Gasket for use in an electrochemical cell stack

Abstract

A gasket 30 suitable for use in an electrochemical cell stack, the gasket 30 comprises an electrically insulating core 38 having first and second opposing faces 38a 38b, a first metal-containing foil

Description

Field of the Invention

[0001] The present invention relates to a gasket for use in an electrochemical cell stack, in particular, in stacks containing electrolyser cell units or fuel cell units, and methods for manufacturing an electrochemical cell stack. The electrochemical cell stacks of the present invention include cell units having cells of solid oxide, polymer electrolyte membrane, and molten carbonate types. The present invention more specifically relates to electrochemical cell stacks comprising a gasket and further comprising solid oxide electrolyser cell (SOEC) or solid oxide fuel cell (SOFC) units, 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 a gasket for use in an electrochemical cell stack. An electrochemical cell stack comprises a plurality of cell units. The gasket of the present invention 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] Fig. 1 shows a plan view of a fuel cell unit 10 taken from WO 2020 / 126486 Al, 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).

[0007] Fig. 2 is also taken from WO 2020 / 126486 Al. Fig. 2 shows an exploded view of a 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 or oxygen 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, 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 23 (upward) and 21 (downward) create electrical contact between cell units and also provide a support function for the cell 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.

[0008] Each gasket, e.g. gasket 34, (also referred to as "seal") provides a primary sealing function and will usually be a compressible gasket that is subjected to high compressive forces in the vicinity of the fluid ports 22.

[0009] The gaskets 34 may be sized to cover all the dimples 24 of each fluid port 22 to prevent fluid (such as fuel) that may be travelling through the fluid ports 22 in a stack from seeping between the outside of the cell unit 10 and the gaskets (for example gasket 34), into the area external of the cell units, i.e. into the fluid surrounding the cell units 10 (such as oxidant), or the fluid external of the fluid ports from seeping in the other direction - into the fluid ports. This is important to prevent any mixing of the fluid inside the cell unit 10 and the fluid outside the cell unit 10, which will be fuel and oxidant. The polarity of the electrochemically active cell region 50 determines which way round this will be.

[0010] The gaskets 34 may also provide electrical insulation between a first cell unit 10 and an adjacent fluid cell unit 10, so as to prevent a short circuit.

[0011] Gaskets also achieve separation between cell units (also referred to as "cell-to-cell separation"). Controlling cell-to-cell separation is critical for maintaining low ohmic resistance because cell-to-cell separation determines the pressure exerted on the electrical contact points between the cathode and interconnect. In turn, this determines the level of ohmic resistance at the electrical contact points. Maintaining cell-to-cell separation also mitigates electrolyte damage at cathode / interconnect contact points, which can occur if cell units become too close to one another.

[0012] Controlling cell-to-cell separation in stack assemblies requires gaskets to seal at a certain gasket thickness dictated by stack design. Whereas using vermiculite-based gaskets presents difficulties in achieving this because, when compressed in the stack assembly of cells, certain gaskets, such as vermiculite-based gaskets, may not seal at the abovementioned thickness dictated by stack design. Further, due to its highly hygroscopic nature, vermiculite-based gaskets undergo volumetric changes with changing air humidity.

[0013] Additionally, vermiculite-based gaskets release gas phase impurities, e.g. HF and vapours of hydroxylated K- and Si-based compounds which may contaminate or even corrode other components of the cell units.

[0014] Vermiculite and other compressible gaskets are often used for low and intermediate temperature cell units (up to approximately 700 °C). They require compression forces to seal between the gasket and a sealing face of the cell unit. Such compression inherently changes the shape and affects the structure of the gasket which in turn affects the cell-to-cell separation and sealing ability of the gasket. Glass based seals are required for high temperature cell units (approximately between 700 and 1100 °C or more), but such seals suffer from recrystallisation and volatility of constituents during operational life. In turn this can cause corrosion at sealing interfaces and release gas phase impurities into cell units and systems, and affects the structural stability of the seals which can lead to cracking in the bulk of the seal or at sealing interfaces, resulting in seal failure.

[0015] The present invention seeks to address, overcome or mitigate at least one of the prior art disadvantages. Summary of the Invention

[0016] In a first aspect, there is provided a gasket for use in an electrochemical cell stack, the gasket comprising an electrically insulating core having first and second opposing faces, a first metalcontaining foil disposed on the first face and a second metal-containing foil disposed on the second face, and wherein the first and second metal-containing foils comprise aluminium or copper. In use, the gasket may be disposed between plates of adjacent / neighbouring cell units. In particular, the gasket may be disposed around fluid ports in the plates of adjacent / neighbouring cell units.

[0017] Advantageously, the first and second metal-containing foils have a high plasticity and ductility and can therefore deform and flex to the contour of and to fill interfacial gaps created by roughness of the plates, thus providing a fluid-tight seal. Thus, fluid-tight sealing between the gasket and cell plates can be achieved without the need for chemical bonding or catalyst materials. Further, the gasket (and therefore the foils) will typically be used to seal against metal plate(s) of cell units, in which case the fluid-tight seal therebetween can be further enhanced by chemical bonding between the foil and cell plates. The high plasticity of the first and second metal-containing foils accommodates differences in coefficients of thermal expansion (CTE) between the electrically insulating core (e.g. ceramic) and the components of the cell units (which may comprise metal).

[0018] Due to the first and second metal-containing foils comprising aluminium or copper, the foils are inert, which minimises corrosion of, or reaction with, the plates of cell units which the gasket contacts in use. Additionally, lateral flow / deformation of the first and second metal-containing foils is heavily constrained due to interfacial friction drag imposed by the plates of neighbouring cell units when the gasket is in situ. The gasket of the first aspect does not require significant compression to promote sealing and also provides a hard stop to control separation between adjacent cell units, thereby minimising the level of ohmic resistance at electrical contact points between plates of adjacent cell units (cell stacks typically requiring compression to ensure good electrical contact between adjacent cell units).

[0019] The first and second metal-containing foils may be disposed upon opposed (preferably planar, preferably parallel planar) faces of the electrically insulating core. The electrically insulating core electrically insulates the first metal-containing foil from the second metal-containing foil. Outer faces of the metal-containing foils are configured to contact opposing plates in electrochemical cell stacks, while the electrically insulating core is configured to electrically insulate said foils, and therefore said plates from one another. The first metal-containing foil (disposed on the first face of the electrically insulating core), the electrically insulating core and the second metal-containing foil (disposed on the second face of the electrically insulating core) may be stacked upon each other in a stacking direction. That stacking direction being configured to be aligned with a stacking direction in the electrochemical cell stack. The gasket is configured to react to a compression force (e.g., applied along the stacking direction), and in a stack, to transfer that compression force through the stack. Said compression force is configured to urge the first metal-containing foil against the first face of the electrically insulating core and to urge the second metal-containing core against the second face of the electrically insulating core (and, in a stack, to urge outer faces of the metal-containing foils against opposing plates (e.g., substrates and / or interconnects).

[0020] Preferably, each of the first and second metal-containing foils comprise an aluminium alloy. Alternatively, each of the first and second metal-containing foils comprise a copper alloy. The first and second metal-containing foils are thin, malleable sheets. The foils may take the form of a monolithic metal sheet, wherein each of the first and second metal-containing foils can be respectively disposed on the first and second faces of the electrically insulating core as separate, single units.

[0021] Preferably, the aluminium alloy comprises one or more of Mn, Cr, Fe, Ti, and V. The alloying element (i.e. one or more of Mn, Cr, Fe, Ti, and V) raises the melting point of the first and second metal-containing foils above operational temperature of an electrochemical stack, while enabling the first and second metal-containing foils to remain ductile.

[0022] The alloying element is preferably taken into solid solution (dissolves) in an aluminium (or copper) crystal lattice. If alloying leads to formation of separate phases, in particular, intermetallic phases, the extent of second phase formation preferably does not cause any significant reduction in plasticity (or ductility) of the alloy. The amount of alloying element added thus needs to be controlled to balance these requirements. If there is a significant reduction in plasticity (or ductility) of the alloy, poor sealing in the areas where the first or second faces of the electrically insulating core contacts the foils may arise. Poor sealing occurs when the foils are unable to deform sufficiently to take up the shape / surface contour on the areas of contact between the foils and the first or second face of the electrically insulating core.

[0023] The alloying element is preferably added to aluminium between 1-15 at.%, and more preferably between 2 to 10 at.%. Preferably, the alloying element is manganese and the first and second metal-containing foils comprise aluminium. More preferably, manganese is added to aluminium in the range of Mn between 2-7 at.%, more preferably between 2-5 at.%.

[0024] Preferably, each of the first and second metal-containing foils is self-supporting. Advantageously, the first and second metal-containing foils hold their shape. They can thus simply be placed on the first and second faces of the electrically insulating core, which avoids additional steps of coating the faces of the electrically insulating core. Accordingly, using first and second metalcontaining foils simplifies and accelerates the assembly process.

[0025] In some arrangements, each of the first and second metal-containing foils has a thickness of between 5-150 pm, optionally between 20-100 pm, optionally between 40-60 pm. In particularly preferred arrangements, each of the first and second metal-containing foils have a thickness of between 20-40 pm or between 60-80 pm. Preferably, the electrically insulating core has a thickness of at least 100 pm, which provides the core with sufficient mechanical strength and sufficient thickness for electrical insulation against typical potential differences in electrochemical cell units. In a preferred arrangement, each of the first and second metal-containing foils have a thickness of approximately 50 pm and the electrically insulating core has a thickness of approximately 100 pm (i.e., total gasket thickness of approximately 200 pm). Use of first and second metal-containing foils which are preferably self-supporting means that vapour deposition methods (e.g. chemical / physical vapour deposition) are avoided.

[0026] Preferably, each of the first and second metal-containing foils has a constant thickness. More preferably, each of the first and second metal-containing foils has a constant thickness at least on a micrometre scale. Effectively, the surface of the metal-containing foils are smooth, i.e., devoid of ridges or other surface features. Preferably, the peak-to-peak surface roughness of each of the first and second metal-containing foils is less than 15 pm and more preferably less than 5 pm. In some preferable arrangements, the peak-to-peak surface roughness is at least 0.2 pm, preferably at least 0.5 pm. In some preferable arrangements, the peak-to-peak surface roughness is between 0.2 and 0.8 pm and in more preferred arrangements is between 0.3 and 0.5 pm. In some preferable arrangements, the average surface roughness (Ra) is between 0.2 and 2 pm.

[0027] Preferably, the electrically insulating core comprises a ceramic. Ceramics provide good electrical insulation and are fluid-tight (i.e., they have resistance to leak paths and diffusion of fluid through their body) and therefore form an effective gasket. In some arrangements, the ceramic comprises an electrically insulating oxide. The ceramic may be a ceramic foil. More preferably, the ceramic or ceramic foil comprises yttria-stabilised (cubic) zirconia (YSZ), alumina or mullite. It is preferable that the ceramic has a thermal expansion behaviour which substantially matches that of the material of the cell plates of cell units (e.g. steel, which has a CTE of around 12 x 10-61 / K). Many zirconia- and magnesia-based ceramics, e.g., zirconia toughened alumina (ZTA) exhibit such behaviour. Placing aluminium foil on both sides of ceramic foil protects the ceramic foil from mechanical damage when this sandwiched assembly is employed as sealing gasket subjected to compression in stack assembly.

