Electrolyzer

Abstract

Electrolytic cells (10, 20, 50) for operation at supercritical conditions are disclosed in which chambers (200, 210, 520) for holding respective fluid reaction products are separated by porous walls that permit flow of electrolyte liquid therethrough and inhibit backflow of the respective reaction products. A controller controls the flow control devices to maintain the supercritical conditions of the electrolyte liquid. Methods of operating the electrolytic cells and methods of fabricating composite porous electrodes for such cells are also disclosed.

Description

[Technical field]

[0001] The present invention relates to an electrolytic cell, in particular to an electrolytic cell for carrying out the electrolysis of supercritical water. [Background technology]

[0002] One application of electrolysis is the production of hydrogen for energy storage. Electricity can be used to separate hydrogen and oxygen from water. The stored hydrogen and oxygen can be recombined in a fuel cell to produce electricity. Meanwhile, the hydrogen (and oxygen) can be stored and transported. With improvements in the efficiency of electrolysis and fuel cell technology, hydrogen energy storage has been proposed as a solution to many energy storage problems, especially the storage of energy from renewable sources.

[0003] The efficiency of electrolysis depends on losses inherent in the design of the electrolysis cell. Such losses can be thought of as giving the electrolysis cell an overpotential, which represents the cell's need for more energy than is theoretically thermodynamically required to continue the electrolysis reaction.

[0004] Overvoltages can arise from a number of different factors. For example, the predominate method of water electrolysis relies on the use of a polymer electrolyte membrane (PEM electrolysis) to separate the cathode and anode to prevent mixing of the hydrogen and oxygen reaction products while allowing ion transport. However, the presence of the PEM membrane introduces overvoltages into the system.

[0005] Further overvoltages are introduced by the formation of reaction product bubbles (e.g., hydrogen and oxygen bubbles) that reside on and block the electrode surfaces, and by the presence of electrolyte (e.g., in the electrolyte solution surrounding the electrodes). Summary of the Invention [Problem to be solved by the invention]

[0006] It is desirable to reduce the overpotentials associated with electrolysis. [Means for solving the problem]

[0007] According to a first aspect, there is provided an electrolytic cell for carrying out continuous electrolysis of an electrolyte solution, comprising: a first electrode and a second electrode; an inlet chamber disposed between the electrodes and configured to receive a flow of electrolyte liquid; a holding chamber associated with one of the electrodes for holding a fluid reaction product produced at the respective electrode, the holding chamber having an outlet for discharging the respective fluid reaction product; a porous wall separating the inlet chamber and the holding chamber, the porous wall being configured to permit electrolyte fluid to flow from the inlet chamber to the holding chamber and configured to inhibit return flow of respective fluid reaction products from the holding chamber to the inlet chamber; An electrolytic cell is provided comprising:

[0008] The term "continuous electrolysis" refers to an electrolysis process in which inlet electrolyte liquid is provided to the chamber for the electrolysis reaction simultaneously with the reaction products (and any remaining electrolyte liquid) being discharged from the chamber, as opposed to a batch process in which electrolysis is carried out using electrolyte liquid that is not replenished during the reaction. The term "reaction" as used herein refers to electrolysis, and in this context may refer to the half-reaction of the electrolysis at each electrode.

[0009] By separating the inlet and holding chambers by porous walls that inhibit return flow of the respective reaction products, the electrolyzer provides a method of separating the reaction products produced at each electrode without relying on ion exchange membranes (such as polymer electrolyte membranes, PEMs, etc., which could otherwise introduce losses and overvoltages into the operation of the electrolyzer). The porous walls are sufficiently porous to allow fluid flow through, essentially allowing ion exchange in either direction.

[0010] By allowing a continuous flow of electrolyte liquid between the inlet chamber and the holding chamber, the porous wall puts the inlet chamber and the holding chamber in fluid communication with each other, so that the pressures in the respective chambers are linked. Compared to configurations that prevent such fluid communication between the chambers, this can prevent excessive pressure differences from being established across the wall that could deform or otherwise damage the integrity of the wall and the electrolytic cell. The risk of such damage can be particularly pronounced when operating at high pressures, such as when the electrolyte liquid is maintained at supercritical pressure. Thus, by providing a porous wall to separate the chambers that hold the respective reaction products, the structural integrity of the electrolytic cell can be protected or improved, particularly for high pressure operation.

[0011] The porous wall can be configured to inhibit return flow of the respective fluid reaction products from the holding chamber to the inlet chamber when there is no pressure differential across the porous wall and / or when there is a pressure drop across the porous wall from the inlet chamber to the holding chamber.

[0012] When there is no pressure differential across the porous wall, the pressure difference within the electrolytic cell does not provide a driving force for fluid to flow through the porous wall. The porous wall can provide a resistance to flow that prevents reaction products held in the holding chamber from flowing back to the inlet chamber. The pressure drop across the porous wall provides a resistance to such flow in the holding chamber back to the inlet chamber when such flow does not follow a pressure gradient. This may be referred to as the inhibition of backflow of fluid reaction products by a pressure gradient, or pressure-driven flow across the porous wall.

[0013] The porous wall and each electrode may be provided by a composite porous electrode separating the inlet chamber and the holding chamber, the composite porous wall having an inlet side adjacent the inlet chamber and an outlet side adjacent the holding chamber. The electrodes may be provided by electrocatalytic regions of the composite porous electrode.

[0014] The electrocatalytic region may be a subregion of the composite porous region.

[0015] The electrocatalytic region may include an electrocatalyst suitable for catalyzing a half-reaction of the electrolysis of an electrolyte solution, the electrocatalytic region being electrocatalytically active. The electrolytic reaction may be the electrolysis of water or an aqueous (aqueous) electrolyte solution.

[0016] The electrocatalyst region may include an electrocatalyst at the electrolyte interface of the electrocatalyst region with the electrolyte liquid (i.e., a surface area of ​​the electrocatalyst region adjacent to the electrolyte liquid in use). For example, a surface area of ​​the electrocatalyst region at the electrolyte interface of the electrocatalyst region may include an electrocatalyst. The surface area may be a region of the electrocatalyst region adjacent to the electrolyte liquid at the electrolyte interface. The surface area may have a thickness of 1 μm from the electrolyte interface.

[0017] For a porous electrocatalytic region, the electrolyte interface may include the interior surfaces (or surfaces) of the pores or channels of the porous region. The electrocatalytic region may include a matrix (or body) and the electrocatalyst may be provided as a coating on the matrix (or body) that defines the electrolyte interface. In other aspects, for example, in the absence of a coating that forms the electrolyte interface, the matrix (or body) of the electrocatalytic region may include the electrocatalyst and define the electrolyte interface.

[0018] The electrocatalytic region may include a coating or layer of electrocatalyst that defines the outlet side of the composite porous electrode, such that the electrolyte interface of the electrocatalytic region includes the outlet side of the composite porous electrode and, optionally, a portion of the interior surface (or surface) of the pores or channels extending through the coating or layer. Where a coating is referred to herein, this may be by any suitable process, for example, a CVD (chemical vapor deposition) process, a sputtering process (such as magnetron sputtering) or electroplating.

[0019] When a coating is applied to the exterior surface of a porous structure (e.g., a porous matrix structure) as described herein, the coating may adopt the porosity of the porous structure because the coating may only coat the physical surface of the porous structure at each surface and may not extend across (i.e., bridge) pores within that surface to close the pores.

[0020] At the electrolyte interface (e.g., in the surface region), the electrocatalyst region may comprise at least 50% by weight, e.g., at least 80% by weight, at least 90% by weight, or may consist essentially of the electrocatalyst. When a coating defines the electrolyte interface of the electrocatalyst region, the coating may comprise at least 50% by weight, e.g., at least 80% by weight, at least 90% by weight, or may consist essentially of the electrocatalyst.

[0021] The mass loading of the electrocatalyst at the electrolyte interface when the electrocatalyst is provided as a coating is at least 0.001 mg / cm -2 , for example 0.001 to 10 mg / cm -2 , for example 0.01 to 1 mg / cm -2 may be also possible.

[0022] The electrocatalytic region may be embedded in the composite porous electrode and thus does not extend to the inlet side. By providing the electrode as part of the composite porous electrode, a particularly simple manufacturing and assembly mode of the electrode and the porous wall in the electrolytic cell can be provided, while still ensuring that the respective fluid reaction products are only produced at a location downstream from the inlet chamber. This manufacturing and assembly mode can be particularly simple, since it can obviate the need to additionally coat or otherwise provide the electrocatalytic region on the porous wall (e.g., as a mesh electrode) to provide the electrode. For example, the composite porous wall may be made by additive manufacturing or powder pressing processes (such as hot pressing (HP) or cold isostatic pressing, or hot isostatic pressing (HIP)) to incorporate the electrocatalytic region.

[0023] The composite porous electrode may include passive regions that are configured to be less electrocatalytically active (for each half-reaction of the electrolysis of the electrolyte solution) than the electrocatalytic regions or to suppress the respective half-reaction.

[0024] The rate of each half-reaction in the passive region (as a whole) may be lower than the rate of each half-reaction in the electrocatalytic region (as a whole), which may make the porous region less active as an electrocatalyst than the electrocatalytic region. The rate of each half-reaction may be the production rate of the respective fluid reaction product (i.e., hydrogen or oxygen, depending on the electrode) in the respective region, for example, the mass of the fluid reaction product produced per unit time (e.g., g / s of hydrogen), or the current density integrated across the electrolyte interface of the respective region (e.g., in A). The rate of each region as used herein is the aggregate rate of the respective region, rather than a specific rate per unit volume, thickness, mass, or surface area (e.g., of the composite porous electrode, or of the electrolyte interface of each region of the composite porous electrode), etc. The passive region and the electrocatalytic region may be configured such that the rate of each half-reaction in the passive region (as a whole) may be lower than the rate of each half-reaction in the electrocatalytic region (as a whole). For example, the velocity in the passive region may be 50% or less, 20% or less, 10% or less, 5% or less, or 1% or less of the velocity in the electrocatalytic region. The velocity in the passive region may be substantially zero.

[0025] The passive region may include fewer electrocatalysts (for electrocatalyzing each half-reaction of the electrolysis of the electrolyte solution) than the electrocatalytic region, e.g., fewer electrocatalysts than the electrocatalytic region, and / or any electrocatalysts in the passive region may be less active as electrocatalysts for each half-reaction than the electrocatalysts in the electrocatalytic region.

[0026] The passive region may include less electrocatalyst of the electrocatalyst region at the electrolyte interface of the passive region with the electrolyte liquid (i.e., within the surface area of ​​the passive region that contacts the electrolyte liquid during use) than is present at the electrolyte interface of the electrocatalyst region (i.e., within the surface area of ​​the electrocatalyst region). In other words, the material composition of the passive region at the electrolyte interface of the passive region (i.e., within the surface area) may include less electrocatalyst than the material composition of the electrocatalyst region at the respective electrolyte interface. For example, this may include less than 5 wt. % electrocatalyst, less than 1 wt. % electrocatalyst, less than 0.1 wt. % electrocatalyst. The composition of the passive region at the electrolyte interface may be evaluated by reference to a surface area of ​​the passive region adjacent to the electrolyte liquid during use, for example, having a thickness of 1 μm.

[0027] For a porous passive region, the electrolyte interface may include the inner surface of the channels or pores of the porous region. The passive region may include a matrix (or body) that defines an electrolyte interface, the matrix (or body) including less than 5% by weight electrocatalyst, less than 1% by weight electrocatalyst, or less than 0.1% by weight electrocatalyst. The passive region may include a matrix (or body) that defines an electrolyte interface and that is provided with a passivation coating that is less electrocatalytically active than the matrix (or body), the passivation coating including less than 5% by weight electrocatalyst, less than 1% by weight electrocatalyst, or less than 0.1% by weight electrocatalyst. Exemplary passivation coatings that may be applied are described elsewhere herein.

[0028] The surface area of ​​the electrocatalytic region may have a first composition. The surface area of ​​the passive region may have a second composition. A nominal electrode for carrying out each half-reaction of the electrolysis of the electrolyte solution in the nominal cell may have a surface area adjacent to the electrolyte solution at the electrolyte interface of the nominal electrode. The surface area may have a thickness of 1 μm from the electrolyte interface.

[0029] The first composition and the second composition are such that a current of 10 mA cm is delivered to a nominal electrode in a nominal cell when a surface area of ​​the nominal electrode has the first composition. -2 For example, at a nominal pressure and temperature of 22.5 MPa and 375° C., the overvoltage required to reach a current density of 10 mA cm at a nominal electrode in a nominal cell when the surface area of ​​the nominal electrode has the second composition. -2 The overpotential may be selected to be less than one-half, one-third, or one-fifth the overpotential required to reach a current density of 100 kV.

[0030] Each half-reaction can be suppressed by providing passive regions as passivation layers or coatings as discussed elsewhere herein.

[0031] Any of the statements above relating to electrocatalytic regions, passive regions, and their characterization as electrocatalytically active or less electrocatalytically active regions may apply to any of the embodiments discussed below in the detailed description.

[0032] The electrocatalytic region may include a coating or layer that includes an electrocatalyst, and the coating or layer may define the outlet side of the composite porous electrode.

[0033] The electrocatalyst may be suitable for catalyzing a half-reaction of the electrolysis of the electrolyte solution, as described above, and suitable electrocatalysts are described below. When the electrocatalytic region includes a layer defining the outlet side of the composite porous electrode, the layer may be provided as a mesh that is attached to the porous wall, regardless of how the porous wall is manufactured. For example, the mesh may be formed from a stretched foil, such as a foil that includes the electrocatalyst, or a conductive foil that is provided with the electrocatalyst as a coating. Examples of suitable conductive foils or meshes include stretched copper, stainless steel, or titanium foils or meshes having an electrocatalytic coating, such as a Ni coating (although other suitable electrocatalysts are described elsewhere herein).

[0034] The composite porous electrode may include a passive region that is configured to be less electrocatalytically active (for each half-reaction of the electrolysis of the electrolyte solution) than the electrocatalytic region or to suppress each half-reaction. The passive region may be as defined in any of the above statements regarding the first aspect of the invention, including the matter regarding the comparative definition of the electrocatalytic region. The passive region may be porous, and the electrocatalytic region may be defined only by a coating or layer that includes the electrocatalyst and defines the outlet side of the composite porous electrode. Thus, the electrolyte interface of the passive region may include the inner surface (or surface) of the pores or channels that extend through the porous passive region, and the electrolyte interface of the electrocatalytic region may not extend to the inner surface of the pores or channels of the composite porous electrode. In such a configuration, the electrocatalytic region is defined substantially entirely towards the outlet side of the composite porous electrode.

[0035] In another aspect, the electrocatalytic region may additionally comprise a porous region of a composite porous electrode, where the electrolyte interface of the electrocatalytic region comprises the interior surfaces (or surfaces) of the pores or channels of the porous region. The electrocatalytic region may comprise a matrix (or body), and the electrocatalyst may be provided as a coating on the matrix (or body) to define the electrolyte interface comprising the interior surfaces (or surfaces). For example, the coating may be formed simultaneously with the coating defining the outlet side of the composite porous electrode. For example, the coating may be applied to the interior and exterior of the matrix material. A passivation coating may then be applied as defined below.

[0036] Whether or not the matrix material of the composite porous electrode defines the electrolyte interface of the electrocatalytic region (i.e., whether or not the matrix material prior to the deposition of any coating is intended to be electrocatalytically active), the matrix material may be electrically conductive and configured to serve as part of the electrode and / or part of an electrical pathway in an electrolytic circuit defined by and including the electrode.

[0037] The composite porous electrode may have an anisotropic porous structure defined by a plurality of tilted channels extending through the electrocatalytic regions and / or passive regions (if present).

[0038] The composite porous electrode may extend linearly along a longitudinal axis and may have an orthogonal thickness direction from the inlet side to the outlet side. The composite porous electrode may have an anisotropic porous structure defined by a plurality of tilted channels, each tilted with respect to both the longitudinal axis and the thickness direction, configured to allow electrolyte liquid to flow from the inlet chamber to the holding chamber. The tilted channels may extend through at least a portion of the electrocatalytic region.

[0039] Composite porous electrodes extending linearly along a longitudinal axis can maximize the surface area for the electrolysis reaction while minimizing installed volume and / or voids between adjacent electrolytic cells.

[0040] When the electrolytic cell is provided in the electrolysis installation according to the second embodiment, the longitudinal axis may be oriented vertically, such that the inclined channel is inclined with the upward component towards the holding chamber (i.e. upwardly).

[0041] The composite porous electrode may be axisymmetric about the longitudinal axis, such that the thickness direction at any point around the longitudinal axis is the local thickness direction that corresponds to the radial direction about the longitudinal axis.

[0042] The electrolytic cell may be implemented by an axisymmetric (e.g. cylindrical) composite porous electrode, in which case the longitudinal axis may be an axis passing through the centroid of the cross section of the composite porous electrode. The electrolytic cell may also be implemented by a non-axisymmetric composite porous electrode, such as a planar electrode that extends linearly along both the transverse and longitudinal axes. The extent of the composite porous electrode along the longitudinal axis may be relatively greater than its extent along the transverse axis, so that it is elongated along the longitudinal axis.

[0043] The inclined channels are believed to inhibit the return flow of the respective fluid reaction products when the longitudinal axis is substantially vertical and the inclined channels are oriented such that they are inclined upwardly toward the holding chamber. In particular, in electrolysis reactions, the fluid reaction products (oxygen and hydrogen) have a lower density than water (or any suitable electrolyte liquid), and as a result, buoyant forces on those fluid reaction products tend to drive those fluid reaction products upwardly, and thus along their respective channels, toward the holding chamber.

[0044] A channel may be tilted relative to an axis or direction when the centroid axis of the channel is tilted relative to the respective axis or direction.

[0045] Each channel may have a cross-section that diverges along the thickness direction. Without wishing to be bound by theory, it is believed that the diverging cross-section promotes a sustained flow of the electrolyte liquid mixture and promotes a lower density of the fluid reaction products along the thickness direction as the proportion of the fluid reaction products in the mixture increases due to sustained reactions within the electrocatalytic regions. The diverging cross-section may be thought to accommodate an expansion of the mixture along the thickness direction and thus inhibit backflow of the fluid reaction products.

[0046] The inlet side of the composite porous electrode may be defined by a passive region configured to be less electrocatalytically active than the electrocatalytic region or to suppress each half-reaction of the electrolysis, and / or the passive region may include a passivation coating defining the inlet side of the composite porous electrode.

[0047] The passive region may be as defined in any of the above statements regarding the first aspect of the invention, including with respect to the comparative definition regarding the electrocatalytic region.

[0048] Thus, each half-reaction of the electrolysis may be inhibited or prevented from occurring at the inlet side of the composite porous electrode, such that the reaction may occur only or primarily in response to the electrolyte solution (or each ion) entering one of the inclined channels in the electrocatalytic region or passing through the inclined channels to the electrocatalytic region defining the outlet side of the composite porous electrode. Any fluid reaction products generated in the holding chamber (e.g., by reaction with the electrocatalytic region defining the outlet side of the composite porous electrode) may be inhibited from flowing back through the composite porous electrode because the less dense fluid reaction products may have to flow downward through the channels against buoyancy forces. This may be referred to as inhibiting backflow of the fluid reaction products due to downstream biased buoyancy effects, because the buoyancy forces in the inclined channels promote downstream flow into the holding chamber, but not upstream flow into the inlet chamber. Furthermore, the fluid reaction products in the holding chamber must flow against such buoyancy forces in order to flow back into the inlet chamber.

[0049] When the passive region includes a passivation coating defining the inlet side of the composite porous electrode, the passivation coating may be a dielectric coating, such as, 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 passivation or providing a passivation coating may include depositing a dielectric coating, such as a coating of the exemplary materials described in the preceding sentence.

[0050] By passivating the inlet side of the composite porous electrode, each fluid reaction product produced at the electrode may only be produced in a location downstream from the inlet chamber (e.g., in an electrocatalytic region or within the composite porous electrode on the outlet side of the composite porous electrode) rather than on the inlet side that bounds the inlet chamber, thereby inhibiting each fluid reaction product from being produced in or migrating to the inlet chamber.

[0051] Each channel may have an average diameter along its length of between 25 and 150 μm.

[0052] As described above, the composite porous electrode may comprise a matrix (or body) and a coating including an electrocatalyst and defining the inner surface of each channel, for example, formed by electroplating the electrocatalyst onto the inner surface of each channel. For example, the matrix (or body) of the composite porous electrode may be formed by additive manufacturing and electroplated to provide the electrocatalyst coating. A passivation coating may then be provided on one side to define the inlet side of the composite porous electrode, for example, by CVD (chemical vapor deposition) of a passivation material such as alumina (Al2O3), zirconia (ZrO2) or titania (TiO2).

[0053] In another example, the channels may be formed by removing material from a work piece to form a porous wall or composite porous electrode, for example, by a laser drilling process.

[0054] There may be a flow path of the electrolyte liquid from the inlet chamber to the holding chamber, the flow path comprising an upstream portion through a passive region of the porous wall and a downstream portion through or adjacent to the electrocatalytic region of the electrode associated with the holding chamber. The passive region may be configured to be less active as an electrocatalyst than the electrocatalytic region or to suppress the respective half-reaction of the electrolysis. The electrocatalytic region may be as defined in any of the above statements regarding the first aspect of the invention. The passive region may be as defined in any of the above statements regarding the first aspect of the invention, including the matter regarding the comparative definition of the electrocatalytic region. Thus, all flow reaching the downstream portion first passes through the upstream portion. In other words, the porous wall (which may be part of a composite porous electrode as defined in any of the above statements regarding the first aspect of the invention) may have an inlet side facing the other electrode (e.g., the inlet side of the composite porous electrode), and the electrocatalytic region may have an ion exchange boundary for ion exchange facing the other electrode and spaced apart from the inlet side. In some embodiments, the ion-exchange boundary may be embedded within a composite porous electrode as defined in any of the above statements regarding the first aspect of the invention. As a corollary, the electrocatalytic region may be described as being within the composite porous electrode and not extending to the inlet side. As used herein, a component, surface, or boundary is "facing" another entity when the component, surface, or boundary faces the other entity.

[0055] The passive regions and electrocatalytic regions may be configured such that the passive regions contribute resistance to flow through them with or without a pressure differential across the porous walls from the inlet chamber to the holding chamber, which may be referred to as inhibiting backflow of fluid reaction products due to the upstream flow resistance of the passive regions.

[0056] The passive area of ​​the porous wall has a thickness t w and transmittance k w and the downstream portion may have a thickness t eand transmittance k e The relative flow permeabilities of the passive and electrocatalytic regions may satisfy the following inequality:

[0057]

number

[0058] In other words, the relative flow permeabilities of the passive and electrocatalyst regions are calculated as the ratio of their respective permeabilities multiplied by the inverse ratio of their thicknesses.

[0059] The relative flow permeability may be 2 or less, e.g., 1 or less, 0.5 or less, or 0.2 or less. The relative flow permeability is related to the contribution each region makes to the overall flow resistance along the flow path. When there is a pressure difference between the inlet chamber and the holding chamber that drives the flow of electrolyte liquid along the flow path and establishes a pressure drop along the flow path, the relative permeability is related to the proportional pressure drop across the respective regions. For example, a relative permeability of less than 5 corresponds to a pressure drop across the passive region of the porous wall providing at least one-sixth of the total pressure drop or flow resistance along the upstream and downstream portions of the flow path, while a relative permeability of 0.2 corresponds to a pressure drop across the passive region being five times greater than the pressure drop across the electrocatalytic region of the electrode. Thus, the passive region provides a significant amount of overall flow resistance, inhibiting fluid reaction products generated in the electrocatalytic region of the electrode from returning to the inlet chamber.

[0060] In some embodiments of the electrolytic cell, the porous wall and the electrode may be provided as a single structure (i.e., as a composite porous electrode), such that the upstream and downstream portions of the flow path are continuous with one another and all flow entering the holding chamber passes first through both the passive region of the porous wall and then through the electrocatalytic region of the electrode. It should be understood that the porous wall can overlap the electrode (i.e., the electrocatalytic region may be porous).

[0061] A passive region (e.g., in a porous wall), an electrocatalytic region of an electrode, or a composite porous electrode that may provide such a region, may comprise (i) an unstructured porous medium, or (ii) a structured array of channels that provide porosity to the wall, electrode, or composite member, respectively.

[0062] For example, a structured array of channels may be provided in an otherwise non-porous material to provide porosity, for example, by forming the respective component by an additive manufacturing process such that the structured array of channels is present in the component, and / or by removing material from the component to provide such channels (e.g., by a laser drilling process). The expression "structured channels" is intended to indicate that a plurality of channels are oriented in a predetermined pattern (e.g., uniformly spaced) relative to one another. The structured channels may be discrete (i.e., non-intersecting channels). The structured channels may generally be linear. The structured array of channels may generally provide anisotropic porosity to the component, and the present disclosure extends to such components having anisotropic porosity.

[0063] The term "unstructured porous media" is used herein to refer to porous media having a network of pores that allow flow through the material, for example, defining a network of tortuous (e.g., non-linearly extending) channels. The term "unstructured" relates to the general irregularity of a particular flow path through the material. For example, unstructured porous media may be provided by sintering a bed of build material (e.g., powdered or granular material) in an additive manufacturing process, or similarly by a powder pressing process (such as hot pressing (HP), cold isostatic pressing or hot isostatic pressing (HIP)), such that voids (e.g., randomly distributed voids) remain in the fused product. Unstructured porous media may have isotropic porosity or may otherwise be referred to as isotropic porous media or as having an isotropic porous structure.

[0064] The flow rate (or by corollary, the flow resistance of each region) through a porous region disclosed herein (i.e., of a porous wall or of a composite porous electrode) can be a function of its permeability k. The volumetric flow rate through a porous wall can be a function of the area A of the wall, the permeability k of the porous wall, the dynamic viscosity of the fluid, the applied pressure difference and the thickness according to Darcy's law. The permeability can be varied by appropriate selection of the porosity, pore size (or pore size distribution). A porous region as described herein can have an appropriate permeability selected to allow electrolyte flow at a desired flow rate for given operating conditions (e.g., pressure and temperature) and geometry of the porous region. For example, one or any porous region as described herein can have a permeability of 0.01 to 10 μm 2 , for example 0.05 to 5 μm 2 , 0.1~2μm 2 , or 0.5 to 1.5 μm 2 , for example 0.7 μm 2 The porous region may have an average pore size of from 2 to 20 μm, for example from 2 to 10 μm, or from 5 to 10 μm.

[0065] The first and second electrodes may have respective ion exchange boundaries facing each other, each ion exchange boundary being a boundary of an electrocatalytic surface or an electrocatalytic region of the respective electrode. There may be a substantially constant minimum separation distance to the opposing ion exchange boundary for at least 50% of the surface area of ​​one of the ion exchange boundaries, and / or the opposing ion exchange boundaries may be substantially locally parallel to each other.

[0066] Opposing ion exchange boundaries are boundaries of opposing electrodes that face each other for ion exchange (eg, through an electrolyte liquid), eg, boundaries of electrocatalytic regions of each electrode.

[0067] There may be a substantially constant minimum separation distance for at least 80%, at least 90%, or substantially all of the surface area of ​​each ion exchange boundary.

[0068] There may be opposing surfaces bounding the inlet chamber, each associated with a respective one of the first and second electrodes. When the composite porous electrode bounds the inlet chamber, this may be a surface of the passive region of the composite porous electrode. There may be a substantially constant minimum separation distance to the opposing surface for at least 50% of the surface area of ​​one of the surfaces. The surfaces may be substantially locally parallel to each other.

[0069] It is desirable to both minimize the separation between opposing ion exchange boundaries and to have the separation be substantially constant so as to provide a relatively uniform reaction rate along the extent of the electrode.

[0070] The term "locally parallel" is intended to mean that when one or both of the ion exchange boundaries are non-planar, a plane aligned with the local shortest separation vector from any point on one of the boundaries to the other boundary intersects the opposing boundaries to define a substantially parallel line. For example, the opposing ion exchange boundaries may be cylindrical or conical and concentric, such that the boundaries may not be parallel to one another, and a plane that locally intersects the two boundaries along the local shortest separation vector will define two respective lines that are substantially parallel to one another.

[0071] The first and second electrodes may each extend linearly parallel to the longitudinal axis and each may be elongate along the longitudinal axis. Along the longitudinal extent of the electrodes where the electrodes are coextensive for ion exchange, the cross section of the electrolytic cell may be substantially constant.

[0072] By configuring the electrolyzer so that the electrodes have a constant cross-section that is coextensive for ion exchange, the electrolyzer configuration can be easily adapted to increase or decrease the longitudinal length of the electrodes (and / or electrolyzer) to increase the capacity of the electrolyzer (e.g., as may be measured by reaction rate, flow rate for a given reaction efficiency (e.g., fraction of electrolyte solution reacted to produce each reaction product), or power input measured in kW).

[0073] The first and second electrodes may be opposed to one another along a common longitudinal extent along which there is an average minimum separation distance between opposing ion exchange boundaries of the electrodes for ion exchange. The ratio of the common longitudinal extent to the average minimum separation distance may be 5 or more, such as 10 or more.

[0074] This ratio corresponds to the elongated configuration of the electrolytic cell, and in particular the elongated configuration of the separation gap between the opposing electrodes. It is generally known that it is desirable to reduce the separation distance between the opposing electrodes, but the long-range extent of the electrodes along which this is possible in the configurations discussed above may be limited by the means for keeping the reaction products generated at each electrode separated (e.g., ion exchange membranes or laminar flow buffers, i.e., by flow between the electrodes maintaining laminar flow conditions to prevent the reaction products from migrating from one side to the other). In the configurations discussed above, those means for keeping the reaction products separated tend to involve ion exchange membranes or be difficult to maintain over any significant long-range extent. The present invention allows the electrodes to be separated by an elongated separation gap, i.e. a separation gap having a long-range extent (along which the electrolyte flows) that is much larger than the separation distance between the electrodes. Without wishing to be bound by theory, it is believed that this may be made possible by the use of a porous wall that provides resistance to reverse flow from the holding chamber to the inlet chamber, preventing reverse flow without relying on high flow inertia from the inlet chamber to the holding chamber. High flow inertia may be achieved by providing a relatively small flow volume, which tends to reduce the surface area of ​​the porous wall. Rather than relying on high flow inertia, the flow volume for a given mass flow through the porous wall can be increased by using a porous wall that inhibits reverse flow (e.g., by implementing a pressure drop across the wall, or otherwise as described herein). This allows the separation gap between the electrodes to be essentially elongated, increasing the ratio between the surface area of ​​each of the electrodes and the volume of electrolyte liquid in the separation gap. The velocity of the electrolyte (e.g., as may be measured by reference to the fraction of the volume of electrolyte liquid that is reacted as it passes through the electrolytic cell) tends to increase as these ratios (i.e., the ratio between the surface area of ​​each of the electrodes and the volume of electrolyte liquid in the separation gap between the electrodes) increase.

[0075] The holding chambers may be configured to receive electrolyte liquid only through their respective porous walls.

[0076] When the electrolytic cell is configured such that all flow through the porous walls interacts with the respective electrodes (e.g., by providing composite porous electrodes), configuring the electrolytic cell such that the holding chambers receive electrolyte liquid only through their respective porous walls ensures that all flow entering the holding chambers interacts with the respective electrodes. Furthermore, by allowing electrolyte liquid to enter the holding chambers only through the porous walls, the flow regime (e.g., flow rate) into the holding chambers can be reliably controlled by controlling the properties of the porous walls and / or properties that affect the flow rate of electrolyte liquid through the porous walls. In other configurations, there may be one or more inlets into the holding chamber that do not go through the porous walls.

[0077] The electrode associated with the holding chamber may be the anode, and in use with an aqueous electrolyte, hydrogen produced at the other electrode, the cathode, is inhibited from migrating into the holding chamber associated with the anode by oxidation at the anode, and oxygen produced at the anode is inhibited from migrating through the porous wall into the inlet chamber.

[0078] The term "aqueous electrolyte solution" as used in this disclosure may refer to any solution that contains at least 50% water by weight and is suitable for electrolytic reactions. Exemplary aqueous electrolyte solutions are discussed elsewhere herein. In addition to water, the electrolyte solution may also contain other inorganic solvents.

[0079] The electrolytic cell may include power supply terminals coupled to the electrodes such that the electrode associated with the holding chamber is the anode and the other electrode is the cathode.

[0080] Alternatively, the electrode associated with the holding chamber may be the cathode and the other electrode may be the anode.

[0081] It will be appreciated that when the electrolytic cell comprises two holding chambers, each associated with a respective one of the first and second electrodes, the above features relate to only one of the holding chambers, such that one of the holding chambers is associated with the electrode that is the anode and the other holding chamber is associated with the electrode that is the cathode.

[0082] One of the inlet chamber and the retention chamber may be an outer annular chamber and the other may be an inner core chamber surrounded by an outer annular chamber.

[0083] The outer annular chamber and the inner core chamber may be arranged concentrically. The annular and core arrangement may provide a particularly compact arrangement of the electrolytic cell while allowing a relatively high ratio between the surface area of ​​the respective electrodes and the volume of the separating gap between the electrodes. The annular and core arrangement may allow the use of a cylindrical structure that is relatively more resistant to deformation under radially outward pressure (e.g., compared to a rectilinear structure of the same structural mass and characteristic dimensions).

[0084] Alternatively, the inlet chamber and the outer chamber may have other configurations, for example they may have a substantially rectangular cross-section (eg, in a plane perpendicular to the longitudinal axis of the electrolytic cell).

[0085] The holding chamber may be associated with the first electrode, and an outlet of the first holding chamber is the first outlet. The second electrode may be a flow past electrode defining a wall of the inlet chamber. The inlet chamber may be for holding fluid reaction products produced at the second electrode and has a second outlet for discharging the respective fluid reaction products.

[0086] The second electrode may define a wall of the inlet chamber opposite the porous wall associated with the first electrode.

[0087] The electrolytic cell may comprise a first holding chamber associated with the first electrode for holding a fluid reaction product produced at the first electrode and discharging the fluid reaction product through a first outlet, and a second holding chamber associated with the second electrode for holding a fluid reaction product produced at the second electrode and discharging the fluid reaction product through a second outlet. The electrolytic cell may comprise a first porous wall and a second porous wall each separating the inlet chamber from a respective holding chamber.

[0088] In other words, the holding chamber described in the preceding statements associated with the first aspect is one of the first and second holding chambers of the electrolytic cell, and the porous wall described in the preceding statements is one of the first and second porous walls of the electrolytic cell.

[0089] Each holding chamber and each porous wall may have any of the features described above in relation to the first aspect of the invention. For example, each porous wall may be provided by a composite porous electrode together with a respective electrode, such that the electrolytic cell comprises two composite porous electrodes having any of the features described above in relation to the first aspect of the invention.

[0090] The first holding chamber and / or the first porous wall may have a different configuration than the second holding chamber and / or the second porous wall, respectively, e.g. the first holding chamber may have a first combination of any of the features described above in relation to the first aspect of the invention, while the second holding chamber may have a different second combination of any of the features described above in relation to the first aspect of the invention. Thus, statements defining an electrolytic cell may be reformulated to define, inter alia, a first holding chamber, a first porous wall (optionally provided by a first composite porous electrode), a second holding chamber, and a second porous wall (optionally provided by a second composite porous electrode), where the first and second holding chambers and / or the first and second porous walls are defined by different combinations of any of the respective features described above in relation to the first aspect of the invention.

[0091] The inlet chambers may have no outlets other than the holding chambers through their respective porous walls. In such a configuration, electrolyte liquid entering the inlet chambers is forced to displace other electrolyte liquid outwardly into the holding chambers, so that providing flow to the inlet chambers can drive the flow of electrolyte liquid through the respective porous walls even in the absence of a significant pressure drop across each of the respective porous walls. Nevertheless, because the porous walls present a greater restriction to flow than the open space within the respective chambers, there will necessarily be a pressure gradient across the walls at steady state conditions, so that the path of least resistance for the fluid downstream of each holding chamber is to the respective outlet, effectively inhibiting backflow of fluidic reaction products into the inlet chambers. This may be referred to as inhibiting backflow of fluidic reaction products by the replacement flow of electrolyte liquid.

[0092] The inlet chamber may be an annular chamber, one of the first retention chamber and the second retention chamber may be an inner core chamber surrounded by the inlet chamber, and the other of the first retention chamber and the second retention chamber may be an outer annular chamber surrounding the inlet chamber.

[0093] The electrolytic cell may further comprise a controller configured to control flow control devices for controlling thermodynamic and / or flow rate conditions within the electrolytic cell.

[0094] For example, the flow control device may include one or more discharge valves downstream of the first and second outlets as described herein. Such valves may be part of the electrolytic cell or may be installed in (or in) the electrolytic facility together with the electrolytic cell. The flow control device may comprise a heater configured to heat the electrolyte liquid upstream of the inlet chamber. The heater may be part of the electrolytic cell or may be installed in (or in) the electrolytic facility together with the electrolytic cell. The flow control device may comprise a compressor configured to compress the electrolyte liquid upstream of the inlet chamber. The compressor may be part of the electrolytic cell or may be installed in (or in) the electrolytic facility together with the electrolytic cell.

[0095] The controller can be configured to control the flow control devices to maintain supercritical pressure and / or temperature conditions for the electrolyte liquid in the inlet and holding chambers, such as a pressure of at least 22 MPa and at least 374° C. for the aqueous electrolyte liquid. Although some embodiments discussed herein relate to operation at supercritical conditions and the appended claims refer to electrolytic cells or electrolytic cell installations in which a controller is configured to maintain supercritical conditions, the present disclosure contemplates electrolytic cells and electrolytic cell installations and methods of operation in which no such controller or control is present to maintain supercritical conditions for the electrolyte liquid as described herein (e.g., by any combination of features contemplated in this disclosure).

[0096] The controller can be configured to control the flow control device to maintain supercritical pressure and / or temperature conditions for the electrolyte liquid in the inlet and holding chambers, such as 22-27 MPa and 374-550° C., e.g., 374-400° C. By maintaining supercritical conditions, losses associated with the electrolysis reaction can be reduced by (i) suppressing the formation of reaction product bubbles on the surfaces of the electrodes and / or by increasing the conductivity of the electrolyte liquid for a given electrolyte concentration of a given amount of electrolyte (or conversely, achieving adequate conductivity using a relatively lower concentration of electrolyte).

[0097] The electrolytic cell may comprise a first outlet associated with the first electrode for discharging a fluid reaction product produced at the first electrode and a second outlet associated with the second electrode for discharging a fluid reaction product produced at the second electrode. The flow control device may include a first discharge valve and a second discharge valve in fluid communication with the first and second outlets, respectively.

[0098] The electrolytic cell may comprise a first release valve and a second release valve. The first release valve and / or the second release valve may be a variably controlled valve.

[0099] The first release valve may be configured to maintain a first target pressure upstream of the valve, and the second release valve may be configured to maintain a second target pressure upstream of the valve. The first release valve and the second release valve may be configured to maintain different target pressures to cause a pressure drop across the porous wall that drives a divergent flow of electrolyte liquid from the inlet chamber through the porous wall into the retention chamber. Alternatively, the first release valve and the second release valve may be configured to maintain the same target pressure, whereby pressure-driven divergent flow of electrolyte liquid from the inlet chamber through the porous wall into the retention chamber is inhibited. The controller may be configured to control the first release valve and / or the second release valve to maintain the respective target pressures.

[0100] The controller may be configured to control the first and / or second discharge valves to maintain a target flow rate or composition from one or each of the first and second outlets based on flow rate, upstream pressure and / or composition data received by the controller, and / or to maintain a target flow rate ratio between the flows out of the first and second outlets based on flow rate, upstream pressure and / or composition data received by the controller. The target flow rate ratio may correspond to a ratio of a total flow rate out of the first outlet to a total flow rate out of the second outlet, or a ratio of a flow rate of a first fluid reaction product out of the first outlet to a flow rate of a second fluid reaction product out of the second outlet.

[0101] The controller may be configured to control the first and / or second discharge valves to maintain respective target flow rates or respective target compositions of the streams from each of the first and second outlets based on flow rate and / or composition data received by the controller for the respective discharge streams.

[0102] The target flow rates as referred to above may be the total flow rate from each outlet, or may be the flow rate of a particular component fluid of the mixture flowing from each outlet, for example, the flow rate of oxygen in a mixture containing oxygen and electrolyte liquid, or the flow rate of hydrogen in a mixture containing oxygen and electrolyte liquid. The target flow rate may be a mass flow rate.

[0103] The flow rate data may be determined by sensors in the electrolytic cells or in the equipment in which the electrolytic cells are installed. For example, there may be a flow meter downstream of each respective discharge valve. There may be one or more flow meters downstream of separate devices in the equipment in which the electrolytic cells are installed. For example, a separation device may separate the flows discharged through each outlet into a respective reaction product flow and an electrolyte liquid (or water) flow, and a flow meter may be installed on the separation means or at each outlet to monitor the flow rate of each component (i.e., reaction product and electrolyte liquid). The combination of the discharge valves, the flow meters for monitoring the flow rates through the respective valves, and a controller controlling the discharge valves based on signals from the flow meters can provide a mass flow controller, which controls the discharge valves based on signals from the flow meters to maintain a target flow rate.

[0104] The upstream pressure data may be determined by one or more pressure sensors in the electrolytic cell or one or more pressure sensors in the equipment in which the electrolytic cell is installed to monitor the pressure of the electrolyte solution upstream of the valve. For example, a pressure sensor may extend into one or each of the chambers holding the respective reaction products and be configured to send a respective pressure signal to the controller, or a differential pressure sensor (which may be a differential pressure transducer) may be configured to respond to a pressure difference between the chambers and send a differential pressure signal to the controller. For example, the controller may be calibrated to maintain the or each respective pressure within a respective target range or to maintain a pressure difference within a target range to maintain a target operating condition (e.g., as an example, a target flow rate of one or each respective reaction product through an outlet).

[0105] The target composition may be a target percentage of the fluid reaction products in the streams discharged through the respective outlets. The composition may be a mass fraction. The composition data may be obtained based on monitoring the flow rates of each component (i.e., each reaction product and electrolyte liquid) of the streams discharged through the respective outlets.

[0106] The controller need not receive flow rate or composition data from which a numerical value of flow rate or component mass fraction can be derived, but by appropriately calibrating the controller, it can receive data related to the flow rate or composition of the stream that can be used to control the or each release valve so that a target flow rate, composition or flow rate ratio can be maintained.

[0107] The controller may be configured to determine whether an excess amount of the second fluid reaction product is present in the outlet stream through the first outlet or whether an excess amount of the first fluid reaction product is present in the outlet stream through the second outlet based on composition data received at the controller for the respective outlet streams. The controller may be configured to control the first and / or second discharge valves to vary the flow rate through the porous wall of the electrolytic cell based on said determination.

[0108] For example, the controller may control the first and / or second release valves to increase the pressure drop from the inlet chamber to the respective outlets to increase the flow rate through the respective outlets. For example, when an outlet is downstream of a porous wall, increasing the flow rate through the porous wall may inhibit backflow of reaction products through the porous wall (e.g., due to inertia of the flow through the porous wall).

[0109] The controller may be configured to maintain thermodynamic and / or flow rate conditions of the electrolyte fluid through the electrolytic cell corresponding to a Reynolds number in the inlet chamber that is less than or equal to 4000, such as less than or equal to 2300. Controlling the electrolyte fluid conditions to meet the above Reynolds number criteria can prevent turbulence and / or transient mixing in the inlet chamber that may otherwise promote migration of reaction products from the first electrode across the separation gap between the electrodes toward the holding chamber.

[0110] The first electrode and / or second electrode disclosed herein may include a respective electrocatalytic region that includes an electrocatalyst (which may otherwise be referred to as an electrocatalytic material), such as an electrocatalyst for water electrolysis (i.e., for the oxidation or reduction reaction of water electrolysis).

[0111] Suitable electrocatalysts include precious 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., 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. The one or more elements may be present in elemental form (e.g., as a (substantially) pure metal), in a mixture (e.g., an alloy), in a compound (e.g., an oxide, hydroxide, nitride, boride, sulfide, phosphide, carbonate, and / or an organic compound such as a metal-organic framework), and / or incorporated into a nanomaterial such as a nanoparticle, nanotube (e.g., carbon nanotube), nanocages (e.g., fullerenes), and / or nanosheets (e.g., graphene). The electrocatalytic region of the first electrode may be selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, and / or Re; 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, and / or Cn; La, Ce, Pr, Nd, Pm, Sm, Eu, Gd , Tb, Dy, Ho, Er, Tm, Yb and / or Lu; Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Ru, Rh, Pd, Os, Ir and / or Pt; P; S; C, and / or combinations thereof.For example, the electrocatalytic region of the first electrode may include (e.g., may consist of) an electrocatalyst that includes (e.g., consists essentially of or consists of) Ag, Au, C, Cd, Ce, Cn, Co, Cr, Cu, Db, Ds, Dy, Er, Eu, Fe, Gd, Hf, Hg, Ho, Hs, Ir, La, Lu, Mn, Mo, Mt, Nb, Nd, Ni, Os, P, Pd, Pm, Pr, Pt, Re, Rf, Rg, Rh, Ru, S, Sc, Sm, Ta, Tb, Tc, Ti, Tm, V, W, Y, Yb, Zn, Zr, and / or combinations thereof. The electrocatalytic region of the first electrode may include (e.g., may consist of) an electrocatalyst including (e.g., consisting essentially of or consisting of) Pt, Ir, Pd, Ni, Fe, Co, P, S, Mo, and / or combinations thereof.

[0112] The electrocatalytic region of the second electrode may be selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, and / or Re; 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, and / or Cn; La, Ce, Pr, Nd, Pm, Sm, E The electrocatalyst may include (e.g., may consist of) the electrocatalyst comprising (e.g., consisting essentially of or consisting of) U, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Ru, Rh, Pd, Os, Ir and / or Pt; P; S; C, and / or combinations thereof. For example, the electrocatalytic region of the second electrode may include (e.g., may consist of) an electrocatalyst that includes (e.g., consists essentially of or consists of) Ag, Au, C, Cd, Ce, Cn, Co, Cr, Cu, Db, Ds, Dy, Er, Eu, Fe, Gd, Hf, Hg, Ho, Hs, Ir, La, Lu, Mn, Mo, Mt, Nb, Nd, Ni, Os, P, Pd, Pm, Pr, Pt, Re, Rf, Rg, Rh, Ru, S, Sc, Sm, Ta, Tb, Tc, Ti, Tm, V, W, Y, Yb, Zn, Zr, and / or combinations thereof. The electrocatalytic region of the second electrode may include (e.g., may consist of) an electrocatalyst including (e.g., consisting essentially of or consisting of) Pt, Ir, Pd, Ni, Fe, Co, P, S, Mo, and / or combinations thereof.

[0113] One of the first electrode and the second electrode may be an anode, and the other of the first electrode and the second electrode may be a cathode. Thus, the electrocatalytic regions of each of the first electrode and the second electrode may include different electrocatalysts.

