Electrochemical cell unit comprising a spacer assembly

Abstract

An electrochemical cell unit comprising a cell layer comprising an electrochemically active area and a spacer assembly. The spacer assembly is formed by a spacer plate and a flow distribution element. The cell layer and the spacer plate are overlaid in a spaced relationship to enclose a first fluid volume therebetween, wherein a first face of the cell layer faces the spacer plate. The flow distribution element is disposed within the first fluid volume. The first fluid volume comprises a first sub-volume and a second sub-volume with the flow distribution element disposed between the first sub-volume and the second sub-volume. The flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume at a plurality of locations along the length of the flow distribution element to direct flow in three-dimensions in the first fluid volume.

Description

ELECTROCHEMICAL CELL UNIT COMPRISING A SPACER ASSEMBLY Field of the Invention

[0001] The present invention relates to electrochemical cell units comprising a spacer assembly, in particular, electrolyser cell units and fuel cell units comprising the spacer assembly, stacks containing such cell units, methods for manufacturing cell units, and stacks thereof, and the use of such cell units. The cell units of the present invention include cells of solid oxide, polymer electrolyte membrane, and molten carbonate types. The present invention more specifically relates to solid oxide electrolyser cell (SOEC) solid oxide fuel cell (SOFC) units and, and these may include metal-supported solid oxide fuel cell (MS-SOFC) or electrolyser cell (MS-SOEC) units. Background to the Invention

[0002] Some electrochemical cell units can produce electricity by using an electrochemical conversion process that oxidises fuel to produce electricity. Some electrochemical cell units can also, or instead, operate as regenerative fuel cells (or reverse fuel cells) units, often known as electrolyser cell units, for example to produce hydrogen and oxygen from water, or carbon monoxide and oxygen from carbon dioxide. Electrochemical cell units may be tubular or planar in configuration, the latter may be arranged overlying one another in a stack arrangement.

[0003] A solid oxide fuel cell (SOFC) that produces electricity is based upon a solid oxide electrolyte that conducts negative oxygen ions from a cathode to an anode located on opposite sides of the electrolyte. For this, a fuel, or reformed fuel, contacts the anode (fuel electrode) and an oxidant, such as air or an oxygen rich fluid, contacts the cathode (air electrode). Conventional ceramic-supported (e.g. anode-supported) SOFCs have low mechanical strength and are vulnerable to fracture. Hence, metal-supported SOFCs have been developed which have the active fuel cell component layer supported on a metal substrate. In these cells, the ceramic layers can be very thin since they only perform an electrochemical function: that is to say, the ceramic layers are not self-supporting but rather are thin coatings / films laid down on and supported by the metal substrate. Such metal supported SOFC stacks are more robust, lower-cost, have better thermal properties than ceramic- supported SOFCs, and can be manufactured using conventional metal welding techniques.

[0004] A solid oxide electrolyser cell (SOEC) may have the same structure as an SOFC but is essentially that SOFC operating in reverse, or in a regenerative mode, to achieve the electrolysis of water and / or carbon dioxide by input of electrical energy and using the solid oxide electrolyte (or other electrolytes as listed above) to produce hydrogen gas and / or carbon monoxide and oxygen.

[0005] The present invention is directed to an electrochemical cell unit and concerns the design of spacer assemblies for them. It is thus applicable to various types of fuel and electrolyser cells, for example, based on solid oxide electrolytes, polymer electrolyte membranes, or molten electrolytes. For convenience, “cell units” is used to refer to “electrochemical cell units”, including fuel cell units and electrolyser cell units.

[0006] Each cell unit in a stack of cell units typically includes a cell layer comprising an electrochemically active cell region (such as a metal-supported or anode-supported electrochemically active cell region) and a spacer plate (also known as an ‘interconnect’ or a ‘separator plate’). A spacer plate typically contacts one side of the cell layer of a cell unit and, in a stack of cell units, and may also contact an opposite side of a cell layer of an adjacent cell unit.

[0007] Fig.1 shows a plan view of a fuel cell unit 10 taken from WO 2020 / 126486 A1, including an electrochemically active cell region 50 provided on a metal support plate 14. The metal support plate 14 has two fluid ports 22 located at either end of the plate 14 for fuel to enter and exit a fuel volume (not shown).

[0008] Fig.2 is also taken from WO 2020 / 126486 A1. Fig.2 shows an exploded view of a fuel cell unit 10, and two gaskets 34. The cell unit 10 comprises a flat metal support plate 14 stacked next to a separator plate 12. The separator plate 12 is shown to have flanged perimeter features 18 around its perimeter. The flanged perimeter features 18 extend out of the predominant plane of the sheet, as found at a central fluid volume area, to form the fluid volume within this cell unit upon assembly of the cell unit. In a middle portion of the cell unit 10, an electrochemically active cell region 50 (i.e. comprising the electrochemically active layers) is provided on the metal support plate 14, located outside of the fluid volume. The metal support plate 14 is provided with multiple small holes (not shown) to enable fluid in the fluid volume to be in fluidic communication with the side of the electrochemical layer that is closest to the metal support plate 14. The fuel electrode layer may be located adjacent the small holes with the fluid volume 20 within the cell unit comprising a fuel flow volume supplied by fuel entering and exiting via the fluid ports 22, which are thus fuel ports 22. The air electrode layer may be on the opposite side of the electrochemically active cell region 50, i.e. on its outer face, and is exposed to air flowing across that layer during use of the cell unit 10. Both the separator plate 12 and the metal support plate 14 are provided with fluid ports 22. Around the fluid ports of the separator plate 12, round dimples 24 are provided extending out of the plane of the base of the fluid volume a distance corresponding to that of the height of the flanged perimeter features 18. This is so that the dimples 24 will contact the opposing surface of the metal support plate 14, just like the flanged perimeter features 18, when the cell unit 10 is assembled. Dimples 32 (upward) and 30 (downward) create electrical contact between cell units and also provide a support function for thecell unit in the central region, extending upwardly to the underside of the metal support plate 14 at the area of the small holes, and downwardly to the opposing surface of the electrochemically active layer of a cell below it.

[0009] Conventionally, electrochemical cell units facilitate a one- or two-dimensional fluid flow field at the side of the cell at which the fuel is supplied (fuel inlet). Fig.3 shows a simplified cross sectional view of the abovementioned prior art cell unit 10 including cell layer 36 comprising the metal support plate 14. Arrow 33 shows the direction of fluid flow (from the inlet to the outlet, both not shown, but disposed to the left and right, respectively, of Fig.3) in the fluid volume 31 enclosed between the cell layer 36 and the spacer plate 12.

[0010] Arrow 33 depicts the direction of fluid flow in the fluid volume 31. In use, fuel flowing through the cell unit 10 from the inlet is gradually consumed over the length of the cell unit 10, i.e., in the direction of the fuel outlet. In effect, the fuel entering via the inlet is consumed in the electrochemical reaction at the electrochemically active area 50 and forms a product of the electrochemical reaction. This means that fuel from the inlet (at the start of arrow 33) gradually gets consumed as it crosses the cell unit 10 and by the time it reaches locations of the electrochemically active area 50 proximal to the outlet (towards the head of the arrow 33) the concentration of unused fuel in the fluid volume 31 is relatively low compared to proximal to the inlet. Accordingly, the availability of fuel for supply to the electrochemically active area 50 varies over the length of the cell unit 10, causing corresponding variations in power and energy density. Each repeat cell unit 10 in a cell stack therefore operates under different conditions (e.g. temperature and fuel concentration) across their length with corresponding efficiency and power / energy compromises.

