Fuel cell stack, bipolar plate and gasket assembly and method of providing a seal around a bipolar plate

Abstract

A fuel cell stack assembly is provided with a bipolar plate (BPP) (2) in combination with a gasket (3), the gasket being adjacent to and covering the edge (5) of each BPP to protect the edge (5) of the corresponding BPP (2) and to electrically and thermally insulate the BPP (2). Advantageously, the gasket (3) is made of an elastically stretchable material and is prestressed by stretching to fit tightly around the edge (5) of the BPP (2) and is held in place by elastic contraction of the gasket (3) around the outer perimeter.

Description

Technical Field

[0001] The present invention relates to a gasket on a bipolar plate of a fuel cell. In particular, the present invention relates to a fuel cell stack, an assembly of a bipolar plate and a gasket and a method of providing a seal around a bipolar plate according to the preambles of the independent claims. Background Art

[0002] Polymer gaskets are commonly used to seal between anode and cathode plates, especially bipolar plates (BPPs). Not only does it require precise positioning during production, but it is also necessary to ensure that the gasket remains in place to achieve a long-term seal. The latter is a challenge because repeated thermal cycling of the fuel cell often causes the gasket to expand and contract relative to the bipolar plate, and eventually the gasket may move and deform significantly to the point of causing leakage.

[0003] Various examples of combinations of electrode plates and gaskets using protrusions or grooves to hold the gasket in place are disclosed in international patent application WO2009 / 010066, U.S. patent applications US2007 / 298310, US2012 / 164560 and US2014 / 0120452, German patent applications DE102014104015, DE102005046461 and DE102006054849 and German utility model DE202017103257.

[0004] US7081316 to Rock discloses a fuel cell having a bipolar plate sandwiched between two gaskets located in grooves on the bipolar plate near the edges of the bipolar plate. The gasket includes openings adjacent to opposite edges for passages required for conveying fuel gas and air along the stack. The bipolar plate assembly is made of metal plates joined so as to provide water passages between the plates for cooling.

[0005] Patent applications US2005 / 079400 to Sugiura and US2002 / 0122970 to Inoue disclose molded gaskets on bipolar assemblies. However, while this provides a good long-term seal, this is a complex and costly solution. Patent US8865362 to Korsgaard assigned to Serenergy A / S discloses a groove in which a gasket is laid to secure the gasket. International patent application WO2013 / 069888 to South Korea discloses a fuel cell assembly in which the gasket is provided with a protrusion along the edge that fits into a corresponding groove.

[0006] Providing long term stability of the gasket also presents a challenge to production as the gasket must be molded onto the plate or precisely positioned. It would be desirable to provide further improvements in the long term stability of the gasket on the bipolar plate and the ease of assembly during production. Summary of the invention

[0007] The object of the present invention is to provide an improvement over the prior art. Specifically, the object is to provide an improved gasket on a bipolar plate BPP and an improved production method. This object is achieved by a fuel cell stack, by an assembly of a BPP with a gasket and by a method of providing a seal around a bipolar plate, as set out in the independent claims and below.

[0008] The assembly comprises a BPP and a gasket for the BPP. Typically, a plurality of such assemblies are stacked to form part of a fuel cell stack, wherein an ion exchange membrane, particularly a proton conducting membrane, is present between adjacent BPPs.

[0009] For example, the BPP is provided with an anode side and a cathode side, which are integrally provided as part of a bipolar plate of a fuel cell stack. Alternatively, the plates are combined into a bipolar plate by attaching the anode plate and the cathode plate back to back to each other (e.g., by gluing or welding), wherein a sealed coolant flow field is located between the anode plate and the cathode plate. An example of such a cooling flow field is a channel, such as a zigzag channel.

[0010] For the BPP, various materials and production methods are possible. For example, a metal sheet, such as a steel sheet, is punched into the correct shape with the protrusions by a corresponding punch. Alternatively, the plate used is made by milling or molding. In the latter case, examples of materials are graphite, graphite-containing polymers, ceramics, metals and metal alloys.

[0011] A sealing non-conductive polymer gasket is provided for each BPP, such that one gasket is positioned between every two adjacent BPPs to seal the volume between the diaphragm and its adjacent BPPs through the gasket.

