WO2024100383A2

WO2024100383A2 - Method

Info

Publication number: WO2024100383A2
Application number: PCT/GB2023/052895
Authority: WO
Inventors: Angus DICKINSON
Original assignee: Johnson Matthey Hydrogen Technologies Limited
Priority date: 2022-11-08
Filing date: 2023-11-07
Publication date: 2024-05-16
Also published as: GB202216610D0; WO2024100383A3

Abstract

A method of manufacturing a catalyst-coated ion-conducting membrane. The method comprises the step of removing at least one part of the ion-conducting membrane covering a region of a support substrate in which a first catalyst layer is absent, prior to a step of heat treatment of the ion-conducting membrane.

Description

METHOD

Field of the Invention

This invention relates to a method of manufacturing a catalyst-coated ion-conducting membrane. In particular, this invention relates to a method of manufacturing a catalyst-coated ion-conducting membrane for an electrochemical device, such as a fuel cell or an electrolyser. This invention also relates to associated methods of manufacturing a membrane-electrode assembly.

Background

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).

Ion-conducting membranes, such as PEMs and AEMs, are also used in fuel cells. In a proton exchange membrane fuel cell (PEM FC) 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.

Catalyst-coated ion-conducting membranes (CCMs) may be employed within electrochemical devices, such as electrolysers and fuel cells. 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.

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 PEM WE 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.

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.

Separate film layers, typically formed from non-ion conducting polymers, may be positioned around the edge region of a CCM, for example on exposed surfaces of the ion-conducting membrane where no electrocatalyst is present (but will also often overlap on to the edge of the electrocatalyst layer) to provide a seal to prevent escape of reactant and product gases, to reinforce and strengthen the edge of the CCM and provide a suitable surface for supporting subsequent components such as sub-gaskets or elastomeric gaskets. An adhesive layer may be present on one or both surfaces of the seal film layer. Such an arrangement is known as a membrane-seal assembly.

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

It is known to form CCMs by sequential deposition of layers. EP2774203B1 describes a method comprising the steps of a) preparing a first catalyst layer on a supporting substrate; b) coating the first catalyst layer with an ionomer dispersion to form an ionomer membrane in contact with the first catalyst layer; and c) applying a second catalyst layer on top of the ionomer membrane. After formation, the CCM is subjected to an annealing step which helps to consolidate the membrane and improve the interface between membrane and electrode layers.

The demand for hydrogen-based solutions for the reduction of carbon emissions is expected to continue to grow rapidly in response to net-zero targets. In order to respond to this demand, rapid increases in the volume of production of key components, such as CCMs, are required. It has been predicted that the required growth of production may be curtailed by shortages of key raw materials, such as platinum group metal catalysts, for example iridium-based catalyst materials, and ion-conducting polymers. There are significant benefits in minimising the use of such key raw materials, in the reduction of waste, and in the facilitation of recycling.

There remains a need to further enhance and develop methods for the production of catalyst- coated ion-conducting membranes, in particular methods which enable large scale manufacturing, whilst optimising the use and recycling of key raw materials. Summary of the invention

The present inventors have identified an enhanced approach for the production of catalyst- coated ion-conducting membranes that addresses some of the manufacturing concerns previously described, for example by facilitating recycling of waste raw materials during manufacture.

In a first aspect of the invention, there is provided a method of manufacturing a catalyst-coated ion-conducting membrane, the method comprising the steps of:

(a) providing a support substrate having a first face, the first face comprising at least one region coated with a first catalyst layer and regions where the first catalyst layer is absent;

(b) forming an ion-conducting membrane on the first face of the support substrate such that the ion-conducting membrane covers the at least one region of the support substrate coated with the first catalyst layer and at least one region of the support substrate in which the first catalyst layer is absent;

(c) removing at least one part of the ion-conducting membrane covering a region of the support substrate in which the first catalyst layer is absent;

(d) heat-treating the ion-conducting membrane;

(e) optionally, applying a second catalyst layer on the surface of the ion-conducting membrane after any one of steps (b) to (d).