[0011] The present invention seeks to address, overcome or mitigate at least one of the prior art disadvantages. Summary of the Invention

[0012] In a first aspect, there is provided an electrochemical cell unit comprising a cell layer comprising an electrochemically active area, and a spacer assembly; wherein the cell layer and the spacer assembly are overlaid with a first face of the cell layer facing the spacer assembly, wherein the first face of the cell layer and the spacer assembly define a first fluid volume and wherein the spacer assembly is configured to direct flow in three-dimensions in the first fluid volume. The spacer assembly therefore allows improved control over directing fluid (e.g. fuel) toward the electrochemically active cell area. Thus, the described arrangement advantageously enables a more even and therefore uniform distribution of fluid (e.g. fuel) across the extent of the electrochemically active area, and corresponding benefit in efficiency and energy density because operating conditions across the cellunit are homogenised. Use of the spacer assembly may reduce or eliminate dual atmosphere requirements for a spacer components because no one plate or component may separate hydrogen and oxygen. This may reduce cost of the spacer assembly and improve reliability of the cell unit.

[0013] More specifically, the electrochemical cell unit of the first aspect comprises: a cell layer comprising an electrochemically active area; and a spacer assembly comprising a spacer plate and a flow distribution element; wherein the cell layer and the spacer plate are overlaid in a spaced relationship to enclose a first fluid volume therebetween, wherein a first face of the cell layer faces the spacer plate wherein the flow distribution element is disposed within the first fluid volume, wherein the first fluid volume comprises a first sub-volume and a second sub-volume, the flow distribution element is disposed between the first sub-volume and the second sub-volume and the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume at a plurality of locations along the length of the flow distribution element to direct flow in three-dimensions in the first fluid volume. The plurality of locations along the length of the flow distribution element may correspond to (i.e., be positioned to direct flow at) a plurality of locations along the length of the electrochemically active area.

[0014] Preferably, the spacer assembly comprises a first face and a second face. The second face faces the cell layer. The first, opposing face of the spacer assembly is configured to contact a neighbouring cell unit, specifically a cell layer thereof. The spacer assembly can be unitary, i.e. made of a single part, or non-unitary, i.e. made of at least two component parts. The cell layer may be referred to as self-supporting (by self-supporting electrochemically active area – e.g., electrode or electrolyte supported – or by a support plate which supports the electrochemically active area). Throughout the specification, it is to be understood that first and second faces oppose one another across a component.

[0015] Preferably, the spacer assembly is configured to direct flow towards the cell layer at a plurality of locations. In some examples, the number of locations is 10 or more. Preferably, the number of locations is 20 or more. More preferably the number of locations is 40 or more. Still more preferably, the number of locations is a plurality is at 100 or more. In some examples, the spacer assembly comprises an orifice at each of the plurality of locations to direct flow towards the cell layer at said location. By directing flow in three-dimensions in the first fluid volume at a plurality of locations, the spacer assembly enables delivery of fluid (fuel) to the electrochemically active area at multiple locations across the extent of the first fluid volume and cell unit (i.e. including away from a fluid inlet and towards a fluid outlet), rather than mainly at locations in the vicinity of a fluid inlet of the cell unit. In use, fuel can be delivered to the electrochemically active area at locations where conventionally, mainly consumed fuel was present (for example, at locations nearer the fluid outlet). As a result, fuelconcentration over the length of the cell unit is more consistent, which minimises variations in current density. In other words, this advantageously enables a more even and therefore uniform distribution of fluid (e.g. fuel) across the extent of the electrochemically active area. This means that each cell unit operates under similar conditions (e.g. temperature and fuel concentration) across its extent.

[0016] The first fluid volume comprises a first sub-volume and a second sub-volume, preferably the first sub-volume is in fluidic communication with an inlet for a first fluid and the second sub-volume in fluidic communication with the first sub-volume, a layer of the electrochemically active area, and an outlet for the first fluid. In some examples, the electrochemically active area is disposed across a central portion of the cell layer and the first and second sub-volumes each extend across at least a portion of the plan view area of the central portion.

[0017] Preferably, fluidic communication between the first and second sub-volumes is substantially perpendicular to an extent of the electrochemically active area. In some examples, fluidic communication between the first and second sub-volumes is substantially perpendicular to a plan view extent of the electrochemically active area.

[0018] The first sub-volume is preferably for the first fluid (e.g., fuel), and the second sub-volume is preferably for a mixture of the first fluid (e.g., unused fuel) and a product of an electrochemical reaction. Preferably, in operation as an electrolyser cell, the first fluid comprises fuel, e.g. comprises H2O (steam) and / or CO2and / or NO2. The product of the electrochemical reaction comprises preferably H2and / or CO and / or NO (when the fuel is H2O and / or CO2and / or NO2, respectively). In operation as a fuel cell, the fuel may be hydrogen and the product may be steam.

[0019] Preferably, the electrochemical cell unit has a first end and a second end with the electrochemically active area disposed therebetween, the inlet to the first fluid volume being at the first end and the outlet from the first fluid volume is at the second end. The inlet and outlet may be proximal to, within or outside the footprint of the cell unit, at the respective ends of the cell unit. Preferably, the first and second ends of the cell unit are opposed to one another. In some examples, the inlet is to the first sub-volume and the outlet is from the second sub-volume. Typically, the inlet and outlet are respective fluid ports (i.e. through-holes) provided in the cell layer and spacer assembly. There is preferably at least one inlet and / or at least one outlet.

[0020] In some examples, at least one of a cross section of the first sub-volume decreases and a cross section of the second sub-volume increases from the first end to the second end of the electrochemical cell unit. This may maintain a higher pressure in the first sub-volume than in the second sub-volume, thereby biasing fluid flow from the first sub-volume toward the second sub- volume at a transition location (i.e. an opening that allows fluid flow, e.g. a pore, an orifice, or a hole).

[0021] Preferably, the spacer assembly comprises a spacer plate and a flow distribution element, wherein the cell layer and the spacer plate are overlaid in the spaced relationship to enclose the first fluid volume therebetween, with the flow distribution element disposed within the first fluid volume, and the flow distribution element is configured to direct flow in three-dimensions in the first fluid volume. Advantageously, the spacer plate and flow distribution element direct flow in three- dimensions to achieve more even fuel distribution over the extent of the cell unit.

[0022] In some examples, the spacer plate and flow distribution element are formed from two layers (i.e. a first layer comprising the spacer layer and a second layer comprising the flow distribution element). In some cases, the spacer plate and flow distribution element may be unitary. Alternatively or additionally, woven, stamped or calendared meshes can be used to create at least two layers of fuel flow with fluidic communication between the layers.

[0023] The flow distribution element is preferably disposed between the first sub-volume and the second sub-volume and the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume along the length of the flow distribution element (and therefore along the length of the cell unit since the length of the flow distribution element and the cell unit are aligned). Typically, the flow distribution element separates the first and second sub-volumes. In other words, the flow distribution element is configured such that it restricts fluid flow between the first and second sub-volumes.

[0024] Preferably, the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume and maintain a higher pressure in the first sub-volume than in the second sub-volume. The fluidic communication between the first and second sub-volumes is optionally at a plurality of locations (e.g. at least 10, more preferably at least 20, more preferably at least 40, more preferably at least 50, more preferably at least 100, typically less than 1000) along the length of the flow distribution element. Preferably, the fluidic communication occurs between a first face of the flow distribution element facing the first sub-volume and a second face of the flow distribution element facing the second sub-volume. In some examples, higher pressure between faces of the flow distribution element at each of the plurality of locations allowing (or driving) fluidic communication between the first sub-volume and the second sub-volume is maintained locally, i.e., at each location of communication. In such cases, it may be that the pressure at certain places of the second sub-volume is higher than certain other places of the first sub volume.

[0025] In some examples, the spacer plate comprises a first face and a second face, wherein the second face of the spacer plate faces the first fluid volume and comprises a plurality of first dimples which protrude into the first fluid volume. Preferably, the second face of the spacer plate bounds and faces the first fluid volume. In some examples, the plurality of first dimples protrude into the first sub-volume. Preferably, the plurality of first dimples protrude into the first and second sub-volumes. More preferably, the plurality of first dimples extend through corresponding through-holes in the flow distribution element. In some examples, the plurality of first dimples contact the cell layer (first face thereof, preferably a support plate of the cell layer).

[0026] In some examples, the first sub-volume is enclosed between a first face of the flow distribution element and the second face of the spacer plate. The first face of the spacer plate faces a neighbouring cell unit, specifically a second face of the cell layer thereof. The second sub-volume may be enclosed between the first face of the cell layer and a second face of the flow distribution element.

[0027] Optionally, the first face of the spacer plate is configured to face a second fluid volume between the cell unit and a neighbouring cell unit, and comprises a plurality of second dimples which protrude into the second fluid volume. Preferably, the first face of the spacer plate bounds the second fluid volume, and the second face of the cell layer bounds the second fluid volume.

[0028] Preferably, the flow distribution element comprises pores. Across each pore there is a higher fluidic pressure in the first sub-volume than in the second sub-volume. This enables fluid to preferentially flow towards the electrochemically active area. Advantageously, this allows fuel to be periodically added to the consumed fuel to replenish it.

[0029] The flow distribution element may be provided with a plurality of pores a) within the first third of the length of the electrochemically active area; b) between the first third and second third of the length of the electrochemically active area; c) between the second third and the end of the length of the electrochemically active area; or a combination of two or more of a) to c). In the preceding, the length of the electrochemically active area is taken to be the dimension along the fluid flow path in the first fluid volume (i.e., between the inlet and outlet).

[0030] Preferably, a cross-sectional area of the pores increases from the first end to the second end of the electrochemical cell unit. Alternatively, a cross-sectional area of the pores decreases from the first end to the second end of the electrochemical cell unit. From the first end to the second end of the electrochemical cell unit may also be referred to as along a length of the electrochemical cell unit. Such an increase or decrease from the first end to the second end may refer to an average cross- sectional area over plural pores across a width and in a portion of the length of the cell unit. For example, the cell unit may be considered to have a number of portions along its length and the (average) cross-sectional area may increase or decrease, as the case may be, from one portion to the next. In some examples, the last portion (i.e. the portion proximal to the second end) may not follow the trend of the preceding portions.

[0031] In some examples, spacing between the pores increases from the first end to the second end of the electrochemical cell unit. Alternatively, the spacing between the pores decreases from the firstend to the second end of the electrochemical cell unit. Such an increase or decrease from the first end to the second end may refer to an average spacing over plural pores across a width and in a portion of the length of the cell unit. For example, the cell unit may be considered to have a number of portions along its length and the (average) spacing area may increase or decrease, as the case may be, from one portion to the next. In some examples, the last portion (i.e. the portion proximal to the second end) may not follow the trend of the preceding portions.

[0032] In some examples, the flow distribution element is inclined relative to the cell layer and / or spacer plate such that at least one of the cross section of the first sub-volume decreases and the cross section of the second sub-volume increases from the first end to the second end of the electrochemical cell unit.

[0033] The size of the cross-sectional area of the pores, the spacing between the pores, the number of pores and / or the inclination of the flow distribution can be adjusted with respect to one another to optimise the distribution of fuel flow across the extent of the electrochemically active area.

[0034] Preferably, the flow distribution element comprises a plate. In some examples, the flow distribution element consists of the plate. The plate may be provided with pores by drilling, machining or stamping, e.g. laser drilling. Alternatively, or additionally, the plate may be inherently porous. Optionally, the plate may carry porous regions made from inherently porous material. For example, the flow distribution element comprises a mesh. The flow distribution element may be a plate carrying a mesh in one or more areas. The flow distribution element may be a metal plate.

[0035] Preferably, the flow distribution element is a manifold which encloses the first sub-volume and which separates the second sub-volume from a third sub-volume (i.e., a third sub-volume of the first volume), wherein the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume and between the second sub-volume and the third sub-volume, and the third sub-volume is in fluidic communication with the outlet. In such arrangements, the first sub-volume is in fluidic communication with the inlet. First fluid (e.g. fuel) is communicated between the first sub-volume and the second sub-volume. The third sub-volume allows passage of unused first fluid and product of electrochemical reaction out of the cell unit. The fluidic communication between the first sub-volume and the second sub-volume can be substantially perpendicular to the extent of the cell unit. In some examples, fluidic communication between the sub-volumes occurs at a plurality of locations across the extent of the cell unit.

[0036] Preferably, the second face of the spacer plate faces the first fluid volume. In some arrangements - where the third sub-volume is present - the second face of the spacer plate faces the third sub-volume of the first fluid volume. The first side of the spacer plate is configured to face asecond fluid volume between the cell unit and a neighbouring cell unit. The first side of the spacer plate can comprise a plurality of second dimples which protrude into the second fluid volume.

[0037] The cell layer may comprise a support plate, which may be made of metal, having a first face and a second face. The support plate carries the electrochemically active area, which is deposited or coated over a porous region of the support plate. The second face of the support plate carries the electrochemically active area. Within a cell unit, the second face of the spacer plate may face the first face of the support plate.

[0038] The first aspect relates to electrolyser cell (EC) units or fuel cell (FC) units, which may be solid oxide electrolyser cell (SOEC) units or solid oxide fuel cell (SOFC) units. The first fluid volume may befor fuel. In an EC, the fuel may be steam or CO2. In a FC, the fuel may be H2, NH3or a hydrocarbon. Asecond fluid volume is provided for an oxidant, such as oxygen, O2, and / or for a sweep gas. In EC, the second fluid volume may be for oxygen produced by the electrolysis reaction and for an optional sweep gas. In FC, oxygen may be introduced from an external source for consumption in the electrochemical reaction.

[0039] In a second aspect there is provided a spacer assembly comprising a spacer plate and a flow distribution element wherein the spacer plate is configured to be overlaid by a cell layer in a spaced relationship to enclose a first fluid volume therebetween and the spacer plate assembly is configured to direct flow in three-dimensions in the first fluid volume. Preferably, the flow distribution element is configured to direct flow in three-dimensions in the first fluid volume. The spacer assembly may be further configured as described above for the first aspect.

[0040] More specifically, in the second aspect there is provided a spacer assembly comprising a spacer plate and a flow distribution element wherein the spacer plate is configured to be overlaid by a cell layer in a spaced relationship to enclose a first fluid volume therebetween, wherein the flow distribution element is configured to be disposed within the first fluid volume and the first fluid volume is configured to comprise a first sub-volume and a second sub-volume, the flow distribution element disposed between the first sub-volume and the second sub-volume and the flow distribution element configured to allow fluidic communication between the first sub-volume and the second sub- volume at a plurality of locations along the length of the flow distribution element to direct flow in three-dimensions in the first fluid volume.

[0041] A third aspect relates to the use of the spacer assembly of the second aspect in a cell unit, as described above.

[0042] In a fourth aspect there is provided a stack of electrochemical cell units comprising a plurality of electrochemical cell units according to the first aspect, wherein a first side of a first electrochemical cell unit faces a second side of a neighbouring electrochemical cell unit in a spaced, opposed,relationship to form a second fluid volume therebetween. In some arrangements, the first face of the spacer plate faces the second side of the neighbouring cell unit. Preferably, the first face of the spacer plate faces the second face of the cell layer (e.g., the outermost layer of the electrochemically active area) of the neighbouring cell unit. The spaced relationship, and therefore second fluid volume, is maintained by the plurality of second dimples on the first side of the spacer plate, which contact the electrochemically active area of the neighbouring electrochemical cell unit.

