Gasket assembly

Abstract

According to a first aspect of the disclosure, there is provided a membrane assembly for use in an electrochemical stack, the membrane assembly having an anode side and a cathode side, and comprising: a proton exchange membrane; a first gasket arranged on the cathode side of the proton exchange membrane; and a second gasket arranged on the anode side of the proton exchange membrane; wherein the first and second gaskets are arranged such that they sandwich at least a portion of a periphery of the proton exchange membrane; and wherein the first gasket extends inwards from the periphery of the proton exchange membrane further than the second gasket, thereby covering more of the proton exchange membrane than the second gasket.

Description

[0001] Gasket assembly

[0002] Field of the invention

[0003] The present disclosure relates to a bonded membrane-gasket assembly for use in an electrochemical stack. More specifically, it relates to a membrane for use in an electrolysis cell, the membrane having a gasket bonded around the periphery of the membrane, thereby to provide enhanced structural support and protection to the periphery of the membrane.

[0004] Background

[0005] Electrochemical stacks may be used in various applications, including in electrolysers and in fuel cells. Electrochemical stacks typically comprise multiple individual cells arranged in series, thereby increasing gas production capacity. Electrolysers typically comprise multiple electrolysis cells arranged in series. Electrolysis cells are devices that use electrical energy to drive the splitting of water into hydrogen and oxygen. These devices are fundamental to various industrial processes and are increasingly important in the production of green hydrogen, a clean fuel that can help reduce carbon emissions and produce oxygen otherwise depleted by combustion processes. A critical component of any electrochemical stack, including fuel cells and electrolysers, is the membrane. The membrane serves as the electrolyte that facilitates the transport of ions between the anode and cathode, while preventing the passage of electrons and the mixing of gases.

[0006] Traditional electrochemical stack membranes are prone to several issues during operation. These issues include mechanical creep, deformation, and chemical degradation, particularly at the periphery of the membrane. Mechanical creep and deformation can lead to a loss of structural integrity, while chemical degradation can result in reduced performance and lifespan of the fuel cell. It is important to understand the mechanisms of degradation involved (both mechanical and electrochemical), which can combine in certain regions. There is a need, therefore, to provide an improved design for the membrane in order to mitigate these issues. As discussed in more detail below, the present disclosure provides a solution that inhibits certain degradation mechanisms.

[0007] Summary of the invention

[0008] According to a first aspect of the disclosure, there is provided a membrane assembly for use in an electrochemical stack, the membrane assembly having an anode side and a cathode side, and comprising: a proton exchange membrane; a first gasket arranged on the cathode side of the proton exchange membrane; and a second gasket arranged on the anode side of the proton exchange membrane; wherein the first and second gaskets are arranged such that they sandwich at least a portion of a periphery of the proton exchange membrane; and wherein the first gasket extends inwards from the periphery of the proton exchange membrane further than the second gasket, thereby covering more of the proton exchange membrane than the second gasket.

[0009] Including first and second gaskets in this manner provides the edge of the proton exchange membrane (PEM) and the peripheral region of the PEM with enhanced structural support, thereby reducing creep and mechanical deformation of the PEM. The first gasket extending further inwards from the periphery of the PEM allows for the cathode side of the PEM to be provided with enhanced protection from chemical degradation, in use. The anode side of the PEM is not as susceptible to chemical degradation, and so the second gasket extending less improves thermal dissipation on the anode side of the PEM, without increasing the overall chemical degradation of the PEM. Arranging the gaskets in the manner thereby improves the lifetime and durability of the PEM, and thus the overall membrane assembly.

[0010] In an embodiment, there is provided a membrane assembly wherein the proton exchange membrane is bonded to at least one of the first gasket and the second gasket. Optionally, the proton exchange membrane may be bonded to each of the first gasket and the second gasket. Bonding the gaskets to the PEM improves the structural integrity of the membrane assembly, and allows for the gaskets to provide the membrane assembly with improved mechanical properties, such as creep and deformation resistance. The durability and lifetime of the membrane assembly is thereby improved.

