WO2024069166A1

WO2024069166A1 - Membrane assembly and method

Info

Publication number: WO2024069166A1
Application number: PCT/GB2023/052498
Authority: WO
Inventors: Angus DICKINSON
Original assignee: Johnson Matthey Hydrogen Technologies Limited
Priority date: 2022-09-29
Filing date: 2023-09-27
Publication date: 2024-04-04
Also published as: GB202214277D0

Abstract

According to the present invention there is provided a membrane-seal assembly suitable for use with a flow field plate of the type comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports. The flow field comprises an inlet region, an outlet region and a main region between the inlet and outlet regions. The membrane-seal assembly comprises: an inner region comprising an ion-conducting membrane; and a border region surrounding the inner region. The border region comprises a seal component area and at least one stiffening area, wherein the seal component area comprises a seal component which is ionically non-conductive, and wherein the stiffening area comprises a stiffening component. The at least one stiffening area is positioned to extend at least partially across the inlet region and/or the outlet region of the flow field of the flow field plate when in use, and wherein the stiffening area has a stiffness greater than the stiffness of the seal component area.

Description

Membrane assembly and method

Field of the Invention

The present invention relates to a membrane assembly, in particular a membrane-seal assembly. The invention also relates to associated methods of manufacturing the membraneseal assembly, and electrochemical devices, such as fuel cells and water electrolysis cells comprising the membrane-seal assembly.

Background of the Invention

A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. A fuel, e.g. hydrogen, an alcohol such as methanol or ethanol, or formic acid, is supplied to the anode and an oxidant, e.g. oxygen or air, is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.

Fuel cells are usually classified according to the nature of the electrolyte employed. Often the electrolyte is a solid polymeric membrane, in which the membrane is electronically insulating but ionically conducting. In the proton exchange membrane fuel cell the ionconducting membrane is proton conducting, and protons, produced at the anode, are transported across the ion-conducting membrane to the cathode, where they combine with oxygen to form water.

A principal component of the proton exchange membrane fuel cell is a five-layer construct conventionally known as a membrane electrode assembly. The central layer is the polymer ion-conducting membrane. On either face of the ion-conducting membrane there is a catalyst layer containing an electrocatalyst designed for the specific electrolytic reaction. The catalyst layers also generally comprise a proton conducting material, such as a proton conducting polymer, to aid transfer of protons from the anode electrocatalyst to the ionconducting membrane and/or from the ion-conducting membrane to the cathode electrocatalyst. Adjacent to each catalyst layer there is a gas diffusion layer. The gas diffusion layer must allow the reactants to reach the catalyst layer and must conduct the electric current that is generated by the electrochemical reactions. Therefore, the gas diffusion layer must be porous and electrically conducting. This five layer construct is conventionally known as a membrane electrode assembly.

A principal component of a water electrolyser is a layered construct also known as a membrane electrode assembly. The central layer is a polymer ion-conducting membrane, which can be a proton conducting membrane or an anion conducting membrane. On either face of the ion-conducting membrane there is a catalyst layer containing an electrocatalyst design for the specific electrolytic reaction. The catalyst layers also generally comprise an ionconducting material, such as a proton conducting polymer (for proton exchange membrane water electrolysers), to aid transfer of ions between the anode electrocatalyst and cathode electrocatalyst across the ion-conducting membrane. Adjacent to each catalyst layer there is a porous transport layer (PTL) or a gas diffusion layer. These layers must allow the reactants to reach the catalyst layer and must conduct the electrical current required for the electrochemical reactions. Therefore, the layers must be porous and electrically conducting.

Conventionally, the membrane electrode assembly, whether for fuel cells or water electrolysers, is constructed so that the central polymeric ion-conducting membrane extends to the edge of the membrane electrode assembly, with the gas diffusion layers (or porous transport layers) and catalyst layers being smaller in area than the polymeric ion-conducting membrane such that there is an area around the periphery of the membrane electrode assembly which comprises ion-conducting membrane only. The area where no catalyst layer is present is an electrochemically non-active region.

Separate film layers, for example seal layers and sub-gaskets, formed from non-ion- conducting polymers are generally positioned at the edge region of the membrane electrode assembly on the exposed surfaces of the ion-conducting membrane where no catalyst layer is present (often overlapping the edge of the catalyst layer). These film layers provide a seal to prevent escape of reactant and product gases, reinforce and strengthen the edge of the membrane electrode assembly 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. This construct including a seal layer is known as a membrane-seal assembly, and is known as a sub-gasketed membrane-seal assembly if a sub-gasket is also present.

Conventionally, a (sub-gasketed) membrane-seal assembly is sandwiched between two flow field plates, such as two bipolar plates. Each flow field plate allows the reactants to reach the respective adjacent gas diffusion layer (or porous transport layer), and conducts the electric current that is generated by (or required for) the electrochemical reactions occurring at the electrodes. A bipolar plate typically comprises a first face, a second face opposite the first face, an inlet port, and an outlet port. Each of the first and second faces typically comprises a flow field comprising a plurality of channels for conveying reactants from the inlet port to the gas diffusion layer (or porous transport layer) and conveying reaction products (e.g. water) to the outlet port. The bipolar plate can further comprise cooling channels disposed between the first and second faces.

The seal materials of the membrane-seal assembly must be suitably flexible to provide an adequate seal with the flow field plate. However, when the membrane-seal assembly is positioned between two flow field plates, one flow field plate can undesirably press the edge region of the membrane-seal assembly into the channels of the flow field of the opposite flow field plate, which can restrict the flow through the flow field and lead to non-uniform reactant (e.g. gas) distribution in the flow field. This phenomenon is known as tenting. Figure 9 shows a cross-sectional illustration of tenting where a seal 900 deforms into a channel 910 of a flow field plate 920.

To mitigate the effects of tenting, it is known to machine a recess into a portion of the flow field of a flow field plate and to attach a complementary bridging member to the flow field plate in the recess. Figure 10 shows a cross-sectional illustration of a bridging member 1000 positioned to extend across channels 1010 in a recess 1020 of a flow field plate 1030. Machining suitable parts in this way can be expensive, difficult to process and not well-suited for large-scale production.