The advantages of such a method include the facilitation of the recovery and reuse of ionconducting polymers from areas of the ion-conducting membrane which are typically later removed and discarded as waste. This recovery is aided by removal of these areas prior to heat treatment of the membrane, which increases and strengthens the crystalline nature of the ion-conducting polymer in the membrane and therefore makes the ion-conducting polymer more resistant to dissolution. Removing the ion-conducting polymer before heat treatment allows milder processing conditions to be used to redisperse and recover the ion-conducting polymer.

The process improvements also provide benefits for the production of membrane-electrode assemblies. Therefore, in a second aspect of the invention there is provided a method of manufacturing a membrane-electrode assembly, the method comprising the steps of: (i) providing a catalyst-coated ion-conducting membrane manufactured using the method according to the first aspect, the catalyst-coated ion-conducting membrane comprising a first face and a second face; and (ii) applying a gas diffusion layer and / or a porous transport layer onto at least one of the first and second faces of the catalyst-coated ion-conducting membrane. In a third aspect of the invention there is provided a catalyst-coated ion-conducting membrane obtained, or obtainable by, the method of the first aspect.

Brief description of the Figures

Figure 1 shows a schematic representation of an example of a method of manufacturing a catalyst-coated ion-conducting membrane.

Figure 2 shows a schematic representation of an example of an alternative method of manufacturing a catalyst-coated ion-conducting membrane.

Detailed Description

Preferred and/or optional features of the invention will now be set out. Any of the preferred and/or optional features of any aspect may be combined, either singly or in combination, with any other preferred and/or optional features of any aspect of the invention unless the context demands otherwise.

The invention provides a method of manufacturing a catalyst-coated ion-conducting membrane. Typically, the catalyst-coated ion-conducting membrane is a catalyst-coated proton exchange membrane or a catalyst-coated anion exchange membrane. The catalyst- coated ion-conducting membrane is suitable for an electrochemical device, such as a fuel cell or an electrolyser.

As used herein the term “catalyst-coated ion-conducting membrane” refers to an ionconducting membrane with a first face and a second face, and which has a first catalyst layer on the first face and, optionally, a second catalyst layer on the second face.

The method comprises step (a) which involves providing a support substrate. The support substrate provides support for the catalyst-coated ion-conducting membrane during manufacture and, if not immediately removed, can provide support and strength during any subsequent storage and/or transport. The material from which the support substrate is made should provide the required support, be able to withstand the process conditions involved in producing the catalyst-coated ion-conducting membrane and be able to be easily removed without damage to the catalyst-coated ion-conducting membrane. Examples of materials suitable for use as a support substrate include a fluoropolymer, such as polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene (FEP - a copolymer of hexafluoropropylene and tetrafluoroethylene), and polyolefins, such as biaxially oriented polypropylene (BOPP). Other examples include laminates, multi-layer extrusions and coated films/foils capable of retaining their mechanical strength/integrity at elevated temperatures, for example temperatures up to 200 °C. Examples include laminates of: poly(ethylene-co-tetrafluoroethylene) and polyethylene naphthalate (PEN); polymethylpentene (PMP) and PEN; polyperfluoroalkoxy (PFA) and polyethylene terephthalate (PET) and polyimide (PI). The laminates can have two or more layers, for example ETFE-PEN-ETFE, PMP-PEN-PMP, PFA-PET-PFA, PEN-PFA, FEP-PI-FEP, PFA-PI-PFA and PTFE-PI-PTFE. The layers may be bonded using an adhesive, such as acrylic or polyurethane.

The support substrate has a first face and a second face, and comprises, on the first face of the support substrate, at least one region coated with a first catalyst layer and regions in which the first catalyst layer is absent.

The catalyst layer is suitably for an electrode (e.g. anode or cathode) of a fuel cell or an electrolyser. The first catalyst layer comprises a catalyst. The catalyst is suitably an electrocatalyst. The catalyst layer can comprise a conductive support, wherein the catalyst is supported on the conductive support. The catalyst can be a finely divided unsupported metal powder, or may, for example, be a supported catalyst wherein small metal nanoparticles are dispersed on an electrically conducting particulate support, such as a carbon support. The catalyst metal is suitably selected from:

(i) the platinum group metals (i.e. platinum, palladium, rhodium, ruthenium, iridium, and osmium),

(ii) gold or silver,

(iii) a base metal, or

(iv) an alloy or mixture comprising one or more of these metals or their oxides.

