Fuel cell assembly
Patent Information
- Authority / Receiving Office
- HK · HK
- Patent Type
- Patents
- Current Assignee / Owner
- POWERCELL SWEDEN AB
- Filing Date
- 2023-09-15
- Publication Date
- 2026-07-10
AI Technical Summary
In existing fuel cell stacks, reactants can easily bypass the flow field at the edge of the flow field plate, resulting in insufficient sealing, poor contact between the bypass stop element and adjacent components, and affecting current output and sealing performance.
A fuel cell assembly is designed with a bypass stop element with a pointed tip to compress the multilayer membrane electrode assembly, ensuring a tight seal. The sealing performance is further enhanced by a sub-gasket and a gas diffusion layer, in conjunction with a bead seal to prevent reactant leakage.
This effectively avoids the bypass flow of reactants, improves the sealing performance and current output of fuel cell components, and reduces manufacturing complexity and cost.
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Abstract
Description
Technical Field
[0001] This invention relates to a fuel cell assembly comprising at least a first flow field plate, a second flow field plate, and a multilayer membrane electrode assembly according to the preamble of claim 1. Such a fuel cell assembly is generally referred to as a unit fuel cell. Background Technology
[0002] Typically, a fuel cell stack comprises multiple membrane electrode assemblies (MEAs) sandwiched between so-called bipolar plates (BPPs). The bipolar plates are combinations of the first and second flow field plates mentioned above, and are usually made of conductive materials such as metals or graphite. Typically, the flow field plates have a flow field for the reactants on one side and a flow field for the cooling fluid on the other. Therefore, the cooling fluid flow fields face each other, while the reactant flow fields face the MEAs. However, other designs are also known, particularly those with a third intermediate layer providing the cooling flow field. During fuel cell stack operation, the current generated by the MEAs results in a potential difference between the bipolar plate assemblies, and its height depends on the uniform distribution of reactants above the electrode surfaces. Therefore, it is necessary to distribute the reactants over the entire surface of the electrodes to obtain the highest current output.
[0003] The downside is that the flow field of the flow field plate also constitutes a flow resistance to the reactants, so the reactants tend to flow around the edge (boundary region) of the flow field plate.
[0004] Therefore, in the prior art, it has been proposed to place a bypass stop element in the boundary region between the flow field and the so-called bead seal, which is adapted to provide a seal of the unit fuel cell to the environment.
[0005] However, it has been shown that due to stacking defects, the sealing contact between the bypass stop element and the adjacent multilayer film electrode assembly or another adjacent flow field plate may be insufficient. Summary of the Invention
[0006] Therefore, the object of the present invention is to provide an improved bypass stop element that reliably prevents the bypass of reactive fluid in the flow field.
[0007] This objective is achieved by the fuel cell assembly according to claim 1 and the flow field plate according to claim 14.
[0008] Below, a fuel cell assembly is provided, comprising at least a first flow field plate and a second flow field plate sandwiching a multilayer membrane electrode assembly. This fuel cell assembly may also be referred to as a unit fuel cell. The flow field plates themselves are typically placed back-to-back, thus providing a so-called bipolar plate. Furthermore, the multilayer membrane electrode assembly includes at least one first electrode facing the first flow field plate, a second electrode facing the second flow field plate, and membranes separating the electrodes. Each flow field plate has a flow field structure projecting from a reference plane of the flow field plate for distributing reactants over an effective region defined by the respective electrode. Additionally, on the electrode-facing front side, at least one sealing element is arranged between the first and second flow field plates, adapted to prevent reactant leakage into the environment, and at least one bypass stop element is arranged in the boundary region between the flow field structure of at least one flow field plate and the sealing element to prevent reactants from bypassing the flow field structure, wherein the bypass stop element projectes from the respective reference plane of the flow field plate.
