.g. essentially consisting of, consisting of, or which is) stainless steel 316 or titanium.

[0444] In any case, the body has a material composition for conducting electrical current, such that the body is configured to conduct a current between an electrocatalytic region of the porous wall (as will be described below) and an electrical connection of an electrolyser, to thereby serve as an electrode of the electrolyser (e.g. an anode or cathode).

[0445] Optionally in block 304, a passivating coating (e.g. a dielectric coating) is applied to a side of the body to define a passive region 202 of the porous wall. In this example, the body material composition is electrocatalytic and so a passivating coating is applied. In a variant example in which the body has a material composition corresponding to a passive region of the porous wall, the porous region corresponding to the body and a passive region corresponding to the passivating coating may be considered as first and second passive regions, each less electrocatalytically active than the porous regions according to any definition herein.

[0446] The passivating coating may be applied by any suitable process, for example a sputtering process such as magnetron sputtering, a chemical vapour deposition (CVD) process, or a dipping process. A side of the body may be masked to prevent coating with the passivating coating (e.g. the outlet side of the body). Optionally, the passivating coating may be applied to both sides of the body (i.e. both the inlet and outlet sides, without masking of either side).

[0447] In block 306, open regions are formed at discrete locations extending through the body to provide the body with an anisotropic porous structure. The open regions correspond to the porous regions 117 to be formed in the body 116. The open regions are therefore formed so that they are elongate along a path through the body having a longitudinal component, as described above with respect to the porous regions 117. The open regions are formed by removing material from the body, for example using a laser drilling process.

[0448] The open regions may be formed with an average cross-sectional diameter along their length of 25-250 pm, for example 50-250 pm, 50-150 pm, 70-150pm, or approximately 120 pm, and may have a generally circular cross section normal to the paths along which they are each respectively elongate.

[0449] The open regions may be formed to have a midpoint diameter of 25-250 pm, for example 25-100 pm, 25-80 pm, or 25-50 pm.

[0450] The open regions may be formed to have an inlet diameter of 25-250 pm, for example 50-250 pm, 50-150 pm, 70-150 pm, or approximately 120 pm.

[0451] The open regions may be formed to have an outlet diameter of 25-250 pm, for example 50-250 pm, 50-150 pm, 70-150 pm, or approximately 120 pm.

[0452] The open regions may be formed to have an average cross-sectional area of 10,000-250,000pm2, for example 15, 000-250, 000pm2, 15, 000-150, 000pm2, 20, 000-150, 000pm2, 50,000-150, 000pm2, or approximately 100,000 pm2. The average cross-sectional area is determined as the volume of the open region divided by the extent of the open region along the thickness direction of the body.

[0453] An example of suitable laser drilling equipment is a "Lasertec 50 Powerdrill" available from DMG Mori Seiki Co., Ltd of Japan, or a high-power ultra-short pulse laser available from Amphos GmbH of Germany (e.g. the "Amphos 2302" or "Amphos 3000" series laser). A further example of suitable laser drilling equipment is the series of machines available from IPG Photonics of the USA referred to as QCW Fiber Lasers (Quasi Continuous Wave Laser) - operable in both pulsed and continuous wave modes, for example to generate pulses from 4-joule to 200-joule at various pulse frequencies e.g. from 100Hz to 5kHz).

[0454] A suitable laser drilling process may be ultrashort-pulse laser drilling (also known as laser micromachining), with ultra-short laser pulses being in the order of pico or femtoseconds, such as 10ps, or from 0.1 ps to 10ps. Such machining processes are discussed in the publication with reference Aizawa, Tatsuhiko & Inohara, Tadahiko; (2019); Pico- and Femtosecond Laser Micromachining for Surface Texturing; 10.5772 / intechopen.83741, also available at: https: / / www.intechopen.com / books / micromachining / pico-and-femtosecond-laser-micromachining-for-surface-texturing

[0455] In block 308, the method comprises applying an electrocatalyst composition to the body so that it flows into the open regions.

[0456] The electrocatalyst composition is a composition which comprises (e.g. consists essentially of, consists of, or is) an electrocatalyst for the respective half-reaction of electrolysis. For example, the electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a mixture of the electrocatalyst for the respective half-reaction of electrolysis and a liquid. The electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a slurry comprising the electrocatalyst for the respective half-reaction of electrolysis and a liquid. The electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a suspension of the electrocatalyst for the respective half-reaction of electrolysis in the liquid. The electrocatalyst may be provided in the form of a particulate. The suspension may be a colloidal suspension (e.g. of the particulate in the liquid). For example, the electrocatalyst composition may comprise (e.g. be, consist essentially of, or consist of) a sol (i.e. a solid-in-liquid colloidal suspension), a conductive ink (i.e. a suspension of electrically conductive electrocatalyst particles in liquid), or paste (i.e. a solid-in-liquid suspension having a sufficiently high solids contents that the suspension behaves as a solid in response to low applied stresses) comprising the electrocatalyst for the respective half-reaction of electrolysis. The liquid, for example a solvent, may influence a viscosity of the electrocatalyst composition. In addition to the electrocatalyst and the liquid, the electrocatalyst composition may comprise binder (e.g. polymericbinder such as a resin binder) and / or one or more additives. Example electrocatalyst compositions are discussed below and elsewhere herein.

[0457] The electrocatalyst composition may be applied to the body by any suitable method.

[0458] By way of example, the electrocatalyst composition may be applied on to a surface of the body and scraped (e.g. dragged over) over the surface in an application direction parallel with the longitudinal direction of the body. The application direction (i.e. forward or backward along the longitudinal direction) may be selected so as to promote directing the electrocatalyst composition into the open region, which may differ depending on the side of the body to which the electrocatalyst composition is applied. For example, when the open regions are elongate along a path towards a side of the body corresponding to the outlet side of the porous wall, and the path is at an angle of 70° relative to the longitudinal direction of the body, the application direction would be forward along the longitudinal direction if applying the electrocatalyst composition on a side of the body corresponding to the inlet side of the porous wall, and backward along the longitudinal direction if applying the electrocatalyst composition on a side corresponding to the outlet side of the porous wall.

[0459] The electrocatalyst composition may be scraped (e.g. dragged over) the surface by an applicator, which may be a flexible applicator having a shape corresponding to a shape of the respective side of the body. When the body is substantially planar, the applicator may have a substantially rectilinear profile terminating at a linear applicator lip. When the body is substantially annular, the applicator may have a corresponding annular profile having a substantially circular lip. It will be appreciated that, for an annular body, the electrocatalyst composition may be applied from a radially outer or a radially inner direction. An applicator for radially outer application may comprise a frustoconical applicator inwardly tapering towards a lip, and configured to slide over the body along the longitudinal direction. An applicator for radially inner application may comprise a frustoconical applicator outwardly tapering towards a lip and configured to slide through the body along the longitudinal direction, in a plunger action.

[0460] Application of a vacuum to one side of the body may assist penetration of the electrocatalyst composition into the open regions at the opposing side of the body. For example, when the electrocatalyst composition is applied from a radially outer direction to an annular body, a vacuum may be applied to the interior of the body to draw the electrocatalyst composition into the open regions at the exterior of the body. Alternatively, when the electrocatalyst composition is applied from a radially inner direction to an annular body, a vacuum may be applied to the exterior of the body to draw the electrocatalyst composition into the open regions at the interior of the body.

[0461] Excess electrocatalyst composition may be removed by a scraper blade, which may have a similar configuration to the applicator but differ by virtue of being relatively less flexible (i.e. having a higher flexural rigidity), such that it is configured to remove excess electrocatalyst rather than flex to direct it into to the open regions.

[0462] Figure 3b shows an example applicator for a cylindrical porous wall 110 having a porous longitudinal extend 111. The applicator comprises two opposing plungers 309, 309’ which are configured to be slidingly and sealingly inserted into opposing ends of the porous wall 110 to compress an electrocatalyst composition therebetween, thereby driving the electrocatalyst composition under pressure to flow into the open regions of the porous wall 110 from the radially inner side (e.g. the outlet side in the case of the first porous wall 110) to the radially out outer side (e.g. the inlet side in the case of the first porous wall 110). The applicator may be used for either porous walls to ensure that the electrocatalyst flows through and occupies the open regions throughout the extent of the body along the thickness direction. One of the applicators 309, 309’ may be removed and the other driven through the longitudinal extent of the porous wall 110 to remove excess electrocatalyst composition from an interior of the porous wall. As shown in Figure 3b, it may be that at least one of the applicators 309, 309’ has a conical end configured to mate (e.g. abut with) the opposing applicator. It may be that an amount of electrocatalyst composition is dosed into the porous wall such that mating between the applicators corresponds to having applied sufficient relative movement to drive the electrocatalyst composition through each of the open regions of the porous wall 110.

[0463] Referring back to Figure 3a, at block 310, the method optionally comprises a drying operation in which the electrocatalyst composition as applied to the body is dried to vaporise (e.g. partially) a liquid component of the electrocatalyst composition. Parameters of a drying operation may be suitably adjusted to achieve a suitable consistency of the electrocatalyst composition for heat treatment (e.g. sintering) at block 312. Such parameters may depend on ambient and conditions (e.g. humidity). By way of example, a drying operation may be conducted at a temperature between 80°C - 120°C for a period of 1-4 hours, for example for 2 hours at 120°C. By way of another example, the drying operation may be conducted at a temperature between 100°C and 300°C fora period of 1-4 hours, for example for 2 hours at200°C. The drying operation may be conducted by placing the body in a drying oven or on a hot plate, for example.

[0464] At block 312, a heat treatment (e.g. sintering) operation is conducted in which the body and the applied electrocatalyst composition is subjected to heat, thereby vaporising a liquid component of the electrocatalyst composition and causing a solid (e.g. particulate) component of the electrocatalyst composition to form a porous region of material (e.g. comprising connected(e.g. sintered or partially fused) granular or particulate elements) comprising an electrocatalyst for the respective half-reaction of electrolysis. The porous region thereby occupies the open region, forming the porous region 117 of the body as described above with respect to the third and fourth examples of Figures 1d and 2a respectively.

[0465] It has been observed that such heat treatment results in the solid electrocatalyst component occupying and bridging across (i.e. extending diametrically across) the open region to form a porous medium.

[0466] It may be that the porous medium has an extent along the thickness direction which is less than an extent of the body. For example, this may result from the electrocatalyst composition penetrating part way through a respective open region during application.

