Electrochemical stack assembly

Abstract

According to a first aspect of the disclosure, there is provided a membrane assembly for use in an electrolysis cell, 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 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] Electrochemical stack assembly

[0002] Field of the invention

[0003] The present disclosure relates to a membrane assembly for use in an electrochemical stack, and to a method of assembling an electrochemical stack dry. More specifically, it relates to a membrane for use in an electrolysis cell with enhanced structural support, allowing for the membrane assembly to be pre-assembled, and for an electrochemical stack comprising the membrane assembly to be assembled dry.

[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 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. A critical component of any electrochemical stack, including fuel cells and electrolysers, is the membrane which may also be referred to as a proton exchange membrane (PEM). The PEM 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] Electrochemical cells (and stacks comprising multiple cells) operate with many components hydrated, including the PEM. Some components, including the PEM, are subject to unpredictable dimensional changes during hydration (and even as a result of variations in environmental humidity). High precision is needed in electrochemical stack assembly and operation, and so typically, electrochemical stacks are assembled "wet", meaning that the components including the PEM are hydrated before assembly. After assembly, the electrochemical stacks and are kept hydrated when not in use (for example, during storage or transport). This increases the complexity of assembly, and increases the cost and difficulty of storing the stacks when not in use.

[0007] There is a need, therefore, to develop components and an assembly method that will allow for electrochemical stacks to be assembled dry. Furthermore, there is a need to develop components that will allow for an assembled stack to be transported and / or stored without the need to keep components hydrated. Summary of the invention

[0008] According to a first aspect of the disclosure, there is provided membrane assembly for use in an electrolysis cell, the membrane assembly having an anode side and a cathode side, and comprising: a proton exchange membrane; a first gasket arranged around a periphery of the cathode side of the proton exchange membrane; and a second gasket arranged around a periphery of the anode side of the proton exchange membrane; wherein at least one of the first gasket and the second gasket are bonded to the proton exchange membrane, thereby to inhibit planar expansion of the proton exchange membrane.

[0009] The first and second gaskets enhance the mechanical properties of the membrane assembly. In particular, the bonded gasket(s) significantly increase the stiffness of the membrane assembly. This allows for the dimensions and shape of the proton exchange membrane to be maintained extremely precise and controlled, after the membrane assembly comprising the gaskets have been assembled.

[0010] In use, the proton exchange membrane must be hydrated in order to efficiently conduct protons. Hydration of the proton exchange membrane proton exchange membrane typically results in unpredictable dimensional changes, and in particular in expansion in both the planar and normal directions. The bonded gasket(s) act to limit dimensional changes during hydration, and in particular to substantially prevent planar expansion. This is extremely beneficial as it allows for dry assembly of an electrochemical cell (and stack), with the membrane assembly only needing to be hydrated when in use. This is because the dimensional changes associated with hydration of the membrane are predictable, and so can be managed (if necessary) during hydration.

[0011] In an embodiment, there is provided a membrane assembly wherein each of the first gasket and the second gasket are bonded to the proton exchange membrane. By bonding each of the gaskets to the proton exchange membrane, further enhancement of the mechanical properties of the membrane assembly may be achieved.

[0012] In an embodiment, there is provided a membrane assembly comprising a proton exchange membrane that is hydrophilic. A hydrophilic proton exchange membrane is advantageous as it allows for easy hydration, thereby to increase ionic conductivity of the proton exchange membrane.

[0013] 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. 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. Furthermore, this ensures complete coverage of the periphery and edge of the membrane, minimizing exposure of the periphery of the membrane to harsh operational environments and potential damage.

[0014] 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. 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. Furthermore, this ensures complete coverage of the periphery and edge of the membrane, minimizing exposure of the periphery of the membrane to harsh operational environments and potential damage.

[0015] 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. Coating the cathode side with a catalyst improves the efficiency of electrochemical reactions, leading to better performance of the electrolysis cell. Using platinum as the catalyst on the cathode side ensures high catalytic activity, enhancing the efficiency and output of the electrochemical reactions.

[0016] 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 iridium or an iridium containing material. Coating the anode side with a catalyst boosts the electrochemical reactions on the anode side, contributing to the overall efficiency of the cell. Using iridium and / or ruthenium as catalysts on the anode side provides high catalytic activity, improving the efficiency and output of the electrochemical reactions.