[0028] Preferably, the gasket has a thickness of between 120-500 pm, optionally between 150-400 pm, optionally between 200-300 pm. In some arrangements, the gasket has a thickness of between 100-400 pm, or between 200-400 pm, or between 100-300 pm or between 200-300 pm, or between 100-200 pm, or between 200-250 pm, or between 150-200 pm or between 250-350 pm.

[0029] In some arrangements, the gasket is annular. Preferably, each of the electrically insulating core and first and second metal-containing foils are annular. Thus, the gasket is advantageously configured for disposal around fluid ports in plates of an electrochemical unit and enables fluid flow through its centre. An elliptical-annular or circular-annular shaped gasket reduces the chance of vortices forming in the fluid flowing therethrough. In other arrangements, the gasket may take other shapes, e.g., triangular-annular or rectangular-annular shaped.

[0030] Preferably, the first metal-containing foil is disposed on a part only of the first face of the electrically insulting core and / or the second metal-containing foil is disposed on a part only of the second face of the electrically insulating core. More preferably, each of the first and second metalcontaining foils has a width dimension that is less than a width dimension of the electrically insulating core. The electrically insulating core may thus have an exposed shoulder - i.e., the electrically insulating core has a protruding edge which protrudes past the inner and / or outer edge of the metalcontaining foils. The exposed shoulder / protruding edge prevents the first and second metalcontaining foils from being squeezed past the edge of the electrically insulating core, e.g., squeezed together and thus contacting one another when under stack compression. This prevents electrical shorting. Preferably, the width dimension of the electrically insulating core is between 5-10% larger than the width dimension of each of the first and second metal-containing foils.

[0031] Preferably, the first metal-containing foil is in direct, physical contact with the first face of the electrically insulating core, and wherein the second metal-containing foil is in direct physical contact with the second face of the electrically insulating core. In such arrangement, there is no adhesion layer between the first and second metal-containing foils and the first and second faces of the core, respectively. Additionally, in a preferred arrangement, the first and second metal-containing foils are not brazed to the respective first and second faces of the electrically insulating core. When the gasket is positioned within an electrochemical cell stack, sealing of the first and second metal-containing foils to the respective firstand second faces of the electrically insulating core is achieved by deforming the foils under stack assembly compression. Under such compression, the first and second metalcontaining foils (e.g., foils comprising aluminium) will fill any gaps in the electrically insulating core and cell faces / plates to be sealed and take up the shape of the surface contour of the electrically insulating core and cell faces / plates.

[0032] In a second aspect, there is provided an electrochemical cell unit component comprising: a first plate and a second plate in spaced arrangement, and an electrochemically active cell region wherein the first plate, the second plate, and the electrochemically active cell region overlay one another to form an electrochemical cell unit, wherein a fluid port is provided in each of the first plate and the second plate (the respective fluid ports may be aligned), the component further comprising a gasket according to the first aspect, wherein the gasket is disposed around the fluid port of the first plate and / or around the fluid port of the second plate. In effect, the gasket can be disposed between adjacent / neighbouring cell units in an electrochemical cell stack. Preferably, the fluid ports are for fuel or oxygen.

[0033] Preferably, the first plate is a support plate which carries the electrochemically active cell region and the second plate is an interconnect. In this arrangement, the support plate supports the electrochemically active cell region. For example, the electrochemically active cell region may be coated or deposited over a porous region of the support plate. Preferably, both first and second plates are metallic, for example, both first and second plates may comprise steel. As discussed above, interface of the metal-containing foil with metallic plate(s) at elevated temperatures (a few hundred degrees centigrade) may lead to chemical bonding at the interface therebetween. As a result, sealing via chemical bonding is achieved alongside mechanical sealing in such cases. This may particularly be the case when the steel comprises a transition metal, e.g. a transition metal oxide, e.g., one or more of Co, Cr, Mn. In some cases, both first and second plates are interconnects, for example if the electrochemically active cell region is self-supporting.

[0034] In some arrangements, a surface of the first and / or second plate has an adhesion promoter or a reactive interface for chemical bonding with the first and / or second metal-containing foils. The adhesion promoter or reactive interface may comprise a transition metal, e.g. a transition metal oxide or electrolyte, e.g., one or more of Co, Cr, Mn, Fe or ceria (CeOj).

[0035] In a third aspect, there is provided a stack of electrochemical cell units comprising a plurality of electrochemical cell units overlaying one another in a stacking direction, wherein each electrochemical cell unit comprises a first plate and a second plate in spaced arrangement, and an electrochemically active cell region, wherein the first plate, the second plate, and the electrochemically active cell region overlay one another to form the electrochemical cell unit, wherein a fluid port is provided in each of the first plate and the second plate (the respective fluid ports may be aligned), wherein a gasket according to the first aspect is disposed around the fluid port of a first plate of a first electrochemical cell unit and a fluid port of a second plate of a neighbouring cell unit, such that the gasket is disposed between neighbouring cell units.

[0036] Preferably, the first plate is a support plate which carries the electrochemically active cell region and the second plate is an interconnect. In this arrangement, the support plate supports the electrochemically active cell region. For example, the electrochemically active cell region may be coated or deposited over a porous region of the support plate. Preferably, both first and second plates are metallic (e.g., steel for example, the abovementioned steel).

[0037] In a fourth aspect, there is provided a method of manufacture of an electrochemical cell stack, the method comprising: providing a first plate comprising a fluid port, placing (to form a gasket) around the fluid port of the first plate: o an electrically insulating core having first and second opposing faces o a first metal-containing foil contacting the first face of the electrically insulating core and o a second metal-containing foil contacting the second face of the electrically insulating core. placing a second plate comprising a fluid port on the second metal-containing foil, wherein the first and second metal-containing foils comprise aluminium or copper, wherein an electrochemically active cell region is disposed between the first plate and the second plate, wherein the fluid ports of the first and second plates are configured to allow fluid to flow therethrough, the method further comprising compressing the first and second plates.

[0038] As such, compressing the first and second plates takes place with the gasket therebetween. Advantageously, sealing of the first and second metal-containing foils to the first and second faces of the electrically insulating core and the sealing of the first and second metal-containing foils to the first and second plates is achieved by deforming the first and second metal-containing foils under stack assembly compression. As a result, the first and second metal-containing foils fill the gaps in the surfaces of the plates (and any gaps in the electrically insulating core) and adopt the shape of the surface contour of the cell plates (faces) to be sealed. As discussed above, the electrochemically active cell region may be attached to (e.g., self-supporting) and / or carried by (e.g., coated or deposited upon) one of the first and second plates. The gasket and the electrochemically active cell region may be disposed between the first and second plates (in other words, they each face the same faces of the plates).

[0039] Preferably, the first plate is a support plate which carries the electrochemically active cell region and the second plate is an interconnect. In this arrangement, the support plate supports the electrochemically active cell region. For example, the electrochemically active cell region may be coated or deposited over a porous region of the support plate. Preferably, both first and second plates are metallic. More preferably, both first and second plates are interconnects. The first and second plates referred to above may be part of the same cell unit. In other cases, the first and second plates may be part of two separate cell units, and the placing of the first plate includes placing of a first cell unit (including the first plate and a second plate joined to one another, and the or an electrochemically active cell region) and the placing of the second plate includes placing of a second cell unit (including the second plate and a first plate joined to one another, and the or an electrochemically active cell region).

[0040] Preferably, the method further comprises heating at a temperature between 500-650 °C. Heating may be performed after placing the second plate. Heating may be performed after compressing the first and second plates, or while the first and second plates are under compression (i.e., compressing and heating may be simultaneous). Advantageously, heating in the range of between 500-650 °C causes the ductility and flexibility of the first and second metal-containing foils to increase so that they can more easily take up the shape of the surface contours of the first and second plates and provide a better seal. It also leads to chemical bonding between the metalcontaining foil and a steel substrate (in such cases as one or both plates comprise steel), thereby providing a better seal.

[0041] In some arrangements, the compressing is performed between 1-30 kN, optionally between 5-15 kN. Such pressures are advantageously in line with pressures applied during running of an electrochemical cell stack. Accordingly, the gasket can be sealed within the stack without requiring an additional manufacturing step.

[0042] Preferably, the electrically insulating core and the first and second metal-containing foils are annular. Advantageously, the annular first and second metal-containing foils are aligned to enable fluid flow through the centre of the gasket. Thus, the gasket is advantageously configured for disposal around fluid ports in plates of an electrochemical unit.

[0043] A fifth aspect relates to the use of the gasket of the first aspect in an electrochemical cell stack. The electrochemical cell stack may comprise a plurality of cell units, wherein the cell units are fuel cell units or electrolyser cell units.

[0044] In a sixth aspect, a kit of parts is provided. The kit of parts comprises: • an annular electrically insulating core having first and second opposing faces, • an annular first metal-containing foil and an annular second metal-containing foil, • wherein the annular first and second metal-containing foils comprise aluminium or copper.

[0045] Preferably, the kit of parts further comprises a first plate and a second plate, wherein a fluid port is provided in each of the first plate and the second plate. In some arrangements, the first plate is a support plate and the second plate is an interconnect. Preferably, the kit of parts further comprises an electrochemically active cell region. In some arrangements, one of the first or second plates comprises or carries the electrochemically active cell region.

[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 cross-sectional view of a gasket according to the present invention.

[0050] Fig. 4 is a top-down view of the gasket of Fig. 3.

[0051] Fig. 5 is an aluminium-manganese phase diagram.

[0052] Fig. 6 is a cross-sectional view of part of an electrochemical cell stack including the gasket of the present invention positioned between adjacent cell units.

[0053] Fig. 7 is a cross-sectional view of part of an electrochemical cell stack including a cell unit and a gasket. Detailed Description

[0054] 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, for example 300-400 cell units.

[0055] The cell units described herein may be fuel cell units, such as SOFC units, or electrolyser cell units, such as SOEC units.

[0056] In general, the present invention relates to a gasket for use in an electrochemical cell stack, the gasket comprising an electrically insulating core having first and second opposing faces, a first metal-containing foil disposed on the first face and a second metal-containing foil disposed on the second face, and wherein the first and second metal-containing foils comprise aluminium or copper. In use, the gasket may be disposed between plates of adjacent / neighbouring cell units. In particular, the gasket may be disposed around fluid ports in the plates of adjacent / neighbouring cell units. The terms gasket and seal may be used interchangeably herein unless the context requires otherwise. It will be understood that gaskets typically rely on compression to affect sealing.

[0057] Advantageously, the first and second metal-containing foils have a high plasticity and ductility and can therefore deform and flex to the contour of and to fill interfacial gaps created by roughness of the plates, thus providing a fluid-tight seal. Thus, fluid-tight sealing between the gasket and cell plates can be achieved without the need for chemical bonding or catalyst materials. Further, the gasket (and therefore the foils) will typically be used to seal against metal plate(s) of cell units, in which case the fluid tight seal therebetween can be further enhanced by chemical bonding between the foil and cell plates. The high plasticity of the first and second metal-containing foils accommodates differences in CTE values between the electrically insulating core (e.g. ceramic) and the components of the cell units (which may comprise metal). Due to the first and second metalcontaining foils comprising aluminium or copper, there is minimal corrosion of, or reaction with, the plates of cell units which the gasket contacts in use. Additionally, lateral flow / deformation of the first and second metal-containing foils is heavily constrained by the plates of neighbouring cell units when the gasket is in situ. The gasket does not require significant compression to promote sealing and also provides a hard stop to control separation between adjacent cell units, thereby minimising the level of ohmic resistance at electrical contact points between plates of adjacent cell units.