[0043] In a fifth aspect there is provided a method of manufacturing an electrochemical cell unit comprising providing a cell layer comprising an electrochemically active area; providing a spacer assembly; and overlaying the cell layer and the spacer assembly with a first face of the cell layer facing the spacer assembly, wherein the first face of the cell layer and the spacer assembly define a first fluid volume, wherein the spacer assembly is configured to direct flow in three-dimensions in the first fluid volume. The spacer plate and flow distribution element are configured to cooperate to control flow in three-dimensions. Preferably, the electrochemical cell unit is the cell unit of the first aspect, described above.

[0044] More specifically, the fifth aspect provides a method of manufacturing an electrochemical cell unit comprising: providing a cell layer comprising an electrochemically active area; providing a spacer assembly comprising a spacer plate and a flow distribution element; and overlaying the cell layer and the spacer assembly with a first face of the cell layer facing the spacer assembly, wherein the first face of the cell layer and the spacer assembly define a first fluid volume, wherein the flow distribution element is disposed within the first fluid volume, wherein the first fluid volume comprises a first sub- volume and a second sub-volume, the flow distribution element is disposed between the first sub- volume and the second sub-volume and the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume at a plurality of locations along the length of the flow distribution element to direct flow in three-dimensions in the first fluid volume.

[0045] In a sixth aspect there is provided a method of manufacturing a stack of electrochemical cell units comprising providing a plurality of electrochemical cell units and stacking said cell units one upon another such that a first side of a first electrochemical cell unit faces a second side of a neighbouring electrochemical cell unit in a spaced, opposed, relationship to form a second fluid volume therebetween. Preferably, the electrochemical cell units are those according to the first aspect or manufactured according to the fifth aspect. In some examples, the first face of the spacer plate faces the second side of the neighbouring cell unit. More preferably, the first face of the spacer plate faces the second face of the cell layer (i.e. the outermost layer of the electrochemically active area) of the neighbouring cell unit to form the second fluid volume therebetween. In this arrangement, the secondfluid volume is maintained by the plurality of second dimples on the first side of the spacer plate, which contact the second face of the electrochemically active area of the neighbouring electrochemical cell unit.

[0046] In order that the present invention be more readily understood, various aspects of specific embodiments will now be described in conjunction with the attached drawings. Brief Description of the Drawings

[0047] Fig.1 is a plan view of a prior art cell unit.

[0048] Fig.2 is an exploded perspective view of the cell unit of Fig.1.

[0049] Fig.3 is a simplified cross-sectional view of a prior art cell unit according to Figs.1 and 2.

[0050] Fig.4 is a cross-sectional view of an embodiment of a cell unit according to the present invention.

[0051] Fig.5 is a plan view of a flow distribution element of an embodiment of a cell unit according to the present invention.

[0052] Fig.6 is a cross-sectional view of a further embodiment of a cell unit according to the present invention.

[0053] Fig.7 is a cross-sectional view of a further embodiment of a cell unit according to the present invention.

[0054] Fig.8 illustrates a method of manufacturing an electrochemical cell unit, in accordance with the present invention. Detailed Description

[0055] The drawings are included for illustrative purposes only. Some of the figures indicate only one electrochemical cell unit (hereafter referred to simply as a “cell unit”) in a electrochemical cell stack (also referred herein simply as a “stack”), however, it will be readily apparent that a stack may include two or more electrochemical cell units.

[0056] The cell units described with reference to Figs.4 to 8 may be fuel cell units, such as SOFC units, or electrolyser cell units, such as SOEC units.

[0057] In general, the present invention relates to an electrochemical cell unit comprising a spacer assembly which enables improved control over directing fluid (e.g. fuel) toward the electrochemically active cell area. The described arrangement advantageously enables a more even and therefore uniform distribution of fluid (e.g. fuel) across the extent of the electrochemically active area, thereby improving uniformity of conditions (e.g. temperature, fuel concentration) across a cell unit (i.e. repeat unit) and thus across a stack.

[0058] Fig.4 shows a cross section of an electrochemical cell unit 40 comprising a cell layer 44. The cell layer 44 comprises an electrochemically active area 44a. The cell layer 44 has a first face 44b and a second face 44c. The cell layer 44 also includes a support plate 44d. In the arrangement of Fig.4, the electrochemically active area 44a is provided on top of the support plate 44d. As a result, a lower face of the support plate 44d forms the first face 44b of the cell layer 44, and the second face 44c of the cell layer 44 is formed by an outermost layer of the electrochemically active area 44a and, where not covered by the electrochemically active area 44a, an upper face of the support plate 44d.

[0059] The cell unit 40 further includes a spacer assembly 42. The cell layer 44 and spacer assembly 42 are overlaid with the first face 44b of the cell layer 44 facing the spacer assembly 42. The first face 44b of the cell layer 44 and the spacer assembly 42 define a first fluid volume 46 (also termed a “first fluid passage”) therebetween. The spacer assembly 42 is configured to direct fluid flow in three- dimensions in the first fluid volume 46. For example, the first fluid volume 46 may comprise a first sub-volume 46a (also termed a “first sub-passage”) and a second sub-volume 46b (also termed a “second sub-passage”). Fluid can enter the first sub-volume 46a in an X-Y plane (from a fluid port – not shown) and can be directed from the first sub-volume 46a to the second sub-volume 46b by the spacer assembly 42. In arrangements such as that shown in Fig.4, the spacer assembly 42 includes a plurality of pores 48a, 48b, 48c to direct the fluid from the first sub-volume 46a to the second sub- volume 46b. In Fig.4, the cross-sectional area of the pores increase in size from pore 48a (proximal to the entry to the first sub-volume) to 48c (distal to the entry to the first sub-volume), but this need not be the case. Instead, each of the pores 48 may have the same cross-sectional area.

[0060] The support plate 44d is provided with a porous region (depicted by multiple small holes 47) to enable fluid in the first fluid volume 46 to contact the side of the electrochemically active area 44a that is closest to the support plate 44d (i.e. to enable fluidic communication between the first fluid volume 46 and an (innermost) electrode of the electrochemically active area 44a that is proximal to the support plate 44d). In the arrangement of Fig.4, the fluid can contact the electrochemically active area 44a once it has passed from the first sub-volume 46a to the second sub-volume 46b via the spacer assembly 42.