[0114] For example, the first electrode may be selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt, Au, Ag, and / or Re; 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, and / or Cn; La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and and / or Lu; Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and / or Lu; Ru, Rh, Pd, Os, Ir, and / or Pt; P; S; C, and / or combinations thereof, and the second electrode may be an anode having an electrocatalytic region including (e.g., consisting of) a first electrocatalyst including (e.g., consisting essentially of or consisting of) Ru, Rh, Pd, Os, Ir, and / or Lu. s, Ir, Pt, Au, Ag, and / or Re; 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, and / or Cn; La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and / or Lu; Sc, Y, La, Ce, Pr, The cathode may have an electrocatalytic region that includes (e.g., consists of) a second electrocatalyst that includes (e.g., consists essentially of or consists of) Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and / or Lu; Ru, Rh, Pd, Os, Ir, and / or Pt; P; S; C, and combinations thereof, where the first and second electrocatalysts may be different (i.e., have different compositions).

[0115] The first electrode may be an anode having an electrocatalytic region including (e.g., consisting of) a first electrocatalyst including (e.g., consisting of) Ag, Au, C, Cd, Ce, Cn, Co, Cr, Cu, Db, Ds, Dy, Er, Eu, Fe, Gd, Hf, Hg, Ho, Hs, Ir, La, Lu, Mn, Mo, Mt, Nb, Nd, Ni, Os, P, Pd, Pm, Pr, Pt, Re, Rf, Rg, Rh, Ru, S, Sc, Sm, Ta, Tb, Tc, Ti, Tm, V, W, Y, Yb, Zn, Zr, and / or combinations thereof, and the second electrode may be an anode having an electrocatalytic region including (e.g., consisting of) a first electrocatalyst including (e.g., consisting essentially of or consisting of) Ag, Au, C, Cd, Ce, C In another embodiment, the cathode may have an electrocatalytic region that includes (e.g., consists of) a second electrocatalyst that includes (e.g., consists essentially of or consists of) n, Co, Cr, Cu, Db, Ds, Dy, Er, Eu, Fe, Gd, Hf, Hg, Ho, Hs, Ir, La, Lu, Mn, Mo, Mt, Nb, Nd, Ni, Os, P, Pd, Pm, Pr, Pt, Re, Rf, Rg, Rh, Ru, S, Sc, Sm, Ta, Tb, Tc, Ti, Tm, V, W, Y, Yb, Zn, Zr, and / or combinations thereof, and the first and second electrocatalysts may be different (i.e., may have different compositions).

[0116] The first electrode may be an anode having an electrocatalytic region including (e.g., consisting of) an electrocatalyst including (e.g., consisting essentially of or consisting of) Co, Fe, Ir, Li, Ni, P, S, Ti, Zn, and / or combinations thereof, and the second electrode may be a cathode having an electrocatalytic region including (e.g., consisting of) an electrocatalyst including (e.g., consisting essentially of or consisting of) Ce, Co, Fe, Ho, Ir, Mo, Ni, Pd, Pt, Ru, Sm, W, and / or combinations thereof, where the first electrocatalyst and second electrocatalyst may be different (i.e., may have different compositions).

[0117] The first electrode may be an anode having an electrocatalytic region that includes (e.g., consists of) a first electrocatalyst that includes (e.g., consists essentially of or consists of) Ni, Fe, Co, P, S, and / or combinations thereof, and the second electrode may be a cathode having an electrocatalytic region that includes (e.g., consists of) a second electrocatalyst that includes (e.g., consists essentially of or consists of) Pt, Ir, Pd, Ni, Mo, and / or combinations thereof, where the first and second electrocatalysts may be different (i.e., have different compositions).

[0118] The second electrode may be an anode having an electrocatalytic region that includes (e.g., consists of) a second electrocatalyst that includes (e.g., consists essentially of or consists of) Ni, Fe, Co, P, S, and / or combinations thereof, and the first electrode may be a cathode having an electrocatalytic region that includes (e.g., consists of) a first electrocatalyst that includes (e.g., consists essentially of or consists of) Pt, Ir, Pd, Ni, Mo, and / or combinations thereof, where the first and second electrocatalysts may be different (i.e., may have different compositions).

[0119] In some examples, the electrocatalytic region of the first electrode includes (e.g., consists essentially of or consists of) Ni (e.g., elemental Ni) and the electrocatalytic region of the second electrode includes (e.g., consists essentially of or consists of) Pt (e.g., elemental Pt).

[0120] The electrocatalyst region may include an electrocatalyst that is deposited on the matrix (or body) of the electrocatalyst region as a coating, or the matrix (or body) may include the electrocatalyst (e.g., in the absence of an electrocatalyst coating).

[0121] For example, the matrix (or body) of an electrode, such as a composite porous electrode, may include (e.g., consist of) a nickel-based alloy, such as a nickel-based superalloy. The nickel-based alloy (e.g., nickel-based superalloy) may be a nickel-chromium alloy (e.g., nickel-chromium superalloy), such as an Inconel® alloy. The nickel-chromium alloy (e.g., nickel-chromium superalloy) may include about 50% or more, e.g., about 70% or more, by weight, of nickel and about 5% or more, e.g., about 10% or more, by weight, of chromium. The nickel-chromium alloy (e.g., nickel-chromium superalloy) may further include iron, manganese, copper, silicon, carbon and / or sulfur, as well as normal impurities. For example, the nickel-chromium alloy (e.g., nickel-chromium superalloy) may be Inconel® 600. Inconel (registered trademark) 600 is composed of at least about 72.0 wt.% nickel, about 14.0 wt.% to about 17.0 wt.% chromium, about 6.0 wt.% to about 10.0 wt.% iron, about 1.0 wt.% or less (i.e., inclusive) manganese, about 0.5 wt.% or less (i.e., inclusive) copper, about 0.5 wt.% or less (i.e., inclusive) silicon, about 0.15 wt.% or less (i.e., inclusive) carbon, about 0.015 wt.% or less (i.e., inclusive) sulfur, and typical impurities, the total alloy content being 100 wt.%.

[0122] An aqueous (ie, water-based) electrolyte solution for use with the electrolytic cell may be an aqueous solution of one or more alkali metal salts, such as one or more alkali metal hydroxides or carbonates. For example, the electrolyte solution may be an aqueous solution of potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium carbonate (Li2CO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), or any combination thereof (lithium, sodium, and potassium carbonates (Li2CO3, Na2CO3, K2CO3, etc.). In one example, the electrolyte solution is an aqueous solution of potassium hydroxide (KOH) having a concentration of 1 mol / L (i.e., 1 M). In another example, the electrolyte solution is an aqueous solution of sodium hydroxide (NaOH) and potassium carbonate (K2CO3), where the concentration of sodium hydroxide (NaOH) in the solution is 1 M and the concentration of potassium carbonate (K2CO3) in the solution is 0.5 M. Further examples of aqueous electrolyte solutions include organic-containing aqueous electrolyte solutions, where exemplary organics include carbohydrates (e.g., cellulose), organic solvents (e.g., alcohols), and lipids (e.g., triglycerides).

[0123] According to a second aspect, a source of electrolyte solution, optionally an aqueous electrolyte solution; An electrolytic cell according to the first aspect for carrying out continuous electrolysis of an electrolyte solution; An electrolysis installation is provided, comprising:

[0124] When an electrode of an electrolyzer of an electrolysis installation is defined as being provided with an electrocatalytic area, the electrocatalytic area being suitable for catalyzing a half-reaction of the electrolysis of an electrolyte solution, the electrocatalytic area being electrocatalytically active. When the electrolyzer includes a passive area associated with the electrode (e.g., a passive area of ​​a composite porous electrode having an electrocatalytic area), the passive area is less electrocatalytically active than the respective electrocatalytic area for catalyzing a respective half-reaction of the electrolysis of an electrolyte solution.

[0125] The electrolysis installation may comprise a plurality of electrolytic cells according to the first aspect of the invention.The electrolysis installation may comprise a flow control device as defined herein.

[0126] According to a third aspect, there is provided a method of operating an electrolytic cell according to the first aspect, comprising the steps of: providing an inlet flow of an electrolyte liquid to an inlet chamber for carrying out an electrolytic half-reaction with the first electrode and the second electrode to produce respective fluid reaction products; the electrolyte solution and / or associated ions flow at least in part through the or each porous wall to react with the respective electrodes; A method is provided wherein the or each holding chamber holds a respective fluid reaction product and each porous wall inhibits return flow of the fluid reaction product from the holding chamber to the inlet chamber.

[0127] The method may include controlling the inlet and / or outlet conditions of the electrolytic cell such that there is no pressure differential across the or each porous wall and / or such that there is a pressure drop across the or each porous wall from the inlet chamber to the respective holding chamber.

[0128] Electrolyte liquid may be received in the or each holding chamber only through its respective porous wall.

[0129] The method may include operating the electrolytic cell such that an electrode associated with the holding chamber or associated with one of the holding chambers is the anode, and the electrolyte may be an aqueous electrolyte, such that hydrogen produced at the other electrode, the cathode, is inhibited from migrating through oxidation at the anode into the holding chamber associated with the anode, and oxygen produced at the anode is inhibited from migrating through the porous wall into the inlet chamber.

[0130] The electrodes may be associated with passive regions, e.g., passive regions of the respective composite porous electrodes defining the electrodes or passive regions along the flow path from the inlet chamber to the holding chamber that extend through the respective electrodes. The passive regions may be as defined in any of the above statements. The passive regions may be configured to be less electrocatalytically active than the electrocatalytic regions or to suppress the respective half-reactions of the electrolysis. For each electrode associated with the holding chamber, the rate of the respective half-reaction of the electrolysis in the respective electrocatalytic regions is greater than the rate of the respective half-reaction of the electrolysis in the respective passive regions.

[0131] The rate of each half-reaction may be the rate of production of the respective fluid reaction product (i.e., hydrogen or oxygen depending on the electrode), for example in kg / s. The rate of each region as used herein is the aggregate rate of the respective region, rather than a specific rate per unit volume, thickness, mass, etc. For example, the rate in the passive region may be 50% or less, 20% or less, 10% or less, 5% or less, or 1% or less of the rate in the electrocatalytic region. The rate in the passive region may be substantially zero.

[0132] The passive region may define an upstream portion along a flow path from the inlet chamber to the holding chamber, as defined above. A flow of electrolyte liquid into the holding chamber, or each of the holding chambers, may pass along the upstream portion of the flow path through the passive region, resulting in a pressure drop in the flow prior to reacting with the electrocatalyst region.

[0133] Thermodynamic and / or flow rate conditions may be controlled to maintain supercritical pressure and temperature conditions for the electrolyte liquid in the inlet chamber and the or each holding chamber, such as a pressure of at least 22 MPa and at least 374°C for the aqueous electrolyte liquid.

[0134] The electrolytic cell may comprise a first release valve and a second release valve as defined above. The first release valve may maintain a first target pressure upstream of the valve, and the second release valve may maintain a second target pressure upstream of the valve. The first and second target pressures may be different such that there is a pressure drop across the porous wall that drives a divergent flow of electrolyte liquid from the inlet chamber through the porous wall into the holding chamber. Alternatively, the first and second target pressures may be substantially equal such that there is a pressure-driven divergent flow of electrolyte liquid from the inlet chamber through the porous wall into the holding chamber. The controller may control the first and / or second release valves to maintain the respective target pressures.

[0135] The controller may control the first and / or second discharge valves to maintain a target flow rate or composition from one or each of the first and second outlets based on flow rate data, upstream pressure data and / or composition data received by the controller. The controller may control the first and / or second discharge valves to maintain a target flow rate ratio between the flows out of the first and second outlets based on flow rate data and / or composition data received by the controller. The target flow rate ratio may correspond to a ratio of a total flow rate out of the first outlet to a total flow rate out of the second outlet, or a ratio of a flow rate of a first fluid reaction product out of the first outlet to a flow rate of a second fluid reaction product out of the second outlet.

[0136] The controller may, for example, determine whether an excess amount of the second fluid reaction product is present in the outlet stream through the first outlet or may determine whether an excess amount of the first fluid reaction product is present in the outlet stream through the second outlet based on composition data received at the controller for each outlet stream. The controller may control the first and / or second discharge valves to vary the flow rate through the porous wall of the electrolytic cell based on the determination.

[0137] The electrolyser may be operated to maintain thermodynamic and / or flow rate conditions such that the Reynolds number in the inlet chamber is 4000 or less, such as 2300 or less.

[0138] According to a fourth aspect, there is provided a method of operating a composite porous electrode in an electrolytic cell, comprising the steps of: forming a composite porous electrode by an additive manufacturing or powder pressing process in the form of a sheet-like or tubular wall having a thickness direction between two opposing major surfaces of the porous electrode; The building material of the additive manufacturing process or the powder of the powder pressing process is dispersed such that a composite porous electrode is formed by a layered structure between two main surfaces including at least two layers having different material compositions, and in use, a flow through the porous electrode between the two opposing main surfaces along the thickness direction passes through the at least two layers; A method is provided in which one of the layers forms an electrocatalytic region of a porous electrode that is spaced from at least one of the major surfaces of the electrode.

[0139] The electrocatalytic region may include an electrocatalyst for catalyzing an oxidation or reduction reaction with the aqueous electrolyte solution.

[0140] Layers of the porous electrode other than the electrocatalytic regions provide passive regions that are less electrocatalytically active than the electrocatalytic regions for catalyzing each half-reaction of the electrolysis of the electrolyte liquid, and the passive regions may optionally include insulating or dielectric materials for suppressing each half-reaction of the electrolysis of the electrolyte liquid.

[0141] The method may comprise placing a composite porous electrode in an electrolytic cell to provide an electrolytic cell or electrolytic cell installation according to the first or second aspect.

[0142] According to a fifth aspect, there is provided a method for producing a composite porous electrode for an electrolytic cell, comprising the steps of: forming a composite porous electrode body such that the body extends linearly along a longitudinal axis and has an orthogonal thickness direction from a first major surface to an opposing major surface; forming a plurality of angled channels extending through the body from the first and second major surfaces, each of the channels being angled with respect to both the longitudinal axis and the thickness direction; Including, The plurality of gradient channels may include During the manufacture of the body by additive manufacturing processes, or A method is provided in which the body is formed after manufacture by removing material from the body, such as by a laser drilling process.

[0143] A channel may be tilted relative to an axis or direction when the centroid axis of the channel is tilted relative to the respective axis or direction.

[0144] Each channel may have an average diameter along its length of from 25 to 150 μm, for example from 25 to 100 μm, 25 to 75 μm or about 50 μm.

[0145] The body may be axisymmetric about the longitudinal axis, such that the thickness direction at any point around the longitudinal axis is the local thickness direction that corresponds to the radial direction about the longitudinal axis.

[0146] The body may be non-axisymmetric, such as a planar electrode that extends linearly along both the transverse and longitudinal axes. The extent of the composite porous electrode along the longitudinal axis may be relatively greater than its extent along the transverse axis, so that it is elongated along the longitudinal axis.

[0147] The body may include an electrocatalytic material (i.e., an electrocatalyst) for catalyzing the electrolytic half-reaction of the electrolyte solution. Suitable catalysts and electrolyte solutions that may be used are discussed elsewhere herein.

[0148] Each channel may be formed to have a cross-section that diverges along the thickness direction.

[0149] The method may further include providing a coating comprising an electrocatalyst on the interior surfaces of the channels and / or on one or both major surfaces of the body to provide an electrocatalytic region of the body, and / or, optionally, providing a passivation coating on the major surfaces of the body over the coating comprising an electrocatalyst.

[0150] The controller described herein may include a processor. The controller and / or processor may include any suitable circuitry to perform the methods as described herein and illustrated in the drawings. The controller or processor may include at least one application specific integrated circuit (ASIC), at least one field programmable gate array (FPGA), single or multi-processor architecture, sequential (von Neumann) / parallel architecture, at least one programmable logic controller (PLC), at least one microprocessor, at least one microcontroller, and / or a central processing unit (CPU) to perform the methods and / or the functions described for which the controller or processor is configured.

[0151] The controller may include, or the processor may be in communication with, one or more memories that store the data described herein and / or store machine-readable instructions (e.g., software) for implementing the processes and functions described herein (e.g., determining parameters and executing control routines).

[0152] The memory may be any suitable non-transitory computer-readable storage medium, one or more data storage devices, and may include a hard disk and / or a solid-state memory (such as a flash memory). In some examples, the computer-readable instructions may be transferred to the memory via wireless signals or via wired signals. The memory may be a permanent non-removable memory or may be a removable memory (such as a Universal Serial Bus (USB) flash drive). The memory may store a computer program including computer-readable instructions that, when read by the processor or controller, cause the implementation of the methods described herein and / or illustrated in the figures. The computer program may be software or firmware, or a combination of software and firmware.

[0153] Except where mutually exclusive, features described in relation to any one of the above embodiments may be applied mutatis mutandis to any other embodiment. Further, except where mutually exclusive, any feature described herein may be applied to any embodiment and / or may be combined with any other feature described herein.

[0154] The invention will now be described, by way of example only, with reference to the accompanying drawings. [Brief description of the drawings]

[0155] [Figure 1] FIG. 1 is a schematic cross-sectional view of a first exemplary electrolytic cell. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a second exemplary electrolytic cell. [Figure 3a] FIG. 1 is a cross-sectional view illustrating a schematic of an exemplary electrode arrangement of an electrolytic cell as disclosed herein. [Figure 3b] FIG. 1 is a cross-sectional view illustrating a schematic of an exemplary electrode arrangement of an electrolytic cell as disclosed herein. [Figure 3c] FIG. 1 is a cross-sectional view illustrating a schematic of an exemplary electrode arrangement of an electrolytic cell as disclosed herein. [Figure 3d] FIG. 1 is a cross-sectional view illustrating a schematic of an exemplary electrode arrangement of an electrolytic cell as disclosed herein. [Figure 3e] FIG. 1 is a cross-sectional view illustrating a schematic of an exemplary electrode arrangement of an electrolytic cell as disclosed herein. [Figure 3f] FIG. 1 is a cross-sectional view illustrating a schematic of an exemplary electrode arrangement of an electrolytic cell as disclosed herein. [Figure 3g] FIG. 1 is a cross-sectional view illustrating a schematic of an exemplary electrode arrangement of an electrolytic cell as disclosed herein. [Figure 4a] 1 is a flow diagram of a method for making a composite porous electrode. [Figure 4b] 1 is a flow diagram of a method for making a composite porous electrode. [Diagram 5] FIG. 13 is a schematic cross-sectional view of a third exemplary electrolytic cell. [Figure 6] FIG. 1 is a schematic diagram showing the layout of an electrolysis facility. [Figure 7] 1 is a flow diagram of a method for controlling the operation of an electrolysis facility. [Figure 8a] 1 is a flow diagram of a method for making a composite porous electrode. [Figure 8b] 1 is a flow diagram of a method for making a composite porous electrode. [Figure 9] FIG. 1 is an optical micrograph (377.5x magnification) of the surface of a porous electrode formed by laser drilling channels into the wall of an alumina coated Inconel® alloy 625 tube. [Figure 10] FIG. 10 shows an image of a cross section of the porous electrode shown in FIG. 9 obtained by X-ray computed tomography (XCT). [Figure 11(a)] FIG. 11 is an enlarged view of a portion of the image shown in FIG. [Figure 11(b)]FIG. 1 is an optical micrograph (377.5x magnification) of the surface of a porous electrode formed by laser drilling channels into the wall of an alumina coated Inconel® alloy 625 tube. [Figure 12(a)] FIG. 2 is a representative gas chromatogram of cathode gas obtained from an electrolyser according to the invention, characterizing (from left to right) three peaks related to hydrogen, oxygen and nitrogen content. [Figure 12(b)] FIG. 2 is a representative gas chromatogram of the anode gas obtained from an electrolyser according to the invention, characterizing (from left to right) three peaks related to hydrogen, oxygen and nitrogen content. [Figure 13(a)] FIG. 2 is a representative gas chromatogram of an oxygen calibration gas. [Figure 13(b)] FIG. 1 shows representative gas chromatograms of hydrogen and nitrogen calibration gases. [Figure 14] FIG. 13 is a contour plot of a simulation of the flow through a model electrolyser. [Figure 15] FIG. 13 is a contour plot of a simulation of the flow through a model electrolyser. [Figure 16] FIG. 13 is a contour plot of a simulation of the flow through a model electrolyser. [Figure 17a] 16 is a graph comparing compositional results from the simulations of FIG. 14 and FIG. 15. [Figure 17b] 16 is a graph comparing compositional results from the simulations of FIG. 14 and FIG. 15. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0156] FIG. 1 illustrates in schematic cross-sectional view a first exemplary configuration of an electrolytic cell 10 comprising an inlet chamber 100 and a holding chamber 110 .

[0157] In this example, the electrolytic cell 10 is in the form of a straight duct having adjacent inlet chamber 100 and holding chamber 110 separated by a first porous wall 115. The chambers 100, 110 are elongated along the longitudinal axis A of the electrolytic cell from a first end at which there is an inlet 12 to the inlet chamber 100 to an opposing second end at which there is a first outlet 113 of the holding chamber 110 and a second outlet 104 of the inlet chamber 100. In other examples, the inlet and holding chambers may be of any suitable shape or form, and the present disclosure is not limited to chambers having a straight form as in this first example.

[0158] In this example, the holding chamber 110 is associated with the first electrode 111 and configured to hold a fluid reaction product generated at the first electrode 111 in use, while the inlet chamber 100 is associated with the second electrode 102 and configured to hold a fluid reaction product generated at the second electrode 102 in use. The first electrode 111 and the second electrode 102 may be connected to, and form part of, an electrolysis circuit that includes a power source in use.

[0159] The inlet 12 to the inlet chamber 100 is configured to receive electrolyte liquid from a source of electrolyte liquid that is, in use, coupled to the inlet 12. The inlet chamber 100 is configured to transport electrolyte liquid along the inlet chamber 100 from the inlet 12 to an opposing second outlet 104 such that the electrolyte liquid (or associated ions) reacts with a second electrode 102 associated with the inlet chamber 100.

[0160] In this example, the second electrode 102 is a flow past electrode (as described in more detail below) that defines the walls of the inlet chamber 100, in particular the first porous wall 115 and the wall facing the first electrode 111, such that the inlet chamber 100 is defined between the first porous wall 115 and the second electrode 102, and the porous wall 115 is disposed between the first electrode 111 and the second electrode 102.

[0161] The first porous wall 115 is configured to allow a divergent stream of electrolyte liquid in the inlet chamber 100 to flow through the first porous wall 115 and into the retention chamber 110. The porous medium provides a resistance to flow such that the flow rate of electrolyte liquid through the porous medium is a function of the pressure differential across the medium and the permeability of the porous medium.

[0162] For example, a branched stream of electrolyte liquid may be flowed through the first porous wall 115 under the action of a pressure differential between the inlet chamber 100 and the holding chamber 110. The first porous wall 115 is configured such that when a pressure differential exists between the inlet and outlet chambers, the first porous wall 115 performs (i.e., causes) a pressure drop corresponding to the branched stream of electrolyte liquid as it passes through the first porous wall 115. The pressure drop represents a natural resistance to flow through the porous wall 115.

[0163] A corollary is that since flow rate is a function of pressure differential and permeability as noted above, the first porous wall 115 still provides a resistance to flow in the absence of a pressure differential across it, and therefore a higher pressure is required at the outlet side of the porous wall than at the inlet side to drive reverse flow through the first porous wall.

[0164] Thus, the first porous wall 115 is configured to inhibit backflow of electrolyte liquid and / or any fluid reaction products produced at the first electrode 111 (i.e., backflow from the holding chamber 110 toward the inlet chamber 100) because such backflow would be opposed to a pressure gradient across the first porous wall 115 (i.e., in the case of pressure-driven bifurcation flow through the first porous wall 115) or because, in the absence of a pressure differential across the wall, such backflow would have no motive force to overcome the flow resistance of the first porous wall.