[0058] Fig. 3 shows a cross-sectional view of a gasket 30 for use in an electrochemical cell stack (not shown). In use, the gasket 30 is positioned between a first cell unit and an adjacent / neighbouring cell unit and around fluid ports of neighbouring plates of those cell units. The gasket 30 is multifunctional. For instance, gasket 30 provides a sealing function when disposed around the fluid ports of plates of adjacent cell units and is compressed between the plates under compressive forces applied to the electrochemical cell stack assembly. Sealing of the fluid ports prevents fluid from seeping between the outside of a cell unit and gasket 30, into the area external of the cell units, or fluid external of the fluid ports from seeping in the other direction, i.e., into the fluid ports. Gasket 30 also provides electrical insulation between adjacent cell units, thus preventing a short circuit. Gasket 30 also maintains separation between parts of adjacent cell units, which in turn maintains low ohmic resistance at electrical contact points between cell units. The materials of the component parts of gasket 30 (i.e. first and second metal-containing foils 32, 36 and electrically insulating core 38) are inert and thus do not cause the plates (e.g., two interconnects) between which the gasket 30 is disposed to corrode, as gas-phase impurities such as HF are not released.

[0059] The gasket of Fig. 3 has an electrically insulating core 38 having first and second opposed faces 38a, 38b. A first metal-containing foil 32 is disposed on the first face 38a. A second metal-containing foil 36 is disposed on the second face 38b. The first and second metal-containing foils 32, 36 are thin metal sheets which are self-supporting.

[0060] The first metal-containing foil 32 is in direct, physical contact with the first face 38a of the electrically insulating core 38, and the second metal-containing foil 36 is in direct physical contact with the second face 38b of the electrically insulating core 38. No adhesion layer is required between the metal-containing foils 32, 36 and the faces 38a, 38b, respectively. Further, the metal containing-foils 32, 36 are not brazed to faces 38a, 38b. In a preferred arrangement, sealing of the first and second metal-containing foils 32, 36 to the respective faces 38a, 38b is achieved by deforming the first and second metal-containing foils 32, 36 under electrochemical cell stack assembly compression and optionally, heat. Compression causes the first and second metal-containing foils 32, 36 to fill any interfacial gaps in the faces 38a, 38b of the core 38 and of the plates of the adjacent cell units to be sealed.

[0061] The first and second metal-containing foils 32, 36 may comprise aluminium or copper. For example, both first and second metal-containing foils 32, 36 may comprise aluminium. Alternatively, the first metal-containing foil 32 may comprise aluminium and the second metal-containing foil 36 may comprise copper. In another arrangement, the first metal-containing foil 32 may comprise copper and the second metal-containing foil 36 may comprise aluminium. In yet another arrangement, both first and second metal-containing foils 32, 36 may comprise copper. In a preferred arrangement, the first and second metal-containing foils 32, 36 comprise an aluminium or copper alloy, e.g., an aluminium-manganese alloy. In this regard, alloying allows for the physical properties (e.g. melting point) of the foil(s) to be enhanced or modified to better suit a particular purpose.

[0062] The electrically insulating core 38 may be an electrically insulating oxide such as a ceramic. The ceramic may be yttria-stabilised (cubic) zirconia (YSZ), alumina or mullite.

[0063] In the arrangement of Fig. 3, the thickness dimension of gasket 30, and therefore its component parts, extends along arrow A. The first and second metal-containing foils 32, 36 have a constant thickness (i.e., are of equal thickness), at least on a micrometer to tens of micrometers scale. The surfaces of the first and second metal-containing foils 32, 36 is smooth and thus devoid of ridges or other surface features. Each of the first and second metal-containing foils 32, 36 have a thickness of between 5-150 pm. The electrically insulating core 38 has a minimum thickness of approximately 100 pm. In the arrangement of Fig. 3, the core 38 has a thickness of approximately 100 pm and each of the first and second metal-containing foils 32, 36 have a thickness of approximately 50 pm. The total thickness of gasket 30 is thus approximately 200 pm. Gasket 30 thus has sufficient thickness to provide a hard stop to control and thus maintain separation between cell units.

[0064] In the arrangement of Fig. 3, the width dimension of the gasket 30 and thus its component parts extend along arrow B, which is substantially perpendicular to arrow A. The first and second metal-containing foils 32, 36 each have a width dimension that is less than a width dimension of the electrically insulating core 38. In some arrangements, the width dimension of the electrically insulating core 38 is between 5-10% larger than the width dimension of each of the first and second metalcontaining foils 32, 36. In this arrangement, the width dimensions of the first and second metalcontaining foils 32, 36 are equal, but they may be different in alternative arrangements. The first and second metal-containing foils 32, 36 are thus disposed on only a part of the electrically insulating core 38, i.e., there are exposed areas of the faces 38a,38b of the electrically insulating core 38 which are not covered by the first and second metal-containing foils 32, 36. The electrically insulating core 38 effectively has an exposed shoulder or edge which protrudes or extends further in the width dimension than the first and second metal-containing foils 32, 36. The exposed shoulder or edge is depicted as being at the outer diameter of the gasket 30, but an exposed shoulder may additionally or alternatively be present at the inner diameter of the gasket 30 around through hole 31 (as shown in Fig. 6). The exposed shoulder(s) of core 38 prevents the first and second metal-containing foils 32, 36 from being squeezed together beyond the edges of core 38 and thus contacting each other while under compression. This prevents an electrical short circuit.

[0065] In the arrangement of Fig. 3, a through hole (not shown in Fig. 3, but shown as 31 in Fig. 4) passes vertically (i.e. in the direction of arrow A) through the gasket 30 to enable the gasket 30 to be positioned around fluid ports of plates of adjacent cell units in an electrochemical cell stack (not shown). In effect, a though hole is present and passes through each of the first and second metalcontaining foils 32, 36 and the core 38. In a preferred arrangement, the individual through holes in each of the first and second metal-containing foils 32,36 and the core 38 are aligned, such that a single passageway for fluid flow is defined through the gasket 30. Accordingly, in this embodiment, and in the case of an annular gasket, the through holes are concentric. Additionally, it is preferred that the individual through holes each have the same diameter, which in turn minimises disruption to fluid flow.