[0061] The spacer assembly 42 includes a spacer plate 41 and a flow distribution element 43. The spacer plate 41 has a first face 41b and a second face 41a. The first fluid volume 46 is enclosed between the second face 41a of the spacer plate 41 and the first face 44b of the cell layer 44, said faces facing one another in a spaced, opposed relationship across the first fluid volume 46. In this embodiment, the spacer plate 41 and flow distribution element 43 are separate, non-unitary components. Arrow A denotes the height of the first fluid volume 46 (between a plane (flat) of the spacer plate 41 and the support plate 44d). The first sub-volume 46a is enclosed between a first face 43b of the flowdistribution element 43 and a second face 41a of the spacer plate 41. The second sub-volume 46b is enclosed between the first face 44b of the cell layer 44 and a second face 43b of the flow distribution element 43. Heights of the first and second sub-volumes 46a, 46b are a portion of the height A of the first fluid volume 46. In the case of Fig.4, the heights of the sub-volumes 46a, 46b vary along their length (and may be constant across their width – into and out of the plane of Fig.4) but this need not be the case. Said variation is characterised in the first sub-volume 46a height decreasing and the second sub-volume 46b height increasing in the overall direction of fluid flow in the first fluid volume 46. The first sub-volume 46a is in fluidic communication with an inlet (not shown, but disposed to the left side of Fig.4) for a first fluid (e.g., fuel, e.g. water (steam) and / or CO2for EC operation, or hydrogen for FC operation). The second sub-volume 46b is in fluidic communication with each of the first sub- volume 46a, the electrochemically active 44a (e.g. the innermost layer of the electrochemically active 44a, as shown in Fig.4, via the porous region (e.g., holes 47 of the support plate 44d)) and an outlet (not shown, but disposed to the right side of Fig. 4) for first fluid. Arrow 49 represents the overall direction of fluid flow – from inlet to outlet – in the first fluid volume 46 (and the sub-volumes 46a, 46b). The first sub-volume 46a is for the first fluid and the second sub-volume 46b is for a mixture of the first fluid and a product of an electrochemical reaction (i.e. unused fuel and, e.g. hydrogen and / or CO, respectively).

[0062] The flow distribution element 43 is a plate which is disposed within the first fluid volume 46 and separates the first sub-volume 46a from the second sub-volume 46b. Pores 48 in the flow distribution element 43 allow fluidic communication between the first and second sub-volumes 46a, 46b, and that fluidic communication is substantially perpendicular to a plan view extent of the electrochemically active area 44a. In this case, the flow distribution element 43 is inclined relative to the cell layer 44 and spacer plate 41 and slopes away from the cell layer 44 and towards the spacer plate 41. The effect of this slope is that the cross-section of the first sub-volume 46a decreases from a first end of the cell unit 40 (inlet end) to a second end of the cell unit 44 (outlet end), i.e. in the direction of arrow 49. The inclined flow distribution element 43 causes the cross-section of the second sub-volume 46b to increase in the direction of arrow 49 from the first end to the second end of the cell unit 40. Therefore, when fluid enters the cell unit 40, flow distribution element 43 controls fluidic communication between the first and second sub-volumes 46a, 46b (both restricting and allowing fluidic communication) resulting in a distribution of the pressure of the fluid along the first sub-volume 46a. As a result, first fluid may pass from the first sub-volume 46a to the second sub-volume 46b at each of the pores 48, including those towards the outlet end of the cell unit 40.

[0063] The plate of the flow distribution element 43 comprises pores 48a, 48b, 48c (only three being shown in Fig. 4 for clarity). The plate 43 may be provided with pores by drilling / machining, e.g.mechanical or laser drilling. Alternatively, the plate 43 can be inherently porous, or the plate 43 may carry porous regions made from inherently porous material.

[0064] Across each pore 48a, 48b, 48c of the flow distribution element 43, there is a higher fluid pressure in the first sub-volume 46a than the second sub-volume 46b. Pores 48 allow fluidic communication to be controlled between faces of the flow distribution element 43 while the non- porous parts of the flow distribution element 43 restrict fluid flow between the first sub-volume 46a and the second sub-volume 46b.This forces first fluid to flow towards the electrochemically active area 44a (i.e. upwards in the arrangement shown in Fig. 4) over the length of the flow distribution element 43 – at each pore thereof. This improves distribution of first fluid along the length of the cell unit 40 (i.e., improves how even the distribution is) and thus improves uniformity of conditions across the extent of the cell unit 40. Specifically, in use, first fluid (e.g., fuel) is injected to the second sub- volume 46b at plural locations for supply to the electrochemically active area 44a, including at locations proximal to the fluid outlet. As a result, temperature, fuel concentration, and current density over the length of cell unit 40 is more consistent, which minimises variations in the Nernst potential along said length. Accordingly, the present arrangement prevents premature degradation of component parts of the cell unit 40 and stacks thereof.

[0065] As can be seen in Fig.4, the cross-sectional area of the pores 48a, 48b, 48c increases from the first to the second end of the cell unit 40. In an alternative embodiment, the cross-sectional areas of the pores 48 are consistent along the direction of the first end to the second end of the cell unit 40. In an alternative embodiment, the cross-sectional areas of the pores 48 decrease in the direction of the first end to the second end of the cell unit 40. The spacing between the pores 48a, 48b, 48c may be consistent, increase or decrease from the first end to the second end of the cell unit 40.

[0066] The second face 41a of the spacer plate 41 faces the first fluid volume 46. In this case, the second face 41a includes a plurality of first dimples 45a which protrude upwards into the first fluid volume 46. In some embodiments, the plurality of first dimples 45a extend through corresponding gaps in the flow distribution element 43 such that (peaks of) the first dimples 45a may contact the first face 44b of the cell layer 44 (e.g., the support plate 44d). The first dimples 45a thereby maintain spacing between the first face 44b of the cell layer 44 and the second face 41a of the spacer plate 41, said spacing for the first fluid volume 46. The first dimples 45a may also provide electrical connection between the cell layer 44 and the spacer plate 41. The cell layer 44 and the spacer plate 41 may be connected (directly or indirectly) around their periphery (e.g., by welding) and that connection may provide the electrical connection therebetween (additional or alternative to via first dimples 45a).

[0067] The first face 41b of the spacer plate 41, which is configured to face a second fluid volume located between cell unit 40 and a neighbouring cell unit (not shown), includes a plurality of seconddimples 45b which protrude into the second fluid volume (not shown). In an alternative embodiment, the spacer plate 41 is planar or flat (i.e. does not comprise dimples).

[0068] A flow of fluid in the direction of arrow 49 through the cell unit 40 of Fig. 4 will now be described. A first fluid (e.g. fuel, e.g. water (steam) and / or CO2) enters the first fluid volume 46 of cell unit 40 via an inlet (not shown, to the left side of Fig.4). Specifically, the first fluid flows into the first sub-volume 46a, which is in fluid communication with the inlet. The first sub-volume 46a is enclosed between the second face 43a of the flow distribution element 43 and the second face 41a of the spacer plate 41. Some of the first fluid is then forced through pore 48a of the flow distribution element 43, into the second sub-volume 46b (e.g., by a pressure difference between the sub-volumes). The first fluid which did not pass through pore 48a can traverse further through the first sub-volume 46a to potentially pass through pore 48b into the second sub-volume 46b. There may be some first fluid which does not pass through pore 48a or 48b and can thus pass through pore 48c into the second sub- volume 46b. The second sub-volume 46b can only be accessed by the first fluid from the inlet via the pores 48a, 48b or 48c. Due to the size of the pores 48a, 48b, 48c, the flow of first fluid is restricted through the gap or hole created by the pores 48a, 48b, 48c. Consequently, directly across each of the pores 48a, 48b, 48c the fluidic pressure is higher in the first sub-volume 46a than the fluidic pressure in the second sub-volume 46b on the opposing face of the flow distribution element 43, which forces first fluid across the flow distribution element 43. The first fluid therefore flows in the direction of the first sub-volume 46a to the second sub-volume 46b, towards the cell layer 44 and the electrochemically active area 44a.

[0069] When the first fluid reaches the second sub-volume 46b, it can access the electrochemically active area 44a via the porous region in the support plate 44d. The first fluid that reaches the electrochemically active area 44a undergoes an electrochemical reaction to form products of the electrochemical reaction. Where the cell unit 40 is an electrolysis cell unit, the first fluid (fuel) may be steam (water). In this instance, the product of the electrochemical reaction is hydrogen and oxygen – released on opposite faces of the electrochemically active area 44a – in the case of an oxygen ion conducting electrolyte (i.e., SOEC), hydrogen as a first product of the electrochemical reaction is released into the second sub-volume 46b (of the first fluid volume 46) and oxygen as a second product of the electrochemical cell reaction is released into the second fluid volume (not shown, but bounded by the second face 44c of the cell layer 44). The first product and any unused first fluid is forced through the second sub-volume 46b in the direction of arrow 49 due to the pressure differences across the extent of the cell unit 40 (e.g., because of an outlet (not shown, but typically to the right side of Fig.4) of the first fluid volume 46, in fluidic communication with the second sub-volume 46b).