[0009] To prevent reactant bypass, even if stacking defects affect the seal between the bypass stop element and the membrane electrode assembly sandwiched in between, it is recommended that at least one bypass stop element have a tip suitable for compressing the multilayer membrane electrode assembly. According to this application, the tip is the region of the bypass stop element in which at least a portion of the surface interacting with the membrane electrode assembly is made as small as possible. Therefore, the sealing function of the bypass stop element can be ensured even if the distance between the bypass stop element and the membrane electrode assembly is slightly increased due to stacking tolerances. Thus, the tip increases the pressure within a small and limited area, thereby providing excellent sealing performance.
[0010] According to a preferred embodiment, the multilayer membrane electrode assembly further includes at least one sub-waist, wherein the at least one sub-waist is adapted to frame the multilayer membrane electrode assembly, and wherein the at least one sub-waist is adapted to extend at least partially above at least one bypass stop element, such that the tip of the bypass stop element compresses the at least one sub-waist. This ensures that pressure applied by the tip or bypass element generally does not damage the electrodes or membrane of the multilayer membrane electrode assembly.
[0011] According to another preferred embodiment, the multilayer film electrode assembly further includes at least one gas diffusion layer located between the first electrode and the first flow field plate, and preferably includes a second gas diffusion layer located between the second electrode and the second flow field plate, wherein the at least one gas diffusion layer is adapted to extend at least partially above at least one bypass stop element such that the tip of the bypass stop element compresses at least one gas diffusion layer.
[0012] Typically, a gas diffusion layer provides a certain thickness on the sub-gasket that surrounds and supports the membrane electrode assembly. Therefore, compressing the gas diffusion layer increases the force applied by the tip, thereby increasing the sealing performance of the bypass stop element.
[0013] A further preferred embodiment is a bead seal surrounding the flow field plate and thus the flow field structure, wherein the bead seal protrudes from the reference surface and is adapted to directly or indirectly contact the bead seal of another corresponding flow field plate to prevent reactants from leaking into the environment. Bead seals have proven to provide excellent sealing performance for the environment and are easy to manufacture.
[0014] According to another preferred embodiment, the first flow field plate has at least one first bypass stop element, and the second flow field plate has at least one second bypass stop element, wherein the first and second bypass stop elements are arranged opposite to each other such that the first and second bypass stop elements form at least one bypass stop element assembly, wherein the first bypass stop element has a tip, and the second bypass stop element has a blunt portion, wherein the blunt portion of the second bypass stop element is adapted to be recessed by the tip of the first bypass stop element. The synergistic effect of the two bypass stop elements further enhances the sealing function.
[0015] Therefore, it is advantageous that, in cross-section, the blunt portion of the second bypass stop element is wider than the pointed portion of the first bypass stop element. This allows for certain stacking and alignment tolerances without compromising the function of the bypass stop elements.
[0016] In another advantageous embodiment, the bypass stop element is a continuous element extending at least along the length of the flow field structure, wherein the bypass stop element is connected to the sealing element at least upstream of the flow field structure in the direction of the reactant stream. This design allows for simplified manufacturing. Known bypass stop elements are discrete components that must be manufactured individually, which in turn increases the efficiency of the manufacturing process.
[0017] However, the bypass stop element can also be designed as multiple discrete bypass stop elements, preferably multiple bypass stop element assemblies, arranged in the boundary region between the flow field structure and the bead seal of at least one flow field plate. This allows the flow field plate to be manufactured using existing manufacturing tools and processes with only minor modifications.
[0018] According to another preferred embodiment, the first bypass stop element with a pointed portion is a discrete element, and the second bypass stop element with a blunt portion is a continuous element extending at least along the length of the flow field structure; alternatively, the first bypass stop element with a pointed portion is a continuous element extending at least along the length of the flow field structure, and the second bypass stop element with a blunt portion is a discrete element. By designing one bypass stop element as a discrete element and the other as a continuous element, stacking and alignment tolerances can be increased without compromising the sealing function of the bypass stop elements.
[0019] At least one bypass stop element can be an integral part of the flow field plate, but the bypass stop element can also be a separate element from the flow field plate, wherein, in particular, the bypass stop element is a frame-like element. When the bypass stop element is part of the flow field plate, it can be manufactured simultaneously with the flow field plate, which accelerates the manufacturing process. Separate elements, in turn, allow for quite flexible arrangement.
[0020] Therefore, it is particularly preferred that at least one bypass stop element is part of a sub-gasket or gas diffusion layer. This reduces the total number of parts that must be stacked, thereby reducing the risk of any misalignment and increasing the sealing function of the bypass stop element.
[0021] Because the reactant hydrogen supplied at the anode is a very small molecule, proper sealing on the anode side is particularly difficult. Therefore, preferably, a bypass stop element with a pointed tip is arranged at least on the anode side. The sealing function of the bypass stop element is enhanced by the increased local compressive pressure from the tip.
[0022] Another aspect of the invention relates to a flow field plate, particularly an anode flow field plate for the aforementioned fuel cell assembly, wherein the flow field plate has at least one bypass stop element with a tip adapted to compress the multilayer membrane electrode assembly.
[0023] Further preferred embodiments are defined in the dependent claims, as well as in the specification and drawings. Therefore, elements described or shown in combination with other elements may exist alone or in combination with other elements without departing from the scope of protection.
[0024] Preferred embodiments of the invention are described below with reference to the accompanying drawings, which are merely illustrative and not intended to limit the scope of protection. The scope of protection is defined only by the appended claims. Attached Figure Description
[0025] The attached diagram shows:
[0026] Figure 1: Schematic diagram of the flow field plate according to the first preferred embodiment, particularly the anode flow field plate;
[0027] a: Top view
[0028] b: Cross-sectional view
[0029] Figure 2: Schematic diagram of a flow field plate for a bipolar plate assembly, particularly a cathode flow field plate, the bipolar plate assembly including the flow field plate according to the embodiment shown in Figure 1;
[0030] c: Top view
[0031] d: Cross-sectional view
[0032] Figure 3: A schematic cross-sectional view of a fuel cell assembly including a flow field plate according to the embodiments shown in Figures 1 and 2;
[0033] Figure 4: Schematic cross-sectional view of a fuel cell assembly according to the second embodiment;
[0034] Figure 5: Schematic diagram of the flow field plate according to the third preferred embodiment, particularly the anode flow field plate;
[0035] a: Top view
[0036] b: Cross-sectional view
[0037] Figure 6: Schematic diagram of the flow field plate according to the fourth preferred embodiment, particularly the anode flow field plate;
[0038] a: Top view
[0039] b, c: Cross-sectional views. Detailed Implementation
[0040] In the following text, identical or similar functional elements are indicated by the same reference numerals. The accompanying drawings are schematic only. Therefore, any distances, dimensions, or angles are schematic and do not represent actual dimensions.
[0041] Figures 1, 2, and 3 schematically illustrate a first embodiment of a fuel cell assembly 1. Thus, Figure 1a depicts a schematic top view of the first flow field plate 2, particularly the anode flow field plate, while Figure 2a depicts a schematic top view of the second flow field plate 4, particularly the cathode flow field plate. In fuel cell technology, the anode and cathode flow field plates are combined to form a so-called bipolar plate 6. Therefore, Figures 1b and 2b show cross-sectional views of the bipolar plate 6 including the first and second flow field plates 2, 4, with Figure 1b showing more details of the first (anode) flow field plate 2 and Figure 2b showing more details of the second (cathode) flow field plate 4. Figure 3 depicts a cross-sectional view of a fuel cell assembly 8 including two bipolar plates 6-1 and 6-2, which sandwich a multilayer membrane electrode assembly 10 in between.
