Membrane-seal assembly

Abstract

A catalyst-coated membrane-seal assembly comprises an ion-conducting membrane with a central region, which has a first catalyst layer on a first side and a second catalyst layer on the second side, and a border region which has a first seal material layer on the first side and a second seal material layer on the second side. The edge of the first seal material layer facing the central region is bevelled such that a side of the first seal material layer extends further towards the central region than the opposite side of the first seal material layer.

Description

[0001] MEMBRANE-SEAL ASSEMBLY

[0002] Field of the Invention

[0003] The present invention relates to a catalyst-coated membrane-seal assembly and its use in an electrochemical device, in particular in a water electrolyser.

[0004] Background of the Invention

[0005] The electrolysis of water to produce high purity hydrogen and oxygen can be carried out in both alkaline and acidic electrolyte systems. Those electrolysers that employ a solid protonconducting polymer membrane, or proton exchange membrane (PEM), are known as proton exchange membrane water electrolysers (PEMWEs). Those electrolysers that utilise a solid anion-conducting polymer membrane, or anion exchange membrane (AEM), are known as anion exchange membrane water electrolysers (AEMWEs).

[0006] Ion-conducting membranes, such as PEMs and AEMs, are also used in fuel cells. In a proton exchange membrane fuel cell (PEMFC) the membrane is proton conducting, and protons, produced at the anode, are transported across the membrane to the cathode, where they combine with oxygen to form water.

[0007] Catalyst-coated ion-conducting membranes (CCMs) may be employed within electrochemical devices, such as electrolysers, fuel cells, electrochemical hydrogen pumps, and devices for the electrochemical reduction of carbon dioxide. Such CCMs comprise an ion-conducting membrane, such as a PEM or AEM, with an anode catalyst layer and / or a cathode catalyst layer applied to a face of the membrane, the anode catalyst layer and cathode catalyst layer being applied to opposite faces of the membrane.

[0008] For water electrolyser applications, hydrogen evolution reaction (HER) catalysts are used in such cathode catalyst layers, for example HER catalysts comprising platinum, such as platinum on a carbon support. Oxygen evolution reaction (OER) catalysts are utilised in electrolyser anode catalyst layers. For PEMWE applications, suitable OER catalysts comprise iridium or iridium oxide (IrOx), or oxides containing both iridium and ruthenium. For AEMWE applications, non-platinum group metal OER catalysts may also be used, such as alloys and oxides of nickel, cobalt, iron, and copper.

[0009] For fuel cell applications, oxygen reduction reaction (ORR) catalysts are used in cathode catalyst layers and hydrogen oxidation reaction (HOR) catalysts are utilised in anode catalyst layers. For PEMFC applications, suitable cathode and anode catalyst materials comprise a platinum group metal or an alloy of a platinum group metal with one or more other metals, for example platinum or an alloy of platinum with one or more other metals. Other electrochemical devices may also incorporate CCMs, with the catalyst layers being selected according to the desired electrochemistry. For example, for electrochemical hydrogen pump applications, CCMs may be provided with a first catalyst layer incorporating a hydrogen oxidation reaction (HOR) catalyst (such as a platinum catalyst) on one face of the ion-conducting membrane, and a second catalyst layer incorporating a hydrogen evolution reaction (HER) catalyst (such as a platinum catalyst) on the opposite face of the ionconducting membrane

[0010] Typically, the catalyst-coated membranes are constructed to have a central active region comprising the catalyst layers on each face of the membrane and a surrounding border region upon which seal material layers, typically formed from non-ion conducting polymers, are positioned. These seal material layers aim to prevent escape of reactant and product gases, to reinforce and strengthen the edge of the catalyst-coated membrane and to provide a suitable surface for supporting subsequent components. Such an arrangement is known as a catalyst-coated membrane-seal assembly.

[0011] An adhesive layer may be present on one or both surfaces of the seal material layer. The layers or components in the catalyst-coated membrane-seal assembly are typically bonded by a lamination process. In cases that the catalyst layers are smaller in area than the ionconducting membrane, the seal material layers are typically bonded to exposed surfaces of the ion conducting membrane where no catalyst layer is present (often overlapping the edge of the catalyst layer). The seal material layers may also be bonded to the catalyst layers, in cases in which the catalyst layers extend into the border region and may cover substantially all of the surface of the ion-conducting membrane.

[0012] Catalyst-coated membrane-seal assemblies may be incorporated into a membrane electrode assembly (MEA), which is essentially composed of five layers. The central layer is the ionconducting membrane. On either side of the ion-conducting membrane there is an electrocatalyst layer, containing an electrocatalyst designed for the specific electrochemical reaction. Finally, adjacent to each electrocatalyst layer there is a gas diffusion layer (GDL) or a porous transport layer (PTL), depending on the final MEA application and stack configuration. Such layers allow the reactants to reach the electrocatalyst layer and products to leave.

[0013] It is desirable to reduce the thickness of the ion-conducting membranes used in catalyst- coated membrane-seal assemblies to minimise electronic and ionic resistance. However, the use of thinner membranes can lead to durability issues and part failure, in particular during use in applications where there is a high-pressure differential across the membrane. For example, the use of high gas pressure at the cathode side of a catalyst-coated membrane-seal assembly during electrolyser operation is advantageous as it reduces the requirement for compression of the generated hydrogen and reduces operating costs. However, the use such high pressures can provide significant membrane durability issues.

[0014] There is therefore a need to develop catalyst-coated membrane-seal assemblies with increased robustness at high pressure differentials, in particular which enable the use of thinner ion-conducting membranes with a low resistance.

[0015] Summary of the Invention

[0016] In conventional catalyst-coated membrane-seal assemblies, durability issues may be observed due to the mechanical abrasion of the ion-conducting membrane where the seal material layer overlaps or frames the ion-conducting membrane. Such mechanical stresses can occur due to distortion which may result during operation at high pressure differentials. In particular, these stresses can cause a weakness in the ion-conducting membrane that may lead to tearing of the ion-conducting membrane in the edge regions close to the interface with the seal. The present inventors have identified that by adjusting the configuration of the seal layer, such stresses can be reduced, in particular in situations where a pressure differential will cause the catalyst-coated ion conducting membrane to conform around the seal material layer. Such an improvement offers improvements in component durability.

[0017] Therefore, in a first aspect of the invention there is provided a catalyst-coated membraneseal assembly, suitably for a water electrolyser or a fuel cell, comprising an ion-conducting membrane having a first side and an opposite second side, the catalyst-coated membraneseal assembly comprising:

[0018] (i) a central region comprising a first catalyst layer on the first side of the ion-conducting membrane and a second catalyst layer on the second side of the ionconducting membrane;

[0019] (ii) a border region surrounding the central region, the border region comprising a first seal material layer on the first side of the ion-conducting membrane and a second seal material layer on the second side of the ion-conducting membrane, the first seal material layer and the second seal material layer each having a first side and a second side, the first side of the first seal material layer facing the first side of the ion-conducting membrane and the first side of the second seal material layer facing the second side of the ion-conducting membrane; and wherein the edge of the first seal material layer facing the central region is bevelled such that the second side of the first seal material layer extends further towards the central region than the first side of the first seal material layer.

[0020] The use of a bevelled edge on the seal material layer enables a reduction of the stress placed on the ion-conducting membrane during MEA assembly and during operation.

[0021] In a second aspect of the invention there is provided a membrane-electrode assembly comprising a catalyst-coated membrane-seal assembly according to the first aspect, a first gas diffusion layer or a first porous transport layer on a first side of the catalyst-coated membrane-seal assembly and a second gas diffusion layer or a second porous transport layer on the second side of the catalyst-coated membrane-seal assembly.

[0022] In a third aspect of the invention, there is provided a water electrolyser or a fuel cell comprising a catalyst-coated membrane-seal assembly according to the first aspect or a membrane-electrode assembly according the second aspect.

[0023] Brief Description of the Drawings

[0024] Figure 1 is a plan view of schematic of an example of a catalyst-coated membrane-seal assembly according to the invention.

[0025] Figure 2 is a cross-sectional view of the catalyst-coated membrane-seal assembly shown in Fig 1.

[0026] Figure 3 is a cross-sectional view of a schematic of a further example of a catalyst-coated membrane-seal assembly according to the invention.

[0027] Figure 4 is a cross-sectional view of a schematic of a further example of a catalyst-coated membrane-seal assembly according to the invention.

[0028] Figure 5 is a cross-sectional view of a schematic of a further example of a catalyst-coated membrane-seal assembly according to the invention.

[0029] Figure 6 is a cross-sectional view of a schematic of a further example of a catalyst-coated membrane-seal assembly according to the invention.

[0030] Detailed Description of the Invention

[0031] Preferred and / or optional features of the invention will now be set out. Any aspect of the invention may be combined with any other aspect of the invention, unless the context demands otherwise. Any of the preferred or optional features of any aspect may be combined, singly or in combination, with any aspect of the invention, unless the context demands otherwise. The present invention provides a catalyst-coated membrane-seal assembly which comprises an ion-conducting membrane. The ion-conducting membrane is suitably a protonconducting membrane or an anion-conducting membrane, such as a hydroxy-conducting membrane. The membrane suitably comprises a proton-conducting polymer or an anion- conducting polymer, such as a hydroxyl anion-conducting polymer.

[0032] Preferably, the ion-conducting membrane comprises a proton-conducting polymer, suitably a perfluorinated sulphonic acid polymer material. Examples of suitable proton-conducting polymers include perfluorinated sulphonic acid polymer materials such as Nation™ (Chemours Company), Aquivion® (Solvay Specialty Polymers), Flemion® (Asahi Glass Group) and Aciplex™ (Asahi Kasei Chemicals Corp.) and perfluorosulphonic acid ionomer material supplied by 3M®. Alternatively, the ion-conducting material may be based on a sulphonated hydrocarbon membrane such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, or from JSR Corporation, Toyobo Corporation, and others.

[0033] The ion-conducting membrane may include additional components. For example, the ionconducting membrane may comprise one or more hydrogen peroxide decomposition catalysts. Examples of suitable hydrogen peroxide decomposition catalysts are known to those skilled in the art and include metal oxides or metal salts, such as doped or undoped cerium oxides, manganese oxides or titanium oxides; preferably cerium dioxide (ceria).

[0034] The ion-conducting membrane may comprise a recombination catalyst, in particular a catalyst for the recombination of unreacted hydrogen and oxygen, that can diffuse into the ion-conducting membrane from the electrode layers, to produce water. Suitable recombination catalysts comprise a suitable metal (such as platinum) on a support material (such as carbon).

[0035] The ion-conducting membrane may be reinforced, for example by the inclusion of one or more reinforcing layers. Such reinforcing layers typically comprise a porous polymer reinforcement component, for example a porous ePTFE polymer reinforcement component. Such membrane components are typically embedded within the ion-conducting membrane such that the ion-conducting material is impregnated within the pores of the porous polymer reinforcement component.

[0036] Suitably, the ion-conducting membrane has a thickness at 0% relative humidity of at least about 5 .m. It may be preferred that the ion-conducting membrane has a thickness of at least about 8 .m, at least about 10 .m, or at least about 15 .m. Typically, the thickness of the ion-conducting membrane at 0% relative humidity is less than or equal to about 200 .m, such as less than or equal to 150 .m, or less than or equal to 100 .m. The thickness of the membrane may be determined by analysis of a scanning electron microscope (SEM) image of a cross section of the membrane.

[0037] The use of a catalyst-coated membrane-seal assembly as described herein may be particularly advantageous during use in a water electrolyser facilitating the use of ionconducting membranes with a thickness less than of equal 100 .m during high pressure operation. It may be preferred that the ion-conducting membrane has a thickness at 0% relative humidity in the range of and including 10 to 100 .m, such as 15 to 100 .m, 20 to 100 .m, 30 to 100 .m, or 40 to 90 .m.

[0038] It may be further preferred that the ion-conducting membrane has a thickness at 0% relative humidity in the range of and including 10 to 100 .m and comprises at least one porous polymer reinforcement component, such as two porous polymer reinforcement components. Such ion-conducting membranes are considered particularly suitable for use with the seal configurations as described herein.

[0039] The catalyst-coated membrane-seal assembly comprises a central region. The central region comprises a first catalyst layer (such as an anode catalyst layer) on a first side of the ion-conducting membrane and a second catalyst layer (such as a cathode catalyst layer) on the second, opposite, side of the ion-conducting membrane. The central area is therefore the electrochemically active area of the catalyst-coated membrane. No seal material layers are present in the central region. This enables the desired transfer of electrochemical reactants through the active area to take place.

[0040] Suitably, the central region has a quadrilateral geometry, such as a rectangle or square. However, it will be understood that the central region can be of any geometric shape, such as a circle or oval.