[0017] In an embodiment, there is provided a membrane assembly wherein the first gasket and the second gasket each comprise a substantially gas-impermeable material. Using substantially gas-impermeable materials for the gaskets prevents gas crossover, which is crucial for maintaining the efficiency and safety of the electrolysis cell. 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 chemical degradation. 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.

[0018] 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.

[0019] 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 substantially gas-impermeable, and provide adequate protection from degradation, and improvement to the mechanical properties of the membrane assembly.

[0020] In an embodiment, there is provided a membrane assembly wherein the first gasket is bonded to the proton exchange membrane using one or more of: polyvinyl acetate, polyvinylidene fluoride, and tetra hydrofuran. These bonding materials facilitate a strong and secure bond between the first gasket and the proton exchange membrane.

[0021] In an embodiment, there is provided a membrane assembly wherein the second gasket is bonded to the proton exchange membrane using one or more of: polyvinyl acetate, polyvinylidene fluoride, and tetra hydrofuran. These bonding materials facilitate a strong and secure bond between the second gasket and the proton exchange membrane.

[0022] According to a second aspect of the disclosure, there is provided an electrolysis cell comprising: an anode; a cathode; and a membrane assembly according to the first aspect. An electrolysis cell comprising a membrane assembly according to the first aspect is beneficial as it can be assembled dry, and does not need to be hydrated when not in use. This simplifies assembly and storage of the electrolysis cell. 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 electrochemical cell, reducing the risk of component shifting or damage during operation.

[0023] 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 a secure assembly, maintaining the alignment and integrity of the components.

[0024] Optionally, 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. Applying compressive force via the cell plates enhances the sealing and mechanical stability of the assembly, preventing leaks and ensuring consistent performance.

[0025] In an embodiment, there is provided an electrolysis cell wherein the cathode is configured to apply pressure to the proton exchange membrane. Compressive pressure ensures a good contact between the cathode and the proton exchange membrane, thereby maximising the efficiency of the electrolysis cell.

[0026] In an embodiment, there is provided an electrolysis cell wherein the cathode comprises compressible carbon. Carbon has good electrical conductivity, and can be configured to facilitate mass transport of reactant fluids. By being compressible, a good contact between the cathode and the proton exchange membrane can be maintained.

[0027] In an embodiment, there is provided an electrolysis cell wherein the cathode is configured to apply a substantially constant pressure to the proton exchange membrane when, in use, the proton exchange membrane is hydrated. This ensures a good contact between the cathode and the proton exchange membrane, without applying excessive pressure to the proton exchange membrane, which could cause damage to the proton exchange membrane and / or other components of the electrolysis cell.

[0028] According to a third aspect of the disclosure, there is provided a method of assembling an electrolysis cell according to the second aspect of the disclosure, the method comprising steps of: receiving a membrane assembly according to the first aspect of the disclosure; and assembling the electrolysis cell without hydrating the membrane assembly.

[0029] Typically, a PEM must be hydrated before assembly of the electrolysis cell, with the PEM being kept hydrated regardless of whether the electrolysis cell is in use or not. This increases the complexity and cost of assembly, transport and storage of the electrolysis cell, since it must be kept hydrated. The bonded gasket(s) substantially prevent planar expansion of the PEM, meaning that when the PEM is hydrated, dimensional change substantially only occurs in the axial direction. Axial dimensional change is much easier to accommodate, and so the membrane assembly according to the first aspect allows for the assembly of the electrolysis cell without first hydrating the PEM.

[0030] According to a fourth aspect of the disclosure, there is provided a method of preparing for operation an electrolysis cell according to the second aspect of the disclosure, the method comprising steps of: applying compressive pressure to the electrolysis cell in a direction normal to the plane of the proton exchange membrane; and hydrating the proton exchange membrane.

[0031] Compressive pressure is applied to the electrolysis cell in order to maintain good contact between the components of the electrolysis cell. As noted above, the bonded gasket(s) substantially prevent planar expansion of the PEM. Therefore, the electrolysis cell can be assembled, transported and stored without the PEM being hydrated. When preparing the electrolysis cell for operation, the PEM is hydrated such that proton conduction through the PEM is maximised. During hydration, dimensional change substantially only occurs in the axial direction. Axial dimensional change is much easier to accommodate, and so the membrane assembly according to the first aspect allows for the PEM to be hydrated only when the electrolysis cell is being prepared for operation.