[0165] These two modes or mechanisms of flow resistance provided by the first porous wall (i.e., (i) due to a pressure gradient through the pressure-driven branch flow from the inlet chamber through the porous wall to the holding chamber, and (ii) due to the absence of pressure-driven backflow in the absence of a pressure difference across the porous wall) apply to all embodiments of the porous wall as described herein, and as a result, the embodiments described below may not include a further detailed discussion of these mechanisms. Those skilled in the art will appreciate that the particular configuration of the porous wall may be determined based on the intended operating conditions and whether the electrolyzer is to be operated with a pressure-driven branch flow or without a pressure difference across the wall. For example, a relatively lower permeability and / or a relatively larger thickness may be selected for a porous wall that is to be operated without a pressure difference across the wall, while a relatively higher permeability and / or a relatively smaller thickness may be selected for a porous wall that is to be operated with a pressure difference driving the pressure-driven branch flow to the holding chamber. This is because the branch flow may provide additional flow resistance due to the pressure gradient through the porous wall and also due to the inertia of the branch flow.

[0166] The first electrode 111 is arranged such that, in use, a branched flow of electrolyte liquid passing through the first porous wall 115 into the holding chamber 120 reacts with the first electrode 111 .

[0167] In this example, the first electrode 111 is provided in the form of a layer adjacent to and substantially coextensive with the first porous wall 115. As will become apparent from further discussion below, the present disclosure contemplates that in some embodiments the first electrode 111 is bonded to or integral with the first porous wall 115, or in other embodiments is separate from the first porous wall 115. For example, both the first porous wall and the first electrode may be provided by a composite porous electrode.

[0168] In this example, there is a flow path of electrolyte fluid from the inlet chamber 100 to the holding chamber 110, the flow path comprising an upstream portion through the passive portion of the first porous wall 115 and a downstream portion through or adjacent to the electrocatalytic region of the first electrode 111. The term "passive" is used herein to mean that the passive region is less electrocatalytically active than the electrocatalytic region for each half-reaction of the electrolysis of the electrolyte fluid or inhibits each half-reaction. It is within the skill of the art to select a material for the passive region that is less electrocatalytically active than the electrocatalytic region. Definitions of passive regions being less electrocatalytically active than the electrocatalytic region are given elsewhere in this specification (including in the Summary section) and may be applied to this and other examples. By way of example only, the passive and electrocatalytic regions may be configured such that the rate of each half-reaction of the electrolysis of the electrolyte fluid may be lower in the passive region (as a whole) than in the electrocatalytic region (as a whole). The passive region may be provided by a passivating coating of the matrix (or body), such as a dielectric coating as discussed elsewhere herein.

[0169] When the first electrode 111 is implemented as a flow-through electrode, e.g., coupled to or integral with the first porous wall, the downstream portion of the flow path passes through the electrocatalytic region. For example, when the first electrode is separate from the porous wall (e.g., provided on an opposing wall of a holding chamber), the downstream portion may be adjacent to the electrocatalytic region.

[0170] Thus, in this example, the flow resistance provided by the porous wall as described above is provided by the passive region of the porous wall at a location upstream relative to the electrocatalytic region of the electrode. In use, a first reaction product is produced at the electrocatalytic region of the electrode downstream of the passive region of the porous wall, such that backflow of the fluid reaction product is inhibited by the upstream flow resistance provided by the passive region of the porous wall which inhibits backflow of the first reaction product as described above.

[0171] In some embodiments of the electrolytic cell as contemplated herein, the first porous wall and the first electrode may be provided by a composite porous electrode, such that the downstream portion of the flow path passes through (rather than adjacent to) the respective electrocatalytic region. The upstream boundary of the electrocatalytic region (i.e., the boundary facing the inlet chamber and being the first portion of the electrocatalytic region through which the branch flow to the holding chamber passes) may be referred to as the ion exchange boundary of the electrode. The electrocatalytic region may be porous and may exhibit resistance to flow in the same manner as a passive region. Nevertheless, fluid reaction products may be produced at any location within the electrocatalytic region, such that in this example, the portion of the composite porous electrode relevant to suppression of backflow is the upstream passive region. As mentioned above, flow resistance is believed to be a function of pressure difference and permeability. The specific configuration of the porous wall, and in particular the passive region (e.g., its permeability and thickness), may be determined based on the intended operating conditions and the mode or mechanism relied upon to suppress backflow of the respective reaction products as described above. Nonetheless, in this example, the composite porous electrode is configured such that the upstream portion of the flow path provides a significant proportion of the total flow resistance provided by the upstream and downstream portions.

[0172] This may be expressed as the relative flow permeability of the non-electrocatalytic areas of the porous walls and the electrocatalytic areas of the electrodes; in particular, the relative flow permeability may satisfy the following inequality:

[0173]

number

[0174] where k is the permeability, t is the thickness, the subscript e refers to the electrode (or electrocatalytic region), and the subscript w refers to the wall (or non-electrocatalytic region). The relative permeability may be 2 or less, e.g., 1 or less, 0.5 or less, or 0.2 or less. A relative permeability of less than 5 corresponds to a pressure drop across the non-electrocatalytic region of the porous wall providing at least one-sixth of the total pressure drop or flow resistance along the upstream and downstream portions of the flow path, while a relative permeability of 0.2 corresponds to a pressure drop across the non-electrocatalytic region that is five times greater than the pressure drop across the electrocatalytic region of the electrode.

[0175] Between the first electrode 111 and the second electrode 102 there is a separation gap (i.e. the distance between the ion exchange boundaries of the electrodes) with a substantially constant minimum separation distance between points along the electrodes in this particular example due to the side-by-side arrangement of the electrodes 111, 102. In this particular embodiment, both electrodes 111, 102 extend linearly parallel to the longitudinal axis A.

[0176] In this example, the holding chamber 110 and the inlet chamber 100 are elongate along a longitudinal axis A and extend adjacent one another along coextensive longitudinal extents toward adjacent first and second outlets 113 and 104, although it should be understood that other configurations are possible. For example, the outlets 113, 104 need not be adjacent one another and may emit their respective streams along different directions.

[0177] Suitable electrolyte solutions and electrocatalyst materials for each electrode are disclosed in the Summary and are applicable to this example and all examples herein.

[0178] The operation of the first exemplary electrolytic cell 100 will now be described by way of example with reference to electrolysis with an electrolyte solution that is a liquid water-based (aqueous) electrolyte solution (e.g., electrolyte solution) at subcritical conditions, e.g., at an inlet pressure of less than 22 MPa and an inlet temperature of less than 360° C., e.g., 20 MPa at a temperature of 100° C. The electrolyte solution may include an aqueous solution containing NaOH at a concentration of 0.5 M. In this example of operation, the first electrode 111 is the anode and the second electrode 102 is the cathode. In use, ions are transferred between the electrodes. In this particular example, hydroxide ions (OH - ) is transported through the electrolyte to the anode to produce the first reaction product (oxygen) at the anode.

[0179] An inlet flow of electrolyte liquid is provided to the inlet chamber 100 via the inlet 12 and undergoes a reduction reaction at the second electrode 102 (cathode) to produce a second reaction product, in this example gaseous hydrogen, along with hydroxide ions for migration to the anode. The second reaction product (hydrogen) has a lower density than that of the liquid electrolyte liquid, such that when the longitudinal axis A of the electrolytic cell 10 is oriented vertically, the density of the resulting multi-component mixture is non-uniform and less dense where the reaction product is produced, and thus the production of the second reaction product tends to drive the flow of electrolyte liquid upwards through the inlet chamber 100 towards the second outlet 114 under a buoyancy effect. This buoyancy effect is believed to inhibit migration of the second reaction product across the separation gap towards the first electrode 111.

[0180] In this particular example, a pressure differential exists between the inlet chamber 100 and the holding chamber 110, resulting in a pressure drop across the first porous wall. The pressure differential drives the branched stream of electrolyte liquid through the first porous wall 115 into the holding chamber 110 and through the first electrode 111, which in this particular example is provided adjacent the first porous wall 115 as described above. The branched stream of electrolyte liquid reacts at the first electrode 111 to produce a first reaction product, which in this example is gaseous oxygen (with the transfer of electrons to the anode). The first reaction product has a lower density than the branched stream of liquid electrolyte liquid and may therefore drive the flow of electrolyte liquid upward through the holding chamber 110 under buoyancy effects towards the first outlet 113 as described above.

[0181] In this example operation, the first reaction product (oxygen) passes through the first electrode 111 and is entrained in the branched flow to be retained in the holding chamber 110. The first electrode 111 is defined as being associated with the holding chamber 110 because the first reaction product produced at the first electrode 111 is retained in the holding chamber. In some examples, the first electrode 111 may not be within the holding chamber 110 or adjacent to the holding chamber. For example, the first electrode may be attached to or integral with the first porous wall 115 that separates the inlet chamber 100 and the holding chamber 110.

[0182] Due to the pressure drop across the first porous wall 115, the first reaction product does not tend to migrate towards the inlet chamber 100 because it is resisting the pressure gradient and inertia of the bifurcated flow through the first porous wall 115. Thus, backflow of the fluid reaction product is inhibited by the pressure gradient and / or pressure-driven flow across the porous wall. Thus, the first porous wall 115 inhibits mixing of the reaction products generated at the first and second electrodes in the inlet chamber 100.

[0183] Additionally, the second reaction product may be inhibited from migrating into the holding chamber 110 and mixing with the first reaction product. First, the flow rates and buoyancy effects within the inlet chamber 100 may be such that the second reaction product does not tend to migrate toward the first porous wall 115 and reach the first porous wall and migrate into the holding chamber 110, as described in more detail below. Second, when the second electrode is a cathode and the first electrode is an anode, the second reaction product may be stripped of its electrons upon striking the first electrode such that it becomes positively charged, and thus may reverse direction back toward the second electrode rather than entering the holding chamber 110 as ions (e.g., as protons when the second reaction product is hydrogen).

[0184] It should be understood that while in the above example the first electrode is the anode and the second electrode is the cathode, with an oxidation reaction and a reduction reaction at each electrode, respectively, in other examples the polarity of the electrodes may be reversed.

[0185] The second example of operation of the electrolytic cell 10 differs from the first example described above only in that there is no substantial pressure difference between the inlet chamber and the holding chamber, and therefore there can be substantially no pressure-driven flow of electrolyte liquid through the first porous wall 115, and there can be no or minimal pressure drop across the first porous wall 115. Nevertheless, because the first porous wall 115 is configured to allow the flow of electrolyte liquid, the first porous wall is also configured to allow the flow of ions through the channels or pores of the porous wall. Thus, in a variation of this second example of operation, ions are transferred between the first electrode 111 and the second electrode 102 in the absence of substantial flow of electrolyte liquid through the first porous wall.

[0186] In a variation of this second example operation, ions may flow from the inlet chamber 100 through the first porous wall 115 to the first electrode 111, for example, under the action of an electromotive force. The first porous wall 115 may be non-electrocatalytic, such that the ions may react only with the first electrode 111 to produce a first reaction product that passes through the first porous wall 115. For example, as described above, the first electrode 111 may be provided as a layer on the outlet side of the first porous wall (i.e., the side adjacent the holding chamber 110, as opposed to the side adjacent the inlet chamber 100). The first electrode 111 may be provided as a mesh or foil including an electrocatalytic material attached to the first porous wall 115, or as a coating of an electrocatalytic material provided on the first porous wall 115 or on a mesh or foil attached thereto. In one variation, the first electrode 111 may be supported within the holding chamber 110 as a flow-through electrode or may be spaced apart from the first porous wall 115, for example, defining a wall of the holding chamber 110 opposite the first porous wall (i.e., as a flow-past electrode).

[0187] While the present disclosure contemplates that the electrodes provided in association with the porous wall as described above may have an electrical path to the electrolysis circuit independent of the porous wall, in the exemplary electrolysis cell 10 described herein with reference to Figure 1, the first porous wall 115 is electrically conductive and configured to pass electrical current from the first electrode 111 to the electrolysis circuit. In this particular embodiment, the first porous wall 115 also provides structural support to the first electrode 111.

[0188] As discussed above, in this variation, the first reaction product is generated in response to ions associated with the electrolyte liquid reacting with the first electrode 111 disposed within or defining the wall of the holding chamber 110, such that the first reaction product is generated, for example, within the electrocatalytic region of the first electrode or within the holding chamber 110 downstream of the passive region of the first porous wall 115. Nonetheless, in the absence of a substantial pressure difference between the inlet chamber 100 and the holding chamber 110 that drives a bifurcated flow of the electrolyte liquid into the holding chamber 110, the first porous wall 115 inhibits backflow of the first reaction product into the inlet chamber 100 as discussed above. In particular, as a porous medium, the first porous wall presents a greater resistance to flow of the first reaction product from the holding chamber to the inlet chamber than the flow path through the holding chamber 110 to the first outlet 113, such that the first reaction product preferentially flows toward the first outlet 113. Thus, backflow of the fluid reaction product is inhibited by the upstream flow resistance of the passive porous region. The resistance to flow may be a function of the permeability and thickness of the porous wall, as described elsewhere herein. Furthermore, by producing the first reaction product at a lower density than the electrolyte liquid, the first reaction product may be driven upwardly towards the first outlet 113 in preference to backflow through the first porous wall 115 (a path that may have a horizontal component in use when the longitudinal axis A is vertically aligned).

[0189] Figure 2 illustrates a second exemplary electrolytic cell 20. Similar to the first exemplary electrolytic cell 10 of Figure 1, the electrolytic cell 20 has a holding chamber 210 and an inlet chamber 200 having respective first and second outlets 213 and 204 separated by a first porous wall 215, and is configured to receive a flow of electrolyte liquid through the inlet 22 into the inlet chamber 200, from which a branch flow of electrolyte liquid can pass through the first porous wall 215 into the holding chamber 210.

[0190] The electrolytic cell 20 is arranged such that the inlet chamber 200 is an annular outer chamber and the holding chamber 210 is a core inner chamber surrounded by the inlet chamber 200. In this particular example, the chambers 200, 210 are arranged concentrically about the longitudinal axis A, and the chambers 200, 210 have cylindrical outer boundaries. In various examples, the electrolytic cell may have other concentric and non-concentric configurations. For example, the boundaries of each chamber may be conical and concentric.

[0191] In this example, there is a composite porous electrode 217 that defines both a first porous wall 215 (which may be a porous passive region of the composite porous electrode) and a first electrode 211 (the electrocatalytic region of the composite porous electrode). The composite porous electrode 217 separates the inlet chamber 200 and the holding chamber 210 such that the first electrode 211 is a flow-through electrode. In this example, the inlet chamber 200 is provided with a second electrode 202 that defines the radially inner surface of the cylindrical outer wall of the inlet chamber 200 and is a flow-past electrode.

[0192] As described above with respect to the first exemplary electrolytic cell 10, the composite porous electrode 217 is configured to allow electrolyte fluid to flow from the inlet chamber 200 to the holding chamber 210, but is configured to inhibit backflow of reaction products generated at the composite porous electrode (particularly at the electrocatalytic region of the composite porous electrode) back toward the inlet chamber 200. The composite porous electrode is configured to inhibit backflow of reaction products due to pressure gradients or pressure-driven flow as described above when a pressure differential exists across the wall. The composite porous electrode can also inhibit backflow of reaction products by upstream flow resistance of passive regions as described below, including in the presence or absence of a pressure differential across the composite porous electrode, and / or by other mechanisms when modified as envisioned below with reference to Figures 3 and 5.

[0193] Upstream of the inlet chamber 200 is an inlet manifold 23 configured to receive electrolyte liquid from a source of electrolyte liquid at port 21 and provide an annular flow of electrolyte liquid to the annular inlet 22 of the inlet chamber 200. In this example, the inlet manifold 23 has a diverging conical profile configured to direct the electrolyte flow around a conical flow divider 24. In variations, the manifold 23 may take any suitable shape or configuration. For example, the manifold 23 may have a cylindrical outer wall and there may be a conical flow divider within the manifold 23 to direct the flow towards the annular inlet 22.

[0194] The use of the second exemplary electrolytic cell 20 will now be described, by way of example only, with reference to electrolysis with an electrolyte solution that is, for example, a supercritical water-based (aqueous) electrolyte solution at an inlet pressure of 22.5 MPa and an inlet temperature of 375° C.

[0195] At supercritical conditions, the fluids behave as if they do not have distinct liquid and gas phases. Supercritical electrolytes can be advantageous for use in electrolysis compared to subcritical electrolytes. In particular, supercritical fluids are completely miscible with each other, so that the mixture of fluids forms a single phase with no interface or surface tension between them. Thus, when reaction products remain supercritical rather than gaseous when they are produced (e.g., by having a lower critical temperature and pressure than the electrolyte liquid, or by the temperature and pressure being otherwise higher than their respective critical points), they remain completely miscible with the electrolyte liquid. Thus, reaction product bubbles do not accumulate on the surface of the electrodes. Such accumulation could otherwise inhibit the reaction by preventing local interaction between the electrolyte liquid and the electrodes.

[0196] Furthermore, it is known that the conductivity of electrolyte liquids 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 3000 bar", A. Eberz and EU Franck, Ber. Bunsenges. Phys. Chem. 99, 1091-1103 (1995) No. 9, especially Table 2). Without wishing to be bound by theory, it is believed that the dissociation constant and conductivity of water increase with increasing temperature and pressure. Furthermore, the conductivity of an electrolyte or electrolyte liquid (e.g., an electrolyte solution) is a function of pressure and temperature, and it is observed that the conductivity increases as the pressure and temperature increase toward the critical point. Within the supercritical range (i.e., within the range of pressure and temperature conditions where the temperature is at least the critical temperature of the fluid and the pressure is at least the critical pressure of the fluid), the conductivity may decrease with increasing temperature at constant pressure. However, the conductivity may increase in the supercritical range as the pressure is increased. Thus, the concentration of electrolyte in the electrolyte solution may be decreased by operating at relatively high temperature and pressure. The supercritical range is an example of a relatively high pressure and temperature condition, and it is believed that operation in the supercritical range may provide a relatively higher conductivity of the electrolyte liquid compared to operation in the subcritical range, which is at a temperature and pressure significantly below the critical temperature and pressure. Operation in conditions where the electrolyte liquid conductivity is higher may reduce the ohmic losses associated with the electrolyte while still providing adequate conductivity, or may otherwise allow the use of a different electrolyte associated with reduced ohmic losses.

[0197] By way of example only, a suitable electrolyte solution for use with the first exemplary electrolytic cell and / or the second exemplary electrolytic cell described above is an aqueous electrolyte solution containing NaOH as the electrolyte. As noted above, the conductivity of electrolyte solutions tends to increase with temperature and pressure.

[0198] To illustrate the above trend of increasing conductivity with pressure and temperature, reference may be made to the above-referenced paper by Eberz and Franck, which reports that at 0.1 MPa and 25° C., an electrolyte consisting of NaOH having a concentration of 17% by weight exhibits a conductivity of 0.4 Scm -1 while at 30 MPa and 400°C the electrolyte exhibits a conductivity of 1.3 Scm -1 For a 0.5M NaOH solution, the conductivity at 22.5 MPa and 375°C is approximately 150-200 mS cm -1 while at 0.1 MPa and 25°C the conductivity is about 100 mS cm -1 It is presumed that this may be the case.

[0199] In this example, the first electrode 211 is the anode and the second electrode 202 is the cathode. In use, ions are transferred between the electrodes.

[0200] In a first example of operation of the electrolytic cell 20, an inlet flow of electrolyte liquid is provided to the inlet chamber 200 through the inlet manifold 23 into the annular inlet 22 of the inlet chamber 200. The electrolyte liquid undergoes a reduction reaction at the second electrode 202 (cathode) to produce a second reaction product, in this example supercritical hydrogen, along with hydroxide ions for migration to the anode. The second reaction product (hydrogen) has a density less than that of the electrolyte liquid, but remains fully miscible with the electrolyte liquid since both are supercritical. Nevertheless, when the longitudinal axis A of the electrolytic cell is oriented vertically, the production of the second reaction product tends to drive the flow of electrolyte liquid upwards through the inlet chamber 200 towards the second outlet 204 under the buoyancy effect. As discussed above with reference to the first example, it is believed that this buoyancy effect can inhibit migration of the second reaction product across the separation gap towards the first electrode 211 (as provided by the first composite porous electrode 217).

[0201] The branched stream of electrolyte liquid flows through the first composite porous electrode 217 into the holding chamber 210, passing through the first porous wall 215 and the first electrode 211. The electrolyte liquid or associated ions (e.g., hydroxide ions) undergo an oxidation reaction at the first electrode (anode) 211 to produce a first reaction product, in this example supercritical oxygen (with the transfer of electrons to the anode). The first reaction product has a lower density than the electrolyte liquid and may therefore drive the flow of the branched stream upward through the holding chamber 210 towards the first outlet 213 under buoyancy effects as described above.

[0202] The first reaction product (oxygen) passes through the first electrode 211 and may be entrained in the branched flow so as to be retained within the holding chamber 210 .

[0203] As described above with respect to the first operational example of the first electrolytic cell 10, the first composite porous electrode 217 inhibits backflow of the electrolyte solution and / or any fluid reaction products produced at the first electrode 211, for example, by the resistance to flow provided by the porous walls. Although the present operational example refers to a pressure difference between the inlet chamber 200 and the holding chamber 210 such that backflow is inhibited by a pressure gradient or pressure-driven flow across the porous walls, the exemplary electrolytic cell 20 can equally be operated without a pressure difference, as described above with respect to the first exemplary electrolytic cell 10, and backflow of fluid reaction products can be inhibited by the upstream flow resistance of the passive regions.

[0204] The inventors have found that by preventing mixing of the reaction products as described above, the electrodes can be positioned with a relatively short minimum separation distance between them, thereby reducing ohmic losses in the electrolytic cell.

[0205] Furthermore, the inventors have found that by providing a porous wall that inhibits backflow from the holding chamber to the inlet chamber as described herein, any flow through the porous wall is substantially unidirectional, even when the area of ​​the porous wall is relatively large for a given amount of flow (i.e., the flow rate per unit area through the porous wall is relatively low) compared to previously considered configurations, in which the flow-through electrode may be applied to span a long duct, resulting in a relatively low area of ​​the electrode relative to the flow rate, or a relatively high flow rate per unit area through the flow-through electrode. It is believed that by providing a relatively high flow rate through the flow-through electrode in the previously considered configurations, backflow may be prevented by flow inertia.

[0206] For a given flow rate of electrolyte liquid, if the area of ​​the electrodes is increased in such previously discussed configurations, such inertial effects may be reduced and there may be a risk of local flow reversals that may allow mixing of reaction products. By providing porous walls as disclosed herein, the flow rate per unit area can remain relatively low for a given reaction area of ​​the electrodes (or conversely, the reaction area can be relatively large for a given flow rate), while relying on the porous walls to prevent flow reversals as described herein.

[0207] Thus, the inventors have found that it is possible to provide an electrolytic cell configuration in which the porous walls have a relatively large area for a given flow rate. As a result, the electrodes can have a relatively larger surface area for a given flow rate of electrolyte solution to the electrolytic cell and / or of reaction products produced by the electrolytic cell, allowing a relatively larger surface area for carrying out electrolytic reactions, which may allow a higher reaction rate for a given flow rate of electrolyte solution. These advantages apply equally to all exemplary configurations herein. The expression "surface area" as used herein with reference to an electrode is intended to refer to the area of ​​a substantially continuous surface extending across the respective boundaries of the electrocatalytic regions of the electrode, and not the total surface area of ​​all pores and channels of such electrocatalytic regions (which may be referred to as the area of ​​the electrolyte interface of the electrocatalytic region, or the area of ​​the surface area of ​​the electrocatalytic region adjacent to the electrolyte solution in use). For example, for a substantially flat, rectangular composite porous electrode (or porous electrocatalytic region) having a longitudinal extent X and a lateral extent Y, the surface area refers to the multiplication of dimensions X and Y, rather than the total surface area of ​​all electrocatalytic surfaces throughout any pores and channels of the porous electrode.