[0011] In an embodiment, there is provided a membrane assembly wherein the first gasket at least partially overlaps the entire periphery of the cathode side of the proton exchange membrane. The first gasket overlapping the entire periphery of the cathode side of the membrane ensures complete coverage of the periphery and edge of the membrane, limiting access of electrons, inhibiting degradation reactions, and minimizing exposure to harsh operational environments and potential damage. Further, by overlapping the entire periphery of the membrane, the beneficial improvements provided by the first gasket are extended around the entire periphery of the membrane. In an embodiment, there is provided a membrane assembly wherein the second gasket at least partially overlaps the entire periphery of the anode side of the proton exchange membrane. The second gasket overlapping the entire periphery of the anode side of the membrane ensures complete coverage of the periphery and edge of the membrane, significantly improving support in resisting pressure generated during operation, and minimizing exposure to harsh operational environments and potential damage. Further, by overlapping the entire periphery of the membrane, the beneficial improvements provided by the second gasket are extended around the entire periphery of the membrane.

[0012] In an embodiment, there is provided a membrane assembly wherein the cathode side of the proton exchange membrane is at least partially coated with a catalyst. Optionally, the catalyst comprises platinum and / or a platinum containing material. Coating the cathode side with a catalyst improves the efficiency of electrochemical reactions, leading to better performance of the electrochemical stack. Using platinum and / or a platinum containing material as the catalyst on the cathode side ensures high catalytic activity, enhancing the efficiency and output of the electrochemical reactions.

[0013] In an embodiment, there is provided a membrane assembly wherein the anode side of the proton exchange membrane is at least partially coated with a catalyst. Optionally, the catalyst comprises high surface area iridium based catalysts. Coating the anode side with a catalyst boosts the electrochemical reactions on the anode side, contributing to the overall efficiency of the stack. Using iridium and / or ruthenium as catalysts on the anode side provides high catalytic activity, improving the efficiency and output of the electrochemical reactions.

[0014] In an embodiment, there is provided a membrane assembly further comprising a cathode cell plate and an anode cell plate. Including cathode and anode cell plates adds mechanical stability to the assembly, reducing the risk of component misalignment or damage during operation.

[0015] Optionally, the cathode cell plate and the anode cell plate sandwich at least a portion of: the first gasket, the second gasket, and the membrane. The cell plates sandwiching the gaskets and membrane ensure that the components are secured in the assembly, maintaining the alignment and integrity of the components.

[0016] Optionally, the cathode cell plate and the anode cell plate 109 are arranged to apply a compressive force to the portion sandwiched therebetween of: the first gasket, the second gasket, and the membrane. Applying compressive force via the cell plates enhances the sealing and mechanical stability of the assembly, preventing leaks and ensuring consistent performance. In particular, a reduction of the projected area applying the compressive sealing force optimises gasket sealing stress to levels conducive to pressure retention with an appropriate factor of safety. Further, the load path is especially directed to areas most relevant for sealing.

[0017] In an embodiment, there is provided a membrane assembly wherein the first gasket and the second gasket each comprise a material that is substantially gas impermeable. Using gas impermeable materials for the gaskets prevents gas crossover, which is crucial for maintaining the efficiency and safety of the electrochemical stack. Furthermore, gas-impermeability ensures that the gaskets are able to protect the periphery and edge of the PEM from exposure to reactants, thereby protecting these regions from side reaction chemical degradation.

[0018] In an embodiment, there is provided a membrane assembly wherein the first gasket and the second gasket each comprise a material that is substantially electrically insulating. The electronic insulating properties offered by the gaskets material inhibit the interaction of electrons with the periphery of the membrane, thereby preventing electrochemically induced degradation.

[0019] In an embodiment, there is provided a membrane assembly wherein the first gasket and the second gasket each have a thickness of between 0.025 mm and 0.125 mm. Gaskets with this minimum thickness provide the required protection and enhancement of the mechanical properties of the membrane assembly. Gaskets with a thickness greater than this range may cause problems with assembly and operation of an electrochemical cell incorporating the membrane assembly.

[0020] In an embodiment, there is provided a membrane assembly wherein the first and / or second gasket comprise one or more materials selected from: polyethylene naphthalate, polyethylenimine, linear low-density polyethylene, polyphenylene sulphide. These materials are all gas-impermeable, and provide adequate protection from degradation, and improvement to the mechanical properties of the membrane assembly.

[0021] Brief description of the drawings

[0022] There now follows a brief description of embodiments of the present disclosure, by way of non-limiting examples, with reference made to the following figures in which: Figure 1 illustrates a cross-section through a membrane assembly according to the present disclosure; and

[0023] Figure 2 illustrates a cross section through an electrolysis cell comprising a membrane assembly according to the present disclosure.