[0041] The anode catalyst layer and the cathode catalyst layer (together ‘the catalyst layers’) comprise one or more electrocatalysts. The exact electrocatalyst used will depend on the reaction it is intended to catalyse, and its selection is within the capability of the skilled person. The or each electrocatalyst is suitably selected from:

[0042] (i) the platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium);

[0043] (ii) gold or silver;

[0044] (iii) a base metal; or an alloy or mixture comprising one or more of these metals or their oxides. A base metal is tin or a transition metal which is not a noble metal. A noble metal is a platinum group metal (platinum, palladium, rhodium, ruthenium, iridium or osmium) or gold. Preferred base metals are copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium and tin.

[0045] The one or more electrocatalysts are independently an unsupported catalyst, or a supported catalyst, wherein catalyst particles are dispersed on an electrically conducting support, such as a particulate carbon black material. If the electrocatalyst is a supported catalyst, the loading of metal particles on the support material is suitably in the range 10-90 wt%, preferably 15-75 wt% of the weight of resulting electrocatalyst.

[0046] In the case that the catalyst-coated membrane-seal assembly is for a water electrolyser, hydrogen evolution reaction (HER) catalysts are used in the cathode catalyst layer, for example HER catalysts comprising platinum, such as platinum on a carbon support. Oxygen evolution reaction (OER) catalysts are utilised in the anode catalyst layer. For PEMWE applications, suitable OER catalysts comprise iridium or iridium oxide (IrOx), or oxides containing both iridium and ruthenium. For AEMWE applications, non-platinum group metal OER catalysts may also be used, such as alloys and oxides of nickel, cobalt, iron, and copper.

[0047] In the case that the catalyst-coated membrane-seal assembly is for a fuel cell application, oxygen reduction reaction (ORR) catalysts are used in cathode catalyst layer and hydrogen oxidation reaction (HOR) catalysts are utilised in anode catalyst layer. For PEMFC applications, suitable cathode and anode catalyst materials comprise a platinum group metal or an alloy of a platinum group metal with one or more other metals, preferably with a base metal, preferred base metals as defined above, for example platinum or an alloy of platinum with one or more other metals, preferably with a base metal, preferred base metals as defined above.

[0048] The catalyst layers preferably comprise an ion-conducting polymer, such as a protonconducting ionomer, to improve the ion-conductivity of the layer. Accordingly, the ionconducting material may include ionomers such as perfluorosulphonic acid materials (e.g. Nation® (Chemours Company), Aciplex® (Asahi Kasei), Aquivion® (Solvay Specialty Polymer), Flemion® (Asahi Glass Co.) and perfluorosulphonic acid ionomer material supplied by 3M®), or ionomers based on partially fluorinated or non-fluorinated hydrocarbons that are sulphonated or phosphonated polymers, such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, JSR Corporation, Toyobo Corporation, and others.

[0049] The catalyst layers may comprise additional components. Such components include (but are not limited to): a hydrogen peroxide decomposition catalyst; a hydrophobic additive (e.g. a polymer such as polytetrafluoroethylene (PTFE) or an inorganic solid with or without surface treatment) or a hydrophilic additive to control reactant and water transport characteristics. The choice of additional components will depend on whether the catalyst layer is for use at the anode or the cathode and it is within the capability of a skilled person to determine which additional components are appropriate.

[0050] The thickness of each catalyst layer is not particularly limited and will depend on the intended application. Typically, the catalyst layer thickness is at least 1 pm, typically at least 2 pm or at least 5 pm. The catalyst layer thickness is suitably no more than 20 pm, typically no more than 15 pm, or no more than 10 pm.

[0051] The catalyst-coated membrane-seal assembly comprises a border region surrounding the central (active) region. The border region creates a frame around the central region. The inner edge of the border region has the same geometric shape as the central region.

[0052] Suitably, the ion-conducting membrane in the border region is not completely covered by the first catalyst layer and the second catalyst layer. In some cases the first catalyst layer and the second catalyst layer partially cover the ion-conducting membrane in the border region. The first catalyst layer and the second catalyst layer may each independently cover up to 20% of the surface of the ion-conducting membrane in the border region, for example up to 10%, or up to 5%. In some cases, the catalyst layers extend over the entire surface of the ion-conducting membrane.

[0053] The border region has seal material layers applied to both sides of the catalyst-coated ionconducting membrane.

[0054] Each seal material layer is impermeable to gases and liquids and prevents escape of reactant and product gases and defines the active area of the catalyst-coated membraneseal assembly. The seal material layers should both be non-ion conducting.

[0055] Suitably, each seal material layer is formed from a polymeric material such as polyetheretherketone (PEEK), polyvinylidene difluoride (PVDF), polyimide (PI), polyetherimide, polyethersulphone (PES), polypropylene (PP), polyetherimide (PEI), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), Viton®, polyethylene oxide (PEO), polyphenylene ether (PPE), polyethylene terephthalate (PET), polyacrylonitrile (PAN), poly(p-phenylene sulphide) (PPS), polyethylene naphthalate (PEN), or mixtures thereof. It may be preferred that each seal material layer is formed from PEEK, PI, polyetherimide, PES, PP, PEI, FEP, PEO, PPE, PET, PAN PPS, PEN, or mixtures thereof. It may be further preferred that each seal material layer is formed from PEN, PET or PEI. Such materials provide a suitable level of stiffness for use in combination with the bevelled edge of the seal material layer. Alternatively, the seal film material may be a non-corrodible metal or a metal film, such as a stainless steel, coated with a protective layer of polymer or gold to provide corrosion resistance.

[0056] The present invention may provide particular advantages in cases where the thickness of the first and I or the second seal material layer has a thickness of at least 20 pm, such as in the range of and including 20 to 50 pm. The use of seal material layers of at least 20 pm provides advantageous mechanical stability, however, without the shaping of the seal edge as described herein, such seal material thicknesses can cause increased localised distortion of the catalyst-coated ion-conducting membrane. Suitably, the seal material layer has at least one bonding layer applied to a face of the seal material layer, for example two bonding layers positioned one on each face of the seal material layer. Typically, the bonding layer is configured to face the ion-conducting membrane. In such cases, the bonding layer bonds the seal material layer to the ion-conducting membrane. Alternatively, or in addition, the bonding layer may face a GDL or PTL (if present) and the bonding layer can bond to, and in some cases impregnate into, the GDL I PTL. Suitably, the bonding layer comprises a hot melt adhesive, a pressure sensitive adhesive or a thermosetting adhesive. The adhesive may be polyolefin based, such as a polyethylene or polypropylene adhesive, or other polyolefin material. Suitably, the bonding layer does not shrink appreciably under manufacturing conditions.

[0057] Suitably, the catalyst-coated membrane-seal assembly comprises a first bonding layer positioned between the first seal material layer and the ion-conducting membrane, and a second bonding layer positioned between the second seal material layer and the ionconducting membrane. It may be preferred that the edges of the first and I or the second bonding layers that facing the central region are bevelled

[0058] It may be preferred that bonding layers positioned between the ion-conducting membrane and the seal material layer are configured such that the edge of the bonding layer facing the central region is bevelled such that the side of the bonding layer facing the seal material layer extends further towards the central region than the side of the bonding layer facing the ion-conducting membrane. In such cases, it may be further preferred that the bevel of the bonding layer is aligned with the bevel of the seal material layer.

[0059] Suitably, each seal material layer is in contact with the ion-conducting membrane in the border region (typically via a bonding layer). It may be preferred that each seal material layer overlaps a catalyst layer. For example, it may be preferred that the first seal material layer overlaps the first catalyst layer and I or the second seal material layer overlaps the second catalyst layer. In such cases, the width of the seal material layer which overlaps catalyst layer is suitably between 0.5 mm and 20 mm, such as between 1 and 5 mm. In other cases the catalyst layer extends to the edges of the ion-conducting membrane and each seal material layer is in contact with a catalyst layer (typically via a bonding layer).

[0060] Typically, each seal material layer extends further than the extent of the ion-conducting membrane. In such a configuration the edge of the ion-conducting is protected by the seal material layers. In such cases, the first seal material layer and the second seal material layer are suitably in contact. The first seal material layer and the second seal material layer are typically bonded.

[0061] Advantageously, the inner edge of the first seal material layer is bevelled. By inner edge, it is meant herein the edge of the seal material layer facing the central region and which forms a frame around the central region. For example, in the case of a central region with a quadrilateral geometry, the inner edge of the seal material layer extends around each of the four sides of the central region. The inner edge is configured such that the second side of the first seal material layer (which is the opposite side of the seal material layer to the ionconducting membrane) extends further towards the central region than the first side of the first seal material layer (which is the side facing the ion conducting membrane). Such shaping of the inner edge of the seal material layer offers a reduction in the stresses placed upon the catalyst-coated ion-conducting membrane at the point of contact with the edge of the seal, which is of particular importance during MEA assembly, and during operation at high pressure differentials across the membrane (for example during certain electrolyser applications).

