Bipolar plate for fuel cell, fuel cell stack with bipolar plate, and vehicle

Abstract

The present invention relates to a bipolar plate for a fuel cell, a fuel cell stack with the bipolar plate, and a vehicle. Specifically, in order to provide a bipolar plate for a fuel cell, an anode plate with an anode side and a cooling medium side is provided, wherein a first structural part for constructing an anode flow field is constructed on the anode side, and a cathode plate with a cathode side and a cooling medium side is constructed on the cathode side, wherein a second structural part for constructing a cathode flow field is constructed; wherein a structural element is arranged between the anode plate and the cathode plate for constructing a cooling medium flow field, the structural element is contacted by the cooling medium side of the anode plate and the cathode plate, and has an optimized pressure distribution and greater stability in the fuel cell stack compared to the prior art, and it is proposed that the structural element is composed of an elastic material and the structural element has different heights in different areas of the cooling medium flow field. In addition, a fuel cell stack and a vehicle are disclosed.

Description

Technical Field

[0001] The invention relates to a bipolar plate for a fuel cell, comprising an anode plate with an anode side and a cooling medium side, wherein a first structural part for constructing an anode flow field is constructed on the anode side; a cathode plate with a cathode side and a cooling medium side, wherein a second structural part for constructing a cathode flow field is constructed on the cathode side; wherein structural elements are arranged between the anode plate and the cathode plate for constructing the cooling medium flow field. In addition, the invention relates to a fuel cell stack with such a bipolar plate and a vehicle having such a fuel cell stack. Background Art

[0002] Fuel cells use fuel to generate electrical energy by chemically converting oxygen into water. For this purpose, fuel cells have as a core component a so-called membrane electrode assembly (MEA stands for membrane electrode assembly), which is a structure consisting of a membrane that guides ions (mostly protons) and catalytic electrodes (anode and cathode) arranged on both sides of the membrane. The latter mostly include supported rare metals, especially platinum. In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane electrode assembly at the side of the electrode facing away from the membrane. Usually, a fuel cell is formed by a plurality of MEAs arranged in a stack (stack), and their electrical voltages are added. Bipolar plates (also called flow field plates or separator plates) are usually arranged between the individual membrane electrode assemblies, which ensure the supply of the single cell with an operating medium, i.e., a reactant, and are usually also used for cooling. In addition, the bipolar plates are responsible for electrically conductive contact with the membrane electrode assembly.

[0003] During operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen H2 or a gas mixture containing water, is supplied to the bipolar plate of the anode via an open flow field on the anode side, where a conversion of H2 into protons H2 occurs with the release of electrons. + Electrochemical oxidation (H2→2H + +2e - The transport of protons (hydrated or anhydrous) from the anode chamber to the cathode chamber is achieved via an electrolyte or a membrane which separates the reaction chambers gas-tightly from one another and electrically isolates them. The electrons provided at the anode are conducted to the cathode via electrical lines. Oxygