Improved PEM electrolyser or fuel cell stack

Abstract

A polymer electrolyte membrane (PEM) electrolyser or fuel cell system for the extraction of hydrogen, the electrolyser or fuel cell system comprising first and second end plate assemblies provided at longitudinal and opposed ends of the electrolyser or fuel cell system with an electrolyser stack positioned between the first and second end plate assemblies; the electrolyser stack comprising a plurality of electrolyser cells wherein each cell comprises bi-polar contact plates separated by a catalyst-coated membrane or catalyst coated electrodes and wherein the electrolyser stack is located between a pair of current collectors; wherein each of said current collectors is arranged adjacent said first and second end plate assemblies respectively with a compression arrangement being located at each end of the fuel cell stack to apply a compressive force on each of the current collectors thereby clamping the plurality of bi-polar contact plates and the plurality of catalyst-coated membranes and / or catalyst coated electrodes therebetween to apply uniform pressure across the bi-polar contact plates, wherein the compression arrangement is further configured to be adjustable to vary contact pressure between the plurality of bi-polar contact plates.

Description

IMPROVED PEM ELECTROLYSER OR FUEL CELL STACKTECHNICAL FIELD[1] The present invention relates to an improved polymer electrolyte membrane (PEM) electrolyser for the extraction of hydrogen. The present invention also relates to an improved fuel cell stack which improves fuel cell performance and efficiency.BACKGROUND[2] Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.[3] Hydrogen gas may be used as a fuel for internal combustion engines. Production, storage and transport have introduced difficulties which likely have prevented widespread adoption. Hydrogen constitutes a low emission and renewable fuel source. Hydrogen may also be used as an energy storage medium for use in fuel cells to produce electrical energy.[4] An electrolyser cell is a type of electrochemical device that uses energy to dissociate a compound liquid into its components. For example, water can be dissociated into hydrogen and oxygen (e.g. H2O^H2+O2). In practice, a number of electrolyser cells are arranged into a stack to produce sizable amounts of one or more of the components of a compound liquid such as water or a water solution.[5] The structure of an electrolyser comprises a number of bipolar cells stacked in series, and set together between two end plates, interconnected by tie rods. Each one of the bipolar cells comprises an anodic compartment, and a cathode compartment,separated by a diaphragm or an electrolyte membrane. In turn, each cell is separated from the next one by a conductive wall, the so-called bipolar plate, having opposite polarity on the two faces. The stack of cells is set together by the end plates forming the anode (+) and the cathode (-) terminal connections of the stack. The end plates are forced towards each other by the tie rods which are electrically insulated to avoid a short circuiting of the cells. Water is introduced in the cells, and the produced gases are collected therefrom.[6] A fuel cell on the other hand is an electrical power generation device which is powered by the electrochemical reaction of hydrogen and oxygen. The reaction can be conceptually understood as reverse electrolysis of water, to convert the chemical energy into electrical energy. The structure of a fuel cell stack comprises a plurality of cell units. Each cell unit comprises a proton exchange membrane (PEM) at the middle, with the two sides of the membrane being provided with a layer of catalyst. Each of the two outsides of the catalyst is further provided with a gas diffusion layer. An anode plate and a cathode plate are further provided at the outermost sides adjacent to the gas diffusion layer. After combining all the above elements together, a cell unit is formed.[7] A conventional fuel cell, comprising the above-described fuel stack also includes two end plates that are disposed at either longitudinal end of the fuel cell stack. A number of tie rods which pass through the peripheral parts of the end plates are used to hold the fuel stack and apply a compressive force on the fuel cell stack from either longitudinal end. Adjustment can be made as to how tight each of the tie rods to achieve a pressure that is required for optimizing the conductivity of each cell unit. The provision of the tie rods also assists in fluidly sealing the stack. It has been found that such conventional methods at best only achieve pressure control within alimited range. It is also difficult to maintain or vary the applied pressure while the fuel cell is operating. Furthermore, while tightening the tie rods, in order to ensure that each cell unit is under a consistent pressure, precise measurements must be made to each of the tie rods during the tightening process, which complicates the process and increases the cost for manufacturing the fuel cell.[8] In view of the above, it is desirable to provide an improved method and system for improving the operation of fuel cell systems or electrolyser systems which generally comprise multiple electrolyser cells stacked together.SUMMARY OF INVENTION[9] In an aspect, the invention provides a polymer electrolyte membrane (PEM) electrolyser or fuel cell system for the extraction of hydrogen, the electrolyser or fuel cell system comprising: first and second end plate assemblies provided at longitudinal and opposed ends of the electrolyser or fuel cell system with an electrolyser cell stack positioned between the first and second end plate assemblies; the electrolyser cell stack comprising a plurality of fuel cells wherein each fuel cell comprises bi-polar contact plates separated by a catalyst-coated membrane or catalyst coated electrodes and wherein the electrolyser cell stack is located between a pair of current collectors; wherein each of said current collectors is arranged adjacent said first and second end plate assemblies respectively with a compression arrangement being located at each end of the electrolyser cell stack to apply a compressive force on each of the current collectors thereby clamping the plurality of bi-polar contact plates andthe plurality of catalyst-coated membranes (CCM) or catalyst coated electrodes therebetween to apply uniform pressure across the bi-polar contact plates, wherein the compression arrangement is further configured to be adjustable to vary contact pressure between the plurality of bi-polar contact plates.