[0467] The heat treatment (e.g. sintering) operation may be conducted by placing the body (with applied electrocatalyst composition) in a temperature controlled environment to subject the body to a treatment temperature over treatment time. The temperature controlled environment may be an interior chamber of a heater, such as an oven, or a muffle furnace (e.g. as available from Carbolite Gero, a group company of the Verder Group (Verder International B.V. of Germany)).

[0468] The heat treatment (e.g. sintering) operation may be conducted by ramping up a treatment temperature over a ramp phase of the treatment time. For example, the treatment temperature may be ramped to a peak temperature of between 150°C-1000°C. For example, the peak temperature may be between 250°C and 800°C, between 300°C-600°C, between 300°C-450°C, for example approximately 350°C. In another example, the peak temperature may be between 600-1000°C, for example between 700-1000°C, or between 800-1000°C, or between 900-1000°C, or between 900-950°C, for example approximately 930°C.

[0469] The treatment temperature may be ramped up to the peak temperature from a starting temperature, which may be an ambient (e.g. room) temperature, for example 20°C, or a starting temperature of the heater, such as 30°C. The ramp rate may be between 0.5°C-2°C per minute, for example approximately 1°C per minute. The heat treatment (e.g. sintering) operation may comprise maintaining the treatment temperature at the peak temperature for a dwell phase of the treatment time, for example a dwell phase of between 1-10 hours, for example between 1-8 hours, or 1-6 hours, or 1-4 hours, or approximately 1 hour, or approximately 2 hours, or approximately 4 hours, or approximately 6 hours, or approximately 8 hours.

[0470] It will be appreciated that, in some embodiments, sufficient drying of the electrocatalyst composition may take place during the heat treatment (e.g. sintering) operation itself, such that a separate drying operation (i.e. block 310) is not necessary. In such embodiments, the body maybe subjected to one unitary heating operation which combines drying and heat treatment of the electrocatalyst composition.

[0471] The mechanism for forming the porous region of material during the heat treatment operation may depend on the nature of the electrocatalyst composition, the treatment temperature and the treatment time. It may be that particles of electrocatalyst sinter or fuse with one another during the heat treatment operation, for example, by diffusive processes. It may be that a component (e.g. a polymeric binder) of the electrocatalyst composition melts and / or cures during the heat treatment operation, thereby binding particles of electrocatalyst to one another. It may be that a chemical reaction (e.g. oxidation) takes places during the heat treatment operation, thereby forming a reaction product (e.g. oxide) which binds particles of electrocatalyst to one another.

[0472] In trials of the method using an electrocatalyst composition comprising particulate nickel, it was found that peak treatment temperatures in excess of 400°C, when the heat treatment is carried out in an oxidising atmosphere, may result in disadvantageous oxidation of the electrocatalyst to generate excess quantities of nickel oxide. However, such oxidation effects may be avoided by performing the heat treatment operation in a controlled atmosphere substantially free of oxygen (e.g. an inert or reducing atmosphere), for example an atmosphere comprising (e.g. consisting of) argon or nitrogen and / or hydrogen (e.g. a mix of 95 wt% nitrogen and 5 wt% hydrogen). It will be appreciated that the level of oxidation for a given electrocatalyst composition could be controlled by varying the treatment temperature, treatment time and / or the atmospheric composition.

[0473] The method may include one or more secondary heat treatment operations which are carried out subsequent to the primary heat treatment (e.g. sintering) operation at block 312. For example, the body may be placed in a temperature controlled environment to subject the body to a secondary treatment temperature over a secondary treatment time. The temperature controlled environment may be an interior chamber of a heater, such as an oven, or a muffle furnace (e.g. as available from Carbolite Gero, a group company of the Verder Group (Verder International B.V. of Germany)).

[0474] The secondary heat treatment operation may be conducted by ramping up a secondary treatment temperature over a ramp phase of the secondary treatment time. For example, the secondary treatment temperature may be ramped to a peak temperature of between 500°C-1500°C. For example, the peak temperature may be between 750°C and 1200°C, between 800°C-1000°C, between 850°C-950°C, for example approximately 930°C.

[0475] The secondary heat treatment operation may be conducted in a controlled atmosphere substantially free of oxygen (e.g. an inert or reducing atmosphere), for example an atmosphere comprising (e.g. consisting of) argon or nitrogen and / or hydrogen (e.g. a mix of 95 wt% nitrogen and 5 wt% hydrogen).

[0476] The secondary heat treatment operation may comprise (e.g. be) a stress-relief heat treatment operation intended to relieved weld stresses in the body. Additionally or alternatively, the secondary heat treatment operation may be a secondary sintering operation during which densification of the porous medium takes place, for example by grain boundary diffusion.

[0477] In some examples, the heat treatment operation is considered to comprise a first stage and a second stage. The first stage may be carried out to pyrolyze or burn off non-electrocatalyst components of the electrocatalyst composition such as binder components of the electrocatalyst composition, and may therefore be carried out in an oxidising atmosphere. The second stage may be carried out to sinter electrocatalyst-containing particles to one another, and may therefore be carried out in an inert (or reducing) atmosphere such as an atmosphere comprising (e.g. consisting of) argon or nitrogen and / or hydrogen. The first stage may be carried out with a peak temperature of between 150-500°C, for example between 200-500°C, or between 250-450°C, or between 300-500°C, for example approximately 300°C or approximately 350°C. The second stage may be carried out with a peak temperature of between 500-1000°C, for example between 600-1000°C, or between 700-1000°C, or between 800-1000°C, or between 900-1000°C, or between 900-950°C, for example approximately 930°C. The first stage may last for 2-10 hours, for example 4-8 hours, for example approximately 6 hours. The second stage may last for between 30 and 300 minutes, for example between 30 and 90 minutes, such as approximately 60 minutes.

[0478] Example Electrocatalyst Compositions

[0479] An example electrocatalyst composition is a mixture of a conductive ink available from Creative Materials Inc (of Massachusetts, USA) under the product name 116-25, with a solvent available from Creative Materials Inc under the product name 112-19.

[0480] Conductive ink 116-25 contains from 50 wt. % to 70 wt. % nickel particulate (CAS number 7440-02-0), from 30 wt. % to 50 wt. % non-polar ester solvent, from 5 wt. % to about 10 wt. % polymer resin and less than 2 wt. % carbon black (CAS number 1333-86-4). Conductive ink 116-25 contains greater than about 84 wt. % nickel following curing for 5 minutes at 125 °C. Conductive ink 116-25 has a specific gravity of about 2.21 (measured relative to water), a viscosityof about 25 Pa s, a boiling point greater than about 196 °C and a flash point greater than about 100 °C.

[0481] Solvent 112-19 is the same non-polar ester solvent found in the conductive ink 116-25. It has a boiling point greater than about 196 °C, a flash point of about 100 °C, an upper flammability limit of about 8 vol. % and a lower flammability limit of about 0.9 vol. %, a vapour pressure at 20 °C of about 0.3 hPa, a specific gravity of about 1.092 (measured relative to water) and an autoignition temperature of 370 °C.

[0482] By way of example, electrocatalyst compositions comprising variable amounts of the solvent (e.g. solvent 112-19) have been tested and found to provide a suitable viscosity for flowing into the open regions, with the remainder of the electrocatalyst compositions consisting of the conductive ink (e.g. 116-25).

[0483] Thermal Gravimetric Analysis (TGA) was performed on three such electrocatalyst compositions comprising 5 wt. %, 10 wt. % and 15 wt. % of solvent (112-19), with the remainder consisting of the conductive ink (116-25). The conductive ink and solvent were mixed by dual axial centrifugation (DAC) for 2 minutes at 2000 rpm to form the electrocatalyst compositions. The solids content of the samples ranged from approximately 60 wt. % (5 wt. % solvent) to approximately 40 wt. % (15 wt. % solvent). The viscosity for the respective samples ranged from approximately 5 Pa s (15 wt. % solvent) to approximately 13 Pa s (5 wt. % solvent). The solids content and viscosity values were determined by a rheometry evaluation method conducted at 25 °C using 40 mm parallel plates at a gap of 500 pm, at a shear rate of 1 1 / s. Values relating to the solids content and viscosity of the example electrocatalyst compositions are reported in Table 1 below.Table 1.

[0484] As an alternative to solvent 112-19, solvents 102-03 and / or 113-12 (also available from Creative Materials Inc) could be used to dilute the conductive ink.

[0485] Solvent 102-03 contains from about 90 wt. % to about 100 wt. % of a proprietary diluent and from about 0 wt. % to about 10 wt. % of 2-butoxyethyl acetate. Solvent 102-03 has a boiling point greater than about 190 °C, a flash point of about 90 °C (in a closed cup), a specific gravityof about 1.13 (measured relative to water), an auto-ignition temperature of greater than 400 °C, and a viscosity at 25 °C from about 12 Pa s to about 18 Pa s.

[0486] Solvent 113-12 contains greater than about 95 wt. % 2-butoxyethyl acetate. It has a boiling point of about 192 °C, a flash point of about 76 °C, an upper flammability limit of about 8.54 vol. % and a lower flammability limit of about 0.88 vol. %, a vapour pressure at 20 °C of about 0.29 mmHg, and a specific gravity of about 0.94 (measured relative to water).

[0487] Example Heat Treatment Results

[0488] Heat treatment (e.g. sintering) performance was tested by manufacturing a representative porous wall according to the manufacturing method described above with reference to Figure 3a.

[0489] In block 302, a body for the porous wall was provided, comprising a square planar portion of a nickel-chromium alloy (in particular an Inconel® alloy, Inconel® 600) having a longitudinal dimension of 50mm, a lateral dimension of 50mm, and a thickness dimension of 1mm.

[0490] In block 306, a pattern of open regions were formed in the body by a laser drilling process as described above. The open regions were formed through the full thickness of the body using a millisecond laser operating at 500 Hz. The open regions were formed so that they are elongate along a path which is at an angle of inclination relative to the longitudinal direction of 70°C (and thereby at an angle of 20°C relative to a thickness direction of the planar body). The open regions were drilled in laterally-offset rows to form a regular grid pattern with equal lateral and longitudinal pitch.

[0491] In block 308, an electrocatalyst composition corresponding to the example electrocatalyst composition described above (5 wt. % solvent variant) was applied using an applicator as described above.

[0492] In block 310, a drying operation was conducted, in which the body (and applied electrocatalyst composition) was maintained at 120°C for 2 hours on a high precision hot plate.