[0066] Fig. 4 shows a top-down view of the gasket 30 of Fig. 3. In this arrangement, the gasket 30 (and therefore the electrically insulating core 38 and the first and second metal-containing foils 32, 36) is ring-shaped, particularly annular. The core 34 and the first and second metal-containing foils 32, 36 are arranged such that a through hole 31 extends through the centre of the gasket 30. The through hole 31 is configured for fluid flow through the centre of gasket 30. The electrically insulating core 38 and the first metal-containing foil 32 are arranged in an aligned, concentric manner, with the first metal-containing foil 32 being the smaller ring and the electrically insulating core 38 being the larger ring. As a result, only part of the first metal-containing foil 32 is disposed on the first face 38a of the core 38. The second metal-containing foil 36 is not visible in Fig.4, due to being disposed on the second face 38b of the core 38, but is arranged identically to the first metal-containing foil 32 on the underside of the core 38. Gaskets 30 as described herein are shown to be ring-shaped but it will be understood that other shapes of gasket are possible, for example elliptical, rectangular and so forth, in each case being annular such that they can be used to surround a fluid port and fluidically seal one fluid which passed through the port (and the through-hole of the gasket) from another.

[0067] In use, gasket 30 is positioned between two plates comprising fluid ports of adjacent cell units and is compressed under cell stack assembly compression. Specifically, gasket 30 is disposed around the fluid ports of the plates.

[0068] In some arrangements, each of the first and second metal-containing foils 32, 36 comprise an aluminium or copper alloy. The aluminium alloy may comprise one or more of Mn, Cr, Fe, Ti and V. A particularly advantageous metal-containing foil is achieved by alloying aluminium with manganese. In this regard, Fig. 5 shows an Al-Mn phase diagram. Generally, the purpose of alloying aluminium (or copper) with manganese, (or with one or more of the above elements) is to increase the melting point of the first and second metal-containing foils 32, 36 to mitigate the risk of melting of the foils 32, 36 at stack operating temperatures (e.g. between 500 to 800°C, preferably between 500 to 650°C), while enabling the foils 32, 36 to remain ductile.

[0069] The alloying element, e.g. manganese, is typically taken into solid solution (dissolves) in the aluminium or copper crystal lattice. If alloying leads to formation of separate phases, in particular, intermetallic phases, the extent of second phase formation preferably does not cause any significant reduction in plasticity (or ductility) of the alloy, which can lead to poor sealing in gasket contact area as the metal will not deform sufficiently to take up the shape / surface contour on contact surface. Thus, the amount of alloying addition needs to be controlled to meet these requirements. Typically, the alloying element (e.g. manganese) is alloyed with aluminium between 1-15 at.%, and more preferably between 2-10 at.%. More preferably, manganese is added to aluminium between 2-7 at.%, more preferably between 2-5 at.%.

[0070] Cell-to-cell separation is provided by gasket 30 when in situ and assists in manufacturing a stack maintaining low ohmic resistance. The materials of the component parts of gasket 30 (i.e. first and second metal-containing foils 32, 36 and electrically insulating core 38) are inert and thus do not cause the plates (e.g., two interconnects) between which the gasket 30 is disposed to corrode, as gasphase impurities such as HF are not released.

[0071] Advantageously, first and second metal-containing foils 32, 36 have high plasticity meaning that foils 32, 36 deform and fill interfacial gaps, enabling a fluid-tight seal around fluid ports of plates of neighbouring electrochemical cell units in an electrochemical cell stack. Fluid-tight sealing is further improved by the bulk of the first and second metal-containing foils 32, 36 not allowing gas transport. The high plasticity of the first and second metal-containing foils 32, 36 accommodates differences in CTE values between the electrically insulating core 38 (e.g. ceramic) and the components of the cell units (e.g. metallic). Additionally, lateral flow / deformation of the first and second metal-containing foils 32, 36 is heavily constrained by the plates of neighbouring cell units when gasket 30 is in situ. As well, the foils 32, 36 do not react adversely with metallic parts of cell units.

[0072] Fig. 6 shows a cross-sectional view of a part of an electrochemical cell stack including the gasket 30. In an electrochemical cell stack, a plurality of cell units overlay one another in a stacking direction. The constituent parts shown in Fig. 6 may collectively be termed an electrochemical cell unit component 60. The gasket 30 is positioned between a first cell unit (shown partially) and a second, adjacent (i.e. neighbouring) cell unit (shown partially) (alternatively, the components shown in Fig. 6 may themselves be considered a cell unit). Specifically, the gasket 30 is disposed between a first plate 62 of a first cell unit and a second plate 64 of a second, adjacent cell unit, wherein the first plate 62 and second plate 64 are in a spaced arrangement. Gasket 30 is effectively sandwiched between first and second plates 62, 64. The first metal-containing foil 32 is in direct physical contact with a first side 62a of the first plate 62. The second metal-containing foil 36 is in direct physical contact with a second side 64b of the second plate 64. The first and / or second plate may be formed from a steel. The steel may comprise a transition metal, e.g. a transition metal oxide, e.g., one or more of Co, Cr, Mn.

[0073] In an alternative arrangement, the sides (i.e. surfaces) of the first and / or second plates 62, 64 may have an adhesion promoter or reactive interface for chemical bonding with the first and / or second metal-containing foils 62, 64. The adhesion promoter or reactive interface may comprise a transition metal, e.g. a transition metal oxide or electrolyte, e.g., one or more of Co, Cr, Mn, Fe or ceria (CeO2).