Summary of the Invention

The invention seeks to address the above described problems, desires and needs. In particular, the present invention provides a membrane-seal assembly (and a sub-gasketed membrane electrode assembly), which reduces or eliminates the effects of tenting and is suitable for industrial-scale manufacture.

According to a first aspect of the invention there is provided a membrane-seal assembly suitable for use with a flow field plate of the type comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports, the flow field comprising an inlet region, an outlet region and a main region between the inlet and outlet regions, the membrane-seal assembly comprising: an inner region comprising an ion-conducting membrane; and a border region surrounding the inner region, the border region comprising a seal component area and at least one stiffening area, wherein the seal component area comprises a seal component which is ionically non-conductive, and wherein the stiffening area comprises a stiffening component; wherein the at least one stiffening area is positioned to extend at least partially across the inlet region and/or the outlet region of the flow field of the flow field plate when in use, and wherein the stiffening area has a stiffness greater than the stiffness of the seal component area.

Stiffness (N/m) can be calculated as the quotient of force applied and the displacement produced in the direction of the force.

The stiffening area can comprise the seal component. The stiffening component can be positioned on the seal component. Where the ion-conducting membrane extends into the border region, the stiffening component can be disposed directly on the ion-conducting membrane.

The at least one stiffening area can have a cross-sectional thickness greater than a cross-sectional thickness of the seal component area. Typically, the cross-sectional thickness is a cross-sectional thickness in the through-plane direction. The stiffening component can have a (through-plane) cross-sectional thickness greater than a (through-plane) cross- sectional thickness of the seal component. The at least one stiffening area can protrude from the seal component area in a through-plane direction. For example, the stiffening component can protrude from the seal component of the seal component area. The stiffening area (or stiffening component) can protrude from the seal component area (or seal component) by a distance in the range of and including 0 mm to 3 mm (i.e. less than 3 mm), preferably in the range of and including 10 pm to 2 mm, and more preferably in the range of and including 100 pm to 1 mm. This distance can be within a range defined by any combination of the aforementioned upper and lower limits.

The stiffening component and the seal component can be made of the same material, providing that the stiffening area is stiffer than the seal component area (e.g. by virtue of being thicker). Alternatively, the stiffening component and the seal component can be made of different materials.

The stiffening area can have a cross-sectional thickness substantially the same as a cross-sectional thickness of the seal component area. Typically, the cross-sectional thickness is a cross-sectional thickness in the through-plane direction.

The at least one stiffening area can be flush with the seal component area.

The seal component of the seal component area and the stiffening component can be positioned in the same plane.

The stiffening component can comprise a polymeric material. The polymeric material of the stiffening component can be selected from: polyaryletherketones (PAEK), polyesters, polyazoles such as polybenzimidazole (PBI), silicones, fluorosilicones, polyurethanes, copolyamides, epoxies and fluoroacrylates.

The stiffening component can have a Shore A hardness greater than the Shore A hardness of the seal component.

The stiffening component can have a Young’s modulus greater than the Young’s modulus of the seal component.

The at least one stiffening area can be positioned to extend fully across the inlet region and/or outlet region of the flow field of the flow field plate when in use.

The membrane-seal assembly can further comprise a first face and a second face, wherein the at least one stiffening area comprises two or more stiffening areas disposed on the first face and/or the second face. For example, the first face can comprise two or more stiffening areas. The at least one stiffening area can comprise a stiffening area disposed on the first face and a stiffening area disposed on the second face. That is, the first face can comprise at least one stiffening area, and the second face can comprise at least one stiffening area. Each stiffening area suitably comprises a stiffening component.

The flow field plate can be of the type in which the inlet and/or outlet region independently comprise a recessed portion extending at least partially (or fully) across the pathway, and wherein the stiffening component of the at least one stiffening area is positioned to be receivable by the recessed portion of the inlet and/or outlet region of the flow field plate. For example, the inlet region can comprise the recessed portion, and the at least one stiffening area can comprise a stiffening component positioned to be receivable by the recessed portion of the inlet region. As a further example, the outlet region can comprise the recessed portion, and the at least one stiffening area can comprise a stiffening component positioned to be receivable by the recessed portion of the outlet region. The inlet region and outlet region can each comprise a recessed portion, and the at least one stiffening area can comprise a stiffening component positioned to be receivable by the recessed portion of the inlet region and a (further) stiffening component positioned to be receivable by the recessed portion of the outlet region.

The ion-conducting membrane can extend into the border region. For example, the border region can comprise an inner border region (or overlap region) and an outer border region surrounding the inner border region. The inner border region can comprise the ionconducting membrane and the seal component. Suitably, the inner border region does not comprise the stiffening area. The outer border region is devoid of the ion-conducting membrane and suitably comprises the seal component and the stiffening area.

The ion-conducting membrane can comprise a planar reinforcing component. The planar reinforcing component can be embedded within the ion-conducting membrane. The planar reinforcing component can extend into the border region.

The inner region can further comprise at least one catalyst layer on the ion-conducting membrane. A first catalyst layer can be disposed on a first face of the ion-conducting membrane. A second catalyst layer can be disposed on a second face of the ion-conducting membrane. The membrane-seal assembly can be a catalysed membrane-seal assembly.

The membrane-seal assembly can further comprise a gas diffusion layer (or porous transport layer) on the catalyst layer disposed on the first face and/or second face of the ionconducting membrane.

According to a second aspect, there is provided a membrane-seal assembly according to the first aspect in combination with a flow field plate comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports, the flow field comprising an inlet region, an outlet region and a main region between the inlet and outlet regions. The at least one stiffening area is positioned to extend at least partially (or fully) across the inlet region and/or outlet region of the flow field. The flow field plate can be a bipolar plate.

The membrane-seal assembly and the flow field plate can be arranged in combination in a stack. For example, the membrane-seal assembly can be sandwiched between two flow field plates, such as two bipolar plates.