[0010] In an embodiment, each of the first and second end plate assemblies comprise an end plate and a manifold frame positioned for engagement with the end plate.

[0011] In an embodiment, each of the first and second end plate assemblies and the respective one of the current collectors together form a respective electrode assembly.

[0012] In an embodiment, each of the manifold frames comprise a recess for receiving a respective one of the current collectors.

[0013] In an embodiment, each of said respective current collectors is movably disposed within the corresponding recess.

[0014] In an embodiment, the current collectors are substantially equal to or thicker than their respective recesses.

[0015] In an embodiment, the compressive force applied to the current collectors is by way of introducing a working fluid into the recess for applying the compressive force.

[0016] In an embodiment, the working fluid is introduced into the recess for each manifold frame via a respective fluid inlet port. Preferably, each electrode assembly comprises a respective fluid inlet port.

[0017] In an embodiment, the compressive force is applied directly to the current collectors.

[0018] In an embodiment, the working fluid is an inert gas, an oil or a water.

[0019] In an embodiment, the working fluid is fluidly separated from an input fluid being electrolysed.

[0020] In an embodiment, the working fluid is fluidly separated from an input fluid by one or more O-rings or seals.

[0021] In an embodiment, the catalyst-coated membrane selectively allows hydrogen gas to migrate across the membrane and be collected from an outlet of the electrolyser or fuel cell system.

[0022] In an embodiment, the catalyst-coated membrane comprises one or more carbon meshes.

[0023] In an embodiment, the electrolyser system further comprises at least one inlet for receiving a water or water solution and at least one outlet for expelling hydrogen gas.

[0024] In an alternative embodiment, the fuel cell system comprises at least one inlet for hydrogen, at least one inlet for oxygen and at least one outlet for expelling generated water.

[0025] In an embodiment, each of the bi-polar contact plates comprises a manifold fluidly connectable to each other and / or the at least one inlet and the at least one outlet of the electrolyser.

[0026] In an embodiment, the electrolyser or fuel cell system further comprises a plurality of tie rods passing through a peripheral region of each end plate assembly for positioning the electrolyser stack positioned between the first and second end plate assemblies.

[0027] In another aspect, the invention provides a method of compressing an electrolyser cell stack of a polymer electrolyte membrane (PEM) electrolyser or fuel cell system, the method comprising:providing first and second end plate assemblies at longitudinal and opposed ends of the electrolyser stack or fuel cell stack and for positioning a fuel cell stack between the first and second end plate assemblies; positioning a manifold frame adjacent each of said endplate assemblies wherein each manifold frame further comprising a recess for housing respective current collectors adjacent to an outermost bi-polar contact plate of the fuel cell or electrolyser stack; injecting a fluid into one or both of the respective recesses of the manifold frames housing the current collectors of the first and second end plate assemblies so as to apply a compressive force to move the current collectors to or towards each other thereby increasing a contact pressure between the plurality of bi-polar contact plates of the fuel cell or electrolyser stack.

[0028] In an embodiment, the method further comprises controlling flow of fluid into one or both of the respective recesses to vary the pressure between the bi-polar contact plates.