[0062] It may be preferred that the second side of the first seal material layer (and optionally the second side of the second seal material layer) extends at least 5 .m further towards the central region than the first side of the first seal material layer. It may be preferred that the second side of the first seal material layer extends at least 7 .m, or 10 .m further towards the central region than the first side of the first seal material layer.

[0063] It may be preferred that the second side of the first seal material layer (and optionally the second side of the second seal material layer) extends further towards the central region by at least 10 % of the thickness of the seal material layer, such as in the range of and including 10 to 100 % of the thickness of the seal material layer, and preferably in the range of 20 to 100 % of the thickness of the seal material layer. For example for a seal material layer of thickness 25 .m, an extension in the range of 10 to 100 % of the thickness of the seal material layer would be an extension in the range of and including of 2.5 to 25 .m.

[0064] The catalyst-coated membrane-seal assemblies as described herein are of particular utility for water electrolyser use, in which higher pressure is typically observed on the cathode side of the membrane than the anode side. Suitably in such cases the catalyst catalyst-coated membrane-seal assembly comprises:

[0065] (i) an ion-conducting membrane (preferably a proton-conducting membrane or an anion conducting membrane) with a central region and a border region;

[0066] (ii) an anode catalyst layer on the first side of the ion-conducting membrane in the central region, the anode catalyst layer comprising an oxygen evolution catalyst, such as an iridium-containing oxygen evolution catalyst (for example iridium oxide (IrOx));

[0067] (iii) a cathode catalyst layer on the second side of the ion-conducting membrane in the central region, the cathode catalyst layer comprising a hydrogen evolution catalyst, such as a platinum-containing oxygen evolution catalyst (for example platinum on carbon);

[0068] (iv) a first seal material layer on the first side of the ion-conducting membrane in the border region (with, optionally, a first bonding material layer positioned in between the first seal material layer and the ion-conducting membrane). The first seal material layer has a bevelled inner edge as described hereinbefore.

[0069] (v) a second seal material layer on the second side of the ion-conducting membrane in the border region (with, optionally, a second bonding material layer positioned in between the second seal material layer and the ionconducting membrane).

[0070] It may be preferred that the second seal material layer has a bevelled inner edge as described hereinbefore for the first seal material layer. In such cases the edge of the second seal material layer facing the central region is bevelled such that the second side of the second seal material layer extends further towards the central region than the first side of the second seal material layer. Such a configuration offers a reduction in the stresses on each side of the ion-conducting membrane which can occur during MEA manufacture and, for example, where there are variations in pressure differential across the membrane during use.

[0071] The catalyst-coated membrane-seal assembly may advantageously be incorporated into a membrane-electrode assembly (MEA) for a fuel cell or a water electrolyser, such as a PEMWE, PEMFC, or AEMWE. In such cases, a first gas diffusion layer (GDL) or a first porous transport layer (PTL) is provided on a first side of the catalyst-coated membrane-seal assembly (corresponding to the first side of the ion-exchange membrane) and a second GDL or a second PTL is provided on the second side of the catalyst-coated membrane-seal assembly (corresponding to the second side of the ion-exchange membrane). The choice of GDL or PTL will depend on the configuration of the electrochemical device and mode of operation and is within the capability of the skilled person.

[0072] Suitable GDLs comprise a gas diffusion substrate and, preferably, a microporous layer. Typical gas diffusion substrates include non-woven papers or webs comprising a network of carbon fibres and a thermoset resin binder (e.g. the TGP-H series of carbon fibre paper available from Toray Industries Inc., Japan or the H2315 series available from Freudenberg FCCT KG, Germany, or the Sigracet® series available from SGL Technologies GmbH, Germany or AvCarb® series from Ballard Power Systems Inc.), or woven carbon cloths. The carbon paper, web or cloth may be provided with a pre-treatment either to make it more wettable (hydrophilic) or more wet-proofed (hydrophobic). The nature of any treatments will depend on the type of electrochemical device and the operating conditions that will be used. The substrate can be made more wettable by incorporation of materials such as amorphous carbon blacks via impregnation from liquid suspensions, or can be made more hydrophobic by impregnating the pore structure of the substrate with a colloidal suspension of a polymer such as PTFE or polyfluoroethylenepropylene (FEP), followed by drying and heating above the melting point of the polymer. Typical microporous layers comprise a mixture of a carbon black and a polymer such as polytetrafluoroethylene (PTFE).