[0012] Each BPP has an edge along the outer perimeter of the BPP. The gasket is adjacent to and covers this edge and extends along and around the outer perimeter of the BPP to protect the edge of the corresponding BPP and to thermally and electrically insulate the BPP. In some practical embodiments, the gasket extends around the outer perimeter of only one of the plurality of BPPs, so that an equal number of gaskets as BPPs are provided to cover the edges of all BPPs.

[0013] In some embodiments, the fuel cell is of a type that operates at high temperatures. The term "high temperature" is a commonly used and understood term in the technical field of fuel cells and refers to an operating temperature above 120°C, in contrast to low temperature fuel cells that operate at lower temperatures (e.g., at 70°C). Optionally, the fuel cell operates in a temperature range of 120°C to 200°C. The gasket is correspondingly made of a polymer material that withstands such temperatures.

[0014] The gasket is made of a deformable (advantageously elastic) polymer so that during assembly of the stack the polymer is deformed by pressure into a secure seal between the BPPs.

[0015] For example, the gasket is made of a fluoropolymer. Examples are fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) or perfluoroalkoxy polymer (PFA). Fluoropolymers offer a high degree of long-term stability even when made very thin.

[0016] Advantageously, the gasket is made of an elastically stretchable material, such as an elastomeric polymer. Particularly useful are fluorinated elastomers, such as fluorinated carbon-based synthetic rubbers, including fluoroelastomers FKM and perfluoroelastomers FFKM or fluorinated silicones.

[0017] For example, in order to provide a tight connection with the BPP, the gasket is provided with an inner perimeter that is smaller than the outer perimeter of the BPP, so that the gasket must be prestressed by stretching before it fits tightly around the edge of the BPP. The gasket is held in place on the edge of the BPP by elastic contraction of the gasket around the outer perimeter. For example, the inner perimeter of the gasket is 1% to 5% shorter than the outer perimeter of the BPP.

[0018] Typically, the stack includes a conduit extending from one end of the stack to the opposite end to allow gas or coolant to flow through the conduit. In practice, a plurality of such conduits are provided for coolant and gas for the reaction. In the stack, such conduits are formed by stacked conduit segments, wherein each conduit segment is arranged to extend through an opening of a corresponding BPP. Such openings have edges that define the internal volume of the conduit segment.

[0019] In some embodiments, two adjacent BBPs are fixed relative to each other, and the gasket extends around the outer perimeter of one BPP (e.g., around the outer perimeter of only one of the plurality of BPPs) into the pipe segment of the adjacent BPP, wherein the gasket abuts at least a portion of the edge of the corresponding pipe segment of the adjacent BPP. Since the gasket abuts the outer perimeter of one BPP and the inner perimeter of the pipe of the adjacent BPP, the two adjacent BPPs are laterally locked to each other, thereby ensuring that they are in place in the stack. By thus locking each two subsequent BPPs to each other in this manner, the BPPs of the entire stack are locked to a fixed position defined by the plurality of gaskets.

[0020] In a practical embodiment, the gaskets of adjacent BPPs in the stack closely abut each other and form an outer seal along the stack.

[0021] Due to the fact that the gasket surrounds the BPPs of the stack, the stack is electrically insulated from the surrounding environment. Optionally, however, each gasket includes a probe opening for receiving an electrical probe in order to measure the potential of each BPP for diagnosis. The probe opening extends from the outside of the gasket through the gasket to the BPP to measure the voltage of the PBB by the probe. For example, the probe opening of the gasket extends to the BPP adjacent to the BPP surrounded by the gasket along the outer perimeter.

[0022] To prevent leakage through the probe opening, the gasket provides a seal between the probe opening and the gas flow field. Optionally, the gasket comprises a rib closely abutting the BPP between the probe opening and the flow field, and / or the BPP comprises a protrusion sealingly abutting the gasket.

[0023] In some generally advantageous embodiments, the gasket includes a rib or ribs against a first side of the BPP, and the BPP includes a protrusion or protrusions on the first side, wherein the rib and the protrusion are arranged side by side and parallel to the outer perimeter. The rib is disposed at a greater distance from the outer perimeter than the protrusion, such that the protrusion blocks the rib from passing over the protrusion toward the outer perimeter and prevents the gasket from sliding outwardly in a direction away from the outer perimeter.