[0029] In an embodiment, the method further comprises providing a plurality of channels etched into each of the plurality of bi-polar contact plates for receiving water to be electrolysed.

[0030] In an embodiment, the method further comprises arranging an inlet for allowing water for spreading water across each of the plurality of porous transport layers (PTL).

[0031] In another aspect, the invention provides a method of compressing a polymer electrolyte membrane stack of a polymer electrolyte membrane (PEM) electrolyser or fuel cell system, the method comprising: providing an electrolyser or a fuel cell system as described herein;injecting a fluid into one or both of the respective recesses housing the current collectors of the first and second end plate assemblies so as to move the current collectors to or towards each other thereby increasing a contact pressure between the plurality of bi-polar contact plates of the fuel cell stack.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:Figure 1 is a cross section of an electrolyser or fuel cell system according to an embodiment of the present invention.Figure 2 is a cross section of the frame manifold in a neutral position according to an embodiment of the present invention.Figure 3 is a cross section of the frame manifold and current collector.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] Figure 1 illustrates a cross section of a polymer electrolyte membrane (PEM) electrolyser or fuel cell system 10 according to a preferred embodiment of the present invention. Reference to electrolyser 10 throughout the specification should be interpreted to mean electrolyser or fuel cell system. The electrolyser 10 is used in the process of electrolysis for the production and extraction of hydrogen gas from a water or water solution.

[0034] In the preferred embodiment, the electrolyser 10 comprises first and second end plate assemblies 12A, 12B one at each of the longitudinal ends of the electrolyser 10. The first and second end plate assemblies 12A, 12B each comprise an end plate 14A, 14B and a manifold frame 16A, 16B. The manifold frames 16A, 16B are positioned for engagement with the end plate 14A, 14B. Each of the respective manifold frames 16A, 16B comprise a recess 18A, 18B for receiving or housing respective current collectors 20A, 20B and receiving a fluid. The electrolyser 10 further comprises a plurality of bi-polar contact plates 24 which form individual electrolyser cells located between the first and second end plate assemblies 12A, 12B. A plurality of tie rods 32 pass through a peripheral region of each of the end plate assemblies 12A, 12B and the plurality of bi-polar contact plates 24 to locate and position a fuel cell stack between the first and second end plate assemblies 12A, 12B.

[0035] The fuel cell stack comprises a plurality of fuel cells wherein each fuel cell comprises one or more bi-polar contact plates 24 separated by a catalyst-coated membranes. In the preferred embodiment, the catalyst-coated membranes are provided in the form of a carbon electrode on the cathode 24A. The fuel cell stack is located between the pair of current collectors 20A, 20B. The electrolyser is arranged such that each of the current collectors 20A, 20B abuts the outermost one of the bipolar contact plates 24.

[0036] The first and second end plate assemblies 12A, 12B are configured having a compression arrangement at each end of the fuel cell stack. The compression arrangement is configured to apply a compressive force on each of the current collectors 20A, 20B arranged adjacent to the respective one of the first and second end plate assemblies 12A, 12B to clamp the plurality of bi-polar contact plates 24 and plurality of catalyst-coated membranes 26 therebetween. The compressionarrangement is configured to apply a uniform pressure across the bi-polar contact plates 24. Furthermore, the compression arrangement is configured to be adjustable so as to vary the contact pressure between the plurality of bi-polar contact plates 24. By way of a non-limiting example, a pressure control valve may be used for controlling pressure of the gas and thereby adjust the contact pressure.

[0037] The end plate assemblies 12A, 12B comprising the end plate 14A, 14B and the manifold frames 16A, 16B and the respective one of the current collectors 20A, 20B together form separate plate assemblies. For example, end plate 14A, manifold frame 16A and current collector 20A may define a positive terminal assembly whereas, end plate 14B, manifold frame 16B and current collector 20B may define a negative terminal assembly or vice versa.

[0038] Each of the respective current collectors 20A, 20B are adapted or configured to be movably disposed within the recess 18A, 18B of the respective one of the manifold frames 16A, 16B. In the preferred embodiment, the recess 18A, 18B is substantially the width of the respective current collector 20A, 20B. In alternative embodiments, the respective current collector 20A, 20B may be thicker than the recess 18A, 18B. It is preferred that when fully recessed and assembled the current collector 20A, 20B abuts the respective outermost bi-polar contact plates 24 at longitudinal ends of the fuel cell stack. As such, when assembled, there is preferably little to no movement of the current collectors 20A, 20B within the respective recesses 18A, 18B without the application of a force.