[0024] Detailed description

[0025] In order to address the challenges discussed previously in relation to existing membranes, the present invention provides a novel membrane assembly design comprising gaskets bonded around the periphery of the membrane. As discussed in more detail below, the gaskets provide enhanced protection and support to the membrane's edges, mitigating the effects of mechanical creep and deformation. Additionally, the gaskets act as a barrier against chemical degradation, thereby extending the operational life and reliability of the proton exchange membrane (PEM) electrolyser. This innovative approach not only improves the durability and efficiency of the membrane but also contributes to the overall performance and longevity of the electrochemical stack.

[0026] Figure 1 illustrates a cross-section through a membrane assembly 100 according to the present disclosure. The membrane assembly 100 comprises a PEM 101, which is a semi-permeable membrane typically comprising a polymer and polymer reinforcement. The PEM polymer is configured to conduct protons, while preventing the conduction of electrons. The function of the PEM 101 is to separate the reactants in an electrolysis cell, to conduct hydrogen ions (protons) and to prevent a direct electrical connection between the anode side and the cathode side of the PEM 101, by preventing the direct conduction of electrons. Various materials may be used for the PEM 101. Some suitable examples are: GORE M275.80, AGO FORBLUE S-SERIES, and NAFION NDP.

[0027] In some examples, the PEM 101 will be saturated with water when in use. In such examples, the PEM 101 may exhibit enhanced proton conduction when saturated with water, with a reduction in proton conduction observed when the water content of the PEM 101 is lowered. In such examples, the PEM 101 does not exhibit significant electrical conductivity when saturated.

[0028] In some examples, the PEM 101 may be coated on the cathode side with a catalyst. In such examples, the catalyst coated on the cathode side facilitates combination of protons with electrons, thereby to produce hydrogen gas. Examples of suitable catalyst materials include platinum and / or a platinum containing material. In some examples, the PEM 101 may be coated on the anode side with a catalyst. In such examples, the catalyst coated on the anode side facilitates the separation of water molecules into oxygen, protons, and electrons. Examples of suitable catalyst materials include iridium and iridium containing materials.

[0029] As illustrated in Figure 1, the membrane assembly 100 further comprises a first gasket 102 and a second gasket 103. The first gasket 102 is arranged on the cathode side of the PEM 101, while the second gasket 103 is arranged on the anode side of the PEM 101. Each of the gaskets extend around the periphery of the PEM 101, and are arranged such that they sandwich (or "pinch") the periphery of the PEM 101. The example illustrated in Figure 1 shows two portions of the first gasket 102 arranged on the cathode side of the PEM 101 and two portions the second gasket 103 arranged on the anode side of the PEM 101. However, it should be appreciated that this is a cross- sectional illustration; the two illustrated portions of the first gasket 102 are in fact two portions of a single continuous first gasket 102 extending around the periphery of the PEM 101, and the two illustrated portions of the second gasket 103 are in fact two portions of a single continuous second gasket 103 extending around the periphery of the PEM 101.

[0030] In some examples, the first gasket 102 and / or the second gasket 103 may extend outwards beyond the periphery of the PEM 101. In other examples, as illustrated in the figures, the gaskets and the periphery of the PEM 101 may be coterminous.

[0031] In some examples, the first gasket 102 and / or the second gasket 103 may be bonded to the PEM 101. In such examples, the bonding may be achieved using any suitable method, for example with adhesive. Examples of suitable bonding materials are polyvinyl acetate (PVAc), polyvinylidene fluoride (PVDF), and tetrafluoroethylene hexafluoropropylene and vinylidene fluoride (THV).

[0032] The first gasket 102 and the second gasket 103 are substantially gas-impermeable, mechanically tough, substantially electrically insulating, and have appropriate thermal properties for use in the operating conditions of the membrane assembly 100, when in use in an electrochemical stack.

[0033] In examples where the first gasket 102 and / or the second gasket 103 are bonded to the PEM 101, the bonded gasket(s) may comprise a material selected to provide the bonded PEM 101 with improved properties. For example, the bonded gasket(s) may comprise a material selected to provide the bonded PEM 101 with one or more of improved creep resistance, deformation resistance, and stiffness. By providing such improved properties, the gaskets act to inhibit damage of the periphery of the PEM 101, which would otherwise be particularly susceptible to damage and possible failure. Examples of such materials include polyethylene naphthalate (PEN), polyethylenimine (PEI), linear low-density polyethylene (LLDPE), and polyphenylene sulphide (PPS) films.