According to a further aspect, there is provided an electrochemical device, such as a fuel cell or an electrolyser comprising the membrane-seal assembly according to the first or second aspect. The fuel cell is preferably a proton exchange membrane fuel cell. The electrolyser can be an anion exchange membrane water electrolysis cell. The electrolyser is preferably a proton exchange membrane water electrolysis cell.

According to a further aspect, there is provided a method of manufacturing a membrane-seal assembly according to the first aspect. The method comprises the steps of:

(a) providing a seal component on or around an ion-conducting membrane so as to define an inner region comprising the ion-conducting membrane and a border region surrounding the inner region, the border region comprising the seal component, wherein the seal component is ionically non-conductive;

(b) depositing a stiffening component precursor material onto the border region; and

(c) curing the stiffening component precursor material to form at least one stiffening area comprising a stiffening component.

Step (b) can comprise depositing the stiffening component precursor material onto the seal component.

According to a further aspect, there is provided a membrane assembly suitable for use with a flow field plate of the type comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports, the flow field comprising an inlet region, an outlet region and a main region between the inlet and outlet regions, the membrane assembly comprising an ion-conducting membrane and a stiffening component, wherein the ion-conducting membrane comprises: an inner region for aligning with the main region of the flow field when in use; and a border region surrounding the inner region and for aligning with the inlet region and/or outlet region of the flow field when in use, wherein the border region comprises at least one stiffening area comprising the stiffening component, wherein the at least one stiffening component is positioned on the ion-conducting membrane so as to extend at least partially across the inlet region and/or the outlet region of the flow field of the flow field plate when in use, and wherein the stiffening area has a stiffness greater than the stiffness of other areas in the border region. Preferably, the stiffening component has a stiffness greater than the ion-conducting membrane.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a first face of a bipolar plate;

Figure 2 is a schematic view of a second face of a bipolar plate;

Figure 3 is a cross-sectional view of a plurality of channels in a flow field plate;

Figure 4 is a schematic view of a face of a flow field plate including a recessed portion;

Figure 5 is a cross-sectional view of a recessed portion of a flow field plate;

Figure 6 is a schematic view of a first face of a membrane-seal assembly;

Figure 7 is a schematic view of a second face of a membrane-seal assembly;

Figure 8 is a schematic side view of a membrane-seal assembly;

Figure 9 is a cross-sectional view of a seal deforming into a channel of a flow field plate; and

Figure 10 is a cross-sectional view of a bridging plate extending across channels of a flow field plate.

Detailed Description of the Invention

Preferred and/or optional features 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. For the avoidance of doubt, the same reference numerals have been used in the drawings to refer to features that are the same. The drawings are not to scale.

Flow field plate

The invention provides a membrane-seal assembly suitable for use with at least one flow field plate. A suitable flow field plate is of the type comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports. The flow field plate can have a flow field on one side only. Alternatively, the flow field plate can have a flow field on each of its sides. The flow field plate can be a bipolar plate. By way of example only, Figures 1 and 2 show a bipolar plate 100 suitable for use with a membrane-seal assembly of the invention. The bipolar plate 100 comprises a first side 102 (shown in Figure 1) and a second side 104 (shown in Figure 2). In this example, the bipolar plate 100 comprises three inlet ports 110, 120, 130 and three outlet ports 115, 125, 135. In this example, each of the inlet and outlet ports are apertures extending through the full thickness of the bipolar plate 100.

The first inlet port 110 is in fluid communication with the first outlet port 115 via a flow field 140 on the first side 102 of the bipolar plate 100 (Figure 1). The first inlet port 110 can supply a reactant to the flow field 140. The first outlet port 115 can transport exhaust material away from the flow field 140. For example, the first inlet port 110 may be a fuel inlet port, for example a hydrogen gas inlet port.

The flow field 140 comprises an inlet region 142, an outlet region 144 and a main region 146 between the inlet and outlet regions. When assembled with a membrane-seal assembly, typically the main region 146 substantially corresponds to the part of the flow field that is directly adjacent the electrochemically active area of the membrane-seal assembly. The inlet and outlet regions 142, 144 of the flow field 140 are typically directly adjacent the non-ion- conducting border region of the membrane-seal assembly. Each of the inlet region 142, the main region 146 and the outlet region 144 comprises a plurality of channels for providing the least one pathway through the flow field 140. The plurality of channels comprises a series of alternating grooves 148 and ridges 150 (sometimes referred to as lands’). The number and arrangement of channels in the flow field is not particularly limited. Figure 3 shows a cross- sectional representation of an exemplary plurality of channels 300 comprising a series of alternating grooves 148 and ridges 150.

The first side 102 can further comprises a sub-gasket recess 160 for receiving a subgasket. The sub-gasket can help to provide a suitable seal between the first side 102 of the bipolar plate 100 and a membrane-seal assembly.

The second inlet port 120 is in fluid communication with the second outlet port 125 via a flow field 140’ on the second side 104 of the bipolar plate 100 (Figure 2). The second inlet port 120 can supply a reactant to the flow field 140’. The second outlet port 125 can transport exhaust material away from the flow field 140’. The second inlet port 120 may be an oxidant inlet port, for example an air or oxygen gas inlet port.

The flow field 140’ comprises an inlet region 142’, an outlet region 144’ and a main region 146’ between the inlet and outlet regions. Each of the inlet region 142’, the main region 146’ and the outlet region 144’ comprises a plurality of channels for providing the least one pathway through the flow field 140’. The plurality of channels comprises a series of alternating grooves 148’ and ridges 150’. The number and arrangement of channels in the flow field is not particularly limited.

The second side 104 can further comprises a sub-gasket recess 160’ for receiving a sub-gasket. The sub-gasket can help to provide a suitable seal between the second side 104 of the bipolar plate 100 and another membrane-seal assembly. The third inlet port 130 and the third outlet port 135 are optional. Where present, the third inlet port 130 is in fluid communication with the third outlet port 135 via internal channels (not shown). The internal channels can be disposed between the first side 102 and the second side 104. Preferably, the third inlet port 130 is a coolant inlet port for supplying a coolant to the internal channels, which can serve as cooling channels.

For the sake of brevity, the following description is made with reference to the first side 102 of the bipolar plate only. However, the same features can independently also be present on the second side 104 of the bipolar plate.

Figure 4 shows a further example of a bipolar plate 400 suitable for use with a membrane-seal assembly of the invention. Optionally, at least one (and preferably both) of the inlet region 142 and/or the outlet region 144 of the flow field 140 comprises a recessed portion 170. The recessed portion 170 is the area bounded by the dashed line in Figure 4. The recessed portion 170 extends laterally across the pathway provided by the plurality of channels of the inlet region 142 and/or outlet region 144.

Figure 5 shows a cross-sectional schematic representation of a recessed portion 170. The recessed portion 170 comprises a plurality of channels for providing the at least one pathway through the flow field 140. The plurality of channels comprises a series of alternating grooves 148 and ridges 152. The bottom of the grooves 148 are typically in the same plane (i.e. a bottom of groove plane, P1). Typically, the (not recessed) main region 146 comprises lands 150 forming a main lands plane, P2. Typically, the recessed portion 170 comprises lands 152 forming a recessed lands plane, P3. The recessed lands plane P3 is positioned between the bottom of groove plane P1 and the main lands plane P2. The (through-plane) distance between the lands of the main portion 150 (i.e. main lands plane P2) and the lands of the recessed portion 152 (i.e. recessed lands plane P3) defines a recess depth, d. That is, the recessed portion 170 is recessed from the main region 146 by the recess depth, d. The recess depth can be in the range of and including 0 mm to about 1 mm. A recess depth in this range can help to maintain an acceptable fluid flow rate through the channels with an acceptable pressure drop. A too large recess depth can compromise fluid flow through the channels and result in a large pressure drop.

Membrane-seal assembly

Figures 6 and 7 show an exemplary embodiment of a membrane-seal assembly 600 of the present invention. The membrane-seal assembly 600 has a first face 602 (shown in Figure 6) and a second face 604 (shown in Figure 7).

The membrane-seal assembly 600 comprises an inner region 606 and a border region 608 surrounding the inner region 606. The inner region refers to a planar area in the xy-direction (in-plane direction) and which extends through the thickness of the membrane-seal assembly in a through-plane direction (z-di recti on).

The border region refers to a planar area in the xy-direction (in-plane direction) and which extends through the thickness of the membrane-seal assembly in a through-plane direction (z-direction), the border region extends around the periphery of the inner region.

The inner region 606 comprises an ion-conducting membrane. The border region 608 comprises a seal component area 640 for sealing the ion-conducting membrane. The seal component area 640 comprises a seal component. The seal component is ionically non- conductive. The border region 608 further comprises at least one stiffening area for providing an area of greater stiffness in the border region, for example, compared to the seal component area. The stiffening area suitably comprises a stiffening component. The stiffening area has a (through-plane) stiffness greater than other areas of the border region, such as the seal component area 640.

Each or both of the first and second faces 602 and 604 can independently comprise one or more stiffening areas. For example, at least one stiffening area can be disposed on the first face 602, the second face 604 or both the first and second faces 602 and 604. The stiffening area is positioned to extend at least partially (and preferably fully) across an inlet region and/or an outlet region of a flow field of a flow field plate (e.g. bipolar plate) when in use (e.g. transversely or laterally across the at least one pathway). For example, the stiffening area 650 (on the first face 602) is positioned to extend across the inlet region 142 of the flow field 140 of bipolar plate 100. The stiffening area 652 (on the first face 602) is positioned to extend across the outlet region 144 of the flow field 140 of bipolar plate 100. Similarly, the stiffening area 650’ (on the second face 604) is positioned to extend across the inlet region 142’ of the flow field 140’ of bipolar plate 100. The stiffening area 652’ (on the second face 604) is positioned to extend across the outlet region 144’ of the flow field 140’ of bipolar plate 100. In these embodiments, the stiffening area 650, 652, 650’ and 652’ are in the form of a band or patch. The membrane-seal assembly of the invention can comprise any combination of stiffening areas 650, 652, 650’ and 652’.

Providing a stiffening area in the border region of a membrane-seal assembly, which is positioned to at least partially extend across the at least one pathway of a flow field when in use, can suppress tenting effects. Additionally, incorporating a stiffening area as an integral part of the membrane-seal assembly enables the membrane-seal assembly of the present invention to be used with existing, commercially available flow field plates without the need to manufacture and use additional bridging member parts. This simplifies the manufacturing process and can reduce manufacturing cost. Consequently, methods of manufacturing membrane-seal assemblies of the present invention are also better suited for industrial scale manufacturing.

The membrane-seal assembly can further comprise a first catalyst layer on the first face of the inner region 606 (e.g. on a first face of the ion-conducting membrane). The membrane-seal assembly can further comprise a second catalyst layer on the second face of the inner region 606 (e.g. on a second face of the ion-conducting membrane). The membraneseal assembly can further comprise a catalyst layer on the first and second faces of the inner region 606 (e.g. on a first and second face of the ion-conducting membrane). The catalyst layer on the first and/or second face(s) can overlap with or extend into the border region 608. The membrane-seal assembly can be a catalysed membrane-seal assembly.

The membrane-seal assembly can further comprise a gas diffusion layer (or porous transport layer) on the catalyst layer of the first and/or second face(s). The gas diffusion layer(s) (or porous transport layer(s)) can overlap with the border region 608.

The membrane-seal assembly (or, as the case may be, the membrane assembly) is preferably a roll-good product. As such, the membrane-seal assembly (or membrane assembly) can be wound into a roll suitably for storage and transport.

Inner region

The inner region is suitably defined by an inner perimeter of the seal component and optionally the stiffening component. The inner region can substantially align with or overlay the main region of the flow field of the flow field plate, when in use. Typically, the inner region is an ionically conductive area of the membrane-seal assembly, for example a proton conductive region. The inner region comprises an ion-conducting membrane. The inner region can further comprise a planar reinforcing component.