[0032] In an embodiment, there is provided a method wherein during hydration of the proton exchange membrane, applied compressive pressure is modulated such that the pressure experienced by the proton exchange membrane in the direction normal to the plane of the proton exchange membrane remains substantially constant. This is advantageous as it prevents excessive pressure being applied to the proton exchange membrane when it experiences axial expansion during hydration, thereby preventing damage to components of the electrolysis cell, including the PEM. In an embodiment, there is provided a method wherein the applied pressure is configured such that is experienced substantially uniformly across the surfaces of the proton exchange membrane. This is advantageous as it ensures that good contact is maintained between the components of the electrolysis cell.

[0033] Brief description of the drawings

[0034] 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:

[0035] Figure 1 illustrates a cross section of a membrane assembly;

[0036] Figure 2 illustrates a cross-section through an example of a membrane assembly and a compressible carbon cathode;

[0037] Figure 3 illustrates an example of a membrane assembly viewed from the cathode side of the PEM;

[0038] Figure 4 illustrates a cross-section through an example of an electrolysis cell;

[0039] Figure 5 illustrates a flow chart of a method of assembling an electrolysis cell; and

[0040] Figure 6 illustrates a flow chart of a method of preparing an electrolysis cell for operation.

[0041] Detailed description

[0042] In order to address the challenges discussed previously in relation to existing membranes, the present invention provides a novel membrane assembly design comprising gaskets arranged around, and bonded to, the periphery of the proton exchange membrane. As discussed in more detail below, the gaskets provide structural support to the edges of the proton exchange membrane, enhancing the stiffness and strength of the membrane assembly, while also preventing mechanical creep and deformation. The enhanced stiffness and strength provided by the bonded gaskets allows for an electrolysis cell comprising the membrane assembly to be assembled dry, and removes the need for the electrolysis cell to remain hydrated when not in use (for example, during transport and / or storage).

[0043] Figure 1 illustrates a cross-section through a membrane assembly 100 according to the present disclosure. The membrane assembly 100 comprises a proton exchange membrane (PEM). The PEM 101 is a semi-permeable membrane, typically comprising a polymer, which 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.

[0044] 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.

[0045] 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 or a platinum containing material.

[0046] 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 or an iridium containing material.

[0047] 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 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 potions 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 potions of a single continuous second gasket extending around the periphery of the PEM 101. This is illustrated more clearly in Figure 3, as discussed in more detail below.

[0048] 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. At least one of the first gasket 102 and the second gasket 103 are bonded to the PEM 101. In some examples, each of the first gasket 102 and the second gasket 103 are bonded to the PEM 101. 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), although other bonding methods and materials are envisaged.

[0049] The first gasket 102 and the second gasket 103 are each substantially gas- impermeable, substantially electrically insulating, mechanically tough, and have appropriate thermal properties for use in the operating conditions of the membrane assembly 100, when in use in an electrolysis cell.

[0050] The bonded gasket(s) comprise a material selected to provide the bonded PEM 101 with improved properties, thereby to inhibit planar expansion of the PEM 101. Examples of such materials include polyethylene naphthalate (PEN), polyethylenimine (PEI), linear low-density polyethylene (LLDPE), and polyphenylene sulphide (PPS).

[0051] In some examples, the bonded gasket(s) may comprise a material further 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 may also 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).

[0052] The substantially 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.

[0053] Figure 2 illustrates a cross section through an example of a membrane assembly 100 that further comprises a compressible cathode that is in contact with the surface of the PEM 101. In examples where the PEM 101 is coated with a catalyse on the cathode side, as described above, the compressible cathode may be in contact with the catalyst coating. The compressible cathode is configured to apply pressure to the surface of the PEM 101, thereby to ensure a good contact between the cathode and the PEM 101. In some examples, the compressible cathode is configured such that it is able to accommodate any changes in the thickness of the PEM 101, without substantially altering the pressure applied to the surface of the PEM 101. In some examples, the mitigation may be provided in conjunction with a modulation of external pressure applied to the electrolysis cell, in order to maintain a substantially constant pressure to the surface of the PEM 101.

[0054] Maintaining a substantially constant pressure to the surface of the PEM 101 can be beneficial, particularly when the hydration level of the PEM 101 is altered. In use, the PEM 101 is hydrated to maximise the proton conductivity of the PEM 101. As discussed above, the bonded gasket(s) are configured to substantially prevent planar expansion of the PEM 101. Thus, when the PEM 101 is hydrated, the thickness of the PEM 101 may increase due to axial expansion, since planar expansion is substantially prevented by the bonded gasket(s). Applying excessive pressure to the PEM 101 can cause damage to the PEM 101 and to other components, and may prevent the PEM 101 from becoming fully hydrated. The compressible cathode can help to prevent these issues, by allowing axial expansion of the PEM 101, without resulting in a significant increase in the pressure experienced by the PEM 101.