If the catalyst is a supported catalyst, the loading of metal particles on the (e.g. carbon) support material is suitably in the range of and including 10 to 90 wt%, preferably in the range of and including 15 to 75 wt% of the total weight of resulting electrocatalyst. It may be preferred that the catalyst metal in the first catalyst layer is platinum, which may be alloyed with other precious metals or base metals. It may be further preferred that the catalyst in the first catalyst layer is platinum on a carbon support.

The catalyst layer typically comprises additional components, such as an ion-conducting polymer, to improve ionic conductivity within the layer. Preferably, the first catalyst layer is electronically conducting.

Typically, the first catalyst layer has a thickness in the range of and including 2 to 20 .m, such as in the range of and including 2 to 10 .m.

The first face of the support substrate has at least one region coated with a first catalyst layer. It will be understood that the dimensions of the one or more regions coated with a first catalyst layer will depend on the configuration of the electrochemical device into which the formed catalyst-coated ion-conducting membrane is designed to be incorporated. Typically, the region(s) coated with the first catalyst layer correspond to the active catalyst area of the formed catalyst-coated ion-conducting membrane. Suitably, such regions are in the shape of a quadrilateral, such as a rectangle or a square. It may be preferred that the regions coated with a first catalyst layer do not extend to the edges of the support substrate.

Typically, the one or more regions coated with a first catalyst layer are discrete patches. By discrete patches it is meant that the first catalyst layer is applied to the support substrate in discrete areas which are not connected to each other.

The first face of the support substrate also has at least one region of the support substrate where the first catalyst layer is absent. In such regions, the support substrate is typically uncoated. It will be understood that the dimensions of the one or more regions of the support substrate where the first catalyst layer is absent will depend on the dimensions of the support substrate and the configuration of the electrochemical device incorporating the formed catalyst-coated ion-conducting membrane. Typically, the one or more regions in which the first catalyst layer is absent surround the regions coated with a first catalyst layer.

The one or more regions of the support substrate coated with the first catalyst layer may be prepared using, for example, coating methods such as a slot-die (slot, extrusion) coating process, inkjet printing, gravure printing, curtain coating, or a spray coating process.

Suitably, step (a) can further comprise the sub-steps of: (i) depositing a first catalyst dispersion on the support substrate; and (ii) drying the first catalyst dispersion to form the first catalyst layer. Typically, the catalyst dispersion comprises the catalyst material and an ion-conducting polymer dispersed in a solvent, such as water, a polar solvent (other than water), or a mixture of water and a polar solvent (other than water). The polar solvent can be a polar protic solvent. Preferably, the polar solvent is an alcohol, more preferably a C1.4 alcohol, such as be methanol, ethanol, or propan-1-ol. The first catalyst dispersion can be dried at a temperature in the range of and including 50-100 °C, preferably in the range of and including 60-80 °C.

The method comprises step (b) forming an ion-conducting membrane on the first face of the support substrate. The ion-conducting membrane is formed such that it covers the one or more regions of the support substate coated with the first catalyst layer. Preferably, the formed ion-conducting membrane is in direct contact with the first catalyst layer. The ion-conducting membrane is formed such that it also covers at least one region of the support substrate in which the first catalyst layer is absent. Typically, the ion-conducting membrane formed in step (b) covers substantially all of the first face of the support substrate, such as at least 90%, or at least 95% of the area of the first face of the support substrate. The ion-conducting membrane is suitably formed by a method comprising the steps of (i) depositing a first ion-conducting polymer dispersion onto the first face of the support substrate; and (ii) drying the first ion-conducting polymer dispersion to form (part of) the ion-conducting membrane.

Typically, the first ion-conducting polymer dispersion comprises ion-conducting polymer dispersed in a continuous phase comprising one or more solvents. The first ion-conducting polymer dispersion can comprise a continuous phase comprising (or consisting of) water, a polar solvent (other than water), or (preferably) a mixture of water and a polar solvent (other than water). The polar solvent can be a polar protic solvent. Preferably, the polar solvent is an alcohol, more preferably a C1.4 alcohol. The C1.4 alcohol can be methanol, ethanol, propan-1- ol, propan-2-ol, n-butanol, iso-butanol, butan-2-ol, and tert-butyl alcohol, or a mixture thereof. Preferably, the C1.4 alcohol is ethanol and/or propan-1 -ol. Preferably, the continuous phase comprises (or consists essentially of) water and an alcohol. More preferably, the continuous phase comprises (or consists essentially of) water and at least one of ethanol or propan-1 -ol. Most preferably, the continuous phase comprises (or consists essentially of) water and ethanol.