Ion-conducting membrane

The ion-conducting membrane comprises an ion-conducting polymer. The ionconducting polymer can be a proton conducting polymer or an anion conducting polymer. Preferably, the ion-conducting polymer is a proton-conducting polymer. Preferred ionconducting polymers are partially- or fully-fluorinated sulphonic acid polymers e.g. perfluorinated sulphonic acid polymers. For example, the ion-conducting polymer may be based on a perfluorinated sulphonic acid material such as Nation® (Chemours Company), Aguivion® (Solvay Specialty Polymers), Flemion® (Asahi Glass Group) and Aciplex® (Asahi Kasei Chemicals Corp.). Alternatively, the ion-conducting materials may be based on a sulphonated hydrocarbon polymer, such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, JSR Corporation, Toyobo Corporation, and others. The ion-conducting membrane can extend into the border region. For example, the border region can comprise an inner border region (or overlap region) and an outer border region surrounding the inner border region. The inner border region can comprise the ionconducting membrane and the seal component. Suitably, the inner border region does not comprise the stiffening area. The outer border region is devoid of the ion-conducting membrane and suitably comprises the seal component and the stiffening area.

The ion-conducting membrane can comprise a planar reinforcing component. The planar reinforcing component can be embedded within the ion-conducting membrane. Preferably, the planar reinforcing component is porous (i.e. comprises pores). The reinforcing component can confer mechanical strength to the ion-conducting membrane. The reinforcing component can contain a porous reinforcing material, such as an expanded polytetrafluoroethylene (ePTFE) material or a nanofibre network, such as a network comprising polybenzimidazole (PBI) fibres or glass fibres. The planar reinforcing component can extend into the border region.

Catalyst layers

A first catalyst layer can be provided on one face (e.g. the first face) of the ionconducting membrane. A second catalyst layer can be provided on the other face (e.g. second face) of the ion-conducting membrane. The first catalyst layer can be an anode catalyst layer. The second catalyst layer can be a cathode catalyst layer. For example, the inner region can comprise the first catalyst layer (e.g. anode catalyst layer) on the first face of the ionconducting membrane. The inner region can comprise the second catalyst layer (e.g. cathode catalyst layer) on the second face of the ion-conducting membrane.

The first and second catalyst layers comprise an electrocatalyst. The electrocatalyst of the first and second catalyst layers is preferably different. The electrocatalyst can be unsupported metal particles (e.g. finely divided unsupported metal powder) or may be a supported electrocatalyst wherein metal particles (e.g. nanoparticles) are dispersed on an electrically conductive support, such as an electrically conducting particulate carbon support.

The metal particles of the electrocatalyst are 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. Preferably, the metal in the metal particles of the electrocatalyst is a platinum group metal or an alloy of a platinum group metal. The most preferred electrocatalyst metal is platinum, which may be alloyed with other precious metals or base metals. 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), silver or gold. Preferred base metals are copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium and tin.

Gas diffusion layer

The inner region can further comprise a gas diffusion layer disposed over the catalyst layer. For example, a first gas diffusion layer can be disposed adjacent to the first catalyst layer. A second gas diffusion layer can be disposed adjacent to the second catalyst layer.

The gas diffusion layer can overlap with a part of the border region.

For water electrolyser applications, the inner region can further comprise a porous transport layer disposed over the catalyst layer. For example, a gas diffusion layer can be disposed adjacent to the first catalyst layer and a porous transport layer can be disposed adjacent to the second catalyst layer. The porous transport layer can overlap with a part of the border region.

Border region

The border region surrounds the inner region. The border region suitably comprises a seal component area and a stiffening area. The seal component area comprises a seal component. The stiffening area suitably comprises a stiffening component. The inner perimeter of the seal component, and optionally the at least one stiffening component, can define the inner region. The border region can surround the main region of the flow field of the flow field plate, when in use. The border region can align with the inlet region and/or outlet region of the flow field of the flow field plate, when in use. The border region suitably covers the inlet region and outlet region of the flow field of the flow field plate, when in use. The border region is suitably ionically non-conducting.

The ion-conducting membrane can extend at least partially into the border region, for example, under the seal component or between two seal components disposed on either face of the ion-conducting membrane. In such embodiments, the border region can comprise an inner border region (or overlap region) and an outer border region surrounding the inner border region. The inner border region can comprise the ion-conducting membrane and the seal component. Preferably, the inner border region does not comprise the stiffening area. The outer border region is devoid of the ion-conducting membrane and preferably comprises the seal component and the stiffening area. Preferably, the seal component area in the outer border region is substantially planar. Preferably, the seal component area in the outer border region has a substantially uniform thickness. The border region (and preferably an outer border region) can comprise one or more porting apertures positioned to be complementary to the inlet port (i.e. an inlet port aperture) and outlet ports (i.e. an outlet port aperture) of a flow field plate. For example, apertures 610, 620 and 630 can be positioned so as to align with inlet ports 110, 120 and 130 respectively, when used with bipolar plate 100. Similarly, apertures 615, 625, and 635 can be positioned so as to align with outlet ports 115, 125 and 135 respectively, when used with bipolar plate 100.

Seal component area

The seal component area suitably forms a frame around the inner region. The seal component area suitably forms a frame around the ion-conducting membrane of the inner region. The seal component can be positioned on a peripheral portion of the ion-conducting membrane, such that the ion-conducting membrane overlaps with the seal component. In other embodiments, the seal component can be positioned around the edge of the ionconducting membrane without an overlap. Where a catalyst layer is present on at least one face of the ion-conducting membrane, the seal component can overlap with the catalyst layer. In other embodiments, the seal component and the catalyst layer do not overlap.

