FUEL CELL WITH ELASTOMER LAYERS AND METHOD FOR MANUFACTURING A FUEL CELL

Description

[0001] The invention relates to a fuel cell comprising a membrane electrode assembly inserted into a recess in a frame, a first bipolar plate being arranged on the first side of the membrane electrode assembly, and a second bipolar plate being arranged on the second side opposite the first side. Furthermore, the invention relates to a method for producing a fuel cell.

[0002] Fuel cells, such as those used in fuel cell systems for powering motor vehicles, comprise a membrane electrode assembly formed from a proton-conducting membrane with the anode on one side and the cathode on the other. The electrodes are poured or sprayed onto the membrane or hot-pressed using a calendering process to achieve intimate contact. Reactant gases are supplied to the electrodes, namely, on the anode side, in particular hydrogen, and on the cathode side, oxygen or an oxygen-containing gas, in particular air. During the electrochemical reaction, the hydrogen reacts with the oxygen in the air to form water.

[0003] Bipolar plates are provided to supply the membrane electrode assembly with reactant gases in its active region. Generally, metallic beads combined with an elastomer layer are used for the fluid-mechanical sealing of the fuel cell, and in particular the bipolar plates. This results in the essential functions of a seal—elasticity and roughness compensation—being separated from each other and assigned to the appropriate material. The roughness compensation is entirely assigned to the elastomer layer, while the essential elastic component of the seal is provided by the metallic bead.

[0004] In order to achieve a uniform compression curve of the bead along the sealing line of the bipolar plate, the bead has varying geometries along the bipolar plate plane. The manufacturing process required for this geometric variation results in the bead roof not being flat, but being deformed during the forming process. This means that dents and humps form on the bead roof, making the bead uneven in the single-digit micrometer range. Typically, elastomer layers with a thickness of less than 50 µm are used, which cannot adequately compensate for and / or seal this unevenness. To provide an adequate seal, the height of the seal must correspond to the height of the flow field, i.e. the bipolar plate and the gas diffusion layer arranged between the bipolar plate and the membrane electrode assembly. A seal must therefore have a height of typically 0.2 mm to 0.7 mm, preferably 0.3 mm to 0.6 mm.

[0005] In the conventional production of fuel cells, particularly the sealing system for the fuel cell, the metallic bead with elastomer layer, for example, is produced in a discrete manufacturing process. The prefabricated bipolar plate is fed into this process. The elastomer can be applied, for example, using a screen printing process or an injection molding process. For these processes, the choice of materials is very limited due to processing and adhesion. Although these requirements can be met well with the chemically very stable but expensive fluororubber, the necessary Shore hardness must be achieved by foaming these materials. This results in long drying and curing times. Furthermore, screen printing processes are very prone to failure, which entails a high level of effort for quality assurance, particularly complex leak testing.

[0006] DE 10 2011 105 072 B3 discloses a method for manufacturing a membrane electrode assembly for a fuel cell, wherein thin sealing elements are arranged on a frame of the membrane electrode assembly. The material described for the sealing elements is not suitable for enabling surface roughness compensation with the bipolar plate under the compression forces typical for fuel cells, thus achieving a sufficient fluid-mechanical seal.

[0007] DE 10 2018 217 291 A1 describes a method for sealing a fuel cell, wherein a sealing film is applied to at least one sealing point of the fuel cell.

[0008] DE 10 2012 221 730 A1 discloses a method for sealing a coolant chamber of a bipolar plate of a fuel cell. The membrane electrode assembly is provided with sealing elements on both sides.

[0009] DE102016121614A1 discloses a fuel cell comprising a membrane electrode assembly and a frame which frames the membrane electrode assembly in an overlapping manner on one side, wherein bipolar plates are arranged on both sides of the membrane electrode assembly, wherein the frame is sealingly connected to a bipolar plate in a circumferential manner by means of a thermoplastic adhesive.

[0010] DE 10 2019 202682 A1 discloses a fuel cell comprising a membrane electrode assembly and a frame which frames the membrane electrode assembly in an overlapping manner on one side, wherein bipolar plates are arranged on both sides of the membrane electrode assembly, wherein the frame comprises a first frame-shaped layer and a second frame-shaped layer which are connected to one another by an adhesive layer formed from an adhesive and which, in their entirety, form the frame.

[0011] Therefore, it is an object of the present invention to provide a fuel cell and a method for producing a fuel cell which reduces the above-mentioned disadvantages.

[0012] This object is achieved by a fuel cell having the features of claim 1 and by a method having the features of claim 6. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0013] The fuel cell is characterized in particular by the fact that an edge region of the frame, on a side facing the first bipolar plate, has a first elastomer layer formed as a foil; that the edge region of the frame, on its second side facing the second bipolar plate, has a second elastomer layer formed as a foil; and that the elastomer layers arranged on the frame are configured to fluid-mechanically seal the bipolar plates by means of roughness compensation and the provided elasticity. This creates a fuel cell that is simpler and therefore cheaper to manufacture and has good sealing properties. Furthermore, a wider selection of suitable materials for the elastomer layers is available.

[0014] The material for the elastomer layers is preferably selected from a group: acrylate rubber (ACM), acrylonitrile butadiene rubber (NBA), ethylene propylene diene (monomer) rubber (EPDM), fluororubber (FPM, XFPM), methyl vinyl rubber (MVQ), hydrogenated acrylonitrile butadiene rubber (HNBR), fluorosilicone rubber (FVMQ), polyester urethane rubber (AU, PUR), styrene butadiene rubber (SBR), natural rubber (NK), isobutene isoprene rubber (IIR), chlorosulfonated polyethylene (CSM), chloroprene rubber (CR), perfluororubber (FFPM), tetrafluoroethylene / propylene rubber (FEPM), or polytetrafluoroethylene (PTFE). Furthermore, it is advantageous if the elastomer layers have a Shore hardness of less than 30° A. To achieve the required Shore hardness, it is preferred if the elastomer layers are formed from foamed elastomer material.Furthermore, it is preferred if the thickness of the elastomer layers on each side is a maximum of 50 µm and in the pressed state less than 30 µm each.

[0015] In particular, it is preferred if the frame, the first elastomer layer, and the second elastomer layer form a film composite. The film composite is therefore a multilayer film composite.

[0016] In order to save material, it is preferred if the first elastomer layer and / or the second elastomer layer only partially covers the edge area of ​​the frame.

[0017] In this context, it is particularly advantageous if the first elastomer layer covers a first region on the first side of the edge region of the frame, if the second elastomer layer covers a second region on the second side of the edge region of the frame and if the covered regions are asymmetrical with respect to a longitudinal axis.

[0018] Furthermore, in order to adjust the required sealing, it is preferred if the first elastomer layer differs from the second elastomer layer in thickness and / or material.

[0019] Furthermore, it is advantageous if the fuel cell has a second frame with a second recess, if the first frame and the second frame are arranged stacked, and if one of the elastomer layers is arranged as a film between the first frame and the second frame, on the edge region thereof. In particular, one of the gas diffusion layers can be arranged in the second recess of the second frame. The second recess of the second frame preferably has a larger area than the recess of the first frame. The frames are preferably made of different materials in order to assign the frames different functions within the fuel cell structure. Furthermore, it is preferred if the second frame is arranged offset radially outwards with respect to the first frame.Likewise, to improve the seal, it is preferred if a third elastomer layer formed as a film is arranged between the second frame and the bipolar plate adjacent to the second frame.

[0020] The process is characterized in particular by the following steps: Providing a frame material formed as a first film, a first elastomer layer formed as a second film, and a second elastomer layer formed as a third film; superimposing and connecting the layers to form a frame sealing functional layer such that the first elastomer layer is arranged on a first side of the frame material and the second elastomer layer is arranged on a second side of the frame material opposite the first side; cutting the frame sealing functional layer into individual frame elements and cutting out a recess from the frame elements; positioning the membrane electrode assembly in the recess of the frame element; providing two bipolar plates and positioning the first bipolar plate on the first side of the membrane electrode assembly and positioning the second bipolar plate on the second side of the membrane electrode assembly opposite the first side;and positive connection of the membrane electrode assembly with the frame element and the bipolar plates.

[0021] This enables cost-reduced fuel cell production by offering a wider range of materials through modified processes and material adhesion requirements. Due to the robust process, reduced quality control is also possible, so that a simplified leak test is sufficient. The connection can be made using a binder as a material bond. However, it is preferred that a detachable connection be achieved between the frame element, the membrane electrode assembly, and the bipolar plates. This can be achieved, for example, by pressing, i.e., by exerting pressure perpendicular to the bipolar plate.

[0022] The expanded material selection includes materials such as acrylate rubber (ACM), acrylonitrile butadiene rubber (NBA), ethylene propylene diene (monomer) rubber (EPDM), fluororubber (FPM, XFPM), methyl vinyl rubber (MVQ), hydrogenated acrylonitrile butadiene rubber (HNBR), fluorosilicone rubber (FVMQ), polyester urethane rubber (AU, PUR), styrene butadiene rubber (SBR), natural rubber (NK), isobutene isoprene rubber (IIR), chlorosulfonated polyethylene (CSM), chloroprene rubber (CR), perfluororubber (FFPM), tetrafluoroethylene / propylene rubber (FEPM), or polytetrafluoroethylene (PTFE). In order to preferably adjust the Shore hardness to less than 30° A, it is preferred if the process additionally provides for foaming of the elastomer material.

[0023] In particular, for the distribution of the reactant gases on the active region of the membrane electrode assembly, it is preferred if two additional gas diffusion layers are provided and arranged between the frame sealing functional layer and the bipolar plates, on both sides, and are connected to them in a form-fitting and material-fitting manner.

[0024] In particular, it is provided that the step of combining the layers to form a frame sealing functional layer is carried out by transferring, spraying, pouring, calendering or transferring in order to generate the frame sealing functional layer.

[0025] Furthermore, it is advantageous if the first elastomer layer and / or the second elastomer layer adheres to the frame material only in certain areas by means of film transfers, such that the frame sealing functional layer only has the first elastomer layer and / or the second elastomer layer in certain areas.

[0026] In this context, it is particularly preferred if the region of the first elastomer layer and the region of the second elastomer layer are applied asymmetrically with respect to a longitudinal axis of the membrane electrode assembly. In this context, it is preferred if the first elastomer layer and the second elastomer layer have different thicknesses and / or a different material composition and / or different materials.

[0027] To further simplify the process, it is preferred if the frame material, the first elastomer layer, and the second elastomer layer are each provided wound on a roll. Roll production reduces the investment required for fuel cell production. Another advantage of a roll process is that the layers are applied faster than with screen printing. Adjusting the adhesion of the elastomer layers to the frame material is easier, and the drying and curing processes can be simplified.

[0028] The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also to be considered encompassed and disclosed by the invention that are not explicitly shown or explained in the figures, but that emerge and can be produced from the explained embodiments through separate combinations of features.

[0029] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. These show: Fig. 1 is a schematic representation of a fuel cell with two elastomer layers, Fig. 2 is a schematic representation of the framed membrane electrode assembly with frame sealing functional layer, Fig. 3 is a further schematic representation of a framed membrane electrode assembly with frame sealing functional layer, Fig. 4 is a further schematic representation of a framed membrane electrode assembly with frame sealing functional layer, and Fig. 5 is a schematic representation of another fuel cell with three elastomer layers and two frames.

[0030] Figure 1shows a fuel cell with a membrane electrode assembly 4 inserted into a recess 2 of a frame 3. A first bipolar plate 5 is arranged on a first side of the membrane electrode assembly 4, and a second bipolar plate 6 is arranged on a second side opposite the first side. The membrane electrode assembly 4 comprises a proton-conducting membrane 16, on the first side of which an anode 12 is arranged, and on the second side opposite the first side of which a cathode 13 is arranged. The anode 12 and the cathode 13 can have a catalyst layer made of a noble metal or mixtures of noble metals such as platinum, palladium, ruthenium, or the like, which serve as reaction accelerators in the reaction of the fuel cell.

[0031] In such a polymer electrolyte membrane fuel cell (PEM fuel cell), fuel or fuel molecules, particularly hydrogen, are split into protons and electrons at the anode 12. The membrane 16 allows the protons (e.g., H +< ) to pass through, but is impermeable to the electrons (e -< ). The membrane 16 is formed from an ionomer, preferably a sulfonated tetrafluoroethylene polymer (PTFE) or a polymer of perfluorinated sulfonic acid (PFSA). Alternatively, the membrane 16 can also be formed as a sulfonated hydrocarbon membrane. The following reaction occurs at the anode 12: 2H 2 → 4H +< + 4e -< (oxidation / electron release).

[0032] While the protons pass through the membrane 16 to the cathode 13, the electrons are conducted via an external circuit to the cathode 13 or to an energy storage device. A cathode gas, particularly oxygen or oxygen-containing air, is provided at the cathode 13, so that the following reaction takes place: O 2 + 4H +< + 4e -< → 2H 2 O (reduction / electron absorption).

[0033] Each of the two electrodes, namely the anode 12 and the cathode 13, is assigned a gas diffusion layer 14, 15. The gas diffusion layers 14, 15 are preferably made of carbon fiber paper (CFP). Other suitable fiber and / or nonwoven layers can also serve as a gas diffusion layer and the basis for a gas diffusion electrode.