The continuous phase of the first ion-conducting polymer dispersion can comprise the polar solvent other than water (e.g. C1.4 alcohol) in an amount in the range of <90 wt.%, preferably 10-85 wt.%, or more preferably 20-80 wt.% based on the total weight of the continuous phase. In some embodiments, the continuous phase of the first ion-conducting polymer dispersion can comprise the polar solvent other than water (e.g. C1.4 alcohol) in an amount in the range of <70 wt.%, preferably 10 wt.% to 50 wt.%, and more preferably 20 wt.% to 40 wt.%. The continuous phase can comprise the polar solvent other than water (e.g. C1.4 alcohol) in any combination of the limits of these ranges. Unless explicitly stated otherwise, the upper and lower limits of all numerical ranges disclosed in this application are included within the range.

The continuous phase of the first ion-conducting polymer dispersion can comprise water in an amount in the range of >10 wt.%, preferably 15-90 wt.%, and more preferably 20-80 wt.%. The continuous phase can comprise water in any combination of the limits of these ranges.

The first ion-conducting polymer dispersion comprises an ion-conducting polymer, which is dispersed in the continuous phase. The ion-conducting polymer can be a proton-conducting polymer or an anion-conducting polymer, such as a hydroxyl anion-conducting polymer. Examples of suitable proton-conducting polymers include perfluorosulphonic acid ionomers (e.g. Nation® (Chemours), Aciplex® (Asahi Kasei), Aquivion™ (Solvay Speciality Polymers), Flemion® (Asahi Glass Co.), or ionomers based on a sulphonated hydrocarbon such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, JSR Corporation, Toyobo Corporation, and others. Examples of suitable anion-conducting polymers include A901 made by Tokuyama Corporation and Fumasep FAA from FuMA-Tech GmbH.

The first ion-conducting polymer dispersion can comprise the ion-conducting polymer in an amount in the range of 5-80 wt.%, preferably 10-50 wt.%, preferably 15-30 wt.%, and most preferably 15-20 wt.% based on the total weight of the first dispersion. The first ion-conducting polymer dispersion can comprise the ion-conducting polymer in any combination of the limits of these ranges. For example, the first ion-conducting polymer dispersion can comprise the ion-conducting polymer in an amount in the range 10-20 wt.%.

The first ion-conducting polymer dispersion is an ion-conducting membrane precursor. When dried, the first ion-conducting polymer dispersion forms a (first) ion-conducting membrane layer. The ion-conducting membrane layer is suitably electrically insulating. The ionconducting membrane layer can be for (part of) the electrolyte of a fuel cell or electrolyser.

The first ion-conducting polymer dispersion can further comprise one or more additives such as a hydrogen peroxide decomposition catalyst, a radical decomposition catalyst (such as ceria), and/or a recombination catalyst.

Hydrogen peroxide decomposition catalysts are known in the art and may be selected from the group consisting of metal oxides, such as cerium oxides, manganese oxides, titanium oxides, beryllium oxides, bismuth oxides, tantalum oxides, niobium oxides, hafnium oxides, vanadium oxides and lanthanum oxides, suitably cerium oxides, manganese oxides or titanium oxides, preferably cerium dioxide (ceria).

A recombination catalyst catalyses the reaction of H2 and O2 to form H2O. Suitable recombination catalysts can comprise a metal (such as platinum) on a high surface area oxide support material (such as silica, titania, or zirconia). More examples of recombination catalysts are disclosed in EP0631337 and WO00/24074. The recombination catalyst is suitably dispersed in the continuous phase of the first ion-conducting polymer dispersion.