The seal component comprises a seal material. The seal material is suitably a polymeric material, and preferably an elastomer. The seal material can be selected from the group of: silicones, fluorosilicones, polyurethanes, co-polyamides, polyazoles, epoxies and fluoroacrylates. Specific examples of suitable seal materials include: polyvinylidenefluoride (PVDF), polyetherimide (PEI), polyimide (PI), polyethersulphone (PES), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), Viton®, polyethylene oxide (PEO), polyphenylene ether (PPE), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyacrylonitrile (PAN), poly(p-phenylene sulphide) (PPS), polybenzimidazole (PBI), polyolefins and silicones.

The seal component suitably has a Young’s modulus of less than 3 GPa, preferably less than 2.5 GPa, and more preferably less than 2 GPa. The seal component suitably has a Young’s modulus of at least 200 MPa. Where the Young’s modulus is too high, the seal component does not form a suitable fluid-tight seal. The Young’s modulus can be obtained using the measurement defined in ASTM E111 - 17 using a Houndsfield tensiometer.

Preferably, the membrane-seal assembly comprises a seal component on each of its first and second faces.

The seal component can be configured to provide a seal around the inlet port(s) and/or outlet port(s) of the flow field plate, when in use. For example, the edges of the porting apertures preferably comprise the seal component.

Stiffening area The stiffening area provides a region of higher stiffness in the border region, for example, when compared to the seal component area. Stiffness (N/m) can be calculated as the quotient of force applied and the displacement produced in the direction of the force. Stiffness can be determined using a standard test method as defined in ASTM D1043-16.

The stiffening area is positioned in the border region so as to extend at least partially (and preferably fully) across the inlet and/or outlet region(s) of the flow field of the flow field plate, when assembled with the flow field plate (i.e. when in use). The stiffening area is suitably positioned to extend across the at least one pathway (e.g. transversely or laterally across the plurality of channels for providing the at least one pathway) in the inlet and/or outlet region(s) of the flow field, when in use. The stiffening area can be positioned so as to be adjacent at least one porting aperture present in the border region. Preferably, the stiffening area is adjacent and spaced apart from an edge of at least one porting aperture present in the border region such that the edge of the porting aperture is composed of the seal material of the seal component area. Preferably, the stiffening area is disposed adjacent at least one porting aperture present in the border region and between the at least one porting aperture and the inner region, preferably in the form of a patch or band. Preferably, the stiffening area is adjacent the at least one porting aperture and extends across a full dimension (e.g. width or length) of the porting aperture.

The additional stiffness in this region can prevent the border region from deforming into the plurality of channels in the flow field. That is, tenting can be suppressed. At the same time, the bulk properties of the border region (e.g. the seal component) are not materially affected so that an adequate fluid-tight seal may still be provided.

The stiffening area suitably comprises a stiffening component. The stiffening component provides increased stiffness to the border region in the stiffening area. Preferably, the stiffening component is exposed at a surface of the stiffening area. The stiffening component can directly contact the flow field plate, when assembled with the flow field plate (i.e. when in use).

The stiffening area can further comprise the seal component. The stiffening component can be disposed on the seal component, for example, as an additional component to the seal component.

The stiffening area can have a (through-plane) cross-sectional thickness greater than a (through-plane) cross-sectional thickness of the seal component area. The greater thickness of the stiffening area can provide an area of greater stiffness or rigidity compared to the seal component area. In this embodiment, the stiffening component and the seal component can be made of the same material, for example, as a single piece. Alternatively, the stiffening component and the seal component can be made of different materials. For example, the stiffening component can be made from an inherently stiffer or harder material than the seal component.

The stiffening component can be disposed in the same plane as the seal component. For example, the stiffening component can be embedded within the seal component.

The seal component can surround (in the same plane) the stiffening component.

The stiffening area can have a (through-plane) cross-sectional thickness substantially the same as a (through-plane) cross-sectional thickness of the seal component area. The stiffening area can be flush with the seal component area (i.e. have the same cross-sectional thickness at the boundary between the seal component area and the stiffening area).

Providing a stiffening component as an additional or integral part of the border region of the membrane electrode assembly can reduce the complexity of building a fuel cell stack and increases versatility in manufacturing design, which enables a faster and more cost efficient manufacturing process.

The stiffening component is suitably ionically non-conductive. The stiffening component is not the ion-conducting membrane. The stiffening component is not a sub-gasket for providing a fluid tight seal between the membrane-seal assembly and the flow field plate.

Preferably, the stiffening component and the seal material of the seal component are suitably different in the sense that they have different chemical compositions. Put another way, preferably they are different chemical substances. The stiffening component is preferably made from a polymeric material. A suitable polymeric material can be selected from the group of: polyaryletherketones (PAEK), polyesters, polyazoles, silicones, fluorosilicones, polyurethanes, co-polyamides, epoxies and fluoroacrylates. Specific examples of suitable materials for the stiffening component include: polyether ether ketone (PEEK), polyethylene naphthalate (PEN), poly(ethylene terephthalate) (PET), polyvinylidenefluoride (PVDF), polyetherimide (PEI), polyimide (PI), polyethersulphone (PES), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), Viton®, polyethylene oxide (PEO), polyphenylene ether (PPE), polyacrylonitrile (PAN), poly(p-phenylene sulphide) (PPS), polybenzimidazole (PBI), polyolefins and silicones.

Preferably, the stiffening component is formable by curing a printable stiffening component precursor material.

Preferably, the stiffening component is made of a stiffer material than the seal component. The stiffening component suitably has a Young’s modulus greater than the Young’s modulus of the seal component.

Stiffness can be measured by a standard test method defined in ASTM D1043-16.

Where the flow field plate is of the type comprising a recessed portion, the stiffening component can be configured to be receivable by the recessed portion of the inlet region and/or the outlet region of the flow field of the flow field plate. For example, the stiffening component 650 can be configured to be complementary to the recessed portion 170 of the inlet region 142 (Figures 4 and 6). Independently, the stiffening component 652 can be configured to be complementary to the recessed portion 170 of the outlet region 144. As a further example, where the flow field plate is of the type in which each of the inlet region and the outlet region comprise a recessed portion which extends laterally across the pathway provided by the plurality of channels, the at least one stiffening component can comprise a (first) stiffening component positioned to be receivable by the recessed portion of the inlet region and a (second) stiffening component positioned to be receivable by the recessed portion of the outlet region.