[0493] In block 312, a heat treatment operation was conducted to form a porous wall with porous regions extending through the body. The heat treatment operation was conducted using a muffle furnace, and consisted of a ramp phase at 1°C per minute to raise a treatment temperature from a starting temperature of 30°C to a peak temperature of 350°C, at which it was maintained for a dwell time of 3 hours.

[0494] Figures 4a-4d show SEM (scanning electron microscopy) images of a side of the porous wall at various levels of magnification, with scales indicated on the drawings ranging from 100 pm (Figure 4a) down to 10 pm (Figure 4d). Figure 4a shows ends of four porous regionsterminating at a side of the body. Figures 4b-4d show the porous medium within the porous region, showing a generally a porous structure formed by partially sintered (e.g. fused) granular or particulate elements (in this example, comprising nickel) defining open spaces between them. As can be seen from Figures 4b-4d, the spacing between granular or particulate elements appears to vary, but without a directional configuration of the various that might significantly bias flow in a particular direction.

[0495] Heat treatment (e.g. sintering) performance was tested in a further example. In this example, a square planar portion of a nickel-chromium alloy (in particular an Inconel® alloy, Inconel® 600) was coated with an electrocatalyst composition corresponding to the example electrocatalyst composition described above (5 wt. % solvent variant). A drying operation was conducted in which the plate (and applied electrocatalyst composition) was maintained at 120°C for 2 hours on a high precision hot plate. A two-stage heat treatment operation was then conducted as described above using a muffle furnace. In the first stage, conducted in an oxidising atmosphere, the plate was heated from room temperature at a rate of 5°C per minute to a peak temperature of 300°C, at which the plate was held for 6 hours. In the second stage, conducted in an argon atmosphere, the temperature was increased to 930°C, at which temperature the plate was held for a dwell time of 15 minutes. Figure 4e shows three subsequent SEM (scanning electron microscopy) images (a)-(c), obtained at 1000x magnification, of different regions of the porous medium formed on sintering of the electrocatalyst composition. The porous, sintered structure is evident.

[0496] Stacked Porous Walls

[0497] Aspects of the present disclosure relate to porous walls formed from a stack of plates, according to the examples of Figures 1e-f and 2b-c above. The third and fourth example porous walls of Figures 1d and 2a are previously-considered examples also disclosed in WO2022 / 195110.

[0498] Figures 5-9 relate to the configuration of a porous wall for an electrolyser (as described herein), in particular a porous wall comprising a plurality of stacked plates configured to define a body of the porous wall and a plurality of porous regions extending through the body. Such porous walls may be referred to herein as stacked porous walls, and may be used interchangeably with any of the example porous walls discussed in the examples and elsewhere herein (e.g. for example electrolysers or electrolysis installations). Such porous walls have initially been described with reference to Figures 1e-1f and 2b-2c, and further disclosure relevant to the methods of manufacture is provided below.

[0499] Figure 5a shows a cross section of an example stacked porous wall 2000 having a body which is elongate along a longitudinal axis A. The body has a thickness direction which is orthogonal to the longitudinal axis A and extends from a first inlet side of the porous wall to a second outlet side. In this example the stacked porous wall is an annular (e.g. cylindrical) porous wall having an axisymmetric profile about the longitudinal axis A. The stacked porous wall comprises a plurality of porous regions extending through the body at discrete locations, to permit a fluid to flow from the inlet side to the outlet side (e.g. from an inlet chamber to an outlet chamber of an electrolyser). The configuration of porous regions within the axisymmetric profile of the porous wall is not axisymmetric, since the porous wall has a discontinuous porous structure defined by the porous regions which are discretely and optionally non-symmetrically arranged around the porous wall, but the profile of the porous wall as defined by its inner and outer walls can be considered axisymmetric.

[0500] In Figure 5a, a longitudinal portion of the porous wall is shown, and the porous wall may extend further upward and downward (in the orientation shown in the drawing), as indicated by the dashed lines extending from upper and lower ends.

[0501] The body of the porous wall comprises (or is formed by) a plurality of plates 2002, stacked along a stacking direction to form the body. The stacking direction may be parallel with the longitudinal direction A, as shown in this example. The plurality of plates includes a set of porous plates 2004 through which one or more porous regions 2006 extend. In particular, each porous region is defined by a respective array of porous zones 2008 extending through a respective subset 2010 of adjacent plates of the plurality of porous plates. The porous zones of adjacent plates in the subset 2010 overlap along the thickness direction, thereby cumulatively defining the respective porous region 2006.

[0502] In the example of Figure 5a, each porous region 2006 is defined by a progression of porous zones 2008 of respective plates 2004, so that the porous region 2006 extends through the porous wall from the inlet side to the outlet side along a direction having an upward component. Each porous zone 2008 has an extent along the thickness direction which is less than the thickness of the respective plate, such that the porous region is only formed by a plurality of such porous zones defined in a plurality 2010 of adjacent stacked plates. In this example, each porous region 2006 is shown as formed by seven adjacent stacked plates, but in other examples this number may be more or less (e.g. at least three, at least four or at least five plates). In the cross-section of Figure 5a, a single porous region 2006 is defined by a respective subset 2010 of stacked plates, but it will be appreciated that additional porous regions 2006 may be defined by the same subset 2010 of stacked plates, for example at laterally or angularly offset locations ofthe porous wall (as will be further described with reference to Figures 6 and 7). Further subsets of plates defining respective porous regions may be longitudinally offset from each other and / or may overlap along the longitudinal direction.

[0503] Figure 5b shows a cross-section of a further example stacked porous wall 2020 which is similar to the example stacked porous wall 2000 as described above with respect to Figure 5a, but with porous regions 2006 defined at the same cross-sectional location which overlap along the longitudinal direction. As shown in Figure 5b, the respective porous plates which define the porous zones for these porous regions may comprise two or more discrete porous zones, separated along the thickness direction.

[0504] Figure 5c shows a corresponding cross-section of a further example stacked porous wall 2040 which is similar to the example stacked porous wall 2020 as described above with respect to Figure 5b, but with porous regions 2046 extending through less than the full thickness of the porous wall, such that each porous region 2046 forms part of a corresponding flow region 2045 which does extend through the full thickness of the porous wall (as in the example porous wall of Figure 1f described above), the remainder of each flow region 2045 being an open region 2047 (e.g., unobstructed by a porous medium). Within the individual stacks, there are flow zones 2049 corresponding to the respective flow regions 2045, which are either a porous zone (corresponding to the porous region) or an open zone (corresponding to the open region 2047) accordingly. The arrangement (i.e. , positional configuration) of the flow zones and flow regions in Figure 5c directly corresponds to the arrangement of the porous zones and porous regions in Figure 5b, and so both examples will be initially described together with any differing terminology for the examples provided as respective alternatives, before discussing the differences that arise. A set of plates comprising such flow zones for forming each flow region may be referred to as a through-flow set of plates (each having respective flow zones for flow regions as described above, as opposed to porous zones for porous regions), which otherwise directly corresponding to the porous set of plates as described above and below such that “porous set” and “through-flow set” may be applied interchangeably.

[0505] In each example porous wall 2020, 2040 of Figures 5b-5c, there is a repeating arrangement of patterns of porous zones 20061 flow zones 2049 at the respective cross-sectional location to define the porous regions 2006 I flow regions 2045. In each example, there is a repeating arrangement of three patterns of porous zones 20061 flow zones 2049 at the respective cross-sectional location, including a first pattern 2012 defining three porous zones I flow zones 2049 at the respective cross-sectional location, a second pattern 2014 defining two porous zones 2008 / flow zones 2049 at the respective cross-sectional location, and a third pattern 2016 definingtwo porous zones 2008 I flow zones 2049 at the respective cross-sectional location. The third pattern 2016 is identified in Figures 5b and 5c at a location longitudinally separated from the identified first and second patterns for clarity of the drawings, but it will be appreciated that the first, second and third patterns are arranged in sequence, in a repeating arrangement of adjacent plates, to define the respective porous regions 20061 flow regions 2045.

[0506] In the example of Figure 5c in particular, the flow zones 2049 of the respective stacks that define and correspond to a porous region 2046 are porous zones, and the flow zones 2049 that define and correspond to an open region 2047 are open zones. As discussed with respect to the example porous wall of Figure 1 f, within a flow region 2045, a porous region 2046 which does not extend through the full thickness of the body may be located anywhere along the flow region 2045, and in this example is shown at an intermediate location corresponding to the second to fourth stacks of each flow region (counting from bottom to top in the orientation shown in Figure 5c). A porous medium may be provided at such an intermediate location of the flow region 2045 by providing the porous medium only to the respective flow zones (porous zones) of a respective subset of the adjacent plates forming the flow region (e.g., to each plate individually or as a group), and not applying the porous medium to the flow zones (open zones) of the remaining plates of the subset of adjacent plates forming the flow region.

[0507] In each of the examples of Figures 5a-5c, each porous region 2006, 2046 defines a respective network of flow paths through the body - i.e., a network of flow paths through the respective porous region 2006, 2046 and discrete from the other porous regions. The porous regions 2006, 2046 may comprise an electrocatalyst as described with respect to the example porous walls discussed elsewhere herein, such that when provided in an electrolyser to provide an electrode, the porous regions define an electrocatalytic region of the respective electrode for an electrolysis half-reaction. The porous regions may each comprise a porous medium formed from an electrocatalyst-containing particulate, examples of which are described elsewhere herein.

[0508] It may be that the material composition of the porous regions 2006, 2046 differs from a material composition of the body. It may also be that the body comprises a passive region of the respective electrode to inhibit electrolysis, as described elsewhere herein. As also described elsewhere herein, the inlet side of the body may be defined by a passive region which is configured to be less electrocatalytically active than the electrocatalytic region, and the passive region may comprise a passivating coating defining the inlet side of the body to inhibit electrolysis.

[0509] The properties of the porous regions, any respective porous medium and any respective electrocatalyst or electrocatalytic region may be as described elsewhere herein including abovewith respect to any of the preceding example porous walls, for example with regards to the porosity of the porous regions (e.g. a porosity of between 0.2-0.9).

[0510] The plates forming the body may have any suitable material composition as described herein, including for example any material composition as disclosed above with respect to earlier examples in which a body is provided in a non-stacked configuration.

[0511] In variant examples, the regions of a stacked porous wall as described above may be substantially open, for example free of a porous medium contained therein to define a respective network of flow paths. Such regions may be referred to as open regions or open passages that extend through the body.

[0512] Figure 6 shows an example configuration of a portion 2100 of a porous plate 2004 as described above, as viewed normal to the respective stacking direction. The porous plate may have a greater lateral or angular extent than shown, as indicated by the dashed lines at either lateral (or angular) ends of the portion in Figure 6 (indicating a continued extent of the plate). Although the portion shown appears rectilinear in profile, this is considered to be representative of an angular segment of an annular plate, such as an annular plate of the stacked porous walls of the examples of Figures 5a or 5b.

[0513] Figure 6 shows porous zones 2102 of the plate distributed over the plate in a pattern. In this example the porous zones have a substantially circular profile, but in variant examples may have any suitable shape, for example elliptical. The plate may be manufactured with the porous zones already formed, or the porous zones may be formed by removing material from the plate, for example by a laser drilling process as described elsewhere herein, by a chemical etching process, by a spark erosion electrical discharge machining (SE-EDM) process, or by an electron beam drilling (E-beam) process.

[0514] To form porous regions as described above (extending from a first side 2106 to a second side 2108 of the body) by a plurality of adjacent stacked porous plates, the respective porous zones of those plates are distributed along the thickness direction so that they overlap, and are arranged to coincide at the same angular (or lateral) location of the porous wall (as shown in Figures 5a and 5b). This is also illustrated by the overlapping arrangement 2104 of porous zones shown on the left-most side of the portion 2100 of Figure 6. In this example, three of the overlapping zones are provided on the respective portion 2100, and are separated from one another (i.e., non-overlapping), whereas the remaining four overlapping porous zones are provided in adjacent stacked plates and shown in dashed lines for illustrative purposes only.

[0515] In the example of Figure 6, the pattern of porous zones is defined so that porous zones at staggered locations along the thickness direction are provided at angularly (or laterally) offsetlocations of the pattern. As such, a porous plate having the same pattern of porous zones can be angularly (or laterally) offset relative to an adjacent porous plate to align porous zones having different but overlapping locations along the thickness direction at the same angular (or lateral) location. In this way, a subset of adjacent stacked plates defining a porous region may all have a common pattern of porous zones 2102.

[0516] Figure 7 is a further example of a configuration of a portion 2200 of a porous plate 2004 as described above, as viewed normal to the respective stacking direction. The portion 2200 is similar to that described with respect to Figure 6, but differs in the nature of the pattern of porous zones 2202. In particular, unlike the staggered arrangement of Figure 6, the porous zones defined at angularly (or laterally) separate locations 2204, 2206 are at the same location(s) along the thickness direction. Accordingly, porous plates 2004 according to the same pattern cannot be stacked together to form the porous regions, and instead a subset of porous plates having different patterns is provided to form the porous regions 2006. For example, there may be three such patterns (as described with respect to Figure 5b), and they may be provided in a repeating sequence along the longitudinal extent of the porous wall.

[0517] Although the example configurations of a plate described above with reference to Figures 6 and 7 refer to the arrangement of porous zones to cooperatively define porous regions, the disclosure applies equally to the arrangement of flow zones to cooperatively defined flow regions (as discussed elsewhere herein). It may be that for each flow region a subset of the associated flow zones comprise porous zones to define a porous region, and a further subset of the associated flow zones comprise open zones to define an open region.

[0518] Methods of operating an electrolyser as described elsewhere herein apply equally to electrolysers comprising one or more stacked porous walls as described above. Equally, an electrolyser having one or more stacked porous walls as described above can be used with a controller and / or flow control equipment as described elsewhere herein.

[0519] Figure 8 is a flow diagram of a method 2300 of manufacturing a stacked porous wall, for example a stacked porous wall formed of porous plates as described with reference to Figures 5-7.

[0520] In block 2302, a porous set of plates is provided, each having one or more open zones extending through the respective plate. The open zones may correspond to the porous zones of plates as described above, but free of a porous media (and as such referred to as open zones).

[0521] There may be a precursor step in which material is removed from a plurality of precursor plates corresponding to the porous set to form the porous plates and the respective open zones. The removal of material may be performed by any suitable process. Example processes includeby a laser drilling process, by a chemical etching process, by a spark erosion electrical discharge machining (SE-EDM) process, or by an electron beam drilling (E-beam) process.

[0522] In block 2304, an electrocatalyst composition is applied to the porous set of plates, so that it flows into the respective open zones, to form porous zones of the respective plates. The method of applying the electrocatalyst composition may be substantially as described above with respect to other examples herein. The method may be adapted for application to plates rather than a porous wall, for example by causing the electrocatalyst composition to flow through the open zones. Such a method may include using a wiper element to wipe an electrocatalyst composition over a surface of the plate to cause it to flow into the open zones, or use of a plunger element to drive an electrocatalyst composition into and / or through the open zones.

[0523] In addition to applying the electrocatalyst composition, the method may include a heat treatment operation in which an electrocatalyst component of the electrocatalyst composition forms a porous structure for a respective porous region (of the porous wall), whereby upon subsequent stacking of a plurality of plates to form the porous wall, each porous region defines a respective network of flow paths through a body of the porous wall, to permit fluid to flow from a first side of the body to a second side of the body. The heat treatment operation may be substantially as described above with respect to other examples herein. The heat treatment operation may be adapted to heat treat individual plates, a collection of individual plates not provided in a stack, or a stack of plates arranged to form a body of a porous wall. The heat treatment operation may include forming together of the stacked plates.

[0524] The method may further comprise a drying operation to vaporise a component of the electrocatalyst composition, conducted after applying the electrocatalyst composition and before the heat treatment operation. The drying operation may be substantially as described above with respect to other examples herein. The drying operation may be adapted for treatment of individual plates, a collection of individual plates not provided in a stack, or a stack of plates arranged to form a body of a porous wall.

[0525] In block 2306, a plurality of plates, including the porous set of plates, is arranged in a stack to form a body of the porous wall, the body being elongate along a longitudinal direction, and having a thickness direction from a first side to a second side.

[0526] The plurality of plates are stacked so that a plurality of porous regions are defined extending through the body at discrete locations, to permit fluid to flow from the first side to the second side. Accordingly, each of the porous regions is defined by a respective array of porous zones extending through a respective subset of adjacent plates of the porous set of plates,wherein porous zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the porous region.

[0527] A bonding process may join the plates stacked to form the body. The bonding process may be a diffusion bonding process, for example.

[0528] Although the method of Figure 8 has been described by way of example with reference to plates to which an electrocatalyst composition has been applied to form porous zones to cooperatively define porous regions, the disclosure applies equally to the stacking and bonding of a plurality of plates to form flow regions as described above, whereby a subset of adjacent plates corresponding to the flow region comprise define an array of flow zones, and wherein a subset of the associated flow zones comprise porous zones to define a porous region, and a further subset of the associated flow zones comprise open zones to define an open region. The step of applying an electrocatalyst composition can be omitted for selected plates to define open zones, or such open zones can be omitted from a step of applying an electrocatalyst composition (for example by masking off selected flow zones or open zones of a plate, while applying electrocatalyst to others).

[0529] Figure 9 shows a variant example of a method of manufacturing a stacked porous wall, for example a stacked porous wall formed of porous plates as described with reference to Figures 5-7. The method 2400 has similar steps to the flow diagram of Figure 8, but with the stacks assembled to form the body of the porous wall before an electrocatalyst composition is provided.

[0530] In block 2402, a plurality of plates are provided. The plurality of plates comprises a porous set of plates, each having one or more open zones extending through the respective plate. As discussed above with respect to the method 2300 of Figure 8, there may be a similar precursor step to that described above, in which material is removed from a plurality of precursor plates corresponding to the porous set to form the porous plates and the respective open zones.

[0531] In block 2404, the plurality of plates are arranged in a stack to form a body for the porous wall. The plates are arranged so that a plurality of open regions are defined extending through the body at discrete locations, to permit fluid to flow from the first side to the second side. Each of the open regions is defined by a respective array of open zones extending through a respective subset of adjacent plates of the porous set of plates. Open zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the open region.

[0532] Optionally in block 2406, an electrocatalyst composition is applied to the body so that it flows into the open regions, thereby providing a corresponding plurality of porous regions of the porous wall.

[0533] As described above with respect to the example of Figure 8, in addition to the step of applying the electrocatalyst composition, the method may include a heat treatment operation in which an electrocatalyst component of the electrocatalyst composition forms a porous structure for a respective porous region (of the porous wall), whereby each porous region defines a respective network of flow paths through the body of the porous wall, to permit fluid to flow from a first side of the body to a second side of the body. The heat treatment operation may be substantially as described above with respect to other examples herein. The heat treatment operation may include forming together of the stacked plates.

[0534] The method may further comprise a drying operation to vaporise a component of the electrocatalyst composition, conducted after applying the electrocatalyst composition and before the heat treatment operation. The drying operation may be substantially as described above with respect to other examples herein.

[0535] Although the examples of Figure 8 and Figure 9 include the application of an electrocatalyst composition (and optionally subsequent drying and heat treatment), in variant examples, there may be no such application of an electrocatalyst composition, and the porous wall may comprise a plurality of open regions (corresponding to the porous regions defined above, but not comprising a porous medium). Figure 10 schematically shows an example electrolysis installation 10 comprising an electrolyser 100. The electrolyser comprises a flow arrangement as described above with reference to Figure 1a, for example with one or both of the porous walls having a configuration according to any of the first to eighth examples described with respect to Figures 1b-2c.

[0536] In sequential flow order as illustrated, the example electrolysis installation 10 comprises a source of electrolyte fluid 12, a compressor 14 to compress (pressurise) the electrolyte fluid, a heater 16 to heat the electrolyte fluid, an inlet conduit 18 leading to an inlet manifold 20, the electrolyser 100, a first discharge manifold 24 and a second discharge manifold 30.

[0537] In this example, the electrolysis installation is for operation at supercritical conditions at the porous walls of the electrolyser, with an electrolyte fluid which comprises an aqueous electrolyte solution, for example as described above with respect to operation of the electrolyser 100 of Figure 1a. In this example, the compressor 14 is configured to compress the electrolyte fluid to a pressure of at least 22 MPa, for example between 22 MPa and 27 MPa. Further, the heater 16 is configured to heat the electrolyte fluid to a temperature for supercritical conditions at the porous walls of the electrolyser (e.g. at least 374°C, for example 374°C-550°C or 374°C-400°C). Heating may also occur within the electrolyser, for example at the porous walls which define the electrodes. It may be that the heater 16 is configured and / or controlled to heat theelectrolyte fluid to a temperature within 50°C of a critical temperature for the respective electrolyte fluid, for example within 30°C of the critical temperature or within 20°C of the critical temperature. It will be appreciated that the temperature of the electrolyte fluid may be a function of both the compression by the compressor 14 and heating by the heater, and the compressor and heater may be configured and / or controlled so that the electrolyte fluid has the stated conditions after having passed through both. The compressor and the heater may be provided in any order (e.g. a reversed order relative to that illustrated).

[0538] The inlet conduit 18 directs the heated and pressurised electrolyte fluid to the inlet manifold 20, which supports a temperature sensor 22 for monitoring a temperature of electrolyte in the inlet manifold, the temperature sensor being coupled to a controller 56 via a connection 23. Although the connection 23 is illustrated in Figure 10 separately from the temperature sensor 22, it will be appreciated that the connection 21 may be any suitable form of connection, for example a wired or wireless link.

[0539] The inlet manifold 20 is coupled to the electrolyser 100 to provide the electrolyte fluid into the electrolyser 100 for an electrolysis reaction as described above with respect to operation of the example electrolyser 100 of Figure 1a. There are separate first and second outlet pathways 23, 29 coupled with the first and second outlets 132, 142 (as best shown in Figure 1a) of the electrolyser respectively (the first and second outlets being configured to discharge first and second fluid reaction products respectively). Figure 10 schematically shows the first outlet pathway 23 coupled to a centrally located first outlet of the electrolyser 100, whereas the second outlet pathway 29 is coupled to a radially-outwardly (e.g. annular) second outlet of the electrolyser 100.

[0540] The first outlet pathway 23 is in fluid communication with a first discharge manifold 24 which receives a flow of electrolyte fluid and a first reaction product from the first outlet of the electrolyser 100. The first discharge manifold 24 is fluidically coupled to a first discharge valve 34 via a discharge line 25. The first discharge valve 34 may be a control valve that provides a variable restriction to flow therethrough.

[0541] The second outlet pathway 29 is in fluid communication with a second discharge manifold 30. As schematically shown in Figure 10, in this example the first outlet pathway 23 extends through the second discharge manifold 30 while functionally bypassing it (i.e. such that flow within the first outlet pathway 23 does not mix with fluid in the second discharge manifold 30), but in other implementations may be configured differently. As with the first discharge manifold 24, the second discharge manifold 30 is fluidically coupled to a second discharge valve 46 via a discharge line 31, which may be of a similar type as the first discharge valve 34.

[0542] Optionally each of the first discharge manifold 24 and the second discharge manifold 30 is provided with respective a pressure sensor 26, 32 having a pressure sensor element in communication with the fluid discharged from the respective (first or second) outlet of the electrolyser or in the respective chamber immediately upstream of the outlet. Each pressure sensor 26, 32 is coupled to a controller 56 via a respective connection 27, 33 to provide a respective pressure signal to the controller 56 (as above, any suitable form of connection may be provided despite the connections 27, 33 being shown as separate from the respective pressure sensors 26, 32 in the drawing). Alternatively or additionally, a differential pressure sensor may be provided in communication with the respective discharge manifolds or outlet pathways, and connected to the controller 56 to provide a differential pressure signal to the controller 56.

[0543] The first discharge valve 34 and / or the second discharge valve 46 may be a control valve. For example, the first discharge valve 34 and / or the second discharge valve 46 may be a controllable pressure-maintaining valve configured to maintain a target pressure upstream of the respective valve corresponding to target operating conditions in the electrolyser 100 (e.g. supercritical pressure conditions for the electrolyte fluid at the respective porous walls and / or throughout the inlet and outlet chambers of the electrolyser). The first discharge valve 34 and / or the second discharge valve 46 may expand the flow to a lower pressure, for example a pressure at which the respective reaction product is gaseous and the residual electrolyte fluid is liquid, whereby the respective reaction product may be separated from the electrolyte fluid relatively easily (for example by phase separation in an accumulator tank). The residual electrolyte fluid may be recirculated to the source 12 of electrolyte fluid.

[0544] Optionally the electrolysis installation comprises separators 36, 48 downstream of the respective discharge valves 34, 46 for separating the respective fluid reaction product from the electrolyte fluid. Each separator 36, 48 has a respective return line 38, 50 for a flow of discharged electrolyte fluid from the separator, which may be returned to the source of electrolyte fluid for reuse. Each separator 36, 48 further comprises an outlet line for 40, 52 for discharging the respective fluid reaction product. The fluid reaction product may be in gaseous form within the respective separator and discharged through the outlet line as a gas. Optionally, the monitoring apparatus comprises flowmeters 42, 54 on the respective outlet lines for monitoring a flow rate of the respective fluid reaction product, each outputting a respective signal to a controller 56 as described below.

[0545] As shown in Figure 10, there is a controller 56 which is coupled to flow control apparatus and monitoring apparatus in order to control operation of the electrolyser installation 10. The monitoring apparatus may comprise the temperature sensor 22 for monitoring an inlettemperature of electrolyte fluid, the pressure sensors 26, 32 (or differential pressure sensor) for monitoring pressures of fluid within or discharged from the first and second outlets of the electrolyser 100 respectively, and the flowmeters 42, 54 on the outlet lines 40, 52 for monitoring the outlet flows of the reaction products. The flow control apparatus may comprise the monitoring apparatus.

[0546] The flow control apparatus includes one or more components that determine (i.e. influence or affect) conditions within the electrolyser, such as the thermodynamic and / or flow rate conditions within the electrolyser. The flow control apparatus (or equipment) may therefore comprise any or all of the heater 16, the compressor 14, the first and second discharge valves 34, 46, and a cell controller configured to control a current through, and / or a voltage applied between, the first and second electrodes. The controller 56 may comprise the cell controller.

[0547] The thermodynamic conditions relate to the pressure and temperature of fluid within the electrolyser, for example the pressure and temperature of electrolyte fluid provided to the electrolyser, or the pressure and temperature of the electrolyte fluid in combination with the first and / or second reaction products in the respective chambers in which they are retained within the electrolyser. In this example the thermodynamic conditions are a function of a pressure to which the electrolyte fluid is pressurised at the compressor 14, a temperature to which the electrolyte fluid is heated at the heater 16, any heating of the electrolyte fluid at the porous walls of the electrolyser (e.g. as controlled by a cell controller), and optionally the operation of the first and second discharge valves 34, 46 (e.g. a target back pressure which the valves are configured to maintain upstream of the valves).

[0548] The flow rate conditions relate to the flow rate of electrolyte fluid provided to the electrolyser, and optionally to the or each flow rate of a branch flow of electrolyte fluid that passes from the inlet chamber to the or each outlet chamber via a respective porous wall.

[0549] In steady state conditions, the flow rate into the electrolyser is equivalent to the total of first and second flow rates out of the respective first and second outlets. Each outlet flow may depend on the pressure difference between the inlet chamber of the electrolyser (e.g. the pressure to which the compressor 14 compresses the electrolyte fluid) and the respective one of the first and second discharge valves 34, 46, and any flow resistance along the respective flow path (e.g. primarily any associated porous wall, but also any other features of the flow path which may effect a pressure drop, such as bends and flow restrictions).

[0550] Example methods of controlling an electrolysis reaction are discussed in WO2022 / 195110 and WO2024 / 061976 in the name of the applicant.

[0551] As noted above, aspects of the present disclosure relate to stacking plates to form porous walls, and further aspects relate to the formation of more complex (e.g., multi-component) structures for an electrolyser by stacking plates. In this regard, the stacked plates approach is applicable to form multiple porous walls simultaneously, and also to form a structure for an electrolyser, which may be a single-cell or multi-cell electrolyser. A “plate” may refer to a plate as provided within a formed component (e.g., a slice of a porous wall as formed from a stack of plates defining the porous wall), or to a larger plate defining structures for multiple elements (e.g. multiple porous walls, and / or a shell that forms a housing or support structure around one or more porous walls).

[0552] Such use of the stacked plates approach is exemplified below in the context of an example multi-cell electrolyser 300 as initially shown in Figure 11 and further described with reference to Figures 11-26. The associated description also provides disclosure of structures and methods suitable for forming one or more structures for a single-cell electrolyser, or multiple porous walls for use in single or multi-cell electrolysers. and / or other structures for an electrolyser.

[0553] Figure 11 shows a cross-sectional view of an example multi-cell electrolyser 300 comprising a plurality of cells 302 for electrolysis. Each cell 302 substantially corresponds to the example cell 100 of Figure 1a in function and configuration, and is generally elongate along a longitudinal direction A. In this example, each cell 302 has an annular configuration of chambers and porous electrodes (corresponding to the porous walls discussed above), but in variant examples each cell may have alternative configurations and not be annular. Each cell 302 comprises an inner electrode 502 defining an inner chamber 520 (e.g., radially within the inner electrode 502), an outer electrode 402 (e.g., radially outward of the inner electrode 502), an inlet chamber 310 between (e.g., radially between) the inner electrode 502 and the outer electrode 402, and an outer chamber 420 delimited by the outer electrode 402. In view of the annular configuration, each of the inner and outer electrodes 502, 402, the inlet chamber 310 and the outer chamber 420 are annular, whereas the inner chamber 520 is cylindrical (but in other examples may also be annular). The outer chamber 420 is delimited on its radially inner side by the outer electrode 402, and is delimited on its radially outer side by a cavity wall of a shell 404 (as will be further described below). As in other cell configurations described above, the inner and outer electrodes 502, 402 separate the inlet chamber 310 from the respective inner and outer chambers 520, such that in use an electrolyte fluid received in the inlet chamber 310 flows through the inner and outer electrodes 502, 402 for respective half reactions of electrolysis, with the resulting fluid reaction products of electrolysis being retained in the respective inner and outer chambers for discharge from respective outlets. The electrolyser therefore comprises arrays ofthe respective components that form the cells - for example an array of outer electrodes and an array of inner electrodes.

[0554] Example configurations of components of the electrolyser beyond the cells (e.g., inlet and outlet manifolds) will be discussed in further detail below, but very briefly Figure 11 shows an inlet structure 600 for providing an inlet flow of electrolyte fluid to the inlet chambers 310 of the cells, an outer outlet manifold structure 490 for conveying an outlet flow of a fluid reaction product from the respective outer chambers 420, an inner outlet manifold structure 590 for conveying an outlet flow of a fluid reaction product from the respective inner chambers 520, and a seal structure 700 to act between a structure for the inner electrodes and a structure for the outer electrodes. Figure 11 also shows an example outer electrode structure which in this example defines both the shell 404 and the outer electrodes (although in variant examples these may be defined separately).