[0034] To improve fluid or gas flow within the fuel cell 1 and to increase the water content in the membrane 16, the gas diffusion layers 14, 15 can additionally be provided with a microporous layer (not shown in detail). The lateral dimensions of the microporous layer essentially correspond to the lateral dimensions of the respective gas diffusion layers 14, 15.

[0035] An edge region 7 of the frame 3 has, on its side facing the first bipolar plate 5, a first elastomer layer 8 formed as a film, while the edge region 7 of the frame 3 has, on its second side facing the second bipolar plate 6, a second elastomer layer 9 formed as a film. The elastomer layers 8, 9 arranged on the frame 3 are designed to fluid-mechanically seal the bipolar plates 5, 6 by means of surface roughness compensation and the provided elasticity. The frame 3, the first elastomer layer 8, and the second elastomer layer 9 form a film composite. This structure enables sealing of the bipolar plates 5, 6 in that the elastomer layers 8, 9 assume both the surface roughness compensation and the provided elasticity as functions.Alternatively, the elastomer layers 8, 9 can also initially be present as a liquid mass, for example as a lacquer or as a paste, and can be printed or poured onto the frame 3 formed as a film.

[0036] Figure 2 shows the framed membrane electrode assembly 4 with a frame sealing functional layer 11. The frame sealing functional layer 11 is the film composite made of the frame material, i.e. the frame 3, and the first elastomer layer 8 and the second elastomer layer 9. In Figure 2 In contrast to the other framed membrane electrode assemblies with frame sealing functional layer 11, the first elastomer layer 8 is thicker than the second elastomer layer 9.

[0037] Using the example from Figure 3 It can be seen that the first elastomer layer 8 and / or the second elastomer layer 9 only partially covers the edge region 7 of the frame 3.

[0038] In Figure 4a further example is shown in which the first elastomer layer 8 covers a first region on the first side of the edge region 7 of the frame 3, while the second elastomer layer 9 covers a second region on the second side of the edge region 7 of the frame 3, wherein the covered regions are formed asymmetrically with respect to a longitudinal axis 10.

[0039] Furthermore, the first elastomer layer 8 may differ from the second elastomer layer 9 in its material and / or in its material composition.

[0040] Figure 5 shows another fuel cell which, in contrast to the fuel cell according to Fig. 1 a second frame 17 with a second recess 18 into which the first gas diffusion layer 14 is received. A third elastomer layer 19 formed as a film is arranged between the edge region of the second frame 17 and the first bipolar plate 5.

[0041] The method for producing a fuel cell 1 comprises the following steps: providing a frame material formed as a first film, a first elastomer layer 8 formed as a second film, and a second elastomer layer 9 formed as a third film. The films are each wound on a roll, so that a roll process is possible.

[0042] The individual layers, i.e., the individual films, are placed on top of one another and bonded to form a frame sealing functional layer 11 such that the first elastomer layer 8 is arranged on a first side of the frame material, i.e., the frame 3, and the second elastomer layer 9 is arranged on a second side of the frame material opposite the first side. The layers can be applied and bonded by calendering, spraying, casting, printing, or transferring.

[0043] In the fuel cell 1 according to Figure 5, a further film is additionally provided as a second frame material for the second frame 17 and an additional third elastomer layer 19 formed as a film. The individual layers, i.e. the individual films, are placed on top of one another and connected to form a frame sealing functional layer 11 in such a way that the first elastomer layer 8 is arranged on a first side of the frame material, i.e. the frame 3, the second elastomer layer 9 is arranged on a second side of the frame material opposite the first side, the second frame material is arranged on the side of the first elastomer layer 8 facing away from the membrane electrode arrangement 4, and the third elastomer layer 19 is arranged on the side of the second frame material facing away from the first elastomer layer 8. The layers can be applied and connected by calendering, spraying, casting, printing, or transferring.

[0044] The frame sealing functional layer 11 is cut to individual frame elements, and a recess 2 is cut out of the frame elements. Of course, it is also possible to first cut out the recesses 2 and then cut the frame elements. The membrane electrode assembly 4 is positioned in the recess 2 of the frame element, and at least two bipolar plates 5, 6 are provided. The first bipolar plate 5 is positioned on the first side of the membrane electrode assembly 4, and the second bipolar plate 6 is positioned on the second side of the membrane electrode assembly 4 opposite the first side. A gas diffusion layer 14, 15 is arranged between the membrane electrode assembly 4 and the bipolar plates 5, 6. Finally, the membrane electrode assembly 4 is positively connected to the frame element and the bipolar plates 5, 6, as well as to the gas diffusion layers 14, 15. The connection can be materially bonded, i.e.by means of a binder. Alternatively, and preferably, the connection is achieved by mechanical pressure orthogonal to the bipolar plate 5, 6, so that a detachable connection is achieved between the bipolar plate 5, 6 and the frame element comprising the elastomer layers 8, 9. Furthermore, the frame element or the composite of the bipolar plates 5, 6, frame element, and gas diffusion layers 14, 15 can be treated with heat, i.e., with a temperature higher than the melting temperature of the elastomer, so that the elastomer layers 8, 9 melt and penetrate into the roughness depth of the bipolar plates 5, 6. This improves the sealing of the fuel cell 1.