[0042] In the illustrated embodiment, each flow field plate 2, 4 has a front side 20, 40 and a rear side 21, 41. Both the front and rear sides are equipped with flow fields 22, 23, 42, 43, which define an effective region on the flow field plate. The flow fields 22, 42 on the front side 20, 40 are channel-like structures protruding from the reference planes 24, 44 of the flow field plates 2, 4, and are adapted to distribute reactants to the corresponding multilayer film electrode assembly 10 (see FIG. 3). The flow fields 23, 43 on the rear side are adapted to guide cooling fluid. As can be seen from FIG. 1b, FIG. 2b and FIG. 3, due to the back-to-back arrangement of the flow field plates 2, 4, the channel-like structures of the flow fields 23, 43 on the rear side are arranged in such a way that they form closed tubular channels adapted to uniformly distribute cooling fluid above the flow field region.
[0043] The multilayer membrane electrode assembly 10 typically includes a three-layer base membrane electrode assembly 11 having an anode 12, a membrane 13, and a cathode 14. To provide a uniform distribution of reactants to the electrodes, the multilayer membrane electrode assembly 10 also includes gas diffusion layers 15 and 16, which are disposed at the electrodes facing the respective flow field plates 2 and 4. As shown, the gas diffusion layers 15 and 16 are slightly larger than the flow fields 22 and 42, ensuring uniform distribution of reactants across the entire effective region defined by the size and extension of the respective electrodes 12 and 14. Furthermore, the gas diffusion layers 15 and 16 and the three-layer membrane electrode assembly 11 are framed by so-called sub-gaskets 17 and 18, the size and shape of which are adapted to the size and shape of the flow field plates 2 and 4.
[0044] Each flow field plate 2, 4 also includes a fuel inlet 32, an oxidant inlet 34, and a cooling fluid inlet 36, which are in fluid communication (not shown) with the corresponding flow fields 22, 42, 23, 43, for supplying and distributing fuel (especially hydrogen-rich gas), oxidant (especially air), and cooling fluid (especially water) to the effective area of the bipolar plate.
[0045] Similarly, each flow field plate 2, 4 also includes a fuel outlet 33, an oxidant outlet 35, and a cooling fluid outlet 37, which are in fluid communication (not shown) with the corresponding flow fields 22, 42, 23, 43 for discharging fuel, oxidant, and cooling fluid from the active region and from the bipolar plate.
[0046] To prevent accidental mixing of fluids, each inlet 32, 34, 36 and each outlet 33, 35, 37 is framed by bead seals 52, 53, 54, 55, 56, 57. Furthermore, specifically, such flow field plates and flow fields 22, 42 are sealed by bead seals 58, 59 surrounding the entire plate. As shown in the cross-sectional view, the bead seals protrude from the reference planes 24, 44 and have a height greater than the channel-like structure of flow fields 22, 42, 23, 43. Other sealing methods are also applicable.
[0047] As described above, the flow fields 22 and 42 of the flow field plates 2 and 4 create a certain flow resistance to the reactants. Therefore, the reactants tend to bypass the flow fields in the boundary regions 26 and 46 between the flow fields 22 and 42 and the bead seals 58 and 59. This tendency is supported by the gas diffusion layers 15 and 16 that overlap with the flow fields 22 and 42, as the gas diffusion layers extend into the boundary regions, thus guiding the reactants into these regions as well.
[0048] To prevent this bypass, flow field plates 2 and 4 are respectively equipped with bypass stop elements 60 and 70, which protrude from the reference surfaces 24 and 44 of the flow field plates 2 and 4. Therefore, the height of the bypass stop elements 60 and 70 can be similar to or even higher than the height of the bead seal 58.
[0049] In the first embodiment shown in Figures 1 to 3, the bypass stop element of the anode flow field plate (see Figure 1) includes two elongated protrusions 61, 62 extending along the flow field 22. The elongated protrusions 61, 62 are connected to the bead seal 58 via flow-blocking protrusions 63-1, 63-2, 64-1, and 64-2. The flow-blocking protrusions ensure that reactants guided from the inlet 32 to the flow field 22 cannot enter the boundary region 26. The bypass stop elements 60, 70, and in particular the elongated protrusions 61, 62, can be continuous elements, but can also be designed as discrete elements.
[0050] As shown in the cross-sectional view of Figure 1b, the bypass stop element 60 has a tip 66 and a blunt portion 67. Both portions compress the gas diffusion layer 15, but the blunt portion compresses it to a much lesser degree than the tip 66. Therefore, in this embodiment, the blunt portion 67 compresses the gas diffusion layer to a degree similar to that of the flow field 22, thus serving as the final landing point at the edge of the flow field 22. The tip effectively “over-compresses” the gas diffusion layer 15, thereby ensuring that no bypass of reactants is avoided outside the tip 66. It should be noted that even though the tip illustrated is a sharp edge, in reality, due to manufacturing constraints, the tip will be a surface area where the surface is made as small and marginal as possible. In the prior art, known bypass stop elements only show flat portions, which cannot exert sufficient force to reliably block any bypass. This is particularly necessary for the anode side, as small molecules of hydrogen-rich gas can easily bypass ordinary barriers.
[0051] Even if the cathode plate does not have a bypass stop element, it is preferable to use an additional bypass stop element to block the bypass of the oxidant. Therefore, as shown in Figures 2 and 3, the cathode flow field plate 4 is also equipped with a bypass stop element 70, which is similar in principle to the bypass stop element 60 of the anode plate 2, and includes elongated protrusions 71, 72 and flow-blocking protrusions 73-1, 73-2, 74-1 and 74-2. Such a bypass stop element 70, and in particular the elongated protrusions 71, 72, can be a continuous element, but can also be designed as a discrete element.
[0052] Preferably, the bypass stop element 60 of the anode plate 2 and the bypass stop element 70 of the cathode plate 4 are arranged in the same region (see also FIG. 3). Therefore, the combination of the bypass stop element 60 of the anode plate 2 and the bypass stop element 70 of the cathode plate 4 increases the pressure on the gas diffusion layers 15 and 16 in the region of the bypass stop elements 60, 70. This, in turn, allows for improved obstruction of any bypass flow.
[0053] Unlike the bypass stop element 60 of the anode flow field plate 2, the bypass stop element 70 of the cathode plate 4 has no tip, but instead has an extended blunt portion 77 (see Figures 2b and 3). Therefore, as shown in Figure 3, the bypass stop element 70 of the cathode plate 4 is wider than the bypass stop element 60 of the anode plate 2. This allows for a wider alignment tolerance, ensuring that even if the bipolar plates 6-1 and 6-2 (see Figure 3) are misaligned, the tip 66 of the bypass stop element 60 interacts with the blunt portion 77 of the bypass stop element 70, providing increased pressure. Needless to say, the bypass element of the second (cathode) flow field plate 4 could also have a tip. However, the misalignment tolerance would be quite narrow.
[0054] Furthermore, it is even possible that the tip 66 of the bypass stop element 60 deforms or recesses the blunt portion 77 of the cathode bypass stop element 70, as shown in the second embodiment of FIG4. This design allows for higher pressures by providing a bypass stop element whose height exceeds that of the bead seal 58. The excess height is flattened by the recess, resulting in very high compression of the gas diffusion layer, thereby leading to improved bypass flow stopping characteristics. Therefore, preferably, the bypass stop element 60 is made of a rigid material, while the bypass stop element is made of an elastic material or is sufficiently flexible, such as a hollow shape, to allow for the recess.