[0074] In the arrangement of Fig. 6, the second plate 64 carries the electrochemically active cell region 66, which comprises an electrolyte 65 a first electrode 67 and a second electrode (not shown), with the electrolyte disposed between the two electrodes. In Fig. 6, the second plate 64 may be referred to as a metal support plate and the first plate 62 as an interconnect. The metal support plate may be provided with a porous region for fluidic communication with the first electrode 67 (i.e., between a first face and a second face, opposite the first, the first face carrying the first electrode 67). Alternatively, both of the first and second plates 62, 64 may be interconnects (in such cases the electrochemically active cell region is self-supporting).

[0075] Fluid ports 61, 69 are provided in each of the first plate 62 and the second plate 64, the horizontal extent of the fluid ports 61, 69 in the first and second plates 62, 64 being indicated by dashed arrows. The respective fluid ports 61, 69 are aligned to allow for flow of fluid (e.g. fuel or air) therethrough. The through hole 31 of gasket 30 is aligned with the fluid ports 61, 63 of the first and second plates 62, 64.

[0076] In an electrochemical cell stack, there may be a further (second) gasket 30 disposed underneath the second plate 64, and another (third) gasket 30 disposed on top of the first plate 60. Specifically, the first metal-containing foil 32 of the second gasket 30 would contact / abut a first side 64a of the second plate 64. The second metal-containing foil 36 of the third gasket 30 would contact / abut a second side 62b of the first plate 62.

[0077] In other cases, such as the arrangement of Fig. 7, which is similar to the cell unit and gasket arrangement shown in Fig. 2, a cell unit 68 is formed by the second plate 64 carrying the electrochemically active cell region 66 (on the second side 64b of the second plate 64), and a first plate 62. The second side 62b of the first plate 62 is attached to (e.g., by welding or brazing, not shown) the first side 64a of second plate 64, which is an opposite face / side of the second plate 64 to the second side / face 64b of the second plate 64 which carries the electrochemically active cell region 66. Said attachment of the second side 62b of the first plate 62 to the first side 64a of second plate 64 encloses a (first) fluid volume (i.e., the plates 64 and 62 fluidically seal to one another by the attachment around their periphery) which is fluidically isolated from a second fluid volume which may surround the cell unit, and the gasket(s) 30 allows fluidic communication with said enclosed fluid volume. In such cases, the electrochemical cell unit component 60 comprises the cell unit 68 and the gasket 30, the gasket 30 being provided (only) on either outward faces of the cell unit 68 (on the same face of the second plate 64 as carries the electrochemically active cell region, i.e., second side 64b of second plate 64 (as shown in Fig. 6), or on the opposite face of the first plate 62 to the face which faces the second plate 64, i.e. first side 62a of the first plate 62, as shown in Fig. 7). Once assembled, a gasket 30 is positioned between each of neighbouring pair of cell units 68. In some embodiments, cell units have two or more fluid ports and two or more respective gaskets 30 can be positioned between cell units.

[0078] Once gaskets 30 are arranged between all neighbouring / adjacent cell units of an electrochemical stack, the stack is compressed. Compressing the stack causes the first and second metal-containing foils 32, 36 of the plurality of gaskets 30 which will be present in the stack to provide fluid-tight seals on both faces 38a, 38b of the electrically insulating core 38 and on the relevant sides of the first and second plates 32, 36. The first and second metal-containing foils 32, 36 readily deform so as to fill interfacial gaps in the contact area of sealing.

[0079] In accordance with an aspect of the present disclosure, a method of manufacturing an electrochemical cell stack is provided. The following method can be used to manufacture electrochemical cell unit component 60 as shown in Fig. 6, which is a component part of an electrochemical cell stack. The method includes providing the first plate 62 comprising fluid port 61. The first plate 62 may be an interconnect or a support plate. The method further includes placing around the fluid port 61: a. the electrically insulating core 38 having first and second opposing faces 38a, 38b; b. the first metal-containing foil 32 contacting the first face 38a of the electrically insulating core 38; and c. the second metal-containing foil 36 contacting the second face 38b of the electrically insulating core 38.

[0080] Above steps a-c provide component parts of the gasket 30. Effectively, the first metalcontaining foil 32 abuts or contacts the first plate 62. The second plate 64 comprising fluid port 69 is placed on the second metal-containing foil 36, such that fluid port 69 aligns with fluid port 61 of first plate 62.

[0081] Glue may be used between the first and second faces 38a, 38b of core 38 and the respective first and second metal-containing foils 32, 36, and / or the first plate 62 to assist positioning of the gasket components but is not essential, and if used a type that thermally decomposes at temperatures between 50-200°C is chosen.

[0082] The second plate 64 may be a support plate. As described above, the first and second metalcontaining foils comprise aluminium or copper. One of the first or second plates 62, 64 may carry or support the electrochemically active cell region. For example, the second plate 64 shown in Fig. 6 carries electrochemically active cell region 66. As a result, the gasket 30 is disposed between first and second plates 62,64. The electrically insulating core 38 and the first and second metal-containing foils 32, 36 may be annular and can be aligned to enable fluid flow through the centre of gasket 30. Providing the first and second plates may comprise providing respective first and second cell units.

[0083] The method further includes compressing the first and second plates 62, 64. Compression seals the component parts of the gasket 30 to one another and simultaneously seals the first metalcontaining foil to the first plate 62 and the second metal-containing foil to the second plate 64. The first and second metal-containing foils 32, 36 are deformed under compression, causing the foils 32, 36 to fill all gaps in the interfaces between the foils 32, 36 and i) the core 38 and ii) the first and second plates 62, 64. The foils 32, 36 take up the shape of the surface contours of the first and second plates 62, 64 to achieve fluid-tight sealing. Compressing of the components may be performed between 1-30 kN and preferably between 2-18 kN, preferably between 5-15 kN. Such pressures are in line with or are lower than those typically applied during assembly of an electrochemical cell stack comprising vermiculite gaskets.