[0039] Referring to Figure 2, there is provided a cross section of one of the manifold frames 16A and current collector 20A within recess 18A. In the preferred embodiment, the compressive force applied to the current collector 20A to move the current collector 20A towards the other of the current collector 20B by way of a fluid injection. In thepreferred embodiment, the compressive force is pneumatically applied. The fluid in the preferred embodiment is air. The fluid may be provided by known methods such as an air compressor. Alternatively, fluids such as compressed gas or compressed nitrogen may be used. However, in alternative embodiments the compressive force may be hydraulically applied. In said alternative embodiments, the fluid may be a water or an oil for example.

[0040] Referring to the transition from Figure 2 to Figure 3, there is provided a cross section of Figure 2 where the compressive force is applied by introducing a working fluid, the fluid being air in the preferred embodiment, into the recess 18A between the manifold frame 16A and the respective current collector 20A. In the preferred embodiment, each of the end plate assemblies 12A, 12B comprise at least one inlet 28A for injecting the working fluid into the recess 18A, 18B between the manifold frames 16A, 16B and the respective one of the current collectors 20A, 20B. In alternative embodiments, a single inlet port may be used to provide working fluid to both recesses 18A, 18B. Pressure in the working fluid is evenly distributed throughout the fluid thereby applying a uniform compressive force directly onto each of the current collectors 20A, 20B. This uniform compressive force is preferably axially aligned along a longitudinal axis of the electrolyser 10 in opposition to each other thereby clamping the fuel cell stack therebetween.

[0041] The electrolyser 10 comprises at least one inlet 28A, 28B for pumping water into the electrolyser and at least one outlet for collecting hydrogen gas through electrolysis. The inlet(s) and the outlet(s) are separate and distinct from the inlet 28A, 28B for the injection of the working fluid. As mentioned above, the working fluid which is injected into the recesses 18A, 18B between the manifold frames 16A, 16B and the respective current collectors 20A, 20B is fluidly separated from the water or watersolution which is pumped through the electrolyser to be electrolysed. In the preferred embodiment, the working fluid is fluidly separated at each end of the electrolyser by way of an O-ring 30 between the manifold frame 16A, 16B and the respective current collector 20A, 20B. While the preferred embodiment shows a single O-ring 30, multiple O-rings or other sealing methods known in the art may be employed to ensure there is no leakage between the working fluid and the fluid to be electrolysed. The O-ring 30 may be seated in a channel in the manifold frame 16A, 16B and / or the current collector 20A, 20B.

[0042] As mentioned above, the polymer electrolyte cell stack comprises a plurality of electrolyser cells each fuel cell comprising at least one bi-polar contact plate 24 and a catalyst coated membrane or catalyst coated electrode 26. The catalyst coated membrane or electrode 26 allows for the selective passage of hydrogen gas separated through electrolysis while retaining the oxygen gas for disposal, storage and / or release into the atmosphere through an outlet (not shown) in the electrolyser 10. As seen in Figure 1 , the inlet 34 for the water or water solution to be electrolysed may preferably be provided at a lower region of the electrolyser 10. As hydrogen gas is less dense than oxygen gas, the migration of hydrogen gas occurs in part without requiring additional recovery or pumping methods. The hydrogen gas may be removed or otherwise recovered from the electrolyser through outlet 36. The electrolyser 10 may comprise additional inlet and outlets as necessary based on scaling, recovery and storage methods.

[0043] In the preferred embodiment, each of the plurality of bi-polar plates 24 comprises a channel or plurality of channels for receiving and guiding water or water solution across the porous transport layers of the bi-polar contact plates 24 to be electrolysed. The inlet 34 is fluidly connected with each and every channel of theplurality of bi-polar contact plates 24. The bi-polar contact plates 24 may comprise manifolds for fluidly connecting the channel or channels of the adjacent bi-polar contact plates 24 in a fuel cell stack. In this manner water or water solution may be supplied to the outermost bi-polar contact plate 24 and flow through the channel or channels of the outermost bi-polar contact plate most adjacent to the inlet 34 through the intervening bi-polar contact plates 24 to the other outermost bi-polar contact plate 24. Each of the channels of the plurality of bi-polar contact plates 24 are in fluid connection with the at least one inlet 34 and with either the at least one outlet 36 for hydrogen gas or another outlet (not shown) for oxygen gas and / or any other remaining gases or particulates from the water or water solution which was electrolysed.