[0055] Figure 5 illustrates another preferred embodiment of the flow field plates 2 and 4. Compared to the flow field plates of the embodiments in Figures 1 through 4, the bypass stop elements 60 and 70 have only a single bypass blocking protrusion 63, 73, 64, 74, which is positioned upstream of the flow field along the main flow direction of the reactants (shown by arrow 100). If the flow field plates are always arranged in the same direction in the battery stack, the main flow direction of the reactants can be identified. This, in turn, allows for a simplified design, i.e., arranging only a single bypass blocking protrusion 63, 73, 64, 74 upstream, which is sufficient to block the bypass of the reactants. The second bypass blocking protrusions 63-2, 64-3, 73-2, 74-2, as shown in Figures 1 through 4, in turn allow for the rotation of the bipolar plates 6-1 and 6-2, for example, to compensate for height differences in the battery stack that may occur due to manufacturing inaccuracies.
[0056] However, to provide a fuel cell stack of uniform size and to avoid different designs of the flow field plates on the cathode and anode sides, it is preferable to provide flow field plates that can be used as anode and cathode plates, for example, by simply flipping the plates. In this case, the preferred design of flow field plates 2 and 4 is preferred, as schematically shown in Figure 6. In this embodiment, the flow field plate includes two different bypass stop elements, namely bypass stop element 60 and bypass stop element 70, which are arranged on both sides of the flow fields 23 and 43. Since the flow field plate is flipped during the formation of the bipolar plate 6 and subsequent stacking, the bypass stop element 60 with a pointed portion 66 is always paired with the bypass stop element with a blunt portion 77. Therefore, even when using only a single designed flow field plate, a region with an overcompressed gas diffusion layer can also be provided.
[0057] As can be further seen from the illustrated embodiments, the distance D between the bead seals 58, 59 and the bypass stop elements 60, 70 (shown in Figures 3 and 4) was determined to be the maximum possible manufacturing tolerance suitable for arranging the gas diffusion layer at the electrodes, which is to be expected. This ensures that the bypass stop elements always over-compress the gas diffusion layers 16, 17, thereby reliably preventing bypass flow of reactants.
[0058] Bypass stop elements 60 and 70 may be integral parts of the flow field plate, but they may also be separate components arranged between or attached to the bipolar plates, and / or as part of the multilayer membrane electrode assembly 10, such as sub-gaskets 18 and 19. The design of the components of the bypass stop elements may also vary, such that, for example, an elongated protrusion is part of the membrane electrode assembly, a bypass blocking protrusion is part of the bipolar plate, or vice versa.
[0059] In the illustrated embodiment, bypass stop elements 60 and 70 are hollow elements, but it is also possible for at least one bypass stop element or a portion thereof to be solid.
[0060] Furthermore, it is possible for the bypass stop elements 60 and 70 to be made of some or all of an elastic material. However, the bypass stop elements may also be inelastic, or made of both elastic and inelastic materials.
[0061] In summary, due to the excessive compression of the gas diffusion layer, an effective barrier is formed next to the effective region, blocking any bypass flow within the gas diffusion layer. Therefore, the importance of controlling the width and location of the gas diffusion layer is greatly reduced. To provide the necessary pressure, at least one bypass stop element has the smallest possible total surface area, particularly the tip. Thus, the tip allows for high gas diffusion layer compression without affecting other fuel cell performance characteristics, such as…
[0062] • Air tightness
[0063] ·resistance
[0064] Gas distribution
[0065] Quality transport
[0066] Furthermore, high gas diffusion layer compression elements minimize cross-sectional voids in the boundary region between the gas diffusion layer edge and the gas sealing gasket. Regardless of the material used, both the gas diffusion layer compression element and the bypass stop element can be part of the flow field plate material, such as stainless steel sheet or graphite. The gas diffusion layer compression element and the bypass stop element can be made of a different material than the flow field plate and then bonded to it. Inconsistencies may also exist when it comes to materials and shapes to facilitate realization and / or manufacturing processes. Compression and bypass stop elements can be made hollow or solid, or a combination thereof. Partial or complete gas diffusion layer compression elements and bypass stop elements can be made of elastic or inelastic materials, or combinations thereof.