[0045] In order to apply the elastomer layers 8, 9 only in certain areas to the frame material, the first elastomer layer 8 and / or the second elastomer layer 9 is applied to the frame material only in certain areas by means of film transfer and adheres to it. LIST OF REFERENCE SYMBOLS:

[0046] 1 Fuel cell 2 Recess 3 Frame 4 Membrane electrode assembly 5 First bipolar plate 6 Second bipolar plate 7 Edge area of ​​the frame 8 First elastomer layer 9 Second elastomer layer 10 Longitudinal axis 11 Frame sealing functional layer 12 Anode 13 Cathode 14 First gas diffusion layer 15 Second gas diffusion layer 16 Proton-conductive membrane 17 Second frame 18 Second recess 19 Third elastomer layer

Claims

1. A fuel cell (1) having a membrane electrode assembly (4) which is inserted in a recess (2) of a frame (3) and on the first side of which a first bipolar plate (5) is arranged and on the second side of which, opposite the first side, a second bipolar plate (6) is arranged, a peripheral area (7) of the frame (3) having, on its side facing the first bipolar plate (5), a first elastomeric layer (8) formed as a second film, the peripheral area (7) of the frame (3) has, on its second side facing the second bipolar plate (6), a second elastomeric layer (9) formed as a third film, characterized in that the peripheral area (3) is formed as a first foil, in that the frame (3), the first elastomeric layer (8) and the second elastomeric layer (9) form a film composite, and in that the elastomeric layers (8, 9) arranged on the frame (3) are configured to seal the bipolar plates (5, 6) fluid-mechanically by means of roughness depth compensation and the provided elasticity.

2. The fuel cell (1) according to claim 1, characterized in that the first elastomeric layer (8) and / or the second elastomeric layer (9) only partially covers the peripheral area (7) of the frame.

3. The fuel cell (1) according to claim 1 or 2, characterized in that the first elastomeric layer (8) covers a first area on the first side of the peripheral area (7) of the frame (3), in that the second elastomeric layer (9) covers a second area on the second side of the peripheral area (7) of the frame (3), and in that the covered areas are asymmetrical with respect to a longitudinal axis (10).

4. The fuel cell (1) according to any one of claims 1 to 3, characterized in that the first elastomeric layer (8) differs from the second elastomeric layer (9) in thickness and / or in the material used.

5. A method of manufacturing a fuel cell (1) according to any one of claims 1 to 4, comprising the steps of: - Providing a frame material formed as a first film, a first elastomeric layer (8) formed as a second film and a second elastomeric layer (9) formed as a third film, - Superimposing and joining the layers to form a frame sealing functional layer (11) in such a way that the first elastomeric layer (8) is arranged on a first side of the frame material and the second elastomeric layer (9) is arranged on a second side of the frame material opposite the first side, - Cutting the frame sealing functional layer (11) to individual frame elements and cutting out a recess (2) from the frame elements, - Positioning the membrane electrode assembly (4) in the recess (2) of the frame element, - Providing two bipolar plates (5, 6) and positioning the first bipolar plate (5) on the first side of the membrane electrode assembly (4) and positioning the second bipolar plate (6) on the second side of the membrane electrode assembly (4) opposite the first side, and - form-fit connecting of the membrane electrode assembly (4) to the frame element and the bipolar plates (5, 6).

6. The method according to claim 5, characterized in that the step of joining the layers to form a frame sealing functional layer (11) is carried out by means of printing, spraying, casting, calendering or transferring.

7. The method according to claim 6, characterized in that the first elastomeric layer (8) and / or the second elastomeric layer (9) adheres to the frame material by means of film transfer only in certain areas, such that the frame sealing functional layer (11) comprises the first elastomeric layer and / or the second elastomeric layer only in certain areas.

8. The method according to any one of claims 5 to 7, characterized in that the first elastomeric layer (8) and the second elastomeric layer (9) have a different thickness and / or a different material.

9. The method according to any one of claims 5 to 8, characterized in that the frame material, the first elastomeric layer (8) and the second elastomeric layer (9) are each provided wound on a roll.