In particular where the flow field plate is of the type comprising a recessed portion 170, the stiffening component can protrude from the layer of seal component (in the through-plane (z) direction). Figure 8 shows a schematic side view of a membrane-seal assembly 600, in which the stiffening components 650, 652, 650’, and 652’ protrude from the seal component 640 in the through-plane direction. The stiffening components 650, 652, 650’, and 652’ are in the form of an elongate band or patch. The stiffening component can protrude from the seal component by a distance complementary to the distance by which the recessed portion is recessed from the main region. That is, the stiffening component can protrude from the seal component by a distance substantially the same as the recess depth, d. In some embodiments, the stiffening component protrudes from the seal component by more than the recess depth, d. In such embodiments, the stiffening component can be compressed to form a fluid tight seal. The stiffening component can protrude from the seal component so as to protrude beyond the gas diffusion layer (or porous transport layer) (if present).

The stiffening component can protrude from the seal component by a distance in the range of and including 0 mm to 3 mm, preferably 10 pm to 2 mm, and most preferably 100 pm to 1 mm. A larger protrusion distance can provide a more rigid stiffening component, and hence further reduce the prevalence of deformation of the seal component into the channels of the flow field, but can compromise fluid flow rates.

Preferably, the membrane-seal assembly comprises at least two stiffening areas. Each stiffening area can comprise a stiffening component. For example, the stiffening components can be disposed on a first face and/or a second face of the membrane-seal assembly in any combination. The at least one stiffening area can comprise two or more stiffening areas disposed on the first face. For example, (one face of) the membrane-seal assembly can comprise a first stiffening area comprising a stiffening component positioned to extend at least partially across the inlet region of the flow field of the flow field plate; and a second stiffening area comprising a stiffening component positioned to extend at least partially across the outlet region of the flow field of the flow field plate. As a further example, when the flow field plate is of the type comprising a flow field comprising a recessed inlet region and a recessed outlet region, (one face of) the membrane-seal assembly can comprise a first stiffening area comprising a stiffening component configured to be receivable by the recess of the inlet region, and a second stiffening area comprising a stiffening component configured to be receivable by the recess of the outlet region.

The at least one stiffening area can comprise a first stiffening area comprising a stiffening component disposed on the first face and a further stiffening area comprising a stiffening component disposed on the second face. For example, in some preferred embodiments, the membrane-seal assembly comprises a third stiffening area, and optionally a fourth stiffening area, disposed in the border region on the opposite face of the membraneseal assembly to the first and (if present) second stiffening areas. In this embodiment, the third and fourth stiffening areas each comprise a stiffening component positioned to extend at least partially across an inlet region and an outlet region respectively of flow field of a second flow field plate.

The membrane-seal assembly can comprise any combination of first, second, third and fourth stiffening areas comprising stiffening components positioned to extend across the inlet region and/or outlet region of the flow field of bipolar plates disposed either face of the membrane-seal assembly.

In some embodiments, the ion-conducting membrane extends into the border region and the stiffening component is disposed directly onto the ion-conducting membrane (i.e. without a seal component being present). The stiffening component provides an area of higher stiffness in the border region compared to other areas of the ion-conducting membrane in the border region. A seal component can suitably be added in subsequent manufacturing steps.

Method of manufacturing

The invention provides a method of preparing a membrane-seal assembly. The method comprises the steps of:

(a) providing a seal component on or around an ion-conducting membrane so as to define an inner region comprising the ion-conducting membrane and a border region surrounding the inner region, the border region comprising the seal component area, wherein the seal component area comprises the seal component and the seal component is ionically non-conductive;

In some embodiments, step (a) is performed before step (b). In other embodiments, step (a) is performed after step (b) or (c). The stiffening component precursor material is deposited such that it is positioned to extend at least partially across the inlet region and/or the outlet region of a flow field of a flow field plate, when in use. The stiffening area has a stiffness greater than the stiffness of the seal component area.

Step (a)

The step of providing a seal component can comprise the sub-steps of: depositing a seal component precursor material on or around the ion-conducting membrane; and curing the seal component precursor material.

The seal component precursor material can be deposited by printing techniques (e.g. digital printing), such as inkjet printing, disperse jet printing, screen printing, pad coating, aerosol jet printing, and gravure coating.

Suitably, the seal component precursor is a curable material. The step of curing the seal component precursor material can comprise a photo-curing treatment (e.g. exposing the seal component precursor material to visible or UV-light) or a thermal curing treatment.

Alternatively, the step of providing a seal component can comprise positioning a preformed seal component (e.g. as a frame) on and around the ion-conducting membrane.

The ion-conducting membrane can comprise a catalyst layer on one or both of its faces. The ion-conducting membrane can comprise a gas diffusion layer (or porous transport layer) on one or both of its faces. In some embodiments, a catalyst layer can be added after step (a), (b) or (c). In some embodiments, a gas diffusion layer (or porous transport layer) can be added after adding a catalyst layer.

Steps (b) and (c)

Step (b) can comprise printing (e.g. digitally printing) the stiffening component precursor material onto the border region. Suitable printing techniques include: inkjet printing, disperse jet printing, screen printing, pad coating, aerosol jet printing, and gravure coating.

Suitably, the stiffening component precursor is a curable material. The step of curing the stiffening component precursor material can comprise a photo-curing treatment (e.g. exposing the stiffening component precursor material to visible or UV-light) or a thermal curing treatment.

The stiffening component precursor material can be deposited onto the border region such that it is flush with the seal component. Alternatively, the stiffening component precursor material can be deposited onto the border region such that it protrudes from the seal component in the through-plane (z) direction. For example, the stiffening component precursor material can be deposited onto the seal component. In a further embodiment, the seal component can cover the stiffening component.

Where the method comprises depositing a seal component precursor material, the seal component precursor material and the stiffening component precursor material can be cured simultaneously.