[0073] Suitably, an MEA for a fuel cell (such as a PEMFC) has a GDL provided on both sides of the catalyst-coated membrane-seal assembly.

[0074] Suitably, an MEA for a water electrolyser has a PTL provided on one side of the catalyst- coated membrane-seal assembly and a GDL on the other side of the catalyst-coated membrane-seal assembly, for example a PTL provided on a first side of the catalyst-coated membrane-seal assembly (corresponding to the first (anode) side of the ion-exchange membrane) and a GDL provided on the second side of the catalyst-coated membrane-seal assembly (corresponding to the second (cathode) side of the ion-exchange membrane).

[0075] It may also be the case that such MEAs comprise an additional PTL on the cathode side of the catalyst-coated membrane-seal assembly. Such arrangements typically have a GDL positioned between a PTL and the catalyst-coated membrane-seal assembly.

[0076] PTLs for water electrolysers are typically formed from a metal-based porous structure. Such PTLs must be sufficiently conducting and in a form that is compatible with positioning adjacent to the catalyst-coated membrane (without, for example, sharp edges or protrusions that would damage the membrane during use). Such metal-based porous structures may be in the form of, for example, felts or non-woven cloths, mesh, foams and sintered metalcontaining particles. For PEMWE applications, suitable PTLs comprise titanium. For AEMWE applications, suitable PTLs comprise nickel or stainless steel. Such materials are known to the skilled person.

[0077] MEAs as described hereinbefore may suitably be incorporated into a water electrolyser or a fuel cell, such as a PEMWE, PEMFC or AEMWE.

[0078] The invention will now be exemplified with reference to a series of schematic representations of catalyst-coated membrane-seal assemblies.

[0079] Figure 1 shows an example of a catalyst-coated membrane-seal assembly (10) according to the invention. The catalyst-coated membrane-seal assembly has a central region (11) on which a catalyst layer is applied and a border region (12) which surrounds the central region (11) and which includes a seal material layer.

[0080] Figure 2 shows a cross-sectional view along the line a-a of the catalyst-coated membraneseal assembly (10) shown in Figure 1. The central component of the catalyst-coated membrane-seal assembly (10) is an ion-conducting membrane (13). In the central region (11) the ion-conducting membrane (13) has an anode catalyst layer (14) on a first side and a cathode catalyst layer (15) on the second (opposite) side. In the border region (12) a seal material layer (16) is applied on each side of the ion-conducting membrane (13) with an intermediate bonding layer (17) adhering the seal material layer (16) to the membrane, for example formed from a pressure sensitive adhesive. The seal material layer (16) has a first face (18) (shown for only one seal material layer in Figure 2) facing the ion-conducting membrane (13) and a second face (19) (shown for only one seal material layer in Figure 2), on the opposite side of the seal material layer (16). The inner edge (20) of each seal material layer (16) facing the central region (11) is bevelled such that the second face (19) of each seal material layer (16) extends further towards the central region (11) than the first face (18) of each the seal material layer (16). Whilst the inner edge (20) of each seal material layer is shown as bevelled in Figure 2, in some cases it is only the inner edge (20) of the seal material layer (16) on one side of the catalyst-coated membrane-seal assembly (10) that is bevelled (for example the face corresponding to the anode side of the catalyst- coated membrane-seal assembly of a water electrolyser).

[0081] Figure 3 shows a cross-sectional view of an alternative example of membrane-seal assembly (20). In this example, the seal material layers (16) overlap the anode catalyst layer (14) and the cathode catalyst layer (15). A bonding layer is not shown in Figure 3 but, if present, would be positioned to adhere the seal material layer (16) to both the ionconducting membrane (13) and the region of overlap with the catalyst layers (14, 15).

[0082] Figure 4 shows a cross-sectional view of a further example of membrane-seal assembly (30). In this example, the seal material layers (16) extend around and protect the outer edge (31) of the membrane (13). As for Figure 3, bonding layers (not shown in Figure 4) are typically present to adhere the seal material layer (16) to both the ion-conducting membrane

[0083] (13).