[0067] In summary, the proposed bypass stop element can reduce manufacturing costs. The resulting increase in fuel efficiency also increases the value of the fuel cell stack and saves money during operation.
[0068] Figure Labels
[0069] 2 First flow field plate
[0070] 4 Second flow field plate
[0071] 6 bipolar plates
[0072] 8. Fuel Cell Components
[0073] 10 Multilayer film electrode assembly
[0074] 11 Three-layer film electrode assembly
[0075] 12 Anodes
[0076] 13 Membrane
[0077] 14 Cathode
[0078] 15 and 16 gas diffusion layers
[0079] 17 and 18 sub-washers
[0080] 20, 40 Front side of the flow field plate
[0081] 21, 41 Rear side of the flow field plate
[0082] Flow field at the front of 22 and 42
[0083] Flow field behind 23 and 43
[0084] 24, 44 reference planes
[0085] Boundary areas 26 and 46
[0086] 32 Fuel Inlet
[0087] 33 Fuel Exports
[0088] 34 Oxidizing agent inlet
[0089] 35 Oxidizing agent export
[0090] 36 Cooling fluid inlet
[0091] 37 Cooling fluid outlet
[0092] 52, 53, 54, 56, 57 are tire bead seals for inlet / outlet use.
[0093] 58, 59 Bead seals for plates
[0094] 60, 70 bypass stop element
[0095] 61, 71, 62, 72 slender protrusions
[0096] 63, 64, 73, 74 blocking protrusions
[0097] 66. Tip
[0098] 67, 77 Blunt part
[0099] 100. Main flow direction of reactants
Claims
1. A fuel cell assembly (8), which includes at least a first flow field plate (2) and a second flow field plate (4) sandwiching a multilayer membrane electrode assembly (10). The multilayer membrane electrode assembly (10) includes at least three membrane electrode assemblies (11), which consist of a first electrode (12) facing the first flow field plate (2), a second electrode (14) facing the second flow field plate (4), and a membrane (13) for the separation electrodes (12, 14). Each flow field plate (2, 4) has a flow field structure (22, 42, 23, 43) protruding from the reference plane (24, 44) of the flow field plate (2, 4) for distributing reactants on the corresponding electrodes (12, 14), and At least one additional sealing element (52, 53, 54, 55, 56, 57, 58, 59) is arranged between the first and second flow field plates (2, 4), which is adapted to prevent reactants from leaking into the environment. in, At least one bypass stop element (60, 70) is provided in the boundary region (26, 46) between the sealing element (58, 59) of at least one of the flow field structures (22, 42, 23, 43) and the flow field plates (2, 4) to prevent reactants from bypassing the flow field structures (22, 42, 23, 43), wherein the bypass stop element (60, 70) protrudes from the corresponding reference plane (24, 44) of the flow field plates (2, 4). Its features are, At least one bypass stop element has a surface-edge-shaped tip (66) and a blunt portion associated with the tip (66), the tip (66) being adapted to compress the multilayer film electrode assembly (10).
2. The fuel cell assembly (8) according to claim 1, wherein the multilayer membrane electrode assembly (10) further comprises at least one gas diffusion layer (15) located between the first electrode (12) and the first flow field plate (2), and includes a second gas diffusion layer (16) located between the second electrode (14) and the second flow field plate (4), wherein at least one gas diffusion layer (15, 16) is adapted to extend at least partially over at least one bypass stop element (60, 70) such that the surface edge-margined tip (66) of the bypass stop element (60, 70) and the blunt portion associated with the tip (66) compress at least one gas diffusion layer (15, 16).