[0208] As a result, the size of the electrodes can be relatively large compared to the cross-sectional area and / or separation gap defined by the inlet chamber, so that the separation gap between the electrodes can be relatively elongated. These advantages apply to all exemplary configurations herein. For example, the first electrode and the second electrode may face each other along a co-extensional extent along which there is an average shortest separation distance between the opposing ion exchange surfaces of the electrodes for ion exchange. The ratio of the co-extensional extent (i.e., the distance along the longitudinal axis A along which the electrodes face each other for ion exchange) to the average shortest separation distance may be at least 5, for example, at least 20 or at least 50 (5 to 200, 20 to 200, 50 to 150, etc.).

[0209] In the particular example of the second electrolytic cell 200 shown in Figure 2, the electrodes have a common extension of 100mm, while the average minimum separation distance is 1mm, resulting in a ratio of 100. The corresponding radius to the first composite porous wall may be about 6-7mm, so that in practice the gap between the electrodes is more elongated than appears in the drawing. In this example, the composite porous electrode has a diameter of 0.7μm. 2 The composite porous electrode has a permeability k measured for air at 20°C of about 4 m3 of air passing through it with a pressure difference of 10 kPa. 3 / s / m 2 corresponds to a flow velocity of

[0210] When used at the supercritical conditions mentioned above (i.e., 22.5 MPa and 375°C), the thermoneutral voltage for electrolysis is about 1.3 V, which corresponds to 35.62 kWH per kg of hydrogen reaction product produced. This is 110% of the higher heating value of hydrogen (39.4 kWh / kg) and 93.5% of the lower heating value of hydrogen (33.3 kWh), and therefore represents efficient electrolysis. To sustain the electrolysis reaction at these conditions, the ohmic losses in the electrolyzer should be less than or equal to 0.120 V. In this example, the ohmic losses in the electrolyzer (approximately 150 mScm -1 The potential drop across the electrode (associated with ion exchange through an exemplary electrolyte solution of 0.5 M NaOH with a predicted conductivity of 0.1 V) is about 0.11 V when the electrode spacing is 1 mm, while resistive losses associated with bubble formation at the electrodes are eliminated by operation at supercritical conditions. The electrode spacing may be less than 1 mm, for example, 0.5 mm or between 0.5 mm and 1 mm. Suitable electrocatalysts may be determined by one of skill in the art and are discussed elsewhere herein, but by way of example only, suitable electrocatalysts may include nickel or nickel alloy at the anode (which may be the first electrode) and platinum at the cathode (which may be the second electrode).

[0211] The ohmic losses are a function of the electrolyte conductivity and the electrode spacing. For example, if the electrodes are spaced 3 mm apart, the ohmic losses are 2000 mScm -1 Higher electrolyte conductivities such as may be required.

[0212] Although the first exemplary electrolytic cell is described as operating at subcritical conditions for the aqueous electrolyte solution, the first exemplary electrolytic cell and the second exemplary electrolytic cell and any of their variations may be suitable for operation at supercritical conditions. For example, any of the first exemplary electrolytic cell and the second exemplary electrolytic cell may be configured to operate such that the pressure of the electrolyte solution is between 22 MPa and 27 MPa and when the temperature of the electrolyte solution is at least 374°C, e.g., between 374°C and 550°C or between 374°C and 400°C. In general, it may be desirable to operate at lower temperatures and pressures toward the critical point, thereby minimizing the energy resources for pressurizing and heating the electrolyte solution. Although ohmic losses may be lower at higher temperatures and pressures, it is believed that the efficiency benefits that would be obtained at elevated temperature and pressure conditions may be offset by the additional energy required to heat and / or pressurize the electrolyte solution, unless such additional energy is available as excess energy (e.g., excess heat from a heating source that would otherwise be released without heat recovery).

[0213] Figures 3a-3f show exemplary electrode configurations for use with either the first exemplary electrolytic cell 10 or the second exemplary electrolytic cell 20 described with reference to Figures 1 and 2. Figures 3a-3e show cross-sectional views of the respective electrolytic cells 10, 20 in the region in which the electrodes are coextensive along the longitudinal axis A in a plane parallel to the longitudinal axis. When such a configuration is applied to the first exemplary electrolytic cell 10, which has a rectangular cross section in a plane perpendicular to the longitudinal axis, the exemplary cross-sectional configurations shown in Figures 3a-3e are projected through the entire depth of a rectangular duct (i.e. projected along a transverse axis orthogonal to the longitudinal axis and perpendicular to the cross section shown in Figures 3a-3e). The rightmost boundary 312 shown corresponds to the wall of the duct.

[0214] When such a configuration is applied to a second exemplary electrolytic cell 20 having an axisymmetric configuration about a longitudinal axis to define an annular outer chamber and a core inner chamber, the exemplary cross-sectional configuration shown in Figures 3a-3e is rotated 360° about the longitudinal axis A, with the illustrated right end boundary 312 corresponding to the longitudinal axis of the electrolytic cell.

[0215] For simplicity, the following description of the exemplary electrode configurations will refer only to the second exemplary electrolytic cell 20, using corresponding reference numerals where necessary, but as indicated above is equally applicable and adaptable to the first exemplary electrolytic cell.

[0216] 3a shows a partial cross-sectional profile 310 of the axisymmetric electrolytic cell 20 along a plane intersecting and terminating at the longitudinal axis A of the electrolytic cell. The partial cross-sectional profile corresponds to a longitudinal portion of the electrolytic cell 20 between the inlet of the inlet chamber 200 and the second outlet 204 of the inlet chamber 200, along which the first electrode 211 and the second electrode 202 are coextensive due to ion movement along the separating gap between them.

[0217] 2, the inlet chamber 200 is annular and surrounds the core-retaining chamber 210, the two chambers 200, 210 being separated by a cylindrical first porous wall 215. The radially outer cylindrical wall of the inlet chamber 200 is defined by a second electrode 202, which in this example is a flow past electrode (i.e., configured to impede the flow of electrolyte liquid therethrough). A first radially outer inlet side of the porous wall 215 defines the radially inner boundary of the inlet chamber 200 and opposes (i.e., faces) the second electrode 202 across the inlet chamber 200.

[0218] In the exemplary configuration of FIG. 3a, the porous wall 215 is separated from the first electrode 211 and is disconnected from any power source or circuit such that the porous wall 215 does not participate in any electrolytic reaction or conduct current to or from the first electrode 211. Furthermore, the porous wall 215 may be passive as defined herein and may include (or consist of) stainless steel 316, for example. The porous wall may have an isotropic porous structure. A radially inner outlet side of the porous wall 215 facing outward from the second electrode 202 defines a longitudinal boundary of the holding chamber 210. A first end of the holding chamber 210 adjacent the inlet 22 of the inlet chamber 200 is defined by a wall, while an opposing end of the holding chamber 210 is open to define a first outlet of the holding chamber 210 as described above.

[0219] In this example, the first electrode 211 is disposed within the holding chamber 210 with a small radial gap (e.g., 0.25 mm) between the first electrode and the porous wall 215. The separation gap between the electrodes for ion transfer is therefore the radial distance between the radially outer surface of the first electrode 211 and the radially inner surface of the second electrode 202, which are the respective ion exchange boundaries of the first electrode 211 and the second electrode 202 (as these are the closest boundaries of the electrocatalytic regions of the respective electrodes for carrying out the respective reactions). In this example, this separation gap has a substantially constant radial shortest distance around the electrodes along their length along the longitudinal axis. In other words, at each point along any ion exchange boundary, the shortest distance to the opposing ion exchange boundary of the opposing electrode is along a radial direction relative to the longitudinal axis, and that shortest distance is substantially constant from all points on the electrodes. In this example, the electrodes are cylindrical and concentric, so that the ion exchange boundaries are locally parallel to one another (i.e., in a radial plane intersecting any respective point through the electrodes). In a variant, the shortest radial distance to an opposing ion exchange boundary may be substantially constant over at least 50% of the surface area of ​​one of the ion exchange boundaries.

[0220] 3a, the first electrode 211 may be provided as a flow-through mesh electrode that exhibits a lower resistance to flow than the first porous wall 215, e.g., by having a higher permeability and / or a smaller thickness than the first porous wall 215, such that any pressure drop between the inlet chamber 200 and the holding chamber 210 occurs primarily across the porous wall 215 and the flow rate may be determined by the configuration and resistance to flow of the porous wall 215, rather than that of the first electrode 221.

[0221] By way of example only, the first porous wall 215 may include (e.g., may consist of) a material that is not electrocatalytically active or less electrocatalytically active than the electrocatalytic regions for each half-reaction of the electrolysis, such as stainless steel 316 or titanium. The first porous wall 215 may include a matrix (or body) of any suitable material (e.g., whether or not electrocatalytically active for each half-reaction) and may be coated with a dielectric coating to inhibit each half-reaction of the electrolysis, as described elsewhere herein. The first porous wall 215 may be fabricated by additive manufacturing or powder pressing processes to provide a porous structure, such as an isotropic porous structure having a network of interconnected pores or channels for transporting the electrolyte liquid. By way of example, the first electrode 211 may include a core of stainless steel 316 provided with an electrocatalytic coating comprising nickel. The second electrode 211 may include a core of stainless steel provided with an electrocatalytic coating comprising platinum.

[0222] The implementation of the electrode arrangement of Fig. 3a with the electrolytic cell 20 of Fig. 2 results in a configuration without a composite porous electrode, and as a result, any features exclusively related to the use of a composite porous electrode, as described above with reference to the electrolytic cell 20 of Fig. 2, do not apply. For example, the first porous wall 215 does not conduct current to or from the first electrode 211. When applied to the exemplary electrolytic cell as described above, the electrode configuration of Fig. 3a can inhibit backflow of fluid reaction products due to a pressure gradient across the first porous wall or pressure-driven flow through the porous wall when a pressure drop exists from the inlet chamber to the holding chamber, and / or can inhibit backflow of fluid reaction products due to the upstream flow resistance of a passive region.

[0223] Figure 3b shows a further exemplary electrode configuration 320 that differs from that described above with respect to Figure 3a in that the first electrode 221 and the first porous wall 215 are provided by a composite porous electrode 217. In this example, the composite porous electrode is porous throughout, but only a partial region may be electrocatalytic to define the first electrode 211 (the electrocatalytic region). The electrocatalytic region includes an electrocatalyst (electrocatalytic material) for electrocatalyzing each half-reaction of the electrolysis.

[0224] In this particular example, the electrocatalyst region 211 is a layer formed as a coating on a passive region of the composite porous electrode 217. The electrocatalyst region 211 serves as the longitudinal boundary of the holding chamber 210 and defines a radially inner outlet side of the composite porous electrode 217 that faces outwardly from the second electrode 202.

[0225] The passive regions of the composite porous electrode 217 are configured to be less electrocatalytically active for electrolytic reactions than the electrocatalytic regions by virtue of the absence of an electrocatalyst to catalyze the respective reaction.

[0226] Thus, in this particular example, the ion exchange boundary of electrode 211 is the boundary between passive porous region 215 and the electrocatalytic coating deposited thereon. The electrocatalytic region is within composite porous electrode 217 and is thus spaced from the inlet side of composite porous electrode 217 which faces second electrode 202 and bounds inlet chamber 200. Thus, in use, the bifurcated flows of electrolyte fluid pass through passive porous region 215 before encountering electrocatalytic region 211 to undergo their respective half-reactions, inhibiting backflow of the first reaction products produced in electrocatalytic region 211 as described above.

[0227] In this example, the first electrode 211 is configured to be coupled to an electronic circuit for performing electrolysis via a passive region of the composite porous electrode that is substantially inactive as an electrocatalyst for each half-reaction of the electrolysis yet is electrically conductive to conduct electrical current to and from the first electrode 211.

[0228] 2, where the first electrode 211 is the anode and the electrolyte is a supercritical aqueous solution, an exemplary suitable material for the matrix material of the composite porous electrode 217 may be titanium or stainless steel (e.g., stainless steel 316), while an exemplary suitable electrocatalyst for the electrocatalytic region forming the first electrode 211 may be a coating that is nickel. A suitable material for the second electrode (which serves as the cathode) may be stainless steel with an electrocatalytic coating of platinum.

[0229] By way of example only, a composite porous electrode may be fabricated by forming a porous wall of a non-electrocatalytic matrix material by an additive manufacturing or powder pressing process and coating one side of the porous wall with an electrocatalytic material, for example, by a chemical vapor deposition (CVD) process.

[0230] The first composite porous electrode 217 may have a relatively constant permeability throughout both the non-electrocatalytic and electrocatalytic regions (e.g., by having a relatively constant porosity and / or pore size), so that the flow resistance that determines the branch flow rate is the flow resistance of the first composite porous electrode 217 as a whole.

[0231] When applied to an exemplary electrolytic cell as described above, the electrode configuration of FIG. 3b may inhibit backflow of fluid reaction products due to a pressure gradient across the first porous wall or pressure-driven flow through the porous wall when a pressure drop exists from the inlet chamber to the holding chamber, and / or may inhibit backflow of fluid reaction products due to upstream flow resistance of a passive region.

[0232] According to an alternative manufacturing process, the electrocatalyst region 211 may be formed integrally with the passive porous region 215 rather than being deposited as a coating using an additive manufacturing process, as further described below with reference to FIG. 3c.

[0233] 3c illustrates a further exemplary electrode configuration 330 that differs from that described above with respect to FIG. 3b in that the electrocatalytic region 211 of the first composite porous electrode 217 is provided as a layer that is entirely within the composite porous electrode and embedded between the porous passive region and the composite porous electrode 217. Thus, the electrocatalytic region does not define a radially outer inlet side or a radially inner outlet side of the first composite porous electrode 217.

[0234] The reaction takes place primarily or entirely within the electrocatalysis region 211, with the remaining portions of the composite porous electrode 217 (i.e., the portions that are not the electrocatalysis region) being passive (e.g., less electrocatalytically active or electrocatalytically inactive) as described herein in carrying out the electrolysis reaction. Thus, as described above, each ion exchange boundary is embedded within the composite porous electrode 217 at a location downstream of the passive porous region 215 that prevents backflow of the first reaction product produced in the electrocatalysis region 211 due to the upstream flow resistance of the passive region, as described above.

[0235] Because the outlet side of the first composite porous electrode 217 (i.e., the surface adjacent the holding chamber 210) is passive as defined herein, the respective electrolytic reaction does not have to take place at the outlet side of the first composite porous electrode or within the holding chamber 210 itself. As a result, reaction rates may be more directly related to the flow rate of electrolyte liquid and / or associated ions through the composite porous electrode 217, which may allow for more precise control of reaction rates by adjusting the flow through the electrolytic cell, as described in more detail below.

[0236] When applied to an exemplary electrolytic cell as described above, the electrode configuration of FIG. 3c can inhibit backflow of fluid reaction products when there is a pressure drop from the inlet chamber to the holding chamber due to a pressure gradient across the first porous wall or pressure driven flow through the porous wall and / or can inhibit backflow of fluid reaction products due to upstream flow resistance of a passive region.

[0237] By way of example only, the first composite porous electrode may be manufactured by additive manufacturing or powder pressing process. The building material of the additive manufacturing process or the powder of the powder pressing process may be dispersed such that the composite porous electrode is formed by a layered structure between two main faces corresponding to the inlet side and the outlet side of the composite porous electrode. In this case, the layered structure has three layers corresponding to the passive porous region 215 defining the inlet side, the passive porous region defining the outlet side, and the electrocatalytic region therebetween corresponding to the first electrode 211.

[0238] For example, as described in more detail below with reference to Figure 8a, in an additive manufacturing process, the composite porous electrode may be fabricated layer by layer along its longitudinal axis, with build material dispersed and selectively fused to form each successive longitudinal slice of the composite porous electrode. Build material, including passive build material and electrocatalyst for the electrocatalytic regions, may be selectively applied onto each layer in locations corresponding to the locations of the passive regions and electrocatalytic regions of the first composite porous electrode 217, such that the electrocatalytic regions are embedded within the composite porous electrode as originally fabricated.

[0239] A similar process may be used to provide a composite porous electrode having only two regions as shown in FIG. 3b, for example a passive region defining the inlet side of the composite porous electrode, and an electrocatalytic region defining the outlet surface of the composite porous electrode.

[0240] Composite porous electrodes having multiple regions, including at least one non-electrocatalytic region and at least one electrocatalytic region, may also be formed by other methods, such as a powder pressing process, as described in more detail below with reference to Figure 8b. The powder pressing process may include providing a powder in a canister or die having a shape related to the desired shape of the product, and sintering the powder under elevated temperature and pressure to form a component having a porous structure.

[0241] In the example of Figure 3c, the second electrode may be fabricated as described above with reference to Figures 3a and 3b.

[0242] FIG. 3d shows a further exemplary electrode configuration 340 that differs from the configurations described above in that the inlet side of the first composite porous electrode 217, which faces the second electrode 202 and bounds the inner chamber 200, is passivated to suppress reactions at the inlet side of the composite porous electrode. For example, the composite porous electrode 217 may be provided with a passivation coating 219 that defines the inlet side and has a passivating effect on each half-reaction of the electrolysis. The coating 219 may be an insulating or dielectric coating, for example an oxide coating (e.g., an inorganic metal oxide coating) such as silica (SiO2), zinc oxide (ZnO2), or zirconia (ZrO2). In the examples disclosed herein, the thickness of the passivation coating may be a relatively low percentage of the thickness of the composite porous electrode. For example, in a composite porous electrode having a thickness of 1 mm, the thickness of the passivation coating may be 1 to 20 μm, for example 5 to 10 μm. Increasing the thickness increases the coverage of the underlying surface, but excessive thickness may block the pores. Therefore, an appropriate thickness can be selected to balance coverage while keeping the pores open.

[0243] By passivating the inlet surface of the first composite porous electrode 217, it can be ensured that the ion exchange boundaries of the electrocatalytic region 211 are embedded within the first composite porous electrode 217 (i.e., spaced away from the inlet side) to prevent each half-reaction of the electrolysis from taking place at the inlet side of the composite porous electrode adjacent the inlet chamber.

[0244] In this example, the matrix (or body) 211 of the first composite porous electrode 217 onto which the coating 219 is deposited is porous and electrocatalytically active, providing the electrocatalytic region 211 of the composite porous electrode.

[0245] When applied to the exemplary electrolytic cell as described above, the electrode configuration of FIG. 3b can suppress backflow of fluid reaction products due to a pressure gradient across the first porous wall or pressure-driven flow through the porous wall when a pressure drop exists from the inlet chamber to the holding chamber.

[0246] By way of example only, the composite porous electrode 217 of Figure 3d may be fabricated using additive manufacturing or powder pressing processes as described elsewhere herein to provide the composite porous electrode's matrix (or body) 211 as a porous structure, e.g., a substantially isotropic porous structure. The build material or powder for the fabrication of the body 211 may include an electrocatalyst, such that the matrix (or body) 211 becomes electrocatalytically active and forms the electrocatalytic regions of the composite porous electrode 217.

[0247] For example, the matrix (or body) 211 may include (e.g., consist of) nickel or a nickel-based alloy, such as a nickel-based superalloy. A suitable example is a nickel-chromium alloy, such as an Inconel alloy (e.g., Inconel 600). Such materials may be suitable electrocatalysts for catalyzing the electrolytic half-reaction at the anode and for the aqueous electrolyte at the cathode.

[0248] A passivation coating 219 may then be applied to the matrix (or body) 211. For example, the matrix (or body) 211 may be masked where no coating is required (e.g., in this example, at the exit side of the composite porous electrode) and coated with the passivation coating 219, for example, by a sputtering process such as magnetron sputtering.

[0249] As an alternative example, the matrix (or body) 211 of the composite porous electrode 217 of FIG. 3d may be manufactured with a construction material that is substantially inactive or insufficiently active as an electrocatalyst for each half-reaction of the electrolysis, as described above, to provide a porous structure. For example, the construction material may include (e.g., may consist of) stainless steel 316 or titanium. The matrix (or body) 211 may then be coated with a coating that includes an electrocatalyst. For example, the matrix (or body) 211 may be electroplated with a coating of a suitable electrocatalyst to provide the electrocatalytic regions of the composite porous electrode. The coating may be deposited both internally (i.e., in the pores or channels of the matrix 211) and externally (e.g., on the inlet and / or outlet sides of the matrix). Coating the matrix (or body) 211 to provide the electrocatalytic regions may be particularly advantageous when the electrocatalyst is expensive or not suitable for manufacturing a matrix that serves as a support structure for the composite porous electrode. For example, the electrocatalytic region of the cathode may thus be provided for depositing a coating of electrocatalyst, such as platinum, etc. Thereafter, a passivation coating 219 may be deposited on the matrix (or body) 211, as described above.

[0250] FIG. 3e shows a further exemplary electrode configuration 345 that differs from the configuration described above with respect to FIG. 3d in that the matrix (or body) 211 is additionally provided with an electrocatalytic coating 211' as described below.

[0251] In the example of FIG. 3e, the matrix (or body) 211 may include (e.g., consist of) a first electrocatalytic material (i.e., electrocatalyst) that is less electrocatalytically active than the coating 211′. Thus, the electrocatalytic region of the composite porous electrode 217 may include both the matrix (or body) 211 and the electrocatalytic coating 211′ that defines the outlet side of the composite porous electrode. For example, the matrix (or body) 211 may be formed as a porous structure according to the exemplary fabrication method described above with respect to FIG. 3d and may include (or consist of) stainless steel 316. An electrocatalytic coating 211′ may then be deposited on the outlet side of the matrix (or body) 211, for example, by a chemical vapor deposition (CVD) process. The coating 211′ may include an electrocatalyst that is relatively more electrocatalytically active for each half-reaction of the electrolysis, such as nickel (when the composite porous electrode is an anode) or platinum (when the composite porous electrode is a cathode). Thereafter, as described above, a passivating coating 219 may be deposited to define the inlet side of the composite porous electrode 217. Thus, the ion exchange boundary of the composite porous electrode may reside at the interface between the passive region 219 defined by the passivating coating and the matrix (or body) 211, although the majority of each half-reaction of the electrolysis may take place in the portion of the electrocatalytic region defined by the electrocatalytic coating 211′ provided on the matrix.

[0252] When applied to an exemplary electrolytic cell as described above, the electrode configuration of FIG. 3e can inhibit backflow of fluid reaction products due to a pressure gradient across the first porous wall or pressure-driven flow through the porous wall when a pressure drop exists from the inlet chamber to the holding chamber, and / or can inhibit backflow of fluid reaction products due to upstream flow resistance of a passive region.

[0253] FIG. 3f shows a further exemplary electrode configuration 350 in which the first composite porous electrode 217 extends linearly along (i.e., parallel to) the longitudinal axis A and has an orthogonal thickness direction T from an inlet side adjacent the inlet chamber 200 to an outlet side adjacent the holding chamber 210.

[0254] Electrode configuration 350 differs from those described above with respect to each of FIGS. 3a-3e in that composite porous electrode 217 has an anisotropic porous structure defined by a plurality of channels 352 that extend through the thickness of the first composite porous electrode 217 and are configured to allow electrolyte fluid to flow from inlet chamber 200 to holding chamber 210. The channels may extend through electrocatalytic region 211 of composite porous electrode 217. Composite porous electrode 217 has an anisotropic structure in which the channels are arranged in a structured array such that they are oriented along a particular direction to allow flow to penetrate the composite porous electrode in that direction more easily than in other directions. In this example, channels 352 are inclined with respect to both longitudinal axis A and thickness direction such that flow along channels 352 from inlet side to outlet side has an upward component when longitudinal axis A is oriented vertically (as shown in FIG. 3f). The inclined channels may have cross-sections that diverge (i.e., expand) along a direction toward the respective holding chambers as shown in FIG. 3g, which illustrates a further exemplary electrode configuration 355 that differs from that of FIG. 3f only in this respect (i.e., only in that the inclined channels have diverging cross-sections). The centroid axis of each channel is inclined with respect to both the longitudinal axis A and the thickness direction T. It is believed that the diverging cross-sections may allow the lower density fluid reaction products produced in the electrocatalytic regions of the composite porous electrode to preferentially expand and flow downstream (i.e., along the channels toward the holding chambers).

[0255] In both the electrode configurations 350, 355 of Figures 3f and 3g, the composite porous electrode 217 further comprises a non-electrocatalytic or passivating coating 219 defining the inlet surface of the composite porous electrode.

[0256] By way of example only, the composite porous electrode 217 of Figure 3g may be manufactured by the method 40 as described with reference to Figure 4a.

[0257] At block 41, a body for the composite porous electrode is provided. For example, the body may have a shape and size corresponding to the electrocatalytic region 211 of the composite porous electrode. The body may be machined to the desired shape and size. The body may include (e.g., consist of) an electrocatalytic material (electrocatalyst); suitable electrocatalysts for each half-reaction of the electrolysis of the electrolyte solution are discussed elsewhere herein. By way of example only, the body may include a nickel superalloy such as an Inconel® alloy (e.g., Inconel® 600).

[0258] In block 42, as described above, a passivation coating (e.g., a dielectric coating) 219 may be applied to one side of the body to define a passive region 219 of the composite porous electrode, e.g., to define an inlet side of the composite porous electrode 217. The passivation coating may be applied by any suitable process, e.g., a sputtering process such as magnetron sputtering. One side of the body may be masked to prevent coating with the passivation coating (e.g., the outlet side of the body). Optionally, the passivation coating may be applied to both sides of the body (i.e., both the inlet and outlet sides without either side being masked).

[0259] At block 43, graded channels are formed in the body to provide an anisotropic porous structure as described above. For example, the graded channels may be formed by removing material from the body, such as using a laser drilling process. The graded channels may be provided with an average cross-sectional diameter along their length of 25-150 μm, e.g., 25-100 μm, 25-75 μm or about 50 μm. Examples of suitable laser drilling equipment are the "Lasertec 50 Powerdrill" available from DMG Mori Seiki Co., Ltd., Japan, or high power ultrashort pulsed lasers available from Amphos GmbH, Germany (e.g., "Amphos 2302" or "Amphos 3000" series lasers).

[0260] A suitable laser drilling process may be ultrashort pulse laser drilling (also known as laser micromachining), where the ultrashort laser pulses are in the picosecond or femtosecond range, such as 10 ps, ​​or 0.1 ps to 10 ps. Such machining processes are discussed in the reference Aizawa Tatsuhiko and Inohara Tadahiko (2019) "Pico- and Femtosecond Laser Micromachining for Surface Texturing," also available at https: / / www.intechopen.com / books / micromachining / pico-and-femtosecond-laser-micromachining-for-surface-texturing, 10.5772 / intechopen.83741.

[0261] The tilted channel may be formed to provide a diverging (e.g., expanding) cross-section from the inlet side to the outlet side of the composite porous electrode, as described above with reference to FIG. 3g. For example, this may be accomplished by rotating a beam tilted with respect to the centroid axis of the channel about the centroid axis during the laser drilling process. As discussed in Aizawa and Inohara, supra, such rotation may be performed by a beam rotator, in which one or more lens elements in the laser drilling apparatus rotate to rotate the beam axially symmetrically about an axis (i.e., about the centroid axis of the tilted channel).

[0262] An alternative method 45 for manufacturing the composite porous electrode 217 of FIG. 3f is to use an additive manufacturing process, as will be described by way of example with reference to FIG. 4b.

[0263] At block 46, an anisotropic porous matrix (or body) of the composite porous electrode is formed. In this example, it is formed by an additive manufacturing process, for example, by selectively fusing build materials layer by layer, such that angled channels 352 are formed in the matrix during the additive manufacturing process. Suitable additive manufacturing processes may be selective laser sintering (SLS) or metal binder jetting.

[0264] The graded channels may have an average cross-sectional diameter along their length of about 50-200 μm, for example 100-200 μm, and such channels may be suitably manufactured by additive manufacturing equipment having a layer resolution of 30 μm. A suitable build material for additive manufacturing may be nickel powder (or a nickel alloy, such as an Inconel alloy as discussed elsewhere herein, such as Inconel 600).

[0265] In this example, the build material includes an electrocatalyst for catalyzing each half-reaction of the electrolysis of the electrolyte solution, and thus the anisotropic matrix of the composite porous electrode as formed in block 46 provides the electrocatalytic regions of the composite porous electrode. However, in other examples, the build material may be less active as an electrocatalyst than may be required to catalyze the half-reactions, for example, the build material may be titanium. The method optionally includes, in block 47, providing a coating including (e.g., consisting of) an electrocatalyst for each half-reaction in the matrix to form the electrocatalytic regions 211 of the composite porous electrode. For example, the coating may be electroplated on the matrix. For example, the interior surface and / or one or both major surfaces of the body (corresponding to the inlet and outlet surfaces of the composite porous electrode) may be coated with an electrocatalyst.

[0266] At block 48, a passivation coating (eg, a dielectric coating) is applied to the inlet side of the electrocatalyst region 211 to define the passive region 219 of the composite porous electrode 217, as described above.

[0267] 4a and 4b, a substantially majority of the composite porous electrode 219 may be formed by the electrocatalytic region 211, and a passive region 219 may be provided only on the inlet side, which is passivated. Optionally, a further passive region may be provided as a coating on the outlet side, as described above with reference to method 40 of FIG.

[0268] By providing a matrix for the composite porous electrode containing the electrocatalyst such that the electrolyte interface of the electrocatalyst region (i.e., the surface area of ​​the electrocatalyst region adjacent to the electrolyte liquid for each half-reaction of the electrolysis in use) is defined by the matrix and not by an additional coating of the electrocatalyst, the composite porous electrode can be manufactured more simply and reliably. In particular, as is evident from a comparison of method 40 of FIG. 4a with method 45 of FIG. 4b, when the matrix defines the electrolyte interface, no additional coating needs to be applied. The coating applied to the inner surface of the channel or pore through the matrix may be non-uniform, for example, if its geometry results in a non-uniform current density across the respective surface. Moreover, when the matrix defines the electrolyte interface (i.e., in the absence of an additional coating), the electrocatalyst interface is not prone to peeling, as a coating may be.

[0269] A first example of operation of the electrolytic cell 20 of Figure 2 is described above with reference to exemplary supercritical operating conditions, a suitable electrolyte solution, and a configuration in which the first electrode is an anode and the second electrode is a cathode. A modified example of operation of the electrolytic cell 20 of Figure 2 (i.e., modified with respect to the first example described above) will now be described in which the electrolytic cell 20 of Figure 2 includes the electrode array 350 of Figure 3f or the electrode array 355 of Figure 3g.

[0270] In this example, electrolyte liquid is provided at supercritical conditions at inlet 22, as described above. This example operation is equally applicable to the operation of electrolytic cells having a pressure differential across the first composite porous electrode 217 driving a bifurcated flow of electrolyte liquid therethrough, and to the operation of electrolytic cells without such a pressure differential.

[0271] The electrolyte fluid may flow through the inlet chamber 200 to the second outlet 204, as described above, so that the electrolyte fluid or associated ions react with the second electrode 202 (cathode) to produce a second fluid reaction product (e.g., hydrogen).

[0272] The inlet chamber 200 is bounded on one side by a passivation coating 219 on the first composite porous electrode 217 to suppress an electrolytic reaction on the inlet side of the first composite porous electrode 217 to produce a first fluid reaction product (e.g., oxygen).

[0273] During operation, the electrolyte liquid and / or associated ions enter the channels 352 of the first composite porous electrode 217 by general motion of the electrolyte liquid or by electromotive forces on the ions, for example as entrained in a branching flow of electrolyte liquid through the first composite porous electrode 217.

[0274] Upon entering the channels 352, the electrolyte liquid and / or associated ions react with the electrocatalytic region 211 (first electrode). For example, the reaction may take place at the interior surface of the channel 352, which provides the electrolyte interface of the electrocatalytic region and may be defined by either an electrocatalytically active matrix material of the composite porous electrode or an electrocatalytically active coating provided over the matrix material as described above. The reaction produces a first fluid reaction product (oxygen). The first fluid reaction product has a lower density than the electrolyte liquid, but is in a supercritical condition and remains fully miscible with the electrolyte liquid. The lower density of the produced first fluid reaction product drives the first fluid reaction product to flow along an upward direction through each channel 352 and, in doing so, directs it to the holding chamber 210 from where it is released through the first outlet 213 of the holding chamber 210. The buoyancy-driven flow of the first fluid reaction product upward through channel 352 (and forward through first outlet 213) may draw a displacement flow of electrolyte liquid into the channel.

[0275] The inclined channel thereby inhibits backflow of the first fluid reaction product through the first composite porous electrode 217 towards the inlet chamber 200 due to a downstream biased buoyancy effect.

[0276] The graded channels may extend through the electrocatalytic region such that each half-reaction of the electrolysis occurs within the composite porous wall within the electrocatalytic region. The electrocatalytic region may also define an outlet side of the composite porous wall 217 such that each half-reaction of the electrolysis may be carried out in the holding chamber 210 at the outlet side. Alternatively, as described above, the outlet side of the composite porous wall may be defined by a passive region (e.g., by a passivation coating applied to both sides of the body of the composite porous wall before the graded channels are formed) such that each half-reaction of the electrolysis occurs substantially entirely within (e.g., only within) the graded channels.

[0277] When applied to the exemplary electrolytic cell as described above, the electrode configuration of FIG. 3f or FIG. 3g can inhibit backflow of fluid reaction products due to a pressure gradient across the first porous wall or pressure-driven flow through the porous wall when a pressure drop exists from the inlet chamber to the holding chamber. With an appropriate thickness of the passive region defining the inlet side of the composite porous electrode, it can inhibit backflow of fluid reaction products due to the upstream flow resistance of the passive region. Additionally, the electrode configuration can inhibit backflow of fluid reaction products due to downstream biased buoyancy effects as described above. Anisotropic composite porous electrodes may be used with other features as described herein with reference to the examples of FIGS. 1-3e. For example, any of the exemplary configurations of composite porous electrodes as described herein may be modified to include inclined channels within the porous wall or composite porous electrode such that the respective porous wall or composite porous electrode can additionally function to inhibit backflow of the respective fluid reaction products due to downstream biased buoyancy effects as described above. Downstream biased buoyancy effects may be relied upon in preference to establishing a pressure gradient or pressure-driven flow to suppress backflow, and may allow backflow of fluid reaction products to be better suppressed in the absence of a pressure differential across a porous wall or composite porous electrode.

[0278] Additionally, while it is believed that reaction rates within the graded channels of a composite porous electrode may be improved by providing an electrocatalytic region near (but not at) the inlet side of the composite porous electrode, graded channels may also be used in composite porous electrodes in which the upstream portion of the flow path through the passive region of the composite porous wall accounts for a significant proportion or majority of the passive porous region or wall or the total flow path through the composite porous electrode.

[0279] 5 illustrates a further exemplary electrolytic cell 50 that is similar to the electrolytic cell 20 described above with reference to FIG. 2, such that the above description of like features applies equally to the electrolytic cell 50 of FIG. 5 and like reference numerals are used for like components. The electrolytic cell 50 of FIG. 5 differs from the electrolytic cell 20 described above with reference to FIG. 2 in that it comprises a first holding chamber 210 and a second holding chamber 520 on opposite sides of the inlet chamber 200 for holding fluid reaction products produced at the respective first and second electrodes. The first and second porous walls separate the inlet chamber 200 from the first holding chamber 210 and second holding chamber 520, respectively. With respect to the electrolytic cell 20 of FIG. 2, the second porous wall and the second electrode replace the second electrode 202 that defines the radially outer wall of the inlet chamber 200 of FIG. 2.

[0280] In the exemplary electrolytic cell 50 of Figure 5, there is a first composite porous electrode 217 and a second composite porous electrode 528 that provide the respective porous walls and electrodes associated with the first holding chamber 210 and the second holding chamber 520. In this particular example, the first composite porous electrode 217 and the second composite porous electrode 528 are substantially as described above with respect to Figure 3f, having angled channels that encourage fluid reaction products produced at the respective electrodes to flow upward along the channels into the respective reaction chambers and prevent backflow of such fluid reaction products downward through the channels against buoyancy forces. However, it should be understood that either or both of the composite porous electrodes may be replaced with any suitable arrangement of electrodes and porous walls, for example, any of the arrangements as described above with reference to Figures 1-3g.

[0281] The exemplary electrolytic cell of Figure 5 has an annular configuration, with the inlet chamber 200 being an intermediate annular chamber that surrounds the core inner chamber, the first holding chamber 210. The second holding chamber 220 is an outer annular chamber that surrounds the inlet chamber 200 (the intermediate annular chamber). However, it should be understood that the cross-sectional arrangement of Figure 5 is equally applicable to electrolytic cells similar to the electrolytic cell 10 of Figure 1, but with a dual holding chamber arrangement, where the inlet chamber 200, the first holding chamber 210 and the second holding chamber 520 are straight ducts separated by flat composite porous electrodes.

[0282] In this (annular) exemplary electrolytic cell 50, the first outlet 213 for discharging a first fluid reaction product produced at the first electrode (at the first composite porous electrode 217) is at the top of the first holding chamber 210. Unlike the electrolytic cell 20 of Figure 2, there is no second outlet at the top of the inlet chamber 200. Instead, the second outlet 524 for discharging a second fluid reaction product produced at the second electrode (at the second composite porous electrode 528) is at the top of the second holding chamber 520, which is therefore annular in this example.

[0283] One example of operation will be briefly described, focusing only on the differences that may result from the dual holding chamber configuration (i.e., compared to the first example of operation described above with respect to electrolytic cell 20 of FIG. 2).

[0284] In use, supercritical electrolyte liquid is provided (e.g., continuously during operation) to the inlet chamber 200 via the annular inlet 22 of the inlet manifold 23, as described above. The supply of electrolyte liquid displaces electrolyte liquid from the inlet chamber, and in the absence of an exit port from the inlet chamber, such displaced fluid is driven through the composite porous walls to the holding chamber as a first branch flow and a second branch flow. Thus, in this example, the flow of displaced electrolyte liquid through each composite porous wall may be established by the inlet flow rate, rather than by establishing or maintaining a pressure drop across the respective composite porous electrode.

[0285] The pressure in the inlet chamber 200 corresponds to the pressure at the inlet 22, while the pressure in each of the holding chambers 210, 220 corresponds to the pressure at the first outlet 213 and the second outlet 523. As a porous member, each composite porous electrode can constrain the flow rate of electrolyte liquid into the respective holding chamber based on the pressure difference between the inlet chamber and the holding chamber. Thus, a pressure difference can be established between the inlet 22 and each of the first outlet 213 and the second outlet 524, which correspond to the first and second branch flows of electrolyte liquid through the first composite porous electrode 217 and the second composite porous electrode 528, respectively. The relative flow rates of the branch flows may be controlled by controlling the pressures or flow rates associated with the outlets, as described below.

[0286] In this example, each of the first composite porous electrode 217 and the second composite porous electrode 528 is substantially as described above with reference to the composite porous electrode 217 of Figure 3f. In use, electrolyte liquid and / or associated ions do not react with the composite porous electrodes 217, 528 at their respective inlet sides adjacent the inlet chamber due to the presence of a passivation coating (not shown in Figure 5 for simplicity) that defines the inlet side of each of the composite porous electrodes. Thus, the contents of the inlet chamber 200 consist substantially of electrolyte liquid and associated ions and substantially no fluid reaction products are produced at the respective electrodes.

[0287] Each branched stream carries electrolyte liquid and / or associated ions into a respective inclined channel and to the electrocatalytic region of a respective composite porous electrode, where a respective electrolytic half-reaction takes place to produce a respective fluid reaction product. Due to the relatively lower density of the fluid reaction products (compared to the electrolyte liquid), the fluid reaction products tend to flow upwardly and thus along the inclined channel and be retained downstream in a respective reaction chamber.

[0288] By appropriate selection of the electrocatalyst, as discussed elsewhere herein, either of the composite porous electrodes can function as the anode and the other as the cathode.

[0289] 5, backflow of fluid reaction products through the composite porous electrode can be inhibited by the presence of a pressure gradient, or pressure-driven or displacement flow of electrolyte liquid, as described above, and / or by downstream biased buoyancy effects, as described above. Optionally (e.g., depending on the thickness of the passivation layer), backflow may be inhibited by upstream flow resistance of a passive region, as described above with respect to the preceding examples.

[0290] When any of the electrode arrangements of Figures 3a-3g are applied to the electrolytic cell of Figure 5, such that there is a dual arrangement of holding chambers for the respective reaction products, each having its own porous wall or composite porous electrode, backflow may be suppressed by the displacement flow of the electrolyte flow through those porous walls or composite porous electrodes.

[0291] FIG. 6 shows an exemplary electrolytic cell installation 400 comprising an electrolytic cell 50 as described with reference to the exemplary electrolytic cell 50 as described above with reference to FIG. 5 (and further with reference to FIGS. 2 and 3f), which may be according to any embodiment contemplated herein.

[0292] The electrolytic cell installation may alternatively be understood as an electrolytic cell comprising any of the features described above with reference to Figures 1 to 3g and 5, and the additional features to be described with reference to Figure 6. In this regard, it will be understood that references herein to an "electrolytic cell installation" are interchangeable with reference to an "electrolytic cell".

[0293] In sequential flow order, the exemplary electrolytic cell installation 400 includes a source of electrolyte liquid 401, a compressor 402 for compressing (pressurizing) the electrolyte liquid, a heater 403 for heating the electrolyte liquid, an inlet conduit 404 leading to a monitoring manifold 405, an electrolytic cell 50 as described above, a first discharge manifold 420, and a second discharge manifold 430.

[0294] In this example, the electrolytic cell installation is for operation at supercritical conditions with an electrolyte liquid comprising an aqueous electrolyte solution, for example as described above with respect to the first operational example of the electrolytic cell 20 of Fig. 2. Accordingly, the compressor 402 is configured to compress the electrolyte liquid to a pressure of at least 22 MPa, for example between 22 MPa and 27 MPa. Furthermore, the heater 403 is configured to heat the electrolyte liquid to a temperature of at least 374°C, for example between 374°C and 550°C or between 374°C and 400°C.

[0295] An inlet conduit 404 conducts heated and pressurized electrolyte liquid to an inlet manifold 405, which supports a temperature sensor 406 for monitoring the temperature of the electrolyte in the inlet manifold, the temperature sensor being coupled to a controller 450 via a connection 407. Although connection 407 is shown separate from temperature sensor 406 in Figure 6, it will be appreciated that connection 407 may be any suitable form of connection, for example a wired or wireless link.

[0296] Electrolyte fluid flows into the electrolytic cell 50 for the electrolytic reaction as described above with respect to Figures 1-5. There are separate first and second outlet passages 411, 421 coupled to the first and second outlets of the electrolytic cell, respectively (the first and second outlets are configured to discharge the first and second fluid reaction products, respectively). Figure 6 shows the first outlet passage 411 diagrammatically coupled to a first outlet located at the center of the electrolytic cell 50, while the second outlet passage 421 is coupled to a radially outward (e.g., annular) second outlet of the electrolytic cell 50.

[0297] The first outlet passage 411 is in fluid communication with a first discharge manifold 410, which receives a flow of electrolyte liquid and a first reaction product from a first outlet of the electrolytic cell 20. The first discharge manifold 410 is fluidly coupled to a first discharge valve 418 via a discharge line 416. The first discharge valve 418 may be a control valve that provides a variable restriction to the flow therethrough.

[0298] The second outlet passage 421 is in fluid communication with the second discharge manifold 420. As shown generally in Figure 6, in this example the first outlet passage 411 extends through the second discharge manifold 420 while functionally bypassing the second discharge manifold (i.e., such that the flow in the first outlet passage 411 does not mix with the flow in the second discharge manifold 420), but may be configured differently in other embodiments. Similar to the first discharge manifold 410, the second discharge manifold 420 is fluidly coupled via a discharge line 426 to a second discharge valve 428, which may be of a similar type to the first discharge valve 418.

[0299] Optionally, each of the first and second discharge manifolds 410, 420 is provided with a respective pressure sensor 414, 424 having a pressure sensor element in communication with fluid discharged from a respective (first or second) outlet of the electrolytic cell or in a respective chamber immediately upstream of the outlet. Each pressure sensor 414, 424 is coupled to a controller 450 via a respective connection 415, 425 to provide a respective pressure signal to the controller 450 (as above, although the connections 415, 425 are shown in the drawings as separate from the respective pressure sensors 414, 424, any suitable form of connection may be provided). Alternatively or additionally, a pressure differential sensor may be provided in communication with the respective discharge manifold or outlet passage and connected to the controller 450 to provide a pressure differential signal to the controller 450.

[0300] The first release valve 418 and / or the second release valve 428 may be a control valve. For example, the first release valve 418 and / or the second release valve 428 may be a controllable pressure maintaining valve configured to maintain a target pressure upstream of the respective valve corresponding to a target operating condition in the electrolytic cell 50 (e.g., a supercritical pressure condition of the electrolyte liquid). The first release valve 418 and / or the second release valve 428 may expand the flow to a lower pressure, e.g., a pressure where the respective reaction products are gaseous and the residual electrolyte liquid is liquid, so that the respective reaction products can be more easily separated from the electrolyte liquid (e.g., by phase separation in an accumulation tank). The residual electrolyte liquid may be recycled to the source of electrolyte liquid 401.

[0301] Optionally, the electrolysis facility comprises separators 430, 436 downstream of the respective discharge valves 418, 428 for separating the respective fluid reaction products from the electrolyte liquid. Each separator 430, 436 has a respective return line 432, 438 for flow of discharged electrolyte liquid 432, 438 from the separator that can be returned to the source of electrolyte liquid for reuse. Each separator 430, 436 further comprises an outlet line 434, 440 for discharging the respective fluid reaction products. The fluid reaction products may be in gaseous form within the respective separator and may be discharged as gas through the outlet line. Optionally, the monitoring device comprises flow meters 435, 442 on the respective outlet lines for monitoring the flow rate of the respective fluid reaction products, each outputting a respective signal to a controller 450, as described below.

[0302] 6, there is a controller 450 coupled to the flow control devices and monitoring devices to control the operation of the electrolytic cell installation 400. The monitoring devices may include a temperature sensor 406 for monitoring the inlet temperature of the electrolyte fluid, pressure sensors 414, 424 (or pressure differential sensors) for monitoring the pressure of the fluids in or exiting the first and second outlets of the electrolytic cell 50, respectively, and flow meters 435, 442 on the outlet lines 434, 440 for monitoring the outlet flow of reaction products. The flow control devices may include the monitoring devices.

[0303] The flow controller includes one or more components that determine (ie, affect or influence) the conditions within the electrolytic cell, such as the thermodynamic and / or flow rate conditions within the electrolytic cell.

[0304] The thermodynamic conditions relate to the pressure and temperature of the fluids in the electrolytic cell, for example, the pressure and temperature of the electrolyte liquid provided to the electrolytic cell or the pressure and temperature of the electrolyte liquid combined with the first and / or second reaction products in the respective chambers in which they are held in the electrolytic cell. In this example, the thermodynamic conditions are a function of the pressure to which the electrolyte liquid is compressed in the compressor 402, the temperature to which the electrolyte liquid is heated in the heater 403, and the operation of the first and second discharge valves 418 and 428 (e.g., the target backpressure that the valves are configured to maintain upstream of the valves).

[0305] The flow rate conditions relate to the flow rate of the electrolyte liquid provided to the electrolytic cell and, optionally, the or each flow rate of a branch stream of electrolyte liquid passing from the inlet chamber through the respective porous wall into the or each holding chamber.