[0070] The pores 48a, 48b, 48c i.e. openings, in the flow distribution element 43 open along the length of the cell unit 40 (e.g., along the length of the plan view of the electrochemically active area 44a). Accordingly, there are a plurality of locations along the length of the cell unit 40 at which the first fluid can flow from the first sub-volume 46a to the second sub-volume 46b and thus toward the electrochemically active area 44a. At the location of each pore 48, the fluidic pressure in the second sub-volume 46b is lower than the fluidic pressure in the first sub-volume 46a. In the example of Fig. 4, due to the inclination, or slope, of the flow distribution element 43 toward the spacer plate 41, the cross-section of the first sub-volume 46a gradually decreases in the direction of arrow 49 and the cross-section of the second sub-volume 46b gradually increases as a consequence. The decrease in cross-section of the first sub-volume 46a maintains the fluid pressure in the first sub-volume 46a toward the second end of the cell unit 40 to a relatively higher value than if the flow distribution element 43 were not inclined. The increase in cross-section of the second sub-volume 46b leads to a relatively reduced fluid pressure in that volume. Transport of first fluid across the flow distribution element 43 (from the first sub-volume 46a to the second sub-volume 46b) towards the electrochemically active area 44a therefore occurs along the length of the cell unit 40, ensuring fuel is replenished in the second sub-volume 46b. This enhances uniformity of conditions (e.g. temperature and fuel concentration) across the extent of the cell unit 40.

[0071] Once an electrochemical reaction has occurred between the first fluid and the electrochemically active area 44a, the second sub-volume 46b predominantly contains the first product of an electrochemical reaction (e.g. where the first fluid is fuel - steam, the first product is hydrogen if the electrolyte conducts oxygen ions), which is directed toward the second end of the cell unit 40 (i.e. toward the outlet – right side of Fig. 4). The second sub-volume 46b is in fluid communication with the outlet for collection of first product and any remaining first fluid from said sub-volume 46b.

[0072] The purpose of the spacer assembly 42 is to enable a more even first fluid distribution across the extent of the cell unit 40 in order to improve uniformity of conditions across the cell unit 40 (and thus the stack of which cell unit 40 forms a part). In conventional arrangements, such as those shown in Figs.1-3, fluid - e.g., fuel - entering the cell unit 30 can flow through fluid volume 31 in an undirected manner. Fuel that has interacted with the electrochemically active area 34 will mix with the fluid entering the cell unit 30. As such, the concentration of unreacted fuel at a point on the electrochemically active area 34 will change depending on the distance from the fuel inlet as unreacted fuel only enters through that fuel inlet. With the cell unit 40 according to the present invention, however, the spacer assembly 42 acts as a baffle or a manifold to direct first fluid from the first end (inlet end) of the cell unit 40 to the electrochemically active area 44a. First fluid (a portionthereof) can travel away from the inlet within the first sub-volume 46a without mixing with the reacted fluid (i.e. the first product), before traversing a pore 48 to reach the second sub-volume 46b at some distance along the length of the cell unit 40. The concentration of first fluid (e.g., unreacted fuel) is therefore relatively more even across the electrochemically active area 44a.

[0073] It will be apparent that a higher fluidic pressure is present in the first sub-volume 46a than in the second sub-volume 46b, locally, across each pore 48a, 48b, 48c in order for fluid to pass from the first sub-volume 46a to the second sub-volume 46b. Further, the fluid pressure at the inlet end of the first sub-volume 46a is greater than the fluid pressure at the outlet end of the first sub-volume 46a, so that fluid flows across the first sub-volume 46a, towards the second end (outlet) of the first sub- volume 46a.

[0074] In order to balance the different fluid pressure requirements, different factors can be adjusted. For example, as discussed above, the flow distribution element (plate) 43 shown in Fig. 4 slopes away from the cell layer 44 and toward the spacer plate 41 in the direction of arrow 49. This means that the cross section of the first sub-volume 46a gradually decreases from the first end to the second end of the cell unit 40 and the cross section of the second sub-volume 46b increases in the same direction. As a result, the pressure of fluid in the first sub-volume 46a is relatively maintained from the first end to the second end of the cell unit 40 to a relatively higher value than if the flow distribution element 43 were not inclined, while the pressure of the fluid is relatively reduced in the same direction in the second sub-volume 46b. Across a given pore 48, the pressure in the first sub- volume 46a will be higher than the pressure in the second sub-volume 46b (these may be referred to as local pressures or a local pressure difference), such that fluid will flow from the first sub-volume 46a to the second sub-volume 46b through that pore that is remote from the fluid inlet.

[0075] Other examples of factors that can be adjusted to balance the fluid pressure requirements include the size (cross-sectional area) and / or spacing of the pores 48. For example, the cross-sectional area of the pores may increase in size from the first end to the second end of the cell unit 40. Having smaller pores at the first end of the cell unit 40 would restrict fluid flow from the first sub-volume 46a into the second sub-volume 46b, encouraging a larger proportion of the fluid to flow toward the outlet (second end) of the cell unit 40. The relatively larger pores 48 at the second end will promote more fluid to pass from the first sub-volume 46a to the second sub-volume 46b across those relatively larger pores than if the pores had the same cross-sectional area. Similarly, increasing the number of pores per unit area toward the second end will promote fluid flow through the pores toward that end.

[0076] In alternative arrangements, the flow distribution element 43 can be located parallel to the support plate 44d or cell layer 44. In this way, the cross-sections of the first and second sub-volumes 46a, 46b remain constant from the first end to the second end of the cell unit 40. To compensate forlack of inclination in the flow distribution element 43 and to create local positive pressure differentials across the pores / holes in the direction from the first sub-volume 46a to the second sub-volume 46b, the size of the cross-section of the pores 48 and / or the distance / spacing between them (i.e. the pore density) may be adjusted. It is only necessary to adjust or balance one of the pore size, spacing or inclination of the flow distribution element to achieve the desired effect of causing fluid to flow in three-dimensions at a plurality of locations across the extent of the electrochemically active area 44a. It will be apparent, of course, that one or more of the pore size, spacing or inclination of the flow distribution element 43 can be adjusted to provide the fluid distribution. In each case, when fluid enters the cell unit 40, flow distribution element 43 controls fluidic communication between the first and second sub-volumes 46a, 46b (both restricting and allowing fluidic communication) resulting in a distribution of the pressure of the fluid along the first sub-volume 46a. As a result, first fluid may pass from the first sub-volume 46a to the second sub-volume 46b at each of the pores 48, including those towards the outlet end of the cell unit 40.

[0077] Fig. 5 is a simplified plan view of the effect of the flow distribution element 52 across the footprint of a cell unit (depicted as cell unit having similar footprint to that of Fig.1, location and extent of electrochemically active area 44a and ports 22 acting as inlet 22a and outlet 22b are shown for clarity, but it will be understood these are not necessarily part of the flow distribution element 52). At the centres of the groups of multi-directional arrows 54 is a pore 48 (e.g. a hole or orifice), extending through the flow distribution element 52. The arrows are illustrative and indicate that fluid can pass through the flow distribution element 52 (from the first sub-volume to the second sub-volume), toward the electrochemically active area 44a, via pores 48 (as shown in Fig.5, in use, the fluid moves out of the plane of the page). It can be seen that the flow distribution element 52 is configured to direct flow toward the cell layer (not shown) at a plurality of locations, in three-dimensions. Twelve pores 48 are shown in the plate of the flow distribution element 52. This is merely illustrative – there could be fewer or more than twelve pores 48.