[0024] Such protrusions are advantageously provided before the anode and cathode plates are combined into a BPP, for example a tool acting on one side of such plates presses into the material, which causes the protrusions to be formed on the opposite side. In this way, both the cathode and anode plates may be provided with protrusions before being combined into a BPP, so that the BPP finally has protrusions on both sides.

[0025] Optionally, the gasket has a first portion that fits along and around the outer perimeter of only one BPP and a second portion that extends between two adjacent BPPs. Advantageously, the second portion includes ribs on opposite sides to block detachment of the ribs by protrusions of both of the two adjacent BPPs. For example, the two portions form a first leg and a second leg of an L-shaped gasket when viewed in a cross section provided as a section through the gasket material perpendicular to the edge. For sealing purposes, the gasket advantageously extends between two adjacent BPPPs, thereby enclosing a pipe segment to seal the pipe segment.

[0026] As mentioned, typically, the BPP includes flow patterns on either side of the BPP to flow hydrogen on one side and oxygen on the opposite side. Advantageously, each gasket sealingly extends around one of the flow patterns of the BPP to prevent gas from escaping along the outer perimeter. The diaphragm can seal the flow pattern of an adjacent BPP. Optionally, the diaphragm is optionally disposed between the gasket and the BPP such that one of the sides of each gasket is directly adjacent to the surface of the BPP and the opposite side is adjacent to the diaphragm.

[0027] Prior to installation in the stack, the bipolar plate is optionally provided as a unitary assembly of the bipolar plate and the gasket, wherein the gasket is positioned on the BPP, for example by telescoping as explained above, so as to abut and cover the edge and extend along the outer perimeter of the BPP to protect the edge. Each of such unitary assemblies can then be safely transported to a location where a selected number of such BPP / gasket assemblies are combined into a fuel cell stack having a desired number of BPP / gasket combinations.

[0028] For example, the fuel cell in the fuel cell system is a high temperature polymer electrolyte membrane fuel cell (HT-PEM) operating at above 120°C, HT-PEM fuel cells are different from low temperature PEM fuel cells, which operate at temperatures below 100 degrees (e.g., at 70 degrees). The normal operating temperature of the HT-PEM fuel cell is in the range of 120 degrees Celsius to 200 degrees Celsius, for example, in the range of 160 degrees Celsius to 170 degrees Celsius. The polymer electrolyte membrane PEM in the HT-PEM fuel cell is based on an inorganic acid, usually a polymer membrane, such as polybenzimidazole doped with phosphoric acid. Advantageously, the HT-PEM fuel cell can tolerate relatively high CO concentrations, and therefore does not require a PrOx reactor between the reformer and the fuel cell stack, which is why a simple, lightweight and inexpensive reformer can be used, which minimizes the overall size and weight of the system, in line with the purpose of providing a compact fuel cell system, for example, for the automotive industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be described hereinafter with reference to the accompanying drawings, in which

[0030] Figure 1A Diagrammatically illustrate the assembly of BPP and gasket;

[0031] Figure 1B The illustration shows an enlarged corner region of FIG. 1 ;

[0032] Figure 2A The gasket is shown extending into the pipe;

[0033] Figure 2B Shown from the opposite side Figure 2A pipeline;

[0034] Figure 3 is a close-up illustration of a cross section of a gasket;

[0035] Figure 4 showing the probe path in the gasket;

[0036] Figure 5 showing a cross-sectional view of a probe-pathway;

[0037] Figure 6 Illustration of the gasket and flange of the BPP;

[0038] Figure 7 Shows the details of BPP. DETAILED DESCRIPTION

[0039] Figure 1A The diagram illustrates an assembly 1 between a bipolar plate (BPP) 2 and a gasket 3, of which only half is shown for illustrative purposes. In practice, the gasket 3 extends completely around the BPP 2 along the edge 5 of the BPP 2. The gasket 3 has a number of functions, including

[0040] - shock resistance,

[0041] - Protect the edges of the BPP during assembly,

[0042] - electrical insulation,

[0043] - thermal insulation,

[0044] - easy positioning of the BPPs relative to each other during stacking,

[0045] - maintain the position of the BPPs relative to each other,

[0046] - prevent separation or gradual movement of the gasket which could lead to leakage,

[0047] - Despite being airtight, the BPP can still be accessed by an electrical probe.