The first ion-conducting polymer dispersion can be deposited using a slot-die (slot, extrusion) coating process (whereby the dispersion is squeezed out by gravity or under pressure via a slot onto the substrate), knife-coating, bar coating, inkjet printing, gravure printing, curtain coating, or a spray coating process. Preferably, the first dispersion of an ion-conducting polymer can be deposited using slot-die coating, knife coating, bar coating, inkjet printing or gravure printing. Preferably, the first ion-conducting polymer dispersion is deposited using a slot-die coating process. The first ion-conducting polymer dispersion may be dried at a temperature in the range of and including 50 °C to 100 °C, and preferably 60 °C to 80 °C.

It may be preferred that step (b) comprises depositing a plurality of ion-conducting membrane layers. For example, step (b) may comprise the steps of (i) depositing a first ion-conducting polymer dispersion onto the first face of the support substrate layer to form a first ionconducting membrane layer; (ii) optionally drying the first ion-conducting membrane layer; (iii) depositing one or more additional ion-conducting membrane layers onto the first ionconducting membrane layer. The additional ion-conducting membrane layers may be formed from the same composition as the first ion-conducting polymer dispersion or may have a different composition. It may be preferred that each ion-conducting membrane layer is dried before the next layer is deposited. It may be further preferred that the deposition of at least one layer includes the incorporation of a polymer reinforcement, such as a polymer reinforcement comprising expanded polytetrafluoroethylene (ePTFE) or polybenzimidazole (PBI).

The process comprises the step of (c) removing at least one part of the ion-conducting membrane which is formed in step (b) and which covers a region of the support substrate where the first catalyst layer is absent. Typically, the part(s) may be removed by cutting through the membrane around the part to be removed. The part(s) may then be physically removed, for example using vacuum.

Preferably, the part(s) are removed without removing parts of the support substrate, for example by cutting through the membrane around the part to be removed without cutting through the substrate, such as by using a kiss cutting tool. This helps to maintain the structural integrity of the support substrate during subsequent process steps and storage.

The part(s) of the ion-conducting membrane removed in step (c) cover a region of the support substrate in which the first catalyst layer is absent. After the removal step, complete coverage of the first catalyst layer by the ion-conducting membrane is maintained. The part(s) removed in step (c) correspond to regions of membrane which are not required in the formed catalyst- coated ion-conducting membrane, for example edge regions which extend beyond the desired dimensions of the formed catalyst-coated ion-conducting membrane and areas where through-holes are required in the formed catalyst-coated ion-conducting membrane to match a fuel cell or electrolyser stack configuration.

Advantageously, the part(s) removed can be treated to recover ion-conducting polymers used to form the ion-conducting membrane in step (b), for example by dissolution of the ionconducting polymer in an organic solvent, such as ethanol, and separation from additives, if present. The ion-conducting polymer can then be reused in subsequent membrane formation processes reducing wastage of these key raw materials. The recovery process is facilitated and reduced in complexity due to the use of the process as described herein. Firstly, the part(s) removed are not coated with a catalyst layer which avoids the requirement to separate the ion-conducing polymer from components of the catalyst layer, which can be problematic in particular in situations where the catalyst layer contains a different ion-conducting polymer from that used for membrane manufacture. Secondly, the part(s) are removed prior to heat treatment of the membrane. Such heat treatment leads to ordering of the ion-conducting polymer chains in the membrane which reduces membrane solubility and the ease of recovery of the ion-conducing polymer.

The process comprises the step of (d) heat-treating the ion-conducting membrane after the removal of parts of the membrane in step (c). Such heat treatment is carried out at a temperature which increases and strengthens the crystalline nature of the ion-conducting polymer in the membrane and therefore makes the ion-conducting polymer more resistant to dissolution. Heat treatment of the ion-conducting membrane improves the mechanical strength and dissolution resistance of the membrane and can increase the adhesion of the first (and second if present) catalyst layer to the membrane. Typically, the heat treatment is carried out a temperature in the range of and including 140 to 220 °C, preferably in the range of and including 150 to 180 °C.

The process comprises the optional step of (e) applying a second catalyst layer on the surface of the ion-conducting membrane. It will be understood by the skilled person that the second catalyst layer is applied to the opposite face of the ion-conducting membrane from the first catalyst layer such that, once the second catalyst layer is applied, the ion-conducting membrane is positioned between, and typically in direct contact with, the first and the second catalyst layers.