[0078] In the example of Fig.5, first fluid is configured to flow in the first fluid volume from the inlet 22a (in fluidic communication with the first sub-volume) to the outlet 22b (in fluidic communication with the second sub-volume) via the flow distribution element 52. The flow distribution element 52 is provided with a plurality of pores 48 distributed over the extent of the electrochemically active area 44a. The flow distribution element 52 may be provided with a plurality of pores 48 a) within the first third of the length of the electrochemically active area 44a; b) between the first third and second third of the length of the electrochemically active area 44a; c) between the second third and the end of the length of the electrochemically active area 44a; or a combination of two or more of a) to c). In thepreceding, the length of the electrochemically active area 44a is taken to be the dimension along the fluid flow path in the first fluid volume (i.e., between the inlet 22a and outlet 22b).

[0079] Fig.6 shows a cross-sectional view of a further cell unit 60. Like in the arrangement of Fig.4, cell unit 60 has a cell layer 68, including a support plate 68d which carries an electrochemically active area 68a. Cell unit 60 further includes spacer assembly 62 which is configured to direct flow in three- dimensions in a first fluid volume 66. The spacer assembly 62 includes spacer plate 63 and flow distribution element 61. A first fluid volume 66 is enclosed between a first face 68b of the cell layer 68 and a second face 63b of the spacer plate 63. The flow distribution element 61 is disposed in the first fluid volume 66 (which includes first, second and third sub-volumes, 66a-c). Fig.6 indicates the approximate locations of the sub-volumes 66a-c for this specific arrangement.

[0080] In this arrangement, the flow distribution element 61 is a manifold which encloses the first sub-volume 66a. The second face 63b of the spacer plate 63 immediately faces the third sub-volume 66c. The manifold 61 separates the second sub-volume 66b from the third sub-volume 66c. In the arrangement of Fig.6, the first face 68b of the cell layer 68 immediately faces the second sub-volume 66b. The manifold 61 and thus the enclosed first sub-volume 66a is in fluidic communication with the inlet (not shown, but disposed to the left side of Fig.6). Arrow 65 shows direction of first fluid flow (from a first, inlet end, to a second, outlet end).

[0081] A flow of first fluid (e.g. fuel) through the cell unit 60 of Fig.6 will now be described. First fluid enters manifold 61 via an inlet (not shown) at the first end of cell unit 60 and is enclosed in the first sub-volume 66a. The first fluid is directed by the manifold 61 upwards and towards the electrochemically active area 68a via, in the example of Fig. 6, channels 64, which can also be described as nozzles or spouts 64 and are tubular, but are otherwise similar to the pores of Figs.4 and 5 and may be simply referred to as pores. The manifold 61 extends across the extent of the electrochemically active area 68a, meaning that the channels 64 provide a plurality of locations for first fluid to be delivered to - and interact with - the electrochemically active area 58a. The direction of first fluid flow is indicated by arrow 67. Channels 64 allow fuel to enter the second sub-volume 66b so that fuel can access the electrochemically active area 68a. There is thus fluidic communication between the first sub-volume 66a and the second sub-volume 66b. Upon interaction with the electrochemically active area 68a, if the first fluid is fuel (or comprises fuel) the fuel undergoes an electrochemical reaction and first product is released into the second sub-volume 66b.

[0082] In an electrolyser cell, when the first fluid is fuel, e.g., steam and if the electrolyte conducts oxygen ions, then the first product of the electrochemical reaction (hydrogen) will temporarily reside in the second sub-volume 66b. Arrows 69, directed downwards, show the subsequent direction of flow of the products of the electrochemical reaction, i.e., into the third sub-volume 66c. There is thusfluidic communication between the second sub-volume 66b and the third sub-volume 66c. This fluidic communication between the second and third sub-volumes 66b, 66c is enabled by channels 64 through the manifold 61 which cannot be directly accessed from the first sub-volume 66a. The third sub-volume 66c is in fluidic communication with the outlet (not shown) of the cell unit 60. Fluid in the third sub-volume 66c is depicted to flow from left to right in Fig.6 (open arrow 69) with an outlet to the right hand side of Fig.6. This need not be the case. The outlet(s) may be positioned such that fluid in the third sub-volume 66c may flow from right to left in Fig. 6 (a counter-flow arrangement with respect to flow in the first sub-volume 66a) or in or out of the plane of Fig.6 (cross-flow arrangements with respect to flow in the first sub-volume 66a).

[0083] The arrangement of Fig. 6, wherein the flow distribution element 61 is a manifold, advantageously routes the first product of the electrochemical reaction out of the second sub-volume 66b. This further improves uniformity of distribution of fuel across the cell unit 60.

[0084] In a stack of cell units 60, the first face of the spacer plate 63a and the second face 68c of the cell layer 68 face the second fluid volume. It will be appreciated that dimples, such as those described with reference to Figs.4 and 5, or other support structures may be provided in the spacer assembly or in the fluid volumes to space the components and maintain the first and second fluid volumes.

[0085] Fig.7 shows a cross-section of an alternative cell unit 70 including spacer assembly 72. Spacer assembly 72 includes spacer plate 71 and flow distribution element 73, which are integrally formed (i.e. unitary, as depicted) or formed from separate components. Cell unit 70 further includes cell layer 76, having a first face 76a, which faces spacer assembly 72. Cell layer 76 and spacer assembly 72 are overlaid. The first face 76a of the cell layer 76 and the spacer assembly 72 define a first fluid volume 77, the height of which is denoted by arrow B.

[0086] A simplified version of the cell layer 76 is shown. To aid understanding, the cell layer 76 would have substantially the same structure as cell layer 44 (Fig.4) and cell layer 68 (Fig.6).

[0087] The spacer assembly 72 is configured to direct flow in three-dimensions in the first fluid volume 77. First fluid volume 77 is split into two sub-volumes: first sub-volume 77a and second sub- volume 77b. The first sub-volume 77a is in fluidic communication with the inlet (not shown) at a first end of the cell unit 70, and is enclosed between a second face 71b of the spacer plate 71 and a first face 73a of the flow distribution element 73. The first sub-volume 77a is closed at a second end of the cell unit 70. The second sub-volume 77b is in fluidic communication with the outlet (not shown) at a second end of the cell unit 70 and is enclosed between the first face 76a of the cell layer 76 and a second face 73b of the flow distribution element 73. The second sub-volume 77b is closed at the inlet end (i.e. the first end) of the cell unit 70.

[0088] Flow distribution element 73 comprises four groups of pores, 74a, 74b, 74c, 74d. The number of pores (or the density of pores) increase in each group in the direction of arrow 75, which is also the direction of fluid flow from the first end (i.e. the inlet, not shown) to the second end (i.e. the outlet, not shown). Accordingly, pore group 74a has the least number of pores while pore group 74d has the most.