[0055] In some examples, the compressible cathode may comprise carbon. In other examples, other suitable materials may be used, such as titanium.

[0056] In some examples, external pressure applied to the electrolysis cell (such as by one or more hydraulic pistons, for example) may be modulated in order to prevent substantial changes in the pressure experienced by the PEM 101 during changes in hydration. This may be in addition to, or as an alternative to, any pressure modulation that results from the inclusion of a compressible cathode.

[0057] In some examples the pressure may be applied by the controlled compression of a compressible electrode (for example, the compressible cathode).

[0058] Figure 3 illustrates an example of a membrane assembly 100 viewed from the cathode side. The illustrated membrane assembly 100 comprises a first gasket 102 and a PEM 101. The membrane assembly 100 also comprises a second gasket 103, however this is not shown as it is on the side of the membrane assembly 100 that is not visible. The membrane assembly 100 further comprises two alignment holes 112. The alignment holes 112 extend through the first gasket 102 and the second gasket 103, and facilitate the accurate and repeatable alignment of the membrane assembly 100, for example when the membrane assembly 100 is used in an electrolysis cell.

[0059] Figure 4 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 1, are used to separate water (2H2O) into Hydrogen (2H2) and Oxygen (O2). In some examples, multiple electrolysis cells may be arranged in series in an electro, thereby to increase production capacity.

[0060] The electrolysis cell 200 illustrated in Figure 4 is a PEM electrolysis cell. The electrolysis cell 200 comprises a PEM 101, a first gasket 102, and a second gasket 103. At least one of the first gasket 102 and the second gasket 103 are bonded to the PEM 101, thereby to substantially prevent planar expansion of the PEM 101.

[0061] The PEM 101 illustrated in Figure 4 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. 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 and / or ruthenium.

[0062] The electrolysis cell 200 further comprises an anode cell plate 109 and a cathode cell plate 110. As shown in Figure 4, 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 electrolysis cell 200.

[0063] The illustrated electrolysis cell 200 further comprises a bipolar plate 106 arranged at the top of the illustrated cell. 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 corrosion. In some examples, coatings may be used (for example, platinum) in order to improve the corrosion resistance. In other examples, alternative materials may be used for the plate and / or for the coating.

[0064] The bipolar plate 106 further comprises a flow field region 205. In use, reactant fluids flow into, distribute across, and flow and out of the flow field region 205 of the electrolysis cell 200 during the electrolysis process. The flow field region 205 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.

[0065] 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. In some examples, the gas diffusion layer 104 may be used as a deformable element able to convey suitable compressive stress to the PEM 101. In such examples, as discussed in more detail below, the PEM 101 may comprise one or more coating as part of a catalyst coated membrane (CCM) catalyst system.

[0066] 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.

[0067] 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.

[0068] Figure 5 illustrates an example of a method of assembly 300 of an electrolysis cell 200 comprising a membrane assembly 100 as described above. In a first step 301 a membrane assembly 100 according to the present disclosure is received. The membrane assembly 100 is substantially dry (i.e., it has not been hydrated) when it is received, and it is not hydrated prior to assembling the electrolysis cell 200. As described above, the membrane assembly 100 comprises a PEM 101, a first gasket 102, and a second gasket 103, wherein at least one of the first gasket 102 and the second gasket 103 are bonded to the PEM 101, thereby to substantially prevent planar expansion of the PEM 101.

[0069] In a second step 302, an electrolysis cell 200 comprising the membrane assembly 100 is assembled. Assembly of the electrolysis cell 200 is achieved using a typically assembly method, with the key difference being that the PEM 101 is not hydrated before assembly. This is only possible because the bonded gasket(s) substantially prevent planar expansion of the PEM 101 when it is later hydrated, thereby preventing issues that would normally be caused by uncontrolled planar expansion. These issues typically require the PEM 101 to be hydrated prior to assembly, and for the PEM 101 to remain hydrated whether in use or not.