[0555] Figure 12 highly schematically shows a longitudinal arrangement of structures and respective stacks of plates for outer and inner structures for an electrolyser, such as the electrolyser 300 of Figure 11, each of which will be described in further detail with reference to further drawings. Each element of Figure 12 refers to both the structure and the associated stack of plates. Stacks of plates for respective structures can be provided together for bonding in a common bonding step (e.g., diffusion bonding), and by way of example only Figure 12 shows several sub-structures adjacent to one another indicative that they are to be bonded in a common bonding step accordingly, although it is envisaged that other arrangements of sub-structures can be provided. The arrangement of Figure 12 includes an outer stack 401 for an outer structure 400 of the electrolyser that includes the array of outer electrodes, and comprises first and second outer sub-structures (or sub-groups of plates). The first outer sub-structure 406 comprises an outer electrode structure 430 (corresponding to an outer electrode stack 431) comprising the array of outer electrodes. In this example, the first outer sub-structure 406 also comprises an outer electrode support structure 440 (corresponding to an outer electrode support stack 441), and an outer electrode connector structure 450 (corresponding to an outer electrode connector stack 451) - both of which are to be described further below. The second outer sub-structure comprises an outer outlet manifold structure 490 (corresponding to an outer outlet manifold structure stack 491).

[0556] The arrangement further comprises an inner stack 501 for an inner structure 500 of the electrolyser that includes the array of inner electrodes, and comprises first and second inner substructures (or sub-groups of plates). The first inner sub-structure 506 comprises an inner electrode structure 530 (corresponding to an inner electrode stack 530) comprising the array of inner electrodes. In this example, the first inner sub-structure 506 also comprises an innerelectrode support structure 540 (corresponding to an inner electrode support stack 541), and an inner electrode connector structure 550 (corresponding to an inner electrode connector stack 551) - both of which are to be described further below. The second inner sub-structure comprises an inner outlet manifold structure 590 (corresponding to an inner outlet manifold structure stack 591).

[0557] The arrangement further comprises an inlet stack 601 for the inlet structure 600.

[0558] The first and second sub-structures for the respective (e.g., outer and inner) structures can be individually bonded as common structures (e.g., diffusion bonded), and subsequently joined (e.g., bonded) to provide the respective structures 400, 500 (e.g., the outer and inner structures). Similarly, the outer structure 400, inner structure 500 and inlet structure 600 can be assembled together to provide an electrolyser, and may be joined once assembled to provide the electrolyser as an integral structure.

[0559] Although Figure 12 proposes providing selected structures to be provided together as a common sub-structure prior to a further joining process, in variant examples the structures may be provided in different arrangements - for example in a greater or lesser number of substructures to be joined and / or in different sequences.

[0560] Figure 13 shows of a plate 432 of the outer electrode stack 431 for forming the outer electrode structure 430, as viewed normal to a longitudinal or stacking direction of the plate. In this example the plate 432 is generally rectangular (although any suitable shape may be adopted) and adopts a first pattern in the form of a 3x5 grid for the layout of components of the electrolyser. The plate 432 comprises a shell region 433 which forms the outer profile of the plate 432 and in which an array of cut-outs 434 are defined in the first pattern. Within each cut-out 434, there is an annular wall region 436 corresponding to a longitudinal slice of an outer electrode to be formed, separated from the shell region 433 by a gap and structurally connected to the shell region by a plurality of support tabs 436 angularly distributed around the wall region 436 in a first tab pattern. Within the wall region 436 there is a void 437. The plate 432 further comprises a plurality of alignment holes 438 for inserting non-cylindrical alignment features, and one or more identification indents 439 at an edge of the plate 432, the purpose of which is to be described below.

[0561] Although the plate 432 is a plate of the outer electrode stack 431 for forming the outer electrode structure 430, several features of the plate are reproduced in or reproduceable for plates for other structures as will be apparent from the further description.

[0562] Figure 14a shows a partial cross-sectional side view of a stack of plates for the first outer sub-structure 406 of the outer structure 400, which in this particular example incorporates all of (i) the outer electrode stack 431 for the outer electrode structure 430, (ii) the outer electrode support stack 441 for the outer electrode support structure (also referred to herein as a shellsupport stack 441 for the shell support structure 440), and (iii) the outer electrode connector stack 451 for the outer electrode connector structure 450. Dashed boxes are provided around the outer electrode connector stack 451 and outer electrode support stack 441 to illustrate the boundary between the stacks.

[0563] The partial cross-sectional view extends over cell locations in the first pattern, with the longitudinal direction A illustrated in Figure 14a as extending through one of the cell locations.

[0564] Each plate in the stack has a generally similar geometric configuration as shown in Figure 14a, each comprising a shell region 433 and a plurality of wall regions 436 each connected to the shell region 433 by one or more support tabs 435, 445. However, in this example, the support tabs 445 in the outer electrode support stack are provided in a second tab pattern in which the tab positions are offset (e.g. angularly) relative to tabs in the first tab pattern, which is to enable tab removal as will be further discussed below. Accordingly, the support tabs 445 in the outer electrode support stack should not be visible in the cross-sectional view of Figure 14a, and are shown in dashed lines accordingly (indicating the corresponding position at another angular location around the respective wall region).

[0565] In this example, the outer electrode structure 430 for the electrolyser comprises both the shell 404 and an array of outer electrodes, integrally formed as a common structure. The shell 404 is formed by a stack of shell regions 433 as discussed above. As such, the plates for the outer structure simultaneously define two functional components of the electrolyser: the shell 404 which bounds the cells of the electrolyser, and the outer electrodes which are received in the cells. (It is also envisaged that the array of outer electrodes may be separated from material corresponding to the shell regions, and housed in a separate structure which bounds the outer chamber of the respective cells).

[0566] The shell regions and wall regions in the shell support stack 441 and in the outer electrode connector stack 451 cooperatively define shell extensions and electrode extensions which extend the shell 404 and outer electrodes 402 defined by the outer electrode structure.

[0567] While the support tabs 435 between the shell regions 433 and wall regions 436 beneficially hold the wall regions 436 in fixed registration for manufacture, it can be advantageous for the shell 404 to be locally separated from the outer electrodes 402. In particular, it can be advantageous for the outer electrodes to be electronically isolated from the shell 404 (especially when the cells are electrically connected in series as will be described below), and it can also be advantageous to remove any flow obstruction presented by the support tabs 435 in the outer chamber 420. Accordingly, the support tabs 435 in the outer electrode structure are removed after bonding of the outer electrode stack.

[0568] In this example, the support tabs 435 of the outer electrode structure are removed simultaneously with removal of support tabs 435 of the outer electrode connector structure 450, while support tabs 445 of the shell support structure 440 are retained. In this example, the three structures 430, 440, 450 are bonded together as a common sub-structure (the first outer substructure 406), for example by stacking the respective stacks of plates 431 , 441 , 451 together and diffusion bonding them together in a single diffusion bonding process. In other examples, the three structures may initially be formed separately (e.g., using separate diffusion bonding processes), and subsequently joined by any suitable process (e.g., a further diffusion bonding process, or a brazing process such as vacuum brazing.

[0569] As the structures 430, 440, 450 are joined as a common structure, the retained support tabs 445 of the shell support structure 440 continue to support the array of outer electrodes 402 via the outer electrode extensions of the shell support structure 440. The removal process may comprise a cutting process, for example wire electrical discharge machining (wire EDM), which involves longitudinally extending a cutting element (a wire) through the gap between the shell 404 (and shell extensions) and the outer electrodes 402 (and outer electrode extensions). Accordingly, by providing the support tabs 435 of the outer electrode stack 431 and outer electrode connection stack 451 in the first tab pattern while providing the support tabs 445 of the shell support stack 441 in the second tab pattern, the support tabs 445 of the shell support stack 441 can be retained when those of the other stacks are removed.

[0570] The plates of the shell support stack 441 may comprise a dielectric material to electronically isolate the shell 404 from the outer electrodes. For example, the plates of the shell support stack may comprise a dielectric coating on one or both sides, to provide the plates with a core substrate and a dielectric layer. The core substrate may have the same composition as an electrically conductive material forming the plates of the outer electrode stack (e.g., Inconel® 600 or any other material as disclosed elsewhere herein for the body of the porous walls), or a different composition. References herein to electronic isolation refer to isolation of electrical conduction by movement of electrons, as opposed to isolation of electrical conduction by movement of ions (ionic conductivity).

[0571] A dielectric material for a dielectric coating for a plate, or for a passivating coating as discussed elsewhere herein, may comprise a ceramic material, for example a ceramic metal oxide, or a non-oxide ceramic such as silicon carbide or silicon nitride. The dielectric material may comprise, for example, zirconia, alumina, a composite of zirconia and alumina (e.g., ZTA -zirconia toughened alumina), magnesium aluminate, aluminium silicate, silicon carbide, silicon nitride, and fused silica. A suitable material may be selected in conjunction with the coresubstrate, for example to minimize any difference in thermal expansion coefficient. Suitable application techniques for the dielectric coating / layer include sputter coating, magnetron sputtering, thermal spraying, chemical vapour deposition (CVD) and physical vapour deposition (PVD). A further technique for providing a dielectric coating or layer may be anodization of a metal surface of the plate to form a dielectric oxide film. For example, tantalum may be anodized to obtain tantalum oxide film. Anodization of a metal surface of a plate to form a dielectric oxide may transform the plate to comprise a valve metal. Suitable metals for such treatment may include aluminium, yttrium, cerium, titanium, and zirconium.

[0572] Figure 14b shows a partial cross-sectional view of the outer structure 400 after removal of the support tabs 435 of the outer electrode structure 430 and outer electrode connector structure 450. Once again, the support tabs 445 of the shell support structure 440 are retained (albeit at a different cross-sectional position angularly offset from that shown, as indicated by dashed lines). Figure 14b also shows further electrical connection tabs 455 located between shell regions 433 and wall regions 436 in the outer electrode connector structure. Like the support tabs 445 of the shell support structure 440, the electrical connection tabs 455 are shown for the purposes of illustration but are actually located at a different position to that shown in the cross-sectional view - angularly offset from that shown. This permits the electrical connection tabs 455 to be retained when the support tabs 435 are removed. For example, the electrical connection tabs 455 may be provided in the second tab pattern, or another tab pattern not overlapping with the first tab pattern.