[0084] The features of the gasket 30 described above (and particularly in relation to Figs. 3, 4, 6 and 7) apply to the gasket obtained via steps a-c. For example, the first and second metal-containing foils 32, 36 may comprise an aluminium alloy, and wherein the alloying element may be manganese. Additionally, the electrically insulating core 38 may comprise a ceramic comprising YSZ, alumina or mullite. For brevity, not all the features of the gasket 30 will be repeated here.

[0085] The method may also include heating, either after compressing the component parts or while the components are under compression. Stack operating temperatures range from between 450 to 900°C, or between 450-700 °C for a solid oxide cell, particularly one comprising a ceria-based electrolyte. Heating to between 500-800 °C is particularly effective for first and second metalcontaining foils 32, 36 comprising aluminium or copper, or alloys thereof. A temperature range of between 500 to 650°C is advantageous when the first and second metal-containing foils 32, 36 comprise copper or alloys of aluminium.

[0086] 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

1. A gasket for use in an electrochemical cell stack, the gasket comprising an electrically insulating core having first and second opposing faces, a first metal-containing foil disposed on the first face and a second metal-containing foil disposed on the second face, and wherein the first and second metal-containing foils comprise aluminium or copper.

2. The gasket according to claim 1, wherein each of the first and second metal-containing foils comprise an aluminium alloy.

3. The gasket according to claim 2, wherein the aluminium alloy comprises one or more of Mn, Cr, Fe, Ti, and V.

4. The gasket according to any preceding claim, wherein each of the first and second metalcontaining foils is self-supporting.

5. The gasket according to any preceding claim, wherein each of the first and second metalcontaining foils has a thickness of between 5-150 pm, optionally between 20-100 pm, optionally between 40-60 pm.

6. The gasket according to any preceding claim, wherein each of the first and second metalcontaining foils has a constant thickness.

7. The gasket according to any preceding claim, wherein the electrically insulating core comprises a ceramic.

8. The gasket according to claim 7, wherein the ceramic comprises yttria-stabilised zirconia, alumina or mullite.

9. The gasket according to any preceding claim, wherein the gasket has a thickness of between 120-500 pm, optionally between 150-400 pm, optionally between 200-300 pm.

10. The gasket according to any preceding claim, wherein the first metal-containing foil is disposed on a part only of the first face of the electrically insulting core and / or the second metal-containing foil is disposed on a part only of the second face of the electrically insulating core.

11. The gasket according to claim 10, wherein each of the first and second metal-containing foils has a width dimension that is less than a width dimension of the electrically insulating core.

12. The gasket according to claim 11, wherein the width dimension of the electrically insulating core is 5-10% larger than the width dimension of each of the first and second metal-containing foils.

13. The gasket according to any preceding claim, wherein the first metal-containing foil is in direct, physical contact with the first face of the electrically insulating core, and wherein the second metalcontaining foil is in direct physical contact with the second face of the electrically insulating core.

14. An electrochemical cell unit component comprising:a first plate and a second plate in spaced arrangement, and an electrochemically active cell region;wherein the first plate, the second plate, and the electrochemically active cell region overlay one another to form an electrochemical cell unitwherein a fluid port is provided in each of the first plate and the second plate,the component further comprising a gasket according to any one of claims 1 to 13, wherein the gasket is disposed around the fluid port of the first plate and / or around the fluid port of the second plate.

15. An electrochemical cell unit component according to claim 14, wherein the first plate is a support plate which carries the electrochemically active cell region and the second plate is an interconnect.

16. An electrochemical cell unit component according to claim 14 or 15, wherein the first plate and the second plate are metallic.

17. A stack of electrochemical cell units comprising a plurality of electrochemical cell units overlaying one another in a stacking direction:wherein each electrochemical cell unit comprises a first plate and a second plate in spaced arrangement, and an electrochemically active cell region,wherein the first plate, the second plate, and the electrochemically active cell region overlay one another to form the electrochemical cell unit,wherein a fluid port is provided in each of the first plate and the second plate,wherein a gasket according to any one of claims 1 to 13 is disposed around the fluid port of a first plate of a first electrochemical cell unit and a fluid port of a second plate of a neighbouring cell unit, such that the gasket is disposed between neighbouring cell units.

18. A stack according to claim 17, wherein the first plate is a support plate which carries the electrochemically active cell region and the second plate is an interconnect.

19. A method of manufacture of an electrochemical cell stack, the method comprising: providing a first plate comprising a fluid port,placing, to form a gasket, around the fluid port of the first plate:an electrically insulating core having first and second opposing facesa first metal-containing foil contacting the first face of the electrically insulating core and a second metal-containing foil contacting the second face of the electrically insulating core,placing a second plate comprising a fluid port on the second metal-containing foil, wherein the first and second metal-containing foils comprise aluminium or copper, wherein an electrochemically active cell region is disposed between the first plate and the second plate,wherein the fluid ports of the first and second plates are configured to allow fluid to flow therethrough,the method further comprising compressing the first and second plates.

20. The method of claim 19, further comprising heating at a temperature between 500-650 °C.

21. The method of claim 19 or 20, wherein the compressing is performed between 1-30 kN, optionally between 5-15 kN.

22. The method of any one of claims 19 to 21, wherein the gasket is according to any one of claims 2 to 13.

23. Use of the gasket of any one of claims 1 to 13 in an electrochemical cell stack.

24. A kit of parts comprisingan annular electrically insulating core having first and second opposing faces, an annular first metal-containing foil and an annular second metal-containing foil, wherein the annular first and second metal-containing foils comprise aluminium or copper.

25. A kit of parts according to claim 24, further comprising a first plate and a second plate, wherein a fluid port is provided in each of the first plate and the second plate.

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