[0084] Figure 5 shows a cross-sectional view of a further example of membrane-seal assembly (40). In this example, the seal material layers (16) extend around and protect the outer edge (31) of the membrane (13) and the seal material layers (16) overlap the anode catalyst layer

[0085] (14) and the cathode catalyst layer (15). As for Figure 4, bonding layers (not shown in Figure 4) are typically present to adhere the seal material layer (16) to both the ionconducting membrane (13) and the catalyst layers (14, 15).

[0086] Figure 6 shows a cross-sectional view of a further example of membrane-seal assembly (50). In this example, the catalyst layers (14, 15) extend across each face of the ionconducting membrane (13). The seal material layers (16) are adhered to the catalyst layers using bonding layers (17). The inner edge of one of the seal material layer is bevelled and may advantageously align with the bevel of the seal material layer (shown for one edge in Figure 6, (21)).

[0087] The catalyst-coated membrane-seal assembly may be fabricated as follows. A catalyst- coated membrane is produced using techniques known to the person skilled in the art. For example, the anode and cathode catalyst layers may be applied to an ion-conducting membrane through decal transfer of each catalyst layer from a substrate onto the membrane followed by hot pressing, or catalyst layers may be directly applied onto the membrane, for example by slot die (slot, extrusion) coating (whereby the coating is squeezed out under pressure via a slot onto the substrate).

[0088] A seal material layer may then be applied to one or both faces of the catalyst-coated membrane. Suitably, the bevelled edge of the seal material layer is prepared prior to application to the catalyst-coated membrane, for example by angling a cutting tool used to prepare the seal material layer to provide the desired inner edge shape. The bevelled edge may also be prepared using other techniques, such as laser cutting. The shaped seal material layer is then applied to the catalyst-coated membrane, typically followed by a hot- pressing step to form the catalyst-coated membrane-seal assembly. The seal material layers may also be prepared using additive layer techniques, such as 3D-printing.

Claims

Claims1. A catalyst-coated membrane-seal assembly comprising an ion-conducting membrane having a first side and an opposite second side, the catalyst-coated membrane-seal assembly comprising:(i) a central region comprising a first catalyst layer on the first side of the ionconducting membrane and a second catalyst layer on the second side of the ion-conducting membrane;(ii) a border region surrounding the central region, the border region comprising a first seal material layer on the first side of the ion-conducting membrane and a second seal material layer on the second side of the ion-conducting membrane, the first seal material layer and the second seal material layer each having a first side and a second side, the first side of the first seal material layer facing the first side of the ion-conducting membrane and the first side of the second seal material layer facing the second side of the ion-conducting membrane; and wherein the edge of the first seal material layer facing the central region is bevelled such that the second side of the first seal material layer extends further towards the central region than the first side of the first seal material layer.

2. A catalyst-coated membrane-seal assembly according to claim 1 , wherein the edge of the second seal material layer facing the central region is bevelled such that the second side of the second seal material layer extends further towards the central region than the first side of the second seal material layer.

3. A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the first catalyst layer and the second catalyst layer extend into the border region.

4. A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the first catalyst layer is an anode layer for water electrolysis and the second catalyst layer is a cathode layer for water electrolysis.

5. A catalyst-coated membrane-seal assembly according to claim 4, wherein the anode catalyst layer comprises an oxygen evolution reaction (OER) catalyst, such as an iridium- based OER catalyst.6 A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the ion-conducting membrane has a thickness at 0% relative humidity in the range of and including 10 to 100 .m.

7. A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the ion-conducting membrane comprises at least one porous polymer reinforcement component, such as two porous polymer reinforcement components.

8. A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the second side of the first seal material layer extends at least 5 pm further towards the central region than the first side of the first seal material layer.

9. A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the first and I or second seal material layer has a thickness of at least 20 pm.

10. A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the ion-conducting membrane is a proton-conducting membrane.

11. A catalyst-coated membrane-seal assembly according to any one of the preceding claims, wherein the second side of the first seal material layer extends further towards the central region by at least 10 % of the thickness of the seal material layer.

12. A membrane-electrode assembly comprising a catalyst-coated membrane-seal assembly according to any one of claims 1 to 11 , a first gas diffusion layer or a first porous transport layer on a first side of the catalyst-coated membrane-seal assembly and a second gas diffusion layer or a second porous transport layer on the second side of the catalyst- coated membrane-seal assembly.

13. A water electrolyser or a fuel cell comprising a catalyst-coated membrane-seal assembly according to any one of claims 1 to 11 or a membrane-electrode assembly according to claim 12.

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