[0573] Figure 15a shows a partial normal view (i.e., normal to the longitudinal direction) of stack of plates 452 of an outer electrode connector stack 451, with support tabs 455 removed, and mainly showing a top-most plate 452 . In Figure 15a a different pattern is used to the first pattern (3x5)- in particular the partial view is of a 4x4 pattern), but the relevant disclosure is equally applicable to the first pattern and the skilled person will appreciate how to provide a suitable outer electrode connector stack 451 for the first pattern (3x5). Figure 15a shows a similar arrangement as to Figure 13 at each location, with a shell region 453 defining a cut-out in which a wall region 456 for an electrode extension is disposed, connected by one or more electrical connection tabs 457 arranged in a second tab pattern. Prior to support tab removal, the plate 452 would have also included support tabs in the first tab pattern.

[0574] The plates 452 in the outer electrode connector stack 451 are configured and arranged to provide electrical connection pathways to proper subsets (i.e. less than the full set) of the array of outer electrodes - for example to provide an electrical connection pathway to a single outer electrode, or to proper subsets of two or more electrodes. This is achieved by configuring theshell regions 453 of selected plates 452 of the outer electrode connector stack 451 to form part of the connection pathway, with respective electrical connection tabs 457 to associated wall regions 456. In this example, the plates 452 of the outer electrode connector stack 451 each have an electrically conductive substrate (e.g., Inconel® 600 or any other electrically conductive material as disclosed elsewhere herein for the body of the porous walls), and a dielectric coating on one or both sides, thereby electronically isolating the conductive substrate from adjacent layers. The dielectric coating may be as described above with respect to the plates of the shell support stack 441 , but in this example is omitted from the wall regions 456 to retain a conductive pathway to the respective outer electrode.

[0575] Figure 15a shows the top-most plate 452 including an electrical connection extension 458 extending beyond the profile of the stack of plates 451, to provide connection to a circuit. Electrical connection extensions 458’ for further plates (e.g., below the top-most plate in this view) are also shown.

[0576] Figure 15b shows a cutaway partial perspective view through two cell locations in a subset of the outer electrode connector stack 451, including four adjacent plates 452, each plate connected to a respective proper subset of wall regions 456 by electrical connection tabs 457 (in this example, each plate 452 is electrically connected to a single wall region 456 for electrical connection to a respective single outer electrode).

[0577] Figures 16a and 16b show an alternative example of an outer electrode connector stack 1651 and associated outer electrode connector structure 1650. In this alternative example, a plurality of electrical connector elements 1660 for providing electrical connections between respective electrodes and an electrical circuit are retained within outer electrode connector structure 1650. Each electrical connector element 1660 is configured to interface with a respective electrode, in this example having an annular upper surface for coupling to an opposing surface of an outer electrode. Each electrical connector element has a depth equivalent to more than one plate of the outer electrode connector stack 1651, extending through the stack to an external connection tab 1666 configured to extend out of the outer electrode connector structure. The outer electrode connector stack 1651 comprises a stack of plates 1652 defining connector housings for receiving and retaining the electrical connector elements in the first pattern for interfacing with the outer electrodes, with cut-outs and recesses for permitting the external connection tabs to extend therethrough. Figure 16a shows a layer (a) corresponding to a lower plate of the outer electrode stack 431 as described above, a layer (b) corresponding to one or more plates 1652 of the outer electrode connector stack 1651 which define the connector housings, and a layer (c) forming a base of the outer electrode connector stack 1651 andconfigured to support the outer electrical connectors. While the base is shown with cut-outs at each of the cell locations, it should be noted that these are of a smaller diameter than the electrical connection elements and are configured to permit the inner electrodes or an inlet structure to extend therethrough. Figure 16b shows the outer electrode connector structure 1650 as assembled and bonded, for example diffusion bonded as described elsewhere herein. Plates of the outer electrode connector stack 1651 may be configured to hold the electrical connector elements 1660 in the first pattern by being sized to abut and retain the connector elements 1660, or by providing support tabs as described elsewhere herein, which may be retained after any removal of support tabs in the outer electrode structure 430. The plates 1652 of the outer electrode connector structure 1650 may be provided with a dielectric coating as described above, to electronically isolate the electrical connection elements from each other to limit electrical connections to respective pairings of connection elements and electrodes. The continuing disclosure of the example electrolyser 300 and respective structures will refer to the first example outer electrode connector structure of Figures 14a-15b.

[0578] Figure 17a is a partial perspective view of the first outer sub-structure, partially illustrating a compound structure formed by bonding (e.g., diffusion bonding) together plates of the outer electrode stack, the shell support stack, and the outer electrode connector stack, and is provided to illustrate an example form of the assembled stacks, acknowledging that internal details below the top few plates of the structure are generally not visible. Figure 17a shows the shell as defined by shell regions 433 of the outer electrode stack as a continuous body with a shell extension formed by shell regions 443 of the shell support stack. Support tabs 445 of the shell support stack are observable, descending into annular gaps between the outer electrode extensions of the shell support structure and the shell extension. Wall regions 446 of the shell support stack define a continuous annular internal surface, whereas flow zones are visible in wall regions 436 of the plates of the outer electrode stack. It can be observed how the shell extensions defined by the wall regions 446 of the shell support stack serve to extend (e.g., extend the profile of) the outer electrodes defined by the outer electrode stack. It will be appreciated that wall regions of the outer electrode connector stack define similar outer electrode extensions (e.g., at the opposing end of the outer electrodes, in this example).

[0579] At a side face of the structure, identification indents 439 of the plates 432 of the outer electrode stack are visible, and are laterally offset relative to one another to indicate a respective flow zone pattern used in the respective plate (e.g., to provide a visual check of the stack being arranged in the intended manner). As discussed above with reference to the example porous walls of Figures 5a-5c, stacked porous walls for electrodes are configured to define flow regionsextending therethrough, each defined by a respective subset of adjacent plates having one or more flow zones extending therethrough. The wall regions of the outer electrode stack are configured to provide such flow zones. The flow zones in adjacent plates can be defined according to a plurality of patterns so that the overlap in a predetermined manner to cumulative define the flow region, and the lateral offset of the identification indents 439 is provided as a visual indicator of which pattern is used - in this example providing a continuous offset over a set of plates.

[0580] Figure 17b provides a further partial cutaway perspective view of an outer electrode of the above example, amended to show the flow regions 2045 as open (i.e. , omitting the porous medium defining the porous region within the wall), in order to illustrate how the flow zones overlap between adjacent plates 432 to provide a flow region therethrough. Figure 17b shows the partial cutaway perspective of a 3D model for the outer electrode, and also shows a photograph of a corresponding outer electrode (viewable within an outer chamber and coupled to a shell by connection tabs) manufactured from a stack of bonded plates as disclosed herein.

[0581] Figure 18a shows an exploded view of the electrolyser 300 comprising the inlet structure 600 at a base of the outer structure 400 (comprising the first outer sub-structure 406 and the outer outlet manifold 490), and - in exploded relation - the inner structure 500 comprising the array of inner electrodes 502 depending from a support structure 540 and inner outlet manifold structure 590. It can be observed from Figure 18a that the outer structure 400 defines an array of cavities for receiving the inner electrodes 502 of the inner structure 500 to form the electrolyser 300.Figure 18a also shows an isolation arrangement 700 comprising an array of dielectric separators 710 (e.g., annular discs of a ceramic dielectric material such as silicon carbide or a ceramic metal oxide as discussed elsewhere herein) configured to fit around the inner electrodes 502 to electronically isolate the inner structure 500 from the outer structure. The isolation arrangement 700 further comprises upper and lower arrays of fluid seals 720 configured to fit between the dielectric separators 710 and the respective outer and inner structures 400, 500.

[0582] Also shown in Figure 18a are: an inner outlet port 593 defined in an outer surface of the inner outlet manifold structure 590, for discharging fluid from the inner outlet manifold structure; an outer outlet port 493 defined in an outer surface of the outer outlet manifold structure 490, for discharging fluid from the outer outlet manifold structure 490; and an inlet port 609 for receiving a fluid into the inlet manifold for supply the respective cells of the structure. Figure 18a also shows base walls 504 of the inner electrodes, which delimit an end of the inner chambers.

[0583] Referring again to Figure 12, in this example the first inner sub-structure 506 is formed by providing an inner electrode stack 531 defining the array of inner electrodes for the inner electrodestructure 530, an inner electrode connector stack 551 defining an inner electrode connector structure for providing electrical connection pathways to the respective inner electrodes, and an inner support stack 541 providing a structural support arrangement (the inner support structure) for the array of inner electrodes. In this example the respective stacks 531 , 551 , 541 are provided in a common stack for diffusion bonding together to provide the first inner sub-structure, prior to joining with the inner outlet manifold structure in a further joining process - similar to the disclosure above with respect to the outer structure 400. In other examples, there may be a greater or lesser number of inner sub-structures, and any of the structures may be initially formed individually (e.g., by a dedicated diffusion bonding process), and separately joined with other structures to form the inner structure.

[0584] Plate configurations for the stacks of plates for the first inner sub-structure may be substantially as described above with reference to the first outer sub-structure (e.g, with reference to Figures 13-16). However, some features may differ in view of the example form of the inner structure as compared with the example form for the outer structure, in which the array of inner electrodes are cantilever mounted to a supporting structure at one end.

[0585] For example, while plates for the inner electrode stack define a shell region and a wall region as discussed above with respect to the outer electrode stack, the shell region is provided for retaining the wall regions in the first pattern prior to bonding, and the resulting shell (or support) is subsequently removed from an intermediate inner electrode structure comprising both the array of inner electrodes and the shell (or support). Removal of the shell (or support) may be facilitated by applying a barrier or stop-off coating to a plate at a boundary for the shell (or support) which is to be removed. For example, a coating could be applied to a shell re...

Claims

Claims1. A porous wall for an electrode of an electrolyser, the porous wall comprising:a body having an inlet side and an outlet side, wherein the body is elongate along a longitudinal direction, and has a thickness direction from the inlet side to the outlet side;a plurality of flow regions extending through the body at discrete locations to provide the porous wall with a discontinuous porous structure;wherein the body comprises a plurality of bonded stacked plates;wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the plurality of plates, each flow zone configured to permit flow through the respective plate, wherein flow zones of adjacent plates in the flow subset overlap along the thickness direction to cumulatively define the flow region.

2. A porous wall according to claim 1, wherein each of the flow regions comprises a porous region;wherein each of the porous regions is defined by a respective array of porous zones extending through a respective subset of adjacent plates of the plurality of plates, wherein porous zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the porous region.