[0089] In use, first fluid (e.g. fuel) flows into first sub-volume 77a through an inlet (not shown) in the vicinity of arrow 78 at the first end of the cell unit. A portion of the first fluid will be biased to flow through pore group 74a, into the second sub-volume 77b. The first fluid which does not flow through pore group 74a will flow in the direction of arrow 75 and into the second sub-volume 77b via one of (subsequent) pore groups 74b, 74c or 74d. The fluidic pressure across the pore groups 74 typically decreases in the direction shown by arrow 75. The fluidic pressure is highest across the two sub- volumes 77a, 77b at pore group 74a and so pore group 74a comprises fewer pores (or a lower total cross-sectional area) than subsequent pore groups 74b-74d. The distribution and density of pores means that at least some of the first fluid is forced to travel toward the second end / outlet end of the cell unit 70 and through the pore groups located at a further distance from the first end / inlet end, e.g. pore groups 74c and 74d. First fluid, undiluted by product of the electrochemical reaction, can thus access the electrochemically active area of the cell layer 76 at locations further from the inlet than is possible in conventional arrangements such as that of Figs.1-3. This improves fluid distribution across the extent of the cell unit 70, thereby improving uniformity of conditions in the cell unit 70 and in a cell stack, of which cell unit 70 forms a repeat unit.

[0090] First fluid entering second sub-volume 77b is able to interact with the electrochemically active area of cell layer 76 to form a (first) product of an electrochemical reaction (e.g. where the first fluid is fuel, e.g., is H2O (steam) in an electrolysis cell unit, the first product is hydrogen). The first product is released into the second sub-volume 77b, but is unable to flow back into the first sub-volume 77a due to the fluidic pressure differential across the pore groups (i.e. higher fluidic pressure in the first sub-volume 77a than in the second sub-volume 77b). Thus, the first product is forced to flow in the direction of arrow 75 toward the outlet (second end) of the cell unit 70.

[0091] In accordance with an aspect of the present disclosure, a method of manufacturing an electrochemical cell unit is hereby described, with reference to Fig.8. The method 80 comprises: step 82: providing a cell layer comprising an electrochemically active area; step 84: providing a spacer assembly; and step 86: overlaying the cell layer and the spacer assembly, wherein a first face of the cell layer and the spacer assembly define a first fluid volume, wherein the spacer assembly is configured to direct flow in three-dimensions in the first fluid volume.

[0092] In accordance with a further aspect of the present invention, a method of manufacturing a stack of electrochemical cell units is herein described. The method comprises providing, by the method described above, a plurality of electrochemical cell units and stacking said cell units one upon another such that a first side of a first electrochemical cell unit faces a second side of a neighbouring electrochemical cell unit in a spaced, opposed relationship to form a second fluid volume therebetween. The second fluid volume may be maintained by a plurality of dimples.

[0093] The present invention is not to be limited by the above-described aspects and embodiments, and that many variations are within the scope of the appended claims. The various aspects and embodiments may be combined if necessary and appropriate. The drawings serve as exemplary illustrations of the invention only, to aid understanding of the invention.

Claims

CLAIMS 1. An electrochemical cell unit comprising: a cell layer comprising an electrochemically active area; and a spacer assembly comprising a spacer plate and a flow distribution element; wherein the cell layer and the spacer plate are overlaid in a spaced relationship to enclose a first fluid volume therebetween, wherein a first face of the cell layer faces the spacer plate, wherein the flow distribution element is disposed within the first fluid volume, wherein the first fluid volume comprises a first sub-volume and a second sub-volume, the flow distribution element is disposed between the first sub-volume and the second sub-volume and the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume at a plurality of locations along the length of the flow distribution element to direct flow in three- dimensions in the first fluid volume.

2. The electrochemical cell unit of claim 1, wherein the first sub-volume is in fluidic communication with an inlet for a first fluid and the second sub-volume in fluidic communication with the first sub-volume, a layer of the electrochemically active area, and an outlet for the first fluid.

3. The electrochemical cell unit of claim 2, wherein fluidic communication between the first sub-volume and the second sub-volume is substantially perpendicular to an extent of the electrochemically active area.

4. The electrochemical cell unit according to claim 2 or 3, wherein the first sub-volume is for the first fluid, and the second sub-volume is for a mixture of the first fluid and a product of an electrochemical reaction.

5. The electrochemical cell unit according to any one of claims 2 to 4, having a first end and a second end with the electrochemically active area disposed therebetween, the inlet to the first fluid volume being at the first end and the outlet from the first fluid volume is at the second end.

6. The electrochemical cell unit according to claim 5, wherein at least one of a cross section of the first sub-volume decreases and a cross section of the second sub-volume increases from the first end to the second end of the electrochemical cell unit.

7. The electrochemical cell unit according to any preceding claim, wherein the flow distribution element is configured to allow fluidic communication between the first sub- volume and the second sub-volume and maintain a higher pressure in the first sub-volume than the second sub-volume.

8. The electrochemical cell unit according to any preceding claim, wherein the spacer plate comprises a first face and a second face, wherein the second face of the spacer plate faces the first fluid volume and comprises a plurality of first dimples which protrude into the first fluid volume.

9. The electrochemical cell unit according to claim 8, wherein the first face of the spacer plate is configured to face a second fluid volume between the cell unit and a neighbouring cell unit, and comprises a plurality of second dimples which protrude into the second fluid volume.

10. The electrochemical cell unit according to any preceding claim, wherein the flow distribution element comprises pores.

11. The electrochemical cell unit according to claim 10, wherein a cross sectional area of the pores increases from the first end to the second end of the electrochemical cell unit.

12. The electrochemical cell unit according to claim 10 or 11, wherein spacing between the pores increases from the first end to the second end of the electrochemical cell unit.

13. The electrochemical cell unit according to any preceding claim, wherein the flow distribution element comprises a plate.

14. The electrochemical cell unit according to any preceding claim, wherein the flow distribution element is a manifold which encloses the first sub-volume and which separates the second sub-volume from a third sub-volume, wherein the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume and between the second sub-volume and the third sub-volume, and the third sub-volume is in fluidic communication with the outlet.

15. A spacer assembly comprising a spacer plate and a flow distribution element wherein the spacer plate is configured to be overlaid by a cell layer in a spaced relationship to enclose a first fluid volume therebetween, wherein the flow distribution element is configured to be disposed within the first fluid volume and the first fluid volume is configured to comprise a first sub-volume and a second sub-volume, the flow distribution element disposed between the first sub-volume and the second sub-volume and the flow distribution element configured to allow fluidic communication between the first sub-volume and the secondsub-volume at a plurality of locations along the length of the flow distribution element to direct flow in three-dimensions in the first fluid volume.

16. Use of the spacer assembly according to claim 15 in a cell unit according to any one of claims 1 to 14.

17. A stack of electrochemical cell units comprising a plurality of electrochemical cell units according to any one of claims 1 to 14, wherein a first side of a first electrochemical cell unit faces a second side of a neighbouring electrochemical cell unit in a spaced, opposed, relationship to form a second fluid volume therebetween.

18. A method of manufacturing an electrochemical cell unit comprising: providing a cell layer comprising an electrochemically active area; providing a spacer assembly comprising a spacer plate and a flow distribution element; and overlaying the cell layer and the spacer assembly with a first face of the cell layer facing the spacer assembly, wherein the first face of the cell layer and the spacer assembly define a first fluid volume, wherein the flow distribution element is disposed within the first fluid volume, wherein the first fluid volume comprises a first sub-volume and a second sub- volume, the flow distribution element is disposed between the first sub-volume and the second sub-volume and the flow distribution element is configured to allow fluidic communication between the first sub-volume and the second sub-volume at a plurality of locations along the length of the flow distribution element to direct flow in three- dimensions in the first fluid volume.

19. A method of manufacturing a stack of electrochemical cell units comprising providing a plurality of electrochemical cell units each according to any one of claims 1 to 14 and stacking said cell units one upon another such that a first side of a first electrochemical cell unit faces a second side of a neighbouring electrochemical cell unit in a spaced, opposed, relationship to form a second fluid volume therebetween.

Images