[0070] Figure 6 illustrates a method 400 of preparing an electrolysis cell 200 for operation. The electrolysis cell 200 comprises a membrane assembly 100 as described above. Prior to the first step of the method 400, the electrolysis cell 200 is not in operation and thus the PEM 101 is substantially dry. In some examples, the electrolysis cell 200 may have been assembled according to the method 200 described above in relation to Figure 5.

[0071] In a first step 401, compressive pressure is applied to the electrolysis cell 200. Pressure is applied to the electrolysis cell 200 in order to ensure good contact is maintained between the various components of the electrolysis cell 200. The pressure may be applied by any suitable means, for example via one or more hydraulic pistons. In some examples, the means of applying the pressure may be configured such that the applied pressure is experienced by the PEM 101 substantially uniformly across the surface of the PEM 101. This may require, for example, different pressure to be applied to the middle of the electrolysis cell 200 than to the edges. Alternatively, or additionally, this may be provided by a suitably compressible and resilient element included in the stack.

[0072] In a second step 402, the PEM 101 is hydrated. As discussed above, hydration of the PEM 101 is needed before operation of the electrolysis cell 200 in order to ensure good proton conductivity through the PEM 101. As the PEM 101 is hydrated, axial expansion of the PEM 101 will occur, since the bonded gasket(s) act to substantially prevent planar expansion of the PEM 101.

[0073] In a third step 403, as the PEM 101 is hydrated and axial expansion of the PEM 101 occurs, the applied pressure is modulated such that the compressive pressure experienced by the PEM 101 remains substantially constant, despite the axial expansion. This prevents damage to components of the electrolysis cell 200, including the PEM 101, which may otherwise occur during axial expansion of the PEM 101.

[0074] 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 phraseology 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 electrolysis cell, the membrane assembly having an anode side and a cathode side, and comprising: a proton exchange membrane; a first gasket arranged around a periphery of the cathode side of the proton exchange membrane; and a second gasket arranged around a periphery of the anode side of the proton exchange membrane; wherein at least one of the first gasket and the second gasket are bonded to the proton exchange membrane, thereby to inhibit planar expansion of the proton exchange membrane.

2. A membrane assembly according to claim 1, wherein each of the first gasket and the second gasket are bonded to the proton exchange membrane.

3. A membrane assembly according to claims 1 or 2, wherein the proton exchange membrane comprises a hydrophilic material.

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

5. A 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. A 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. A membrane assembly according to claim 6, wherein the catalyst comprises platinum8. A 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. A 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, wherein the first gasket and the second gasket each comprise a material that is substantially gas- impermeable.

11. 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.

12. A 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.

13. A 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 .

14. A membrane assembly according to any preceding claim, wherein the first gasket is bonded to the proton exchange membrane using one or more of: polyvinyl acetate, and polyvinylidene fluoride.

15. A membrane assembly according to any preceding claim, wherein the second gasket is bonded to the proton exchange membrane using one or more of: polyvinyl acetate, and polyvinylidene fluoride.

16. An electrolysis cell comprising: an anode; a cathode; and a membrane assembly according to any previous claim.

17. An electrolysis cell according to claim 16, further comprising a cathode cell plate and an anode cell plate.

18. An electrolysis cell according to claim 17, 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.

19. An electrolysis cell according to claim 18, 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.

20. An electrolysis cell according to any of claims 16 to 19, wherein the cathode is configured to apply pressure to the proton exchange membrane.

21. An electrolysis cell according claim 20, wherein the cathode comprises compressible carbon.

22. An electrolysis cell according to claim 21, wherein the cathode is configured to apply a substantially constant pressure to the proton exchange membrane when, in use, the proton exchange membrane is hydrated.

23. A method of assembling an electrolysis cell according to any of claims 16 to 22, the method comprising steps of: receiving a membrane assembly according to any of claims 1 to 15; and assembling the electrolysis cell without hydrating the membrane assembly.

24. A method of preparing for operation an electrolysis cell according to any of claims 16 to 22, the method comprising steps of: applying compressive pressure to the electrolysis cell in a direction normal to the plane of the proton exchange membrane; and hydrating the proton exchange membrane.

25. A method according to claim 24, wherein during hydration of the proton exchange membrane, applied compressive pressure is modulated such that the pressure experienced by the proton exchange membrane in the direction normal to the plane of the proton exchange membrane remains substantially constant.

26. A method according to claims 24 or 25, wherein the applied pressure is configured such that is experienced substantially uniformly across the surfaces of the proton exchange membrane.

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