[0306] At steady state conditions, the flow rate into the electrolyzer is equivalent to the sum of the first and second flow rates out of the respective first and second outlets. Each outlet flow depends on the pressure difference between the compressor 402 and each of the first and second discharge valves 418, 428, as well as any flow resistance along the respective flow paths (e.g., primarily any associated porous walls, but also any other features of the flow paths that may cause a pressure drop, such as bends and flow constraints).

[0307] The flow rate through either the first or second outlet of the electrolytic cell (which may correspond to a split flow through the upstream porous wall) may depend on the relative pressures at the first and second outlets.

[0308] To sustain the ion exchange and electrolysis reactions, it may be desirable to balance the rates at which the reactions take place at each electrode.

[0309] The reaction rate at each electrode may be a function of several variables, including the composition of the electrolyte liquid, the fluid interactions between the electrolyte liquid and the respective electrode, the area of ​​the electrolyte interfacial surface of the electrocatalytic region of each respective electrode (i.e., the surface area of ​​the electrocatalytic region adjacent the electrolyte liquid in use), the ratio of the surface area of ​​the respective electrolyte interfacial surface to the volume of electrolyte liquid exposed to the electrode (e.g., in the separating gap between the electrodes), and the flow rate of electrolyte liquid associated with each electrode (which may be the flow rate through the electrode in the case of a flow-through electrode, or the flow rate past the electrode in the case of a flow-past electrode).

[0310] The flow resistance characteristics of the porous wall may be selected to achieve an appropriate flow rate of the branched stream of electrolyte liquid through the porous wall. It should be understood that the flow rate is a function of multiple variables that may be varied in the design and construction of the electrolytic cell. In general, the flow rate through the device is determined by the flow coefficient K, as shown in Equation 1 below: v This can be determined by rearranging the equation for

[0311]

number

[0312] In the formula, Q is the flow rate (m 3 h -1 ) and K v is the flow coefficient of the porous wall (m 3 h -1 bar -0.5 ), ΔP is the pressure drop across the porous wall (bar), and SG is the specific gravity of the fluid.

[0313] It should be understood that the flow coefficient may be a constant for the porous wall, and various characteristics of the porous wall may be modified to achieve an appropriate flow coefficient, for example, the porosity of the porous wall and the thickness of the porous wall.

[0314] The flow rate can be determined by Darcy's law, as shown in Equation 2 below.

[0315]

number

[0316] where q is the instantaneous flux (i.e., m of the flux, which is equivalent to Q / A 2 m of fluid per 3 s -1 , A is the flow volume), k is the permeability of the medium (m 2 ), and μ is the dynamic viscosity coefficient (Pa.s -1 ) and ΔP is the total pressure drop (Pa).

[0317] The pressure drop ΔP across the porous wall can be determined as a function of a target back pressure applied to each respective chamber by a discharge valve 418, 428 in fluid communication with the first and second outlets of the electrolytic cell.

[0318] A pressure gradient may exist within the chambers of the electrolytic cell due to the production of reaction products at the electrodes, which are less dense than the electrolyte liquid provided in the respective chambers. Thus, the pressure may vary within the chambers between the location adjacent to the porous wall and the respective outlet of the electrolytic cell, which communicates with the respective discharge valve. Thus, when the discharge valves are configured to maintain a back pressure, the pressure difference between the electrolyte liquid provided in the inlet chamber and the respective back pressure may not be equal to the pressure difference across the porous wall located therebetween. Nevertheless, such pressure gradients within the respective chambers will reach a steady state in use at certain operating conditions (e.g., flow rate, pressure and temperature set points, voltage and current of the electrolytic circuit), so that the pressure at the outlet side of the porous wall may be a function of the back pressure applied at the downstream discharge valve. Thus, the pressure drop across each porous wall may be a function of the back pressure applied to the respective chamber by the discharge valve.

[0319] The release valves associated with each chamber may be controllable, for example by a controller, to vary the backpressure. This may allow the electrolytic cell to be calibrated for use or its operating conditions to be changed during use. Alternatively, the release valves may be configured to maintain a fixed backpressure, for example a pressure that has been determined in the design of the electrolytic cell to be suitable for use in the intended operating conditions.

[0320] In the exemplary installation of Figure 6, in use, the controller 450 controls the operation of the flow control devices to maintain desired conditions within the electrolytic cell. The controller 450 controls the operation of the flow control devices, e.g., the first and / or second release valves, based on the output from the monitoring devices to maintain the desired conditions using a feedback loop. In a variation, the controller may not be present and / or the components of the flow control devices may be pre-configured to set operating points corresponding to predetermined operating conditions of the electrolytic cell.

[0321] The controller 450 can control the flow control device to maintain a flow rate in the inlet chamber and / or each holding chamber of the electrolytic cell corresponding to a desired flow regime, such as laminar flow or laminar and / or transitional flow. When the inlet chamber is configured to hold one of the reaction products (e.g., when there is a single holding chamber associated with a first electrode and the inlet chamber is associated with a second electrode), it may be desirable to avoid turbulent flow in the inlet chamber to inhibit the movement of reaction products generated at one electrode toward the other electrode. A laminar or transitional flow regime can avoid such movement by preventing the movement of fluid (non-ionic) components across uniform streamlines in the flow. Thus, the controller 450 can be configured to control the flow control device to maintain a flow rate in the inlet chamber corresponding to a Reynolds number of 4000 or less (considered to be the limit for transitional flow) or 2300 or less (considered to be the limit for laminar flow). It should be understood that variables other than velocity in the calculation of the Reynolds number, such as, for example, the characteristic dimensions of each chamber (e.g., the radial extent of the inlet chamber) and the inertial and viscous constants of the fluid, may be constants and provided to the controller.

[0322] In some embodiments of the electrolysis system, a controller, such as controller 450 of system 400 in FIG. 6, can control the operation of the electrolysis system, for example, to maintain flows in the electrolysis reactions within target ranges or to balance the electrolysis half-reactions.

[0323] An exemplary method of controlling the electrolysis reaction is described below, by way of example only, with reference to electrolysis facility 400 and with reference to the flow diagram of FIG.

[0324] FIG. 7 is a flow diagram of a method 700 for controlling the or each discharge valve 418, 428 associated with an outlet stream comprising a mixture of a first fluid reaction product and electrolyte liquid and a mixture of a second fluid reaction product and electrolyte liquid, respectively.

[0325] Block 702 represents monitoring data received in the controller 450 from associated sensors of the monitoring devices.

[0326] At block 704, monitoring data is received at the controller from associated sensors of the monitoring devices. For example, the data may be received continuously, periodically, on demand, or at the initiative of the respective sensors (e.g., when the sensors detect a predetermined condition).

[0327] At block 706, the controller evaluates goal criteria related to the monitored data.

[0328] In block 708, the controller determines settings for one or more of the discharge valves 418, 428 for controlling operation of the electrolysis equipment based on the evaluation of the target criteria in block 706. The method continually repeats by returning to block 704.

[0329] In a first example of method 700, the monitoring data is upstream pressure data received from pressure sensors 414, 425 configured to monitor the pressure of fluid discharged from the first and second outlets of each of the electrolytic cells (i.e., the outlets of each chamber of the electrolytic cells) or from a pressure differential sensor.

[0330] Evaluating the target criteria may include determining the difference between the pressure of the fluid released through the first outlet 213 (e.g., associated with the first holding chamber 210) and the pressure of the fluid released through the second outlet 524 (e.g., associated with the second holding chamber 210 or the inlet chamber when the electrolytic cell has a single flow-through electrode), or comparing the pressure of the fluid released from each outlet to a target range of fluid pressures.

[0331] In block 708, settings for one or more of the discharge valves may be determined based on evaluation of the target criteria. For example, there may be a predetermined target range of pressure difference, and settings may be determined to maintain or return the pressure difference to the target range. When the electrolyzer is operated with no pressure difference between the outlets, the target range may include zero pressure difference. When the electrolyzer is operated with a pressure difference between the outlets, the target range may not include zero pressure difference. The target range (or the respective target range for each pressure) may be predetermined, for example, based on operation of the electrolysis equipment to determine a pressure difference that corresponds to a satisfactory performance of the electrolysis equipment with a suitable balance of flow rates between the outlets. Thus, as a result of maintaining the pressure or pressure difference within the respective target range, a target flow rate ratio between the flow exiting the first outlet and the flow exiting the second outlet may be maintained.

[0332] In a second example of method 700, the monitoring data may be flow rate data, for example as received from a flow meter configured to monitor the flow rate of a mixture of fluid reaction product and electrolyte liquid streams discharged from respective outlets 213, 524 of the electrolytic cells (whether upstream of the respective discharge valves 418, 428 or downstream of the respective discharge valves, such as along the respective discharge lines 416, 426). The flow rate data may be received from a flow meter configured to monitor the component flow rates of the respective fluid reaction products separated from the electrolyte liquid, for example from flow meters 435, 442 located on outlet lines for discharging the respective fluid reaction products from separators 430, 436 downstream of the discharge valves 418, 428.

[0333] The target criteria may correspond to maintaining a target flow rate out of one or each of the outlets, or maintaining a target flow rate ratio between the flows out of the first and second outlets. Evaluating the target criteria may include comparing the associated flow rate data to a predetermined target, or determining a ratio of the respective flow rates out of the outlets. The controller may determine a control setting for one or both valves to maintain the flow rates or flow rate ratio within a target range.

[0334] In a third example of method 700, the monitored data may be compositional data relating to the composition of the fluid mixture exiting each outlet. For example, the compositional data may be determined by comparing the flow rates of the component fluid reaction products exiting the separator to the total flow rate of the fluids exiting each outlet, e.g., to determine the mass fraction of each fluid reaction product in the fluid mixture exiting each chamber of the electrolytic cell. Alternatively, the compositional data may be determined as the flow rate of each fluid reaction product, regardless of the flow rate at which the electrolyte liquid is exiting each outlet.

[0335] The target criteria may correspond to maintaining a target composition out of each outlet, for example a target mass fraction or a target flow rate of a fluid reaction product that may be considered to correspond to satisfactory performance of the electrolytic cell. The controller may determine a setting for each release valve based on the composition data. For example, if the mass fraction of the reaction product is determined to be below a target range, this may correspond to too much electrolyte liquid flowing through the respective chamber. Thus, the controller may decide to adjust the setting of the release valve to further restrict the flow through the release valve, thereby increasing the mass fraction of each fluid reaction product.

[0336] Alternatively, the target criteria may correspond to maintaining a target ratio of the flow rates of the respective fluid reaction products out of the respective outlets of the electrolytic cell. For example, there may be a target range of ratios that correspond to satisfactory performance of the electrolytic cell, e.g., by having the flow rate of a first reaction product be within a target range of desired ratios to the flow rate of a second reaction product. The desired ratios may correspond to sustainable performance of each electrolysis reaction (i.e., each half-reaction is balanced).

[0337] The flow rates as mentioned above may be mass flow rates. A flow meter may monitor the volumetric flow rates of the fluids, and the flow meter or controller may be provided with information corresponding to the density of the respective fluids for determining a parameter corresponding to the mass flow rate.

[0338] In a fourth example of the method, the monitoring data may be compositional data relating to the amount of contaminant fluid reaction products in the fluid streams exiting the respective outlets of the reaction chambers. For example, as described above, a first fluid reaction product will be held in a chamber (a holding chamber) for release through a first outlet of the electrolytic cell, while a second fluid reaction product will be held in a chamber (e.g., another holding chamber or an inlet chamber) for release through a second outlet of the electrolytic cell. The release of the second fluid reaction product through the first outlet corresponds to the presence of contaminant fluid reaction products in the respective outlet streams, and vice versa. The monitoring data may be received, for example, from a constituent gas sensor configured to monitor the composition of the gas downstream of the respective fluid reaction product separator (e.g., at the location of the respective flowmeters 435, 442 as described above). Any suitable sensor may be selected, but by way of example only, a thermal conductivity sensor configured to determine the composition of the flow stream based on the amount of energy (e.g., power) being monitored to maintain a temperature probe in the flow stream at a target level may be used. When calibrated based on the respective fluid reaction products (e.g., hydrogen) and contaminating fluid reaction products (e.g., oxygen) expected to be released, e.g., based on the respective specific heat capacities of the fluid reaction products, the sensor, or a controller to which the sensor is coupled, may be configured to determine when the flowstream includes an amount of the contaminating fluid reaction product. For example, it may be calibrated to indicate that the amount is above a threshold value, or it may be configured to estimate or calculate the mass fraction of each of the fluid reaction products (e.g., hydrogen and oxygen).

[0339] The presence of contaminant fluid reaction products may indicate a flow bias toward the respective chamber of the electrolytic cell where the outlet stream containing the contaminant fluid reaction products is released. Thus, the controller may decide to adjust the setting of one or more of the release valves to reduce or eliminate the bias. For example, if an excessive amount of contaminant fluid reaction products is determined in the outlet stream associated with the first release valve 218, the controller may control the first release valve 218 to reduce the flow rate through the first release valve 218 (e.g., by partially closing the valve or setting a higher back pressure to be maintained).

[0340] Although the above examples discuss reactive control methods for maintaining target operating parameters of the electrolytic cell, such control methods may be optional and the electrolytic cell may be configured to allow the electrolysis reaction to proceed without such intervention. Control of the release valve may be particularly suitable for electrolytic cells having a single porous wall (e.g., electrode arrangements such as those shown in Figures 3a-3g), since the holding chamber may need to be maintained at a lower pressure than the inlet chamber to drive the bifurcated flow of electrolyte liquid through the porous walls. Electrolytic cells having a dual porous wall configuration (e.g., as described above with reference to Figure 5) may be more easily configured to operate without controlling the back pressure applied to the respective outlets. For example, each porous wall may be configured to allow a desired flow rate of electrolyte liquid to pass through each of the porous walls in use without reactively controlling or balancing the outlet pressure, e.g., by appropriately selecting the permeability and / or porosity of each porous wall.

[0341] Further exemplary methods of manufacturing a composite porous electrode for use with electrolytic cells 10, 20, 50 as described above with respect to any of Figures 1, 2 and 5 using any of the electrode configurations of Figures 3b-3g will now be described, by way of example, with reference to method 70 of Figure 8a and method 75 of Figure 8b.

[0342] In the examples described below, the composite porous electrode is formed by additive manufacturing or powder pressing processes in the form of a sheet-like or tubular wall having a thickness direction between two opposing major surfaces of the composite porous electrode (i.e., a first surface and a second surface of the composite porous electrode). The composite porous electrode is formed to have a layered structure between the two major surfaces of the electrode, including at least two layers or layered regions having different material compositions, such as electrocatalytic regions and passive regions as described above with reference to Figures 3b-3e. Thus, in use, a bifurcated flow of electrolyte liquid through the composite porous electrode between the two opposing major surfaces along the thickness direction (or radial direction when the electrolytic cell has an axisymmetric configuration) (e.g., from an inlet surface adjacent the inlet chamber to an outlet surface adjacent the respective holding chamber) passes through at least two layers or layered regions. One of the layers or layered regions forms an electrocatalytic region of the porous electrode that is spaced apart from at least one of the major surfaces of the electrode. For example, as discussed above with respect to the example of Figures 3b-3e, the electrocatalytic region 211 is separated from at least the inlet side of the first composite porous electrode 217 opposite the second electrode 202 by a passive region of the composite porous electrode that is configured to be less electrocatalytically active than the electrocatalytic region for, or to suppress, each half-reaction of the electrolysis of the electrolyte solution.

[0343] In method 70 of Fig. 8a, a composite porous electrode is formed by an additive manufacturing process. The composite porous electrode may be formed layer-by-layer (or slice-by-slice) (each successive layer of an additive manufacturing process is not associated with layered electrocatalytic and / or non-electrocatalytic regions of the component being formed and is referred to as a slice in the following description), where a build material (e.g., a powder) is deposited on a bed or platform in successive layers, and the successive layers are progressively selectively sintered or fused to form the composite porous electrode slice-by-slice. Suitable additive manufacturing processes include selective laser sintering (SLS) and metal binder jetting.

[0344] At block 72 of the method, a build material for an additive manufacturing process is dispensed such that a composite porous electrode can be formed with each layer having a different material composition. At block 74 of the method, the composite porous electrode is progressively formed by sintering or fusing the build material. As will be appreciated, in an additive manufacturing process, blocks 72 and 74 are repeated for each successive layer of build material.

[0345] In instances where the porous electrode is substantially flat, at least two layered regions of the electrode having different material compositions may be formed by depositing and then sintering or fusing slices of a first building material having a first composition to form one of the layered regions, such as a passive region (typically formed from multiple fused slices of the building material), and then transitioning to depositing and sintering or fusing slices of a second building material having a different second composition to form another layered region, such as an electrocatalytic region.

[0346] In other examples, for example, where the porous electrode has a tubular structure in which the layered regions are annular and coextensive along the longitudinal extent of the electrode, at least two layered regions of the electrode having different material compositions may be formed by depositing and selectively sintering or fusing slices in a stacking direction corresponding to the longitudinal direction of the electrode, the slices including both a first and a second building material having different compositions in a pattern corresponding to the cross-sectional profile of the layered regions. The slices of building material may include a first building material and a second building material corresponding to the passive and electrocatalytic regions of the composite porous electrode, respectively.

[0347] When the composite porous electrode is formed by a powder pressing process, at least two layers having different material compositions may be formed sequentially, as will now be described by way of example with reference to method 75 of FIG. 8b.

[0348] At block 76, a first powder material (e.g., for a relatively less electrocatalytically active passive region of the composite porous wall, such as stainless steel 316 or titanium) may be provided in a first die having a shape corresponding to a first layer (e.g., passive region) of the composite porous electrode to be produced, and at block 77, the first die may be subjected to pressure to press the contained powder in the appropriate porosity to provide an intermediate product. At block 78, the intermediate product may be transferred to a second die having a shape corresponding to the combination of the first and second layers (e.g., electrocatalytic region), and a second powder material (e.g., nickel or a nickel alloy as described herein, e.g., an Inconel alloy such as Inconel 600, for the electrocatalytic region) may be added in a location of the die corresponding to the second layer. In block 79, a second press is applied to press the second powder material at the appropriate porosity to provide a two-layer product having both layers (e.g., passive and electrocatalytic regions) with their respective compositions. A second press or a separate process may be applied to sinter the two layers or regions together to provide an integrated composite porous electrode (e.g., by applying elevated temperature and pressure). For example, the intermediate product may be sintered in the first die (e.g., in a hot press process) or sintered after removal from the first die and before insertion into the second die (e.g., in a hot or cold press process). The intermediate product may be pressed in the first die but not sintered, and the two layers may be sintered only after both layers are pressed together, whether in the same die or in separate dies. Further regions or layers may be added using further dies and presses. Any suitable powder pressing technique may be used, such as hot pressing (HP), cold isostatic pressing or hot isostatic pressing (HIP).

[0349] Optionally, at block 80, the integrated composite porous electrode may be machined to an appropriate size. For example, the dies for two or more regions may be configured so that the product (e.g., integrated composite porous electrode) has a size and shape that is larger than the net shape of the completed composite porous electrode. For example, each region may have a thickness that is larger than that of the completed composite porous electrode, which may help maintain the structural integrity of the intermediate product for transfer between dies and may shift the requirement for dimensional accuracy to the machining step rather than the pressing step. When the completed composite porous electrode is to be annular, each inner region may be formed as a cylinder. Machining may include drilling a core to define the radially inner surface of the composite porous electrode. Further machining may be performed to remove material (e.g., by lathing) to define the radially outer surface of the composite porous electrode.

[0350] Although several exemplary configurations of electrolytic cells are disclosed herein, it should be understood that the invention cannot be limited to any particular configuration defined in the claims and illustrated in and described with reference to the drawings.

[0351] Working Example The test electrolysis setup, including a source of electrolyte solution 401, a compressor 402, a heater 403, an inlet conduit 404 to a monitoring manifold 405, an electrolytic cell 50, a first discharge manifold 410, and a second discharge manifold 420, was configured as shown generally in FIG.

[0352] The electrolytic cell 50 was constructed in the form of an annular cell as shown diagrammatically in Figure 5. The electrolytic cell 50 included a first holding chamber 210 and a second holding chamber 520 on opposite sides of an entrance chamber 200. The entrance chamber 200 was separated from the first holding chamber 210 by a first (inner) porous wall 217, which served as an electrode for the electrolytic cell 50. The entrance chamber 200 was separated from the second holding chamber 520 by a second (outer) porous wall 528, which also served as an electrode for the electrolytic cell 50. The first (inner) and second (outer) porous walls were each connected to a power supply biased such that the first (inner) porous wall served as a cathode and the second (outer) porous wall served as an anode.

[0353] The first porous wall was created by laser drilling channels into a first tube formed from Inconel® alloy 625 (a nickel-chromium alloy that also contains iron, molybdenum, niobium, and other alloying elements). The first tube had an outer diameter of 0.25 inches (6.35 mm), a tube wall thickness of 0.889 mm, and a longitudinal length of 215 mm. Prior to laser drilling, the exterior and interior surfaces of the first tube were passivated by coating with alumina (Al2O3) by chemical vapor deposition (CVD). The alumina coating was approximately 1 μm thick, as determined by gravimetric estimation. The channels were drilled through the entire thickness of the first tube wall (including the alumina coating) using a millisecond laser operating at 500 Hz. The channels were tilted 20° to the horizontal when the longitudinal axis of the tube was aligned vertically. The channels were drilled in multiple rows to form a pattern as shown in FIG. 9. The patterns were characterized by a 0.2 mm channel-to-channel offset, a 0.2 mm row-to-row offset (resulting in 5 rows per mm), and a circumferential channel number density of 99 holes per circumference of the tube. Each channel was formed using 30 laser pulses and required an energy of 0.2 J. The channel dimensions were assessed using X-ray computed tomography (XCT) and optical microscopy and analysis of the resulting images. The results are shown in Figure 10, Figure 11(a) and Figure 11(b). The channels were found to have diameters of about 60 μm to about 80 μm at the inlet and outlet of the channel (i.e., the outer and inner exterior surfaces of the tube). Figure 11(a) shows a channel found to have an internal radius of about 40 μm using XCT. Figure 11(b) shows channels found to have inlet diameters of about 69.6 μm, about 74.6 μm, and about 65.4 μm by optical microscopy.

[0354] The second porous wall was created by laser drilling channels into a second tube formed from Inconel alloy 625. The second tube had an outer diameter of 0.375 inches (9.525 mm), a tube wall thickness of 0.889 mm, and a longitudinal length of 142 mm. Prior to laser drilling, the exterior and interior surfaces of the second tube were passivated by coating with alumina (Al2O3) by chemical vapor deposition (CVD). The alumina coating was approximately 1 μm thick, as determined by gravimetric estimation. The channels were drilled through the entire thickness of the second tube wall (including the alumina coating) using a millisecond laser operating at 500 Hz. The channels were tilted 20° to the horizontal when the longitudinal axis of the tube was aligned vertically. The channels were drilled in multiple rows to form a pattern as shown in FIG. 9. The pattern was characterized by a channel-to-channel offset of 0.152 mm, a row-to-row offset of 0.2 mm (resulting in 5 rows per mm), and a circumferential channel number density of 196 holes per circumference of the tube. Each channel was formed using 20 laser pulses and required an energy of 0.18 J. Channel dimensions were assessed using XCT and optical microscopy and analysis of the resulting images. The channels were found to have diameters of about 60 μm to about 80 μm at the channel inlets and outlets (i.e., the inner and outer exterior surfaces of the tube).