Claims

1. A membrane-seal assembly suitable for use with a flow field plate of the type comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports, the flow field comprising an inlet region, an outlet region and a main region between the inlet and outlet regions, the membrane-seal assembly comprising: an inner region comprising an ion-conducting membrane; and a border region surrounding the inner region, the border region comprising a seal component area and at least one stiffening area, wherein the seal component area comprises a seal component which is ionically non-conductive, and wherein the stiffening area comprises a stiffening component; wherein the at least one stiffening area is positioned to extend at least partially across the inlet region and/or the outlet region of the flow field of the flow field plate when in use, and wherein the stiffening area has a stiffness greater than the stiffness of the seal component area.

2. A membrane-seal assembly according to claim 1, wherein the stiffening area comprises the seal component.

3. A membrane-seal assembly according to claim 2, wherein the stiffening component is positioned on the seal component.

4. A membrane-seal assembly according to any previous claim, wherein the at least one stiffening area has a cross-sectional thickness greater than a cross-sectional thickness of the seal component area.

5. A membrane-seal assembly according to claim 4, wherein the stiffening component and the seal component are made of the same material.

6. A membrane-seal assembly according to any of claims 1 to 4, wherein the stiffening component and the seal component are made of different materials.

7. A membrane-seal assembly according to any of claims 1 to 3, or 6, wherein the stiffening area has a cross-sectional thickness substantially the same as a cross-sectional thickness of the seal component area.

8. A membrane-seal assembly according to any of claims 1 to 3, 6 or 7, wherein the at least one stiffening area is flush with the seal component area.

9. A membrane-seal assembly according to any previous claim, wherein the seal component of the seal component area and the stiffening component are positioned in the same plane.

10. A membrane-seal assembly according to any previous claim, wherein the stiffening component comprises a polymeric material.

11. A membrane-seal assembly according to claim 10, wherein the polymeric material of the stiffening component is polyaryletherketones (PAEK), polyesters, polyazoles, silicones, fluorosilicones, polyurethanes, co-polyamides, epoxies and fluoroacrylates.

12. A membrane-seal assembly according to any previous claim, wherein the stiffening component has a Shore A hardness greater than the Shore A hardness of the seal component.

13. A membrane-seal assembly according to any previous claim, wherein the stiffening component has a Young’s modulus less than the Young’s modulus of the seal component.

14. A membrane-seal assembly according to any previous claim, wherein the at least one stiffening area is positioned to extend fully across the inlet region and/or outlet region of the flow field of the flow field plate when in use.

15. A membrane-seal assembly according to any previous claim, wherein the border region further comprises at least one porting aperture, wherein at least a part of the at least one stiffening area is positioned between the at least one porting aperture and the inner region so that the at least one stiffening area is positioned to extend at least partially across the inlet region and/or the outlet region of the flow field of the flow field plate when in use.

16. A membrane-seal assembly according to claim 15, wherein the stiffening area is positioned between the at least one porting aperture and the inner region so as to extend at least partially, and preferably fully, across a cross-sectional dimension of the porting aperture.

17. A membrane-seal assembly according to any previous claim, further comprising a first face and a second face, wherein the at least one stiffening area comprises two or more stiffening areas disposed on the first face and/or the second face.

18. A membrane-seal assembly according to claim 17, wherein the first face comprises two or more stiffening areas.

19. A membrane-seal assembly according to claim 17 or 18, wherein the at least one stiffening area comprises a stiffening area disposed on the first face and a stiffening area disposed on the second face.

20. A membrane-seal assembly according to any previous claim, wherein the flow field plate is of the type in which the inlet and/or outlet region independently comprises a recessed portion extending at least partially across the pathway, and wherein the stiffening component is positioned to be receivable by the recessed portion of the inlet and/or outlet region of the flow field plate.

21. A membrane-seal assembly according to any previous claim, wherein the ionconducting membrane extends into the border region.

22. A membrane-seal assembly according to any previous claim, wherein the ionconducting membrane comprises a planar reinforcing component.

23. A membrane-seal assembly according to any previous claim, wherein the inner region further comprises at least one catalyst layer on the ion-conducting membrane.

24. A membrane-seal assembly according to any previous claim, wherein the membrane-seal assembly is a roll-good product.

25. A membrane-seal assembly according to any previous claim in combination with a flow field plate comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports, the flow field comprising an inlet region, an outlet region and a main region between the inlet and outlet regions.

26. A fuel cell comprising the membrane-seal assembly according to any previous claim.

27. An electrolyser comprising the membrane-seal assembly according to any of claims 1 to 25.

28. A method of manufacturing a membrane-seal assembly according to claim 1 , the method comprising the steps of:

(a) providing a seal component on or around an ion-conducting membrane so as to define an inner region comprising the ion-conducting membrane and a border region surrounding the inner region, the border region comprising a seal component area, wherein the seal component area comprises the seal component which is ionically non-conductive;

29. A method according to claim 28, wherein step (b) comprises depositing the stiffening component precursor material onto the seal component.

30. A membrane assembly suitable for use with a flow field plate of the type comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports, the flow field comprising an inlet region, an outlet region and a main region between the inlet and outlet regions, the membrane assembly comprising an ion-conducting membrane and a stiffening component, wherein the ion-conducting membrane comprises: an inner region for aligning with the main region of the flow field when in use; and a border region surrounding the inner region and for aligning with the inlet region and/or outlet region of the flow field when in use, wherein the border region comprises at least one stiffening area comprising the stiffening component, wherein the at least one stiffening component is positioned on the ion-conducting membrane so as to extend at least partially across the inlet region and/or the outlet region of the flow field of the flow field plate when in use, and wherein the stiffening area has a stiffness greater than the stiffness of other areas of the ion-conducting membrane in the border region.

31. A membrane assembly according to claim 30 in combination with a flow field plate of the type comprising an inlet port, an outlet port, and a flow field for providing at least one pathway between the inlet and outlet ports, the flow field comprising an inlet region, an outlet region and a main region between the inlet and outlet regions.