3. The fuel cell assembly (8) according to claim 1 or 2, wherein the multilayer membrane electrode assembly (10) further comprises at least one sub-wafer (17, 18), wherein the at least one sub-wafer (17, 18) is adapted to frame the multilayer membrane electrode assembly (10), wherein the at least one sub-wafer (17, 18) is adapted to extend at least partially over at least one bypass stop element (60, 70), such that the edged tip (66) of the surface of the bypass stop element (60, 70) and the blunt portion associated with said tip (66) compress at least one sub-wafer (17, 18).
4. The fuel cell assembly (8) according to claim 1, wherein, The sealing elements (58, 59) are bead seals surrounding the flow field plates (2, 4) and thus surrounding the flow field structures (22, 42, 23, 43), wherein the bead seals (58, 59) protrude from the reference plane (24, 44) and are adapted to directly or indirectly contact the bead seals (58, 59) of the corresponding other flow field plates (12, 14) to prevent reactants from leaking into the environment.
5. The fuel cell assembly (8) according to claim 1, wherein, The first flow field plate (2) has at least one first bypass stop element (60), and the second flow field plate (4) has at least one second bypass stop element (70), wherein the first bypass stop element (60) and the second bypass stop element (70) are arranged opposite to each other such that the first and second bypass stop elements (60, 70) form at least one bypass stop element assembly, wherein the first bypass stop element (60) has a surface-edge-shaped tip (66) and a blunt portion associated with the tip (66), and the second bypass stop element (70) is a blunt portion (77), wherein the blunt portion (77) of the second bypass stop element (70) is adapted to be recessed by the surface-edge-shaped tip (66) and the blunt portion associated with the tip (66) of the first bypass stop element (60).
6. The fuel cell assembly (8) according to claim 5, wherein, In cross-section, the blunt portion (77) of the second bypass stop element (70) is wider than the tip (66) of the first bypass stop element (60).
7. The fuel cell assembly (8) according to claim 1, wherein the bypass stop elements (60, 70) are continuous elements (61, 71, 62, 72) extending at least along the length of the flow field structure (22, 42, 23, 43), wherein at least upstream of the flow field structure (22, 42, 23, 43) in the direction along the reactant stream (100), the bypass stop elements (63, 73, 64, 74) are connected to the sealing element.
8. The fuel cell assembly (8) according to claim 4, wherein, Multiple discrete bypass stop elements (60, 70) are arranged in the region (26, 46) between the flow field structure (22, 42, 23, 43) and the bead seal (58, 59) of at least one flow field plate (2, 4).
9. The fuel cell assembly (8) according to claim 1, wherein, The first bypass stop element (60) having a surface-edged tip (66) and a blunt portion associated with the tip (66) is a discrete element, and the second bypass stop element (70) having a blunt portion (77) is a continuous element extending at least along the length of the flow field structure (22, 42, 23, 43), or the first bypass stop element (60) having a surface-edged tip (66) and a blunt portion associated with the tip (66) is a continuous element extending at least along the length of the flow field structure (22, 42, 23, 43), and the second bypass stop element (70) having a blunt portion (77) is a discrete element.
10. The fuel cell assembly (8) according to claim 1, wherein at least one bypass stop element (60, 70) is part of the flow field plate (2, 4).
11. The fuel cell assembly (8) according to claim 1, wherein at least one bypass stop element (60, 70) is an element separate from the flow field plate (2, 4), wherein the bypass stop element (60, 70) is a frame-like element.
12. The fuel cell assembly (8) according to claim 1, wherein at least one bypass stop element (60, 70) is part of a sub-gasket (17, 18) or a gas diffusion layer (15, 16).
13. The fuel cell assembly (8) according to claim 1, wherein, A bypass stop element (60) having a surface-edged tip (66) and a blunt portion associated with the tip (66) is arranged on the anode side.
14. A flow field plate (2, 4) for a fuel cell assembly (8) according to claim 1, wherein, The flow field plates (2, 4) have at least one tip (66) with a surface edge and a bypass stop element (60, 70) with a blunt portion associated with the tip (66), the tip (66) being adapted to compress the multilayer film electrode assembly (10).