Components of the second catalyst layer and methods of application of the second catalyst layer are as described hereinbefore for the first catalyst layer. The second catalyst layer may also be applied using a transfer process onto the surface of the membrane, for example using a decal, such as by hot pressing. Typically, the first catalyst layer and the second catalyst layer comprise different catalyst materials. The catalyst materials are chosen depending on the required functionality (e.g. water electrolysis) and operating conditions (e.g. acidic or alkaline) of the formed catalyst-coated ion-conducting membrane.

The application of the second catalyst layer may occur after any one of steps (b), (c) or (d). It may be preferred that the second catalyst layer is applied after step (c) or step (d). It may be further preferred that the second catalyst layer is applied after step (d). Applying the second catalyst layer on the surface of the membrane after heat treatment offers advantages associated with reduced membrane swelling and solvent uptake during the application process.

Preferably, the second catalyst layer is applied to regions of the ion-conducting membrane which correspond to the regions of the ion-conducting membrane with the first catalyst layer applied to the opposite face. Preferably, the regions of the second catalyst layer are centrally positioned over the regions of the first catalyst layer (but on the opposite face of the ionconducting membrane). In the case that the second catalyst layer is applied after step (b), i.e. before removal of the part(s) of the ion-conducting membrane, it is particularly preferred that the second catalyst layer is applied to areas that correspond to the regions of the ionconducting membrane with the first catalyst layer applied to the opposite face, and that the second catalyst layer is not applied to regions of the ion-conducting membrane which do not have the first catalyst layer applied to the opposite face.

Optionally, the process comprises the step of (f) removing the support substrate from the catalyst-coated ion-conducting membrane.

Preferably, the process is a continuous roll-to-roll process.

Optionally, the process comprises the step of (g) applying a seal material to the first face and/or the second face of the catalyst-coated ion-conducting membrane. Typically, the seal material is applied after the removal of the catalyst-coated ion-conducting membrane from the support substrate (subsequent to step (f)), but the seal material may also be applied to one face of the catalyst-coated ion-conducting membrane after heat-treatment of the membrane (subsequent to step (d)) or after application of the second catalyst layer (subsequent to step (e)) and prior to removal from the support substrate. The process as described herein offers a number of advantages with respect to the manufacture of membrane-seal assemblies. For example, the removal of membrane regions prior to seal material application reduces the complexity of the ion-conducting polymer recycling process. In addition, the application of a seal material after the membrane is cut enables the seal material to seal the edges of the cut membrane. These edges are typically exposed after current processes in which the holes cut after seal material application which may be detrimental to membrane stability.

The catalyst-coated ion-conducting membrane manufactured using the above method can also be used in the manufacture of a membrane-electrode assembly. In order to form a membrane-electrode assembly a gas diffusion layer (GDL) and / or a porous transport layer (PTL) is applied onto at least one of the first and second faces of the catalyst-coated ionconducting membrane (with or without prior application of a seal material). The choice of GDL and I or PTL will depend on the nature and configuration of the electrochemical device. Such materials are well known to the skilled person. Figures 1 and 2 depict exemplary methods of the present invention. The dimensions (e.g. thickness) of each layer are not drawn to scale for the sake of clarity.

It will be clear to the skilled person that although the process described below is with reference to the manufacture to a continuous roll of multiple catalyst-coated ion-conducting membrane components, the basic process could be applied to the individual manufacture of a catalyst- coated ion-conducting membrane component.

Figure 1 shows a method for making an ion-conducting catalyst-coated membrane. A support substrate (1) is provided which comprises on the first face (2) of the support substrate (1) regions coated with a first catalyst layer (3) and regions where the first catalyst layer is absent

(4). An ion-conducting membrane (5) is formed on the first face (2) of the support substrate (1) covering the regions of the support substrate coated with the first catalyst layer (3) and an uncoated region (4). Typically, the ion-conducting membrane (5) is formed by a series of coating passes in which a dispersion of ion-conducting polymer is deposited and then dried before a subsequent coating pass (not shown in Figure 1). After formation of the ionconducting membrane, a second catalyst layer (6) is formed on the ion-conducting membrane

(5). Typically the second catalyst layer (6) is deposited in discrete regions which are centrally positioned over the regions of the first catalyst layer (3) (but on the opposite face of the ionconducting membrane). At least one part of the ion-conducting membrane (5) is then removing by cutting through the membrane (5) (but not the support substrate (1)) using a kiss cutting tool and removing the part(s) to leave areas (7) where the membrane has been removed. The catalyst-coated ion-conducting membrane is then heat treated (not shown in Figure 1).