3. A porous wall according to claim 2, wherein for a subset of the flow regions, the array of flow zones comprises an array of open zones defining an open region and an array of porous zones comprising the respective porous region.

4. A porous wall according to any one of claims 2-3, wherein a material composition of the porous regions differs from a material composition of the body; or wherein a material composition of the body is the same as the material composition of the respective porous regions.

5. A porous wall according to any one of the preceding claims, wherein a subset of the plurality of flow regions are defined by a common subset of adjacent plates; andwherein there are a plurality of subsets of the plurality of flow regions, each defined by a respective common subset of adjacent plates and longitudinally offset from each other.

6. A porous wall according to claim 5, wherein for each flow region, the respective subset of adjacent plates comprises plates defined according to a plurality of different patterns of flow zones.

7. A porous wall according to any one of claims 5-6, wherein each of the flow regions comprise a porous medium; andwherein a material composition of the porous medium differs from a material composition of the body.

8. A porous wall according to claim 7, wherein the porous medium comprises an electrocatalyst-containing particulate.

9. A porous wall according to any one of claims 1-8, wherein the plurality of bonded stacked plates are diffusion bonded.

10. A flow arrangement for an electrolyser, comprising:first and second porous walls corresponding to first and second electrodes of the electrolyser;an inlet chamber disposed between the first and second electrodes of the electrolyser; first and second outlet chambers for retaining respective fluid reaction products of electrolysis, separated from the inlet chamber by the first and second porous walls respectively;wherein one of, or each of, the first and second porous walls is a porous wall having a discontinuous porous structure in accordance with any one of claims 1-9;wherein for the or each porous wall having the discontinuous porous structure, the inlet side is adjacent to the inlet chamber and the outlet side is adjacent to the respective outlet chamber, and the plurality of porous regions are to permit flow from the inlet chamber to the outlet chamber.

11. An electrolyser for performing electrolysis of an electrolyte fluid, wherein the electrolyser comprises a cell, the comprising:an inner electrode defining an inner chamber;an outer electrode;an inlet chamber defined between the inner electrode and the outer electrode;an outer chamber delimited by the outer electrode;wherein the inner electrode and / or the outer electrode comprises a porous wall in accordance with any one of claims 1-9.

12. A method comprising:providing a plurality of plates for stacking in a longitudinal direction for forming a porous wall of an electrolyser, each plate comprising a wall region corresponding to a longitudinal portion of the porous wall;wherein the plurality of plates comprises a flow-through set of plates, wherein for each of the flow-through set of plates the respective wall region comprises one or more flow zones extending through the plate to permit fluid to flow through the respective plate;arranging the plurality of plates in a stack in the longitudinal direction to form a body for the porous wall that is elongate along the longitudinal direction, and has a thickness direction from a first side to a second side;wherein the plurality of plates are stacked so that a plurality of flow regions are defined extending through the body at discrete locations, to permit fluid to flow from the first side to the second side;wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the flow-through set of plates, wherein flow zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the flow region.

13. A method according to claim 12, wherein the plurality of plates is for forming an array of porous walls, each plate comprising a plurality of wall regions each corresponding to a longitudinal portion of a respective porous wall;wherein for each of the flow-through set of plates, each of the respective wall regions comprises one or more flow zones;wherein the plurality of plates is arranged in the stack to form an array of bodies for the respective porous walls, wherein each body is elongate in the longitudinal direction and has a thickness direction from a first side to a second side;wherein the plurality of plates are stacked so that, for each body of the array of bodies, a respective plurality of flow regions are defined;wherein each of the flow regions is defined by a respective array of flow zones extending through a respective subset of adjacent plates of the flow-through set of plates, wherein flow114zones of adjacent plates in the subset overlap along the thickness direction to cumulatively define the flow region.

14. A method according to any one of claims 12-13, comprising bonding the stack of plates to provide the or each body;optionally wherein bonding the stack of plates comprises diffusion bonding.

15. A method according to any one of claims 12-14, comprising:applying an electrocatalyst composition to a subset of the flow-through set of plates so that for each wall region of the respective subset of flow-through plates, one or more of the respective flow zones comprises a porous zone;wherein the plurality of plates are arranged in the stack such that for each of the flow regions, the respective array of flow zones extending through the respective subset of adjacent plates comprises one or more porous zones, the flow region thereby comprising a porous region.

16. A method according to claim 15, wherein the subset of the flow-through set of plates to which the electrocatalyst composition is applied is a proper subset of the flow-through set of plates; andwherein the plurality of plates are arranged in the stack so that for at least some of the flow regions, the respective array of flow zones extending through the respective subset of adjacent plates comprises one or more porous zones and one or more open zones.

17. A method according to any one of claims 15-16, comprising applying the electrocatalyst composition to the subset of the flow-through set of plates before arranging the plurality of plates in the stack.

18. A method according to any one of 12-17, wherein the stack of plates provides an outer electrode stack of plates, each plate further comprising:a shell region comprising an array of cut-outs in a first pattern;wherein the plurality of wall regions are arranged in the first pattern, each wall region disposed within a respective cut-out of the shell region and spaced apart from the shell region by a gap;wherein each wall region is structurally connected to the shell region by one or more support tabs;115the method further comprising:diffusion bonding the outer electrode stack of plates, stacked in the longitudinal direction, to provide an outer electrode structure having a longitudinal extent, comprising:an array of outer electrodes in the first pattern, each corresponding to a stacked set of the wall regions of the outer electrode stack;an array of outer chambers in the first pattern, each defined between a shell corresponding to a stacked set of the shell regions of the outer electrode stack, and a respective outer electrode;wherein each outer electrode is structurally connected to the shell by a plurality of the support tabs.

19. A method according to claim 18, further comprising removing the support tabs between the array of outer electrodes and the shell, to structurally separate the outer electrodes and the shell over the longitudinal extent of the outer electrode structure.

20. A method according to any one of claims 18-19, comprising:providing a shell support stack of plates, stacked in the longitudinal direction and diffusion bonded to cooperatively define a shell support structure comprising:an array of outer electrode extensions in the first pattern, each configured to extend a respective outer electrode of the outer electrode structure;a shell extension configured to extend the shell of the outer electrode structure; an array of outer chamber extensions in the first pattern, each defined between the shell extension and a respective outer electrode extension;wherein each outer electrode extension is structurally connected to the shell extension by one or more support tabs extending through the respective outer chamber extension; wherein the outer electrode structure and the shell support structure are bonded in a compound outer structure;wherein the support tabs of the shell support structure are retained when the support tabs of the outer electrode structure are removed, to maintain the outer electrodes in fixed registration with respect to the shell.

20. A method according to any one of claims 18-19, comprising:providing an outer electrode connector set of plates, each plate comprising:116a connector shell region comprising an array of cutouts in the first pattern, wherein the connector shell region is provided with a dielectric coating over a conductive layer; a plurality of connector wall regions in the first pattern, each wall region disposed within a respective cut-out of the connector shell region and spaced apart from the connector shell region by a gap;wherein the connector shell region is structurally connected to a subset of the connector wall regions by one or more respective electrical connection tabs to electrically couple the respective wall regions to the conductive layer;diffusion bonding the outer electrode connector set of plates in a stack to provide an outer electrode connector structure comprising:an array of outer electrode connector extensions in the first pattern, each configured to extend a respective outer electrode of the outer electrode structure;a connector shell extension configured to extend the shell of the outer electrode structure;wherein the connector shell extension comprises a plurality of conductive layers electronically isolated from each other by dielectric layers, each conductive layer electrically coupled to a subset of the outer electrode connector extensions by one or more respective electrical connection tabs, for electrical communication with a respective subset of the outer electrodes.

21. A method according to claim 20, wherein for each plate of the outer electrode connector set of plates, each wall region is structurally connected to the connector shell region by one or more connector support tabs, whereby in the outer electrode connector structure each outer electrode connector extension is structurally connected to the connector shell extension by a respective set of connector support tabs;wherein the method comprises removing the connector support tabs between the array of outer electrode connector extensions and the shell extension.

22. A method according to any one of claims 18 to 21, comprising:providing an outer outlet manifold stack of plates, stacked in the longitudinal direction and bonded to cooperatively define an outer outlet manifold structure comprising an embedded outlet manifold to convey a fluid from the array of outer chambers to an outlet port.

23. A method according to any one of the claims 18-22, comprising:117providing an array of inner electrodes, each inner electrode defining an inner chamber; assembling the array of inner electrodes and the outer electrode structure so that each of the inner electrodes is received within a cavity defined by a respective outer electrode and separated from the respective outer electrode by a gap;whereby the outer electrode structure and the array of inner electrodes cooperatively define an array of cells, each cell comprising:an outer chamber of the array of outer chambers;an outer electrode of the array of outer electrodes;an inner electrode of the array of inner electrodes;an inlet chamber defined between the outer electrode and the inner electrode; and the inner chamber defined by the inner electrode.

24. A structure for an electrolyser, comprising a plurality of longitudinally-adjacent structures, including:an electrode structure comprising an array of electrodes, each comprising a porous wall in accordance with any one of claims 1-11; andone or more of:a support structure configured to support the array of electrodes;a connector structure configured to define a plurality of electrode connection paths, each electrode connection path extending to a respective subset of the electrodes of the array; an outlet manifold structure comprising an embedded outlet manifold to convey a fluid from an array of chambers, each associated with an outlet side of a respective electrode.

25. A structure according to claim 24, comprising the connector structure configured to define a plurality of electrode connection paths, each electrode connection path extending to a respective subset of the electrodes of the array;wherein the connector structure defines a layered arrangement of electrode connection paths, each electronically isolated from the other by intervening layers of a dielectric material.

26. A structure according to any of claims 24-25, wherein there are two arrays of electrodes including an array of outer electrodes and an array of inner electrodes;wherein the structure comprises an outer structure comprising the array of outer electrodes, and an inner structure comprising the array of inner electrodes;118wherein the outer structure and the inner structure cooperatively define an array of cells in the first pattern, each cell comprising:an inner electrode of the array of inner electrodes, defining an inner chamber; an outer electrode of the array of outer chambers, the inner electrode received within the outer electrode;an inlet chamber defined between the inner electrode and the outer electrode; and an outer chamber delimited by the outer electrode.

27. A structure according to claim 26, wherein the outer structure, inner structure, and optionally any inlet structure, are bonded together to provide an integral body.

28. A structure according to any one of claims 26-27, comprising a pressure vessel configured to house an assembly of the outer structure and the inner structure within a pressurized environment.119

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