[0044] The method will now be described with reference to the Figures generally.

[0045] The electrolyser 10 may be assembled by arranging the plurality of bi-polar contact plates 24 in substantial axial alignment with the current collectors 20A, 20B seated within recesses 18A, 18B of the manifold frames 16A, 16B and end plates 14A, 14B. When aligned, a plurality of apertures (not shown) in the periphery of at least the end plates 14A, 14B thereby allowing a plurality of tie rods 32 to pass through pairs of aligned apertures and secured in place to locate and clamp the fuel cell stack and electrolyser 10 together. The current collectors 20A, 20B are moveably disposed within the recess 18A, 18B of the respective manifold frames 16A, 16B and each one located adjacent one of the outermost bi-polar contact plates 24.

[0046] Once assembled, a working fluid is injected into the respective recesses 18A, 18B between the manifold frames 16A, 16B and the current collectors 20A, 20B. The injection of the working fluid causes the buildup of pressure which is uniformly distributed to the current collectors 20A, 20B thereby applying a compressive force to move the current collectors 20A, 20B to or towards each other. As the currentcollectors 20A, 20B move to or towards each other the contact pressure between the plurality of bi-polar contact plates of the fuel cell stack is increased improving efficiency of the fuel cell stack therebetween. The method further provides for controlling the flow of working fluid into one or both of the respective recesses 18A, 18B thereby varying the pressure between the bi-polar contact plates 24. The method provides a solution to optimise the electrolysis process to ensure the most efficient production of hydrogen gas.

[0047] The electrolyser 10 will have an expected efficiency based on the design, shape, size and / or configuration of one or more of the components. However, the contact pressure between the plurality of bi-polar contact plates 24 may vary for a number of factors including, but not limited to, operating temperature changes, warping in the contact plates and / or environmental factors such as temperature and humidity. These factors may reduce or otherwise effect the electrolyser from operating under optimal conditions and therefore effect the efficiency of the electrolysis and therefore, the output of hydrogen gas. This may result in less production than is required or increased costs.

[0048] The inventor has invented a solution which addresses the need to vary the contact pressure uniformly across the contact plates of an electrolyser or fuel cell stack. As a result, the inventor believes that the solution provided herein is independent of the size and shape of the active area which provides for scalability which was previously not accessible for known solutions. In addition, the inventor believes it is independent of the number of cells in a stack of electrochemical systems, it is independent of the thermal expansion / contraction of stack components of electrochemical systems and / or is easy to adjust in response to a dynamic alteration of the gas output pressure in electrochemical systems. This solution advantageouslymay provide a number of benefits including, but not limited to, minimising membrane / separator thinning, conserving integrity of catalyst layers, eliminating heterogeneous local current distribution to give high electrochemical performance with lowest degradation rates, avoids inhomogeneous electrolyte / gas flows, avoids high interfacial electrical contact resistances between components in the stack and / or avoid mass transfer limitation which are caused by deformation (from non-uniform pressure) on stack components.

[0049] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term “comprises” and its variations, such as “comprising” and “comprised of” is used throughout in an inclusive sense and not to the exclusion of any additional features.

[0050] It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect.

[0051] The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

Claims

CLAIMS1. A polymer electrolyte membrane (PEM) electrolyser or fuel cell system for the extraction of hydrogen, the electrolyser or fuel cell system comprising: first and second end plate assemblies provided at longitudinal and opposed ends of the electrolyser or fuel cell system with an electrolyser stack positioned between the first and second end plate assemblies; the electrolyser stack comprising a plurality of electrolyser cells wherein each cell comprises bi-polar contact plates separated by a catalyst-coated membrane or catalyst coated electrodes and wherein the electrolyser stack is located between a pair of current collectors; wherein each of said current collectors is arranged adjacent said first and second end plate assemblies respectively with a compression arrangement being located at each end of the fuel cell stack to apply a compressive force on each of the current collectors thereby clamping the plurality of bi-polar contact plates and the plurality of catalyst-coated membranes and / or catalyst coated electrodes therebetween to apply uniform pressure across the bi-polar contact plates, wherein the compression arrangement is further configured to be adjustable to vary contact pressure between the plurality of bi-polar contact plates.