[0048] Advantageously, the shim 3 is made slightly shorter than the length around the outer perimeter of the BPP so that the shim 3 must be telescoped to fit tightly around the edge 5. This eases assembly and holds the shim 3 in place on the BPP 2.

[0049] For example, the perimeter of the BPP is 1% to 5% longer than the length along the inner perimeter of the gasket. Typically, the BPP is rectangular, and the gasket is rectangular, with two first gasket portions and two second gasket portions that combine to form a rectangle, wherein the first portion is longer than the second portion. Optionally, the long edge 5A of the BPP is 1.5% longer than the corresponding long portion 3A of the gasket 3, so that the gasket 3 for installation is first fitted around the short edge 5B of the rectangular BPP, and then stretched parallel to the long edge 5A of the BPP 2 to fit tightly around the relatively short edge 5B of the BPP 2.

[0050] In order to provide good expansion and contraction capabilities, the gasket is advantageously made of an elastomeric material. Particularly useful are fluorinated elastomers, such as fluorinated carbon-based synthetic rubbers, including fluoroelastomers FKM and perfluoroelastomers FFKM or fluorinated silicones.

[0051] The BPP 2 has a flow channel pattern 4 on either side to flow air on one side to provide oxygen to one side of the membrane and hydrogen fuel to the opposite side of the membrane. A membrane is provided between each pair of stacked BPPs. Air and hydrogen fuel as well as coolant are delivered throughout the stack by corresponding conduits 6.

[0052] To make it easier to identify the extension of the gasket, Figure 1B The enlarged greyscale image in FIG. 1 shows a corner 2A of the assembly 1 of FIG. 1a, where the spacer 3 has a darker tone than the BPP. It is seen that the spacer 3 not only extends around the edge 5 of the BPP 2, but also includes an upstanding raised ring 7, which is attached to the pipe portion 6A of an adjacent BPP 2 in the stack of BPPs 2 to fix the position of two adjacent BPPs 2 relative to each other. The latter is Figure 2A 1 is shown for a stack of 2 BBPs. The entire stack of BPPs is secured in place by using such a spacer 3 comprising an upstanding raised ring 7 on each of the BPPs 2. Figure 2B Corner 2A is shown viewed from the opposite side.

[0053] Figure 3The abutment of the gasket 3 against the BPP 2 is illustrated in more detail. The transverse cross-section of the long portion 3A of the gasket 3 is largely L-shaped, with a short leg 9A forming a right angle with a long leg 9B. The short leg 9A abuts the outer perimeter 5 of the BPP 2, and the long leg 9B forms a spacer between two adjacent BPPs. Within the right angle formed by the two legs 9A, 9B, a set of first longitudinal ribs 8A extend from the long leg 9B. Correspondingly, a set of second longitudinal ribs 8B extend from the opposite side of the long leg 9B. The first rib 8A is illustrated as being rounded, however, typically the second rib 8B is also rounded, as long as it does not press against an adjacent BPP, which is why the second rib is illustrated as having a flat surface abutting against the BPP 2.

[0054] Figure 3 Also shown is a fuel cell membrane 14 located between the BPPs 2 for transporting hydrogen ions between the electrodes. Figure 6 , the fuel cell membrane 14 is illustrated in darker shading. As illustrated, a first gasket side of the gasket directly abuts a surface of one BPP, and an opposite gasket side directly abuts the membrane.

[0055] Since the spacers 3 are elastic and surround the edge 5 of the BPP 2 along the outer perimeter, the edge 5 of the BPP 2 is protected from damage, which is a great advantage. However, access to the BPP should not be prevented to be able to measure the voltage of the BPP, for example for diagnostic purposes. In order to allow an electrical probe to be inserted between the spacers 3 and to contact the BPP, the spacers 3 include a probe path 10 extending from the outside of the spacers 3 to the BPP 2 behind the spacers 3. Figure 5 As best seen in FIG. 8 , the probe passage 10 extends beyond one of the outer second ribs 8B to provide appropriate contact with the BPP 2 .