Figure 2 shows an alternative method for making an ion-conducting catalyst-coated membrane. As for Figure 1 a support substrate (1) is provided which comprises on the first face (2) of the support substrate (1) regions coated with a first catalyst layer (3) and regions in which the first catalyst layer is absent (4). An ion-conducting membrane (5) is formed on the first face (2) of the support substrate (1) covering the regions of the support substrate coated with the first catalyst layer (3) and an uncoated region (4). After formation of the ionconducting membrane (5), at least one part of the ion-conducting membrane (5) is then removed by cutting through the membrane (5) (but not the support substrate (1)) and removing the parts to leave areas (7) where the membrane has been removed. After removal, a second catalyst layer (6) is formed on the ion-conducting membrane (5). Typically the second catalyst layer (6) is deposited in discrete regions which are centrally positioned over the regions of the first catalyst layer (3) (but on the opposite face of the ion-conducting membrane). The catalyst-coated ion-conducting membrane is then heat treated (not shown in Figure 1). Optionally, the heat treatment may be carried out prior to the deposition of the second catalyst layer (g) (after removal of the parts of the ion-conducting membrane (5)).

Claims

1. A method of manufacturing a catalyst-coated ion-conducting membrane, the method comprising the steps of:

(b) forming an ion-conducting membrane on the first face of the support substrate such that the ion-conducting membrane covers the at least one region of the support substrate coated with the first catalyst layer and at least one region of the support substrate where the first catalyst layer is absent;

(d) heat-treating the ion-conducting membrane;

2. A method according to claim 1 , wherein the method comprises an additional step of: (f) removing the support substrate.

3. A method according to claim 1 or claim 2, wherein the method comprises an additional step of: (g) applying a seal material to a first face and/or a second face of the catalyst-coated ion-conducting membrane.

4. A method according to any one of the preceding claims, wherein step (a) comprises the sub-steps of (i) depositing a first catalyst dispersion onto the support substrate; and (ii) drying the first catalyst dispersion to form the first catalyst layer.

5. A method according to any one of the preceding claims, wherein the ionconducting membrane formed in step (b) covers substantially all of the first face of the support substrate.

6. A method according to any one of the preceding claims, wherein step (b) comprises depositing a plurality of ion-conducting membrane layers.

7. A method according to claim 6, wherein each layer is dried before the next ionconducting membrane layer is deposited.

8. A method according to claim 6 or claim 7, wherein the deposition of at least one ion-conducting membrane layer includes the incorporation of a polymer reinforcement.

9. A method according to any one of the previous claims wherein step (c) comprises cutting the ion-conducting membrane around the at least one part to be removed.

10. A method according to claim 9, wherein the support substrate is not cut during the process of cutting the ion-conducting membrane around the at least one part to be removed.

11 . A method according to any one of the previous claims, wherein the at least one part of the ion-conducting membrane removed in step (c) is treated to recover at least one ion-conducting polymer.

12. A method according to any one of the preceding claims, wherein heat-treating the ion-conducting membrane in step (d) comprises heating to a temperature in the range of and including 140 to 220 °C, preferably 150 to 180 °C.

13. A method according to any one of the preceding claims, wherein applying a second catalyst layer on the surface of the ion-conducting membrane in step (f) comprises the sub-steps of (i) depositing a second catalyst dispersion on the surface of the ionconducting membrane; and (ii) drying the second catalyst dispersion to form the second catalyst layer.

14. A method according to any one of the preceding claims, additionally including the step of applying a seal material to the first face and I or the second face of the catalyst- coated membrane after heat treatment of the membrane.

15. A method of manufacturing a membrane electrode assembly, the method comprising the steps of:

(i) providing a catalyst-coated ion-conducting membrane manufactured using the method according to any of claims 1 to 14, the catalyst-coated ion-conducting membrane comprising a first face and a second face; and

(ii) applying a gas diffusion layer and / or a porous transport layer onto at least one of the first and second faces of the catalyst-coated ion-conducting membrane.