2. The electrolyser or fuel cell system according to claim 1 , wherein each of the first and second end plate assemblies comprise an end plate and a manifold frame positioned for engagement with the end plate.

3. The electrolyser or fuel cell system according to claims 1 or 2, wherein each of the first and second end plate assemblies and the respective one of the current collectors together form a respective terminal assembly.

4. The electrolyser or fuel cell system according to any one of claims 1 to 3, wherein each of the manifold frames comprise a recess for receiving a respective one of the current collectors.

5. The electrolyser or fuel cell system according to claim 4, wherein each of said respective current collectors is movably disposed within the corresponding recess.

6. The electrolyser or fuel cell system according to claim 4 or 5, wherein the current collectors are substantially equal to or thicker than their respective recesses.

7. The electrolyser or fuel cell system according to any one of claims 4 to 6, wherein the compressive force applied to the current collectors is by way of introducing a working fluid into the recess for applying the compressive force.

8. The electrolyser or fuel cell system according to claim 7, wherein the working fluid is introduced into the recess for each manifold frame via a respective fluid inlet port.

9. The electrolyser or fuel cell system according to claim 7 or 8, wherein each electrode assembly comprises a respective fluid inlet port.

10. The electrolyser or fuel cell system according to any one of claims 7 to 9, wherein the compressive force is applied directly to the current collectors.

11. The electrolyser or fuel cell system according to any one of claims 7 to 10, wherein the working fluid is an inert gas, an oil or a water.

12. The electrolyser or fuel cell system according to any one of claims 7 to 11 , wherein the working fluid is fluidly separated from an input fluid being electrolysed.

13. The electrolyser or fuel cell system according to any one of claims 7 to 12, wherein the working fluid is fluidly separated from an input fluid by one or more O- rings or seals.

14. The electrolyser or fuel cell system according to any one of claims 1 to 13, wherein the catalyst-coated membrane selectively allows hydrogen gas to migrate across the membrane and be collected from an outlet of the electrolyser or fuel cell system.

15. The electrolyser or fuel cell system according to claim 14, wherein the catalyst- coated membrane comprises a carbon mesh.

16. The electrolyser or fuel cell system according to any one of claims 1 to 15 further comprising at least one inlet for receiving a water or water solution and at least one outlet for expelling hydrogen gas.

17. The electrolyser or fuel cell system according to any one of claims 1 to 16, wherein each of the bi-polar contact plates comprises a manifold fluidly connectable to each other and / or the at least one inlet and the at least one outlet of the electrolyser.

18. The electrolyser or fuel cell system in accordance with any one of the preceding claims further comprising a plurality of tie rods passing through a peripheral region of each end plate assembly for positioning the electrolyser stack positioned between the first and second end plate assemblies.

19. A method of compressing an electrolyser cell stack of a polymer electrolyte membrane (PEM) electrolyser or fuel cell system, the method comprising: providing first and second end plate assemblies at longitudinal and opposed ends of the electrolyser or stack and positioning a fuel cell stack between the first and second end plate assemblies;positioning a manifold frame adjacent each of said endplate assemblies wherein each manifold frame further comprising a recess for housing respective current collectors adjacent to an outermost bi-polar contact plate of the fuel cell stack; injecting a fluid into one or both of the respective recesses of the manifold frames housing the current collectors of the first and second end plate assemblies so as to apply a compressive force to move the current collectors to or towards each other thereby increasing a contact pressure between the plurality of bi-polar contact plates of the fuel cell stack.

20. The method according to claim 18, further comprising controlling flow of fluid into one or both of the respective recesses to vary the pressure between the bi-polar contact plates.

21. The method according to claim 18 or 19, further comprising providing a plurality of flow paths such as pores provided in a porous layer in each of the plurality of bipolar contact plates.

22. The method according to any one of claims 18 to 20, further comprising arranging an inlet for allowing water for spreading water across each of the plurality of bi-polar contact plates.

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