[0056] like Figure 6 As illustrated in FIG, the longitudinal rib 8A on the gasket 3 cooperating with the longitudinal protrusion 11 on the BPP prevents the gasket 3 from sliding outwardly away from the BPP 2. This is important during repeated heating and cooling of the fuel cell. When the gasket 3 is in abutment with the edge 5 of the BPP 2, the longitudinal protrusion 11 on the BPP 2 is disposed between the edge 5 of the BPP 2 and the location of the longitudinal rib 8A of the gasket 3. Optionally, the protrusion is adjacent to the longitudinal rib 8A to hold the gasket 3 in place. A similar arrangement of protrusions is provided for the longitudinal rib 8B on the opposite side of the gasket 3.

[0057] When the BPP has a protrusion 11 on the side where the diaphragm 14 is provided, the diaphragm 14 is correspondingly deformed by the protrusion 11, so that the protrusion can still achieve the purpose of preventing part of the gasket 3 from being disengaged from its dedicated position.

[0058] By way of example, the BPP 2 is provided as a pair of anode and cathode plates that are glued together to form the BPP. Figure 7 An example is illustrated in . In addition to the flow patterns for hydrogen and oxygen (typically air) for the fuel cell, a coolant flow pattern is provided between the anode plate 16 and cathode plate 17 that provides for efficient cooling of the BPP.

[0059] Figure 7 The diagram illustrates the passage 13 from the pipe 6 into the BPP 2. Figure 1A As illustrated in FIG, there are three ducts 6 located near any narrow edge 5B of the BPP 2. Figure 7 1 is connected to each of the pipes 6. One of the six pipes 6 provides coolant into the channel flow pattern provided between the anode plate 16 and the cathode plate 17. Another of the six pipes 6 is used to exhaust coolant from the BPP 2. Hydrogen from one of the other pipes 6 flows to a corresponding set of passages 13 between the anode plate 16 and the cathode plate 17 of the BPP and passes through the openings in the anode plate to the flow pattern 4 on the outer anode side of the BPP. Similarly, oxygen (such as air) flows from the corresponding pipes 6 into the corresponding passages 13 between the anode plate 16 and the cathode plate 17 of the BPP 2 and passes through the openings in the cathode plate to reach the flow pattern 4 on the outer cathode side of the BPP. Figure 4 Such openings 15 are shown in flow communication with a set of passages 13. Correspondingly, one conduit 6 is for the water-containing oxygen-deficient air from the cathode side of the BPP after reaction in the fuel cell, and another conduit 6 is for the anode exhaust gas.

[0060] Figure 7 Also seen is a protrusion cooperating with the second longitudinal rib 8B of the gasket, Figure 3 Similar projections and cooperating ribs are provided at various other locations on the BPP 2 and the gasket 3.

[0061] The projections 11 are advantageously provided by pressing a tool onto one side of the anode plate 16 and / or cathode plate 17 and deforming the plate to receive a depression on one side and a corresponding protrusion on the opposite side. This can be done for metal plates and also during the moulding of plates made of conductive polymers, in particular carbon-containing polymers.

Claims

1. A fuel cell stack, comprising a stack of a plurality of bipolar plates (2), wherein an ion exchange membrane (14) is located between adjacent bipolar plates (2), wherein each of the plurality of bipolar plates (2) has an edge (5) along the outer periphery of the bipolar plate, wherein a plurality of sealing non-conductive polymer gaskets (3) are provided, wherein one gasket (3) is provided between every two adjacent bipolar plates (2) to seal the volume between the membrane (14) and its adjacent bipolar plates (2) through the gasket (3), wherein the gasket (3) is adjacent to and covers the edge (5) and extends along and around the outer perimeter of the bipolar plate (2) to protect the edge (5) of the corresponding bipolar plate (2) and to electrically and thermally insulate the bipolar plate (2), wherein the gasket (3) is made of a deformable elastic polymer, and the deformable elastic polymer is configured to be deformed by pressure into a state of firm sealing between the bipolar plates during assembly of the stack, Features The gasket (3) comprises a rib (8A) abutting against a first side of the bipolar plate (2), the rib (8A) also being made of the deformable elastic polymer, and the bipolar plate comprising a protrusion (11) on the first side, wherein the rib (8A) and the protrusion (11) are arranged side by side and parallel to the outer perimeter, wherein the rib (8A) is arranged at a greater distance from the outer perimeter than the protrusion (11) so that the protrusion (11) blocks the rib (8A) from passing over the protrusion (11) toward the outer perimeter and prevents the gasket (3) from sliding outward in a direction away from the outer perimeter.