[0355] The first porous wall 217 and the second porous wall 528 were arranged as shown in FIG. 5 with a separation gap of about 0.692 mm. The first and second walls were surrounded by an outer tubular housing having a diameter of 19.05 mm. The first core-retaining chamber 210 was defined as the interior space surrounded by the first porous wall 217. The second outer retaining chamber 520 was defined as the space between the second porous wall 528 and the outer tubular housing. The inlet chamber 200 was defined as the space between the first porous wall 217 and the second porous wall 528. In the assembled configuration, the first and second tubes were positioned such that the effective lengths of the electrodes exposed to the inlet chamber for radial flow and ion transfer were equal and were about 40 mm.

[0356] The electrolytic cell was operated using an electrolyte consisting of a 0.5 molar (1.2 wt %) solution of lithium hydroxide (LiOH) in water, prepared by diluting 98% reagent grade lithium hydroxide (available from Sigma-Aldrich) with deionized water to obtain the desired concentration.

[0357] The heater and compressor were operated to maintain the system at a pressure of 230 bar (23 MPa) and a temperature of 385°C.

[0358] The electrolyte flow rate through the electrolytic cell was controlled to be 10 ml / min.

[0359] After initial pressurization and heating of the system with deionized water, the electrolyte was pumped through the electrolyzer upon reaching operating pressure and temperature. The electrolyzer cell was monitored until a voltage drop was observed on the power supply, and then the current supplied to the cell was gradually increased until the operating condition of 500 mA at 1.56 V (corresponding to 80% of the lower heating value of hydrogen) was reached. Electrolysis of the electrolyte was then carried out for 15 minutes.

[0360] The gases output from the first and second holding chambers into the first and second discharge manifolds during electrolysis were collected in corresponding glass vessels filled with deionized water (the product gas displaces the water in the vessels when collected). The gases collected in the glass vessels were analyzed by gas chromatography using an Agilent 6890 gas chromatograph (available from Agilent Technologies, Inc., USA) equipped with a Shincarbon ST column (available from Shinwa Kako Co., Ltd., Japan) supplied with argon as the carrier gas. The gases were detected using a thermal conductivity detector built into the Agilent 6890 gas chromatograph. The gas chromatography run was carried out isothermally at 35°C. 100 μL of gas sample was injected into the column at a time. Calibration plots were also generated by injecting various amounts of oxygen and hydrogen into the gas chromatograph and analyzing the results.

[0361] Representative gas chromatography results of gases obtained from the operation of the electrolyzer are shown in Figures 12 and 13. Figure 12(a) is a representative chromatogram of gas obtained from the cathode (cathode gas), which features (from left to right) three peaks related to hydrogen, oxygen and nitrogen content. Figure 12(b) is a representative chromatogram of gas obtained from the anode (anode gas), which also features (from left to right) three peaks related to hydrogen, oxygen and nitrogen content. Figure 13(a) is a representative chromatogram of oxygen calibration gas. Figure 13(b) is a representative chromatogram of hydrogen and nitrogen calibration gases.

[0362] The compositions of the cathode and anode gases, as obtained by gas chromatography, are given in Table 1. These results were obtained by averaging the measurements over three different injection samples. The corresponding standard deviations of the measurements are also given.

[0363] [Table 1]

[0364] The values ​​in Table 1 have been corrected to account for air ingress into the gas storage vessel by quantifying the amount of nitrogen present in each sample and subtracting an equivalent amount of oxygen according to the ratio of nitrogen to oxygen in air. For example, assuming the N2:O2 ratio in air is 3.7, the volume of oxygen in a sample resulting from air contamination can be calculated as the measured volume of nitrogen in the sample divided by 3.7.

[0365] Modeling and Simulation Simulations of supercritical flow through an exemplary electrolyzer cell were performed to determine the compositional distribution of hydrogen and oxygen reaction products and to evaluate flow patterns related to the diffusion and crossing of species between the respective holding chambers.

[0366] The simulations pertain to an exemplary axisymmetric electrolyzer configuration having an inlet chamber, a radially inner (core) holding chamber separated from the inlet chamber by an inner composite porous electrode, and a radially outer holding chamber separated from the inlet chamber by an outer composite porous electrode. In this exemplary configuration, the inner electrode is the anode, resulting in the inner holding chamber being for holding and releasing oxygen as a reaction product, and the outer electrode is the cathode, resulting in the outer holding chamber being for holding and releasing hydrogen as a reaction product.

[0367] Model Geometry The model geometry is shown in each of Figures 14-16, with the major radial dimensions of the composite porous walls and their separations substantially corresponding to those described above for the tested examples.

[0368] The model has a vertical orientation as shown in the drawing, so that gravity is downward in the drawing orientation. The model is axisymmetric with respect to a longitudinal axis of symmetry A as shown in FIG.

[0369] As shown in FIG. 14, the model has an inlet manifold 923 at its lower end with an inlet boundary 921 having mass flow conditions as described above.

[0370] The manifold 923 opens at the inlet 922 into an annular inlet chamber 9200 that extends substantially linearly between the two composite porous electrodes 9217, 9218 along a length of 100 mm. This length corresponds to the length over which the electrodes face each other for ion exchange, as described elsewhere herein. The inner radius of the annular inlet chamber is 0.125 inches (3.175 mm) and the outer radius of the annular inlet chamber is 3.675 mm, resulting in a separation between the composite porous electrodes of 0.6875 mm.

[0371] Each of the composite porous electrodes 9217 , 9218 has a thickness of 0.9 mm and is simulated with a length equal to that of the annular inlet chamber 9200 .

[0372] Radially inward of the (first) radially inner composite porous electrode 9217 is the (first) radially inner holding chamber 9210 which is a cylinder with a radius corresponding to the inner dimension of the first composite porous electrode 9217. The inner holding chamber 9210 extends upwardly 100 mm beyond the longitudinal extent of the composite porous electrode (as modelled) towards the upper first outlet boundary 9213.

[0373] Radially outward of the (second) radially outer composite porous electrode is a (second) radially outer holding chamber 9520 which is an annular body having an inner radius corresponding to the outer radius of the outer dimension of the second composite porous electrode 9518, and an outer radius of 0.375 inches (9.525 mm). The outer holding chamber 9520 extends upwardly beyond the longitudinal extent of the composite porous electrode (as modeled) to an upper first outlet boundary 9524.

[0374] Model Definitions and Conditions The simulations were carried out using simulation software provided by COMSOL Multiphysics® 5.6, developed by COMSOL AB, Sweden.

[0375] The simulation model reflects the following assumptions: Hydrogen-oxygen-water mixtures with NaOH electrolyte are fully miscible and supercritical single phase at all conditions of interest (pressure >22.MPa, temperature >380°C). Inlet flows to the electrolyzer of up to 30g / min remain laminar within the electrolyzer at operating conditions.

[0376] The simulation models the diffusion of the components of a hydrogen-oxygen-water mixture. Density and viscosity are modeled as a function of local composition and pressure for a reference temperature of 400°C. The simulation models the fluid flow using the weakly compressible Navier-Stokes equations, including gravity (to model buoyancy). The simulation solves for steady-state flow conditions.

[0377] The simulation models the inlet flow as a fully developed (parabolic) laminar flow profile at a specified mass flow rate. The simulation models the outlet boundary as a constant outlet pressure boundary (at 23 MPa). A no-slip condition is applied to the walls of the model chamber. The simulation models the inlet flow as a fully developed (parabolic) laminar flow profile at a specified mass flow rate. The simulation models the outlet boundary as a constant outlet pressure boundary (at 23 MPa). A no-slip condition is applied to the walls of the model chamber. The simulation models the inlet flow as a fully developed (parabolic) flow profile at a pressure of 23 MPa and a temperature of 400°C (134 kg / m -3 The liquid is modelled as water at 200 .mu.m (density 1000, corresponding to a viscosity of 27.4 μPa).

[0378] The simulation models the electrode as a porous medium: the simulation models an isotropic porous electrode with a porosity of ε=0.2 and a pore size of 10 μm.

[0379] The simulation is defined to reflect the assumption that each hydrolysis half-reaction occurs throughout the porous electrode under a uniform current density. The simulation models the reaction using sources and sinks of each component in the porous electrode.

[0380] Simulations show 1.42kg.h for 150 cells in parallel -1 The graph reflects an assumed operating current of 250 A, corresponding to a target hydrogen production rate of 100 mA.

[0381] Simulation conditions The results of the three simulations are discussed below.

[0382] In the first simulation, both electrodes are modeled as isotropic porous electrodes.

[0383] In the second simulation, both electrodes are modeled with anisotropic porosity to simulate the effect of a tilted channel as disclosed elsewhere herein. The anisotropic porosity is implemented to reflect a channel tilt of 20° from vertical. Other parameters of the simulation are identical to the first simulation to study in isolation the effect of implementing anisotropic porosity.

[0384] The third simulation corresponds directly to the first simulation, but the simulation is performed without modeling the effects of gravity (ie, without buoyancy forces).

[0385] Simulation results The results of the three simulations are shown in Figures 14-16, respectively (Simulation 1 - Figure 14, Simulation 2 - Figure 15, Simulation 3 - Figure 16). Each figure includes three contour plots showing the contours of the local molar concentrations of H2O, O2, and H2 as annotated. The contours show the variation of the local molar concentrations in a dimensionless interval of 0.1 (on a scale of 0 to 1). It should be understood that the inflow boundary has a molar concentration of H2O equal to 1, and therefore each progressive contour line in the H2O contour plot along the flow direction toward the outflow boundary represents an incremental decrease in the respective molar concentration of 0.1. Similarly, it should be understood that the inflow boundaries of the other components (H2 and O2) are 0 at the inflow boundary, and therefore each progressive contour line toward the outflow boundary represents an incremental increase in the respective molar concentration of 0.1. The contour lines are generally curvilinear and therefore easily distinguished from the boundaries between the electrodes and the chambers, which are linear.

[0386] 14 and reported in Table 2 below, the first simulation results in a relatively high level of O2 in the first holding chamber 9210 associated with the first composite porous electrode 9217 (acting as the anode), and a relatively lower level of O2 present in the second holding chamber 9520 associated with the second composite porous electrode 9528 acting as the cathode. Similarly, there is a relatively high level of H2 present in the second holding chamber 9520 and a relatively lower level of O2 present in the first holding chamber.

[0387] As shown in the contour plot of H2O concentration, the H2O concentration is significantly lower toward the outlet 9213 of the inner holding chamber than in the outer holding chamber, with noticeable stratification. When the simulation takes into account buoyancy effects and defines the outlets 9213, 9524 as constant pressure boundaries, it is believed that the denser O2 generally held in the first holding chamber 9210 effectively displaces even denser H2O from the first holding chamber 9210. In other words, unreacted H2O does not accumulate in the inner holding chamber due to the accumulation of columns of O2 in the inner holding chamber that are relatively denser than the H2 accumulating in the opposing holding chamber, and the counterbalancing buoyancy forces bias the flow in the branch stream (e.g., the flow of unreacted H2O) toward and through the outer electrode to the outer holding chamber.

[0388] As a result, in the first simulation, flow (e.g., of unreacted HO) may be biased radially toward and through the outer composite porous electrode 9528 (cathode), as evidenced by the relatively high molar concentration of HO in the outer holding chamber 9520. This biasing of the branched flow depends on the flow characteristics associated with the composite porous electrode, with outflow conditions as assumed elsewhere herein. It is believed that this biasing in the branched flow may facilitate the prevention of backflow of H through the cathode (outer composite porous electrode), while allowing a relatively higher cross-flow of O from the anode (inner composite porous electrode) and associated inner holding chamber.

[0389] The second simulation differs from the first in that the model is adapted to simulate anisotropic porosity representing a tilted channel, as defined above. As shown in Figure 15, the second simulation results in a generally similar flow pattern in component concentrations, but with improved separation of reaction products and lower levels of crossover (i.e., lower levels of O2 in the holding chamber associated with the cathode and lower levels of H2 in the holding chamber associated with the anode).

[0390] This is best illustrated in Table 2 below and the graphs in Figures 17a and 17b. Table 2 below reports the local molar and mass concentrations of the components in each outflow. Figure 17a reports the recovery of H2 and O2 in each holding chamber as a percentage of the total mass of each respective reaction product. Figure 17b reports the recovery of the components as molar concentrations.

[0391] [Table 2]

[0392] As discussed elsewhere herein, the anisotropy of porosity corresponding to the inclined channels is believed to suppress backflow (e.g., back diffusion) of the respective reaction products. In particular, such backflow opposes the net flow direction through the respective channels and also opposes the direction of buoyancy forces given the relatively lower density of the reaction products produced in the respective composite porous electrodes compared to water.

[0393] In particular, the separation performance (i.e., cross-over reduction) of the second simulation relative to the first simulation is given for both gases, and cross-flow in both directions is reduced (i.e., backflow of reaction products through each electrode is reduced).

[0394] As a result, a comparison of the second simulation with the first does not support the conclusion that the modification to utilize anisotropic porosity merely adjusts the bias of the unreacted flow of HO towards one electrode or the other. In particular, as shown in Table 1 above, the flow of unreacted HO through each outlet appears to be substantially the same between the two simulations, so that an underlying (but tolerable) bias in the branched stream would still persist. Notwithstanding this, the anisotropic electrode appears to better resist the backflow of O2 through the anode. As a result of this, a larger difference between the fluid densities observed at the inner and outer outlets (and along the longitudinal extent of the holding chamber) is observed due to the relatively higher concentration of O2 in the inner holding chamber, and despite the action of buoyancy forces that would otherwise tend to drive a bias in the branched stream to stratify the fluid.

[0395] The third simulation (results shown in FIG. 16), as defined above, corresponds to the first simulation, but differs in that gravity is not simulated (i.e., buoyancy is not present). Although this is a non-material simulation, it provides a comparative example of the flow patterns of unreacted HO and its effect on the branched streams. In particular, in the absence of buoyancy forces driving the stratification of reaction products in the holding chambers, there will be a relatively larger proportion of unreacted HO in the inner holding chamber and a relatively lower amount in the outer holding chamber, indicating any bias change in the branched streams. Correspondingly, as shown in the results reported in Table 3 below, there will be a relatively lower cross-flow of O into the outer holding chamber, but a relatively higher diffusion of H into the inner holding chamber.

[0396] [Table 3]

[0397] The flow patterns discussed above in the context of the presence of a bias of the split flow towards one electrode, and the associated impact on the separation of reaction products and any cross-flow, are contemplated elsewhere herein. In particular, it has been discussed elsewhere herein how the net split flow through a composite porous electrode (or porous wall) serves to prevent backflow of associated reaction products therethrough, and that the proportion of flow directed through each respective composite porous electrode may vary depending on a number of factors, including, for example, the flow resistance exhibited by each respective composite porous electrode (which may be adjusted to affect the pattern of split flow) and outflow conditions, such as the back pressure maintained.

[0398] This disclosure extends to the subject matter of the following numbered sections:

[0399] Item 1. A method for producing a composite porous electrode for an electrolytic cell, comprising: forming a composite porous electrode by an additive manufacturing or powder pressing process in the form of a sheet-like or tubular wall having a thickness direction between two opposing major surfaces of the porous electrode; The building material of the additive manufacturing process or the powder of the powder pressing process is dispersed such that a composite porous electrode is formed by a layered structure between two main surfaces including at least two layers having different material compositions, and in use, a flow through the porous electrode between the two opposing main surfaces along the thickness direction passes through the at least two layers; The method of claim 1, wherein one of the layers forms an electrocatalytic region of a porous electrode that is spaced from at least one of the major surfaces of the electrode.

[0400] Item 2. The method of item 1, wherein the electrocatalytic region comprises an electrocatalyst for catalyzing an oxidation or reduction reaction with an aqueous electrolyte solution.

[0401] Clause 3. The method of clause 1 or 2, wherein a layer of the porous electrode other than the electrocatalytic region provides a passive region that is less electrocatalytically active than the electrocatalytic region for catalyzing each half-reaction of the electrolysis of the electrolyte solution, the passive region optionally including an insulating or dielectric material for suppressing each half-reaction of the electrolysis of the electrolyte solution.

[0402] Item 4. The method according to any one of items 1 to 3, comprising placing a composite porous electrode in an electrolytic cell to provide an electrolytic cell or electrolytic cell installation according to the first or second aspect or any one of claims 1 to 22 attached hereto.

[0403] Item 5. A method for producing a composite porous electrode for an electrolytic cell, comprising: forming a composite porous electrode body such that the body extends linearly along a longitudinal axis and has an orthogonal thickness direction from a first major surface to an opposing major surface; forming a plurality of angled channels extending through the body from the first and second major surfaces, each of the channels being angled with respect to both the longitudinal axis and the thickness direction; Including, The plurality of gradient channels may include During the manufacture of the body by additive manufacturing processes, or A method in which the body is formed after manufacture by removing material from the body, such as by a laser drilling process.

[0404] Item 6. The method of item 5, wherein each channel is formed to have a cross-section that diverges along the thickness direction.

[0405] Section 7. providing a coating comprising an electrocatalyst on the inner surfaces of the channels and / or on one or both major surfaces of the body to provide an electrocatalytic region of the body; and / or Optionally, providing a passivation coating on the major surface of the body over the coating containing the electrocatalyst. The method according to item 5 or 6, further comprising:

Claims

1. An electrolytic cell for carrying out continuous electrolysis of an aqueous electrolyte solution under supercritical conditions, comprising: a first electrode and a second electrode; an inlet chamber disposed between the electrodes and configured to receive a flow of electrolyte fluid; a first holding chamber associated with the first electrode for holding a fluid reaction product produced at the first electrode, the first holding chamber having a first outlet for discharging each of the fluid reaction products; a second holding chamber associated with the second electrode for holding a fluid reaction product produced at the second electrode, the second holding chamber having a second outlet for discharging each of the fluid reaction products; first and second porous walls separating the inlet chamber and each of the holding chambers, the first and second porous walls being configured to permit electrolyte fluid to flow from the inlet chamber to each of the holding chambers and configured to inhibit return flow of each of the fluid reaction products from each of the holding chambers to the inlet chamber; the porous wall and each of the electrodes are provided by a composite porous electrode separating the inlet chamber and the holding chamber; the composite porous wall having an inlet side adjacent the inlet chamber and an outlet side adjacent the retention chamber; The electrode is provided by an electrocatalytic region of the composite porous electrode.

2. An electrolytic cell for carrying out continuous electrolysis of an electrolyte solution, comprising: a first electrode and a second electrode; an inlet chamber disposed between the electrodes and configured to receive a flow of electrolyte fluid; a first holding chamber associated with the first electrode for holding a fluid reaction product produced at the first electrode, the first holding chamber having a first outlet for discharging each of the fluid reaction products; a second holding chamber associated with the second electrode for holding a fluid reaction product produced at the second electrode, the second holding chamber having a second outlet for discharging each of the fluid reaction products; first and second porous walls separating the inlet chamber and each of the holding chambers, the first and second porous walls being configured to permit electrolyte fluid to flow from the inlet chamber to each of the holding chambers and configured to inhibit return flow of each of the fluid reaction products from each of the holding chambers to the inlet chamber; the porous wall and each of the electrodes are provided by a composite porous electrode separating the inlet chamber and the holding chamber; the composite porous wall having an inlet side adjacent the inlet chamber and an outlet side adjacent the retention chamber; the electrode is provided by an electrocatalytic region of the composite porous electrode; a flow path for electrolyte fluid from the inlet chamber to the holding chamber; The flow path is an upstream portion passing through a passive region of the composite porous electrode; a downstream portion passing through an electrocatalytic region of the composite porous electrode; 11. An electrolytic cell, wherein the passive region is configured to be less electrocatalytically active than the electrocatalytic region or to suppress each half-reaction of the electrolysis.

3. An electrolytic cell as described in claim 2, wherein the passive region includes a passivation coating defining the inlet side of the composite porous electrode.

4. a flow path for electrolyte fluid from the inlet chamber to the holding chamber; The flow path is an upstream portion passing through a passive region of the composite porous electrode; a downstream portion passing through an electrocatalytic region of the composite porous electrode; the passive region is configured to be less electrocatalytically active than the electrocatalytic region or to suppress each half-reaction of the electrolysis; 2. The electrolytic cell of claim 1, wherein the passive region comprises a passivation coating defining the inlet side of the composite porous electrode.

5. the composite porous electrode extends linearly along a longitudinal axis and has an orthogonal thickness direction from the inlet side to the outlet side; the composite porous electrode having an anisotropic porous structure defined by a plurality of inclined channels, each inclined with respect to both the longitudinal axis and the thickness direction, configured to allow electrolyte liquid to flow from the inlet chamber to the holding chamber; Optionally, the angled channel extends through at least a portion of the electrocatalyst region.

6. The inlet chamber is an annular chamber; one of the first retention chamber and the second retention chamber is an inner core chamber surrounded by the inlet chamber; 5. An electrolytic cell according to any preceding claim, wherein the other of the first and second holding chambers is an outer annular chamber surrounding the entrance chamber.

7. 5. The electrolytic cell according to any one of claims 1 to 4, further comprising a controller configured to control flow control devices for controlling thermodynamic and / or flow rate conditions in the electrolytic cell.

8. The electrolytic cell of claim 7, wherein the controller controls the flow control device to maintain supercritical conditions of the electrolyte liquid in the inlet chamber and the holding chamber.

9. The electrolytic cell comprises: a first outlet associated with the first electrode for discharging a fluid reaction product produced at the first electrode; a second outlet associated with the second electrode for discharging fluid reaction products produced at the second electrode; the flow control device includes a first release valve and a second release valve in fluid communication with the first outlet and the second outlet, respectively; The controller controls the first release valve and / or the second release valve to maintain a target flow rate or target composition from one or each of the first and second outlets based on flow rate data, upstream pressure data and / or composition data received by the controller; and / or configured to control to maintain a target flow rate ratio between the flow out of the first outlet and the flow out of the second outlet based on flow rate data, upstream pressure data, and / or composition data received by the controller; Optionally, the target flow rate ratio is: the ratio of the total flow rate out of the first outlet to the total flow rate out of the second outlet; or 8. The electrolytic cell of claim 7, wherein said ratio corresponds to a ratio of a flow rate of a first fluid reaction product exiting said first outlet to a flow rate of a second fluid reaction product exiting said second outlet.

10. the controller is configured to determine whether an excessive amount of the second fluid reaction product is present in the outlet stream through the first outlet or whether an excessive amount of the first fluid reaction product is present in the outlet stream through the second outlet based on composition data received at the controller for each outlet stream; 8. The electrolytic cell of claim 7, wherein the controller is configured to control the first release valve and / or the second release valve to vary a flow rate through a porous wall of the electrolytic cell based on the determining.

11. A liquid electrolyte, optionally comprising a source of aqueous electrolyte; Electrolysis equipment comprising: the electrolytic cell according to any one of claims 1 to 4, for performing continuous electrolysis of the electrolyte solution.

12. A method of operating an electrolytic cell according to any one of claims 1 to 4, comprising the steps of: providing an inlet flow of an electrolyte liquid to the inlet chamber for carrying out an electrolytic half-reaction with the first electrode and the second electrode to produce respective fluid reaction products; the electrolyte solution and / or associated ions flow at least in part through the or each porous wall to react with the respective electrode; A method wherein the or each holding chamber holds a respective one of the fluid reaction products and each of the porous walls inhibits return flow of the fluid reaction products from the holding chamber back to the inlet chamber.

13. a flow path for electrolyte fluid from the inlet chamber to the holding chamber; The flow path is an upstream portion passing through a passive region of the composite porous electrode; a downstream portion passing through an electrocatalytic region of the composite porous electrode; the passive region is configured to be less electrocatalytically active than the electrocatalytic region or to suppress each half-reaction of the electrolysis; The electrolytic cell is as claimed in any one of claims 7 to 9, 13. The method of claim 12, wherein for each electrode associated with a holding chamber, a rate of a respective half-reaction of electrolysis in a respective electrocatalytic region is greater than a rate of a respective half-reaction of electrolysis in a respective passive region.

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