[0034] The gas-impermeable gaskets prevent direct interaction between the reactants and the surface of the PEM 101 in the regions where the gasket covers the surface of the PEM 101. This is particularly beneficial in protecting the edge region of the PEM 101, which may otherwise be susceptible to chemical degradation.

[0035] The cathode side of the PEM 101 is particularly susceptible to chemical degradation, due to the hydrogen pressure gradient present on the cathode side of the PEM 101. The first gasket 102 extends further inwards from the periphery of the PEM 101 on the cathode side, than the second gasket 103 does on the anode side. This allows the first gasket 102 to provide enhanced protection to the cathode side of the PEM 101, thereby reducing chemical degradation of the cathode side of the PEM 101 which may otherwise occur.

[0036] The anode side of the PEM 101 is less susceptible to chemical degradation, and so additional protection from the second gasket 103 is not as important. However, an important consideration for the anode side of the PEM 101 is heat dissipation, which is limited by the second gasket 103 overlapping with the anode side of the PEM 101. Therefore, as illustrated in figure 2, the second gasket 103 does not extend as far inwards from the periphery of the PEM 101 as the first gasket 102 does on the cathode side. This promotes thermal dissipation on the anode side of the PEM 101, thereby improving the lifetime and durability of the membrane assembly 100.

[0037] Figure 2 illustrates cross-section through an example of an electrolysis cell 200 comprising a membrane assembly 100 according to the present disclosure. An electrolysis cell 200, as illustrated in Figure 2, are used to separate water (2H2O) into Hydrogen (2Hz) and Oxygen (O2). In some examples, multiple electrolysis cells may be arranged in series in an electrochemical stack, thereby to increase performance and efficiency. The electrolysis cell 200 illustrated in Figure 2 is a PEM electrolysis cell 200. The electrolysis cell 200 comprises a PEM 101, a first gasket 102, and a second gasket 103. The first gasket 102 extends further inwards from the periphery of the PEM 101 than the second gasket 103, thereby to provide enhanced protection against chemical degradation to the cathode side of the PEM 101.

[0038] The PEM 101 illustrated in Figure 2 is a catalyst coated membrane, with a catalyst coated on the anode and the cathode side of the membrane (not shown). The catalyst on the cathode side of the membrane is selected to facilitate the combination of hydrogen ions (protons) with electrons, thereby to produce hydrogen gas. In some examples, as discussed above, this catalyst may comprise platinum and / or a platinum containing material. The catalyst on the anode side of the membrane is selected to facilitate the separation of water into hydrogen, oxygen, and electrons. In some examples, as noted above, this catalyst may comprise The catalyst may comprise iridium based catalyst.

[0039] The electrolysis cell 200 further comprises an anode cell plate 109 and a cathode cell plate 110. As shown in Figure 2, at least a portion of the first gasket 102, the second gasket 103, and the PEM 101 are disposed between the anode cell plate 109 and the cathode cell plate 110. The anode cell plate 109 and the cathode cell plate 110 are configured to apply a compressive force to the portion of the first gasket 102, the second gasket 103, and the PEM 101 that are disposed between the anode cell plate 109 and the cathode cell plate 110. This compressive force helps to secure and retain the membrane assembly 100 within the electrochemical stack.

[0040] The illustrated electrolysis cell 200 further comprises a bipolar plate 106 arranged at the top of the illustrated stack. A bipolar plate 106 is an electrical conductor, that is used in an electrochemical stack comprising multiple electrolysis cells. In such an arrangement, the bipolar plate 106 simultaneously acts as a cathode to one cell and an anode to another adjacent cell. In the illustrated example, the bipolar plate 106 is arranged on the cathode side of the electrolysis cell 200, meaning that it will act as an anode for an adjacent electrolysis cell (not shown). In some examples, where the electrolysis cell 200 is not arranged in series with another cell, the bipolar plate 106 may instead be a monopolar plate. Any suitable material may be used for the bipolar plate 106. In some examples, titanium may be used as it is strong, has high thermal and electrical conductivity and has low hydrogen permeability. However, titanium can be susceptible to the growth of non-conductive oxide layers. In some examples, coatings may be used (for example, platinum and / or a platinum containing material) in order to improve the corrosion resistance. In other examples, alternative materials may be used for the plate and / or for the coating.