2. A stack according to claim 1, wherein the gasket (3) is made of an elastically stretchable polymer, the inner perimeter of the gasket is smaller than the outer perimeter of the bipolar plate, and wherein the gasket (3) is prestressed by stretching to fit tightly around the edge (5) of the bipolar plate (2) and is held in place by elastic contraction of the gasket (3) around the outer perimeter.

3. The stack according to claim 2, wherein the inner perimeter of the gasket (3) is 1% to 5% shorter than the outer perimeter of the bipolar plate (2).

4. A stack according to any one of claims 1 to 3, wherein the stack includes a pipe (6) extending from one end of the stack to the opposite end to allow gas or coolant to flow through the pipe (6), the pipe (6) being formed by stacked pipe segments (6A), wherein each pipe segment (6A) is an opening extending through a corresponding bipolar plate (2), the opening having an edge defining an inner volume of the pipe segment (6A), wherein the gasket (3) extends around the outer periphery of only one of the plurality of bipolar plates (2) and extends a portion (7) into the pipe segment (6A) of an adjacent bipolar plate (2) and abuts a portion of the edge of the corresponding pipe segment (6A) to fix two adjacent bipolar plates (2) relative to each other.

5. The stack according to any one of claims 1 to 3, wherein the gaskets (3) of adjacent bipolar plates (2) in the stack abut against each other to form an outer seal along the stack.

6. A stack according to any one of claims 1 to 3, wherein each gasket (3) includes a probe opening (10) for receiving an electrical probe, wherein the probe opening (10) extends from the outside of the gasket (3) through the gasket (3) to the bipolar plate (2) to measure the voltage of the bipolar plate (2) by the probe.

7. The stack according to claim 6, wherein the probe opening (10) extends to the bipolar plate (2) adjacent to the bipolar plate whose outer perimeter is covered by the gasket (3).

8. A stack according to any one of claims 1 to 3, wherein the gasket (3) along the outer periphery has a first portion (3A) fitted around the outer periphery of only one bipolar plate (2) and a second portion (3B) extending between two adjacent bipolar plates (2), wherein the second portion (3B) includes ribs (8A, 8B) located on opposite sides to prevent the protrusion (11) from detaching from both of the two adjacent bipolar plates (2), wherein the first portion (3A), the second portion (3B) and the ribs (8A, 8B) are made of the deformable elastic polymer.

9. A stack according to claim 8, wherein the two parts (3A, 3B) form a first leg and a second leg of an L-shaped spacer (3) when viewed in a cross section in a plane perpendicular to the edge (5).

10. A stack according to claim 9, wherein the first leg and the second leg are a short leg (9A) and a long leg (9B), wherein the short leg (9A) is adjacent to and covers the edge (5) and extends along and around the outer periphery of the bipolar plate (2), and wherein the long leg (9B) forms a spacer between two adjacent bipolar plates, and wherein a set of first longitudinal ribs (8A) extend from the long leg (9B) within the right angle formed by the two legs (9A, 9B).

11. The stack according to claim 4, wherein the gasket (3) extends between two adjacent bipolar plates (2) so as to surround the duct segment (6A) to seal the duct segment (6A).

12. A stack according to any one of claims 1 to 3, wherein the bipolar plate (2) includes a flow pattern (4) on either side to allow hydrogen to flow on one side and oxygen to flow on the opposite side, wherein the gasket (3) extends sealingly around one of the flow patterns to prevent the edge (5) of the bipolar plate (2) from detaching.