[0041] The bipolar plate 106 further comprises a flow field region 105. In use, reactant fluids flow into, distribute across, and flow in and out of the flow field region 105 of the electrolysis cell 200 during the electrolysis process. The flow field region 105 is arranged so as to optimise the distribution of reactant fluids across the electrolysis cell 200, thereby improving the efficiency and performance of the electrolysis cell 200.

[0042] The illustrated electrolysis cell 200 further comprises a gas diffusion layer 104. The gas diffusion layer 104 is electrically conductive, and is also configured to facilitate the mass transport of reactant fluids between the bipolar plate 106 and the PEM 101. The gas diffusion layer 104 must be electrically conductive, and must be capable of facilitating mass transport of fluids. In some examples, carbon may be used for a gas transport layer disposed on the cathode side of the electrolysis cell 200.

[0043] The illustrated electrolysis cell 200 further comprises a porous transport layer 107. This is similar to the gas diffusion layer 104, however it is disposed on the anode side of the electrolysis cell 200. On the anode side, the environment is highly oxidising, meaning that the material requirements may be different to those of the gas transport layer. In some examples, the oxidising environment may mean that carbon cannot be used as a porous transport layer 107 material, as carbon is susceptible to chemical degradation in highly oxidising environments. In such examples, an alternative material may be used, such as titanium.

[0044] The illustrated electrolysis cell 200 further comprises meshes 108, arranged to facilitate the mass transport of reactant fluids, and conduction of electrons. The meshes 108 provide a flow field to facilitate convective cooling of the heat-generating anode side of the electrolysis cell 200.

[0045] Although the invention has been described in considerable detail in language specific to structural features, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features described. Rather, the specific features are disclosed as exemplary forms of implementing the claimed invention. Stated otherwise, it is to be understood that the phrases and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. Therefore, while exemplary illustrative embodiments of the invention have been described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention.

Claims

CLAIMS1. A membrane assembly for use in an electrochemical stack, the membrane assembly having an anode side and a cathode side, and comprising: a proton exchange membrane; a first gasket arranged on the cathode side of the proton exchange membrane; and a second gasket arranged on the anode side of the proton exchange membrane; wherein the first and second gaskets are arranged such that they sandwich at least a portion of a periphery of the proton exchange membrane; and wherein the first gasket extends inwards from the periphery of the proton exchange membrane further than the second gasket, thereby covering more of the proton exchange membrane than the second gasket.

2. The membrane assembly according to claim 1, wherein the proton exchange membrane is bonded to at least one of the first gasket and the second gasket.

3. The membrane assembly according to claim 2, wherein the proton exchange membrane is bonded to each of the first gasket and the second gasket.

4. The membrane assembly according to any previous claim, wherein the first gasket at least partially overlaps the entire periphery of the cathode side of the proton exchange membrane.

5. The membrane assembly according to any previous claim, wherein the second gasket at least partially overlaps the entire periphery of the anode side of the proton exchange membrane.

6. The membrane assembly according to any previous claim, wherein the cathode side of the proton exchange membrane is at least partially coated with a catalyst.

7. The membrane assembly according to claim 6, wherein the catalyst comprises platinum or a platinum containing material.

8. The membrane assembly according to any previous claim, wherein the anode side of the proton exchange membrane is at least partially coated with a catalyst.

9. The membrane assembly according to claim 8, wherein the catalyst comprises iridium or an iridium containing material.

10. The membrane assembly according to any previous claim, further comprising a cathode cell plate and an anode cell plate.

11. The membrane assembly according to claim 10, wherein the cathode cell plate and the anode cell plate sandwich at least a portion of: the first gasket, the second gasket, and the membrane.

12. The membrane assembly according to claim 11, wherein the cathode cell plate and the anode cell plate are arranged to apply a compressive force to the portion sandwiched therebetween of: the first gasket, the second gasket, and the membrane.

13. The membrane assembly according to any previous claim, wherein the first gasket and the second gasket each comprise a material that is substantially gas- impermeable.

14. The membrane assembly according to any previous claim, wherein the first gasket and the second gasket each comprise a material that is substantially electrically insulating.

15. The membrane assembly according to any previous claim, wherein the first gasket and the second gasket each have a thickness of between 0.025 mm and 0.125 mm.

16. The membrane assembly according to any previous claim, wherein the first and / or second gasket comprise one or more materials selected from: polyethylene naphthalate, polyethylenimine, linear low-density polyethylene, polyphenylene sulphide.

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