13. An assembly of a bipolar plate (2) and a gasket (3) for use in a stack according to any one of claims 1 to 12, wherein the bipolar plate has an edge (5) along an outer perimeter around the bipolar plate (2), wherein the gasket is adjacent to and covers the edge (5) and extends along the outer perimeter of the bipolar plate (2) to protect the edge (5) and to provide a seal, characterized in that The deformable elastic polymer is made of an elastically stretchable polymer, the inner perimeter of the gasket (3) is smaller than the outer perimeter of the bipolar plate (2), and the gasket (3) is prestressed by stretching to fit tightly around the edge (5) of the bipolar plate (2) and is held in place by elastic contraction of the gasket (3) around the outer perimeter, wherein the inner perimeter of the gasket (3) is 1% to 5% shorter than the outer perimeter of the bipolar plate (2), wherein the gasket (3) includes a stop against a first side of the bipolar plate (2) The bipolar plate comprises a rib (8A), the rib also being made of the deformable elastic polymer, and the bipolar plate comprising a protrusion (11) on the first side, wherein the rib (8A) and the protrusion (11) are arranged side by side and parallel to the outer perimeter, wherein the rib (8A) is arranged at a greater distance from the outer perimeter than the protrusion (11) so that the protrusion (11) blocks the rib (8A) from passing over the protrusion (11) toward the outer perimeter and prevents the gasket (3) from sliding outward in a direction away from the outer perimeter.

14. An assembly according to claim 13, wherein the gasket (3) along the outer periphery of the bipolar plate (2) has a first portion (3A) fitted around the outer periphery of only one bipolar plate (2) and a second portion (3B) extending between two adjacent bipolar plates (2), wherein when viewed in a cross section perpendicular to the edge (5), the two portions (3A, 3B) are made of the elastically stretchable polymer and form a first leg (9A) and a second leg (9B) of the L-shaped gasket (3), wherein the first leg (9B) includes the rib (8A), which is also made of the elastically stretchable polymer.

15. A method of providing a seal around a bipolar plate (2) of a fuel cell stack, the fuel cell stack comprising a plurality of stacked bipolar plates (2), an ion exchange membrane (14) being located between adjacent bipolar plates (2), wherein each of the plurality of bipolar plates (2) has an edge (5) along an outer perimeter of the bipolar plate (2), wherein the method comprises: Providing a plurality of sealed non-conductive polymer gaskets (3); and placing a gasket (3) between every two adjacent bipolar plates (2) to seal the volume between the diaphragm (14) and its adjacent bipolar plates (2) through the gasket (3), characterized in that the method comprises: providing the gasket (3) of elastically stretchable polymer material, the inner perimeter of the gasket being smaller than the outer perimeter of the bipolar plate (2); and when the gasket (3) is placed on the bipolar plate (2), prestressing the gasket (3) by stretching so that the gasket (3) fits tightly around the edge (5) of the bipolar plate (2) and the gasket is held in place by elastic contraction of the gasket (3) around the outer perimeter, so that the gasket (3) is adjacent to and covers the edge (5) of the bipolar plate (2) and extends along and around the outer perimeter of the bipolar plate (2). The invention relates to a bipolar plate (2) and a gasket (3) comprising a first sidewall (8A) and a second sidewall (8A) extending to protect the edge (5) of the corresponding bipolar plate (2) and electrically insulating the bipolar plate (2), wherein the inner perimeter of the gasket (3) is 1% to 5% shorter than the outer perimeter of the bipolar plate (2), wherein the gasket (3) comprises a rib (8A) abutting against a first side of the bipolar plate (2), the rib (8A) also being made of the elastically stretchable polymer material, and the bipolar plate comprising a protrusion (11) on the first side, wherein the rib (8A) and the protrusion (11) are arranged side by side and parallel to the outer perimeter, wherein the rib (8A) is arranged at a greater distance from the outer perimeter than the protrusion (11) so that the protrusion (11) blocks the rib (8A) from passing over the protrusion (11) toward the outer perimeter and prevents the gasket (3) from sliding outward in a direction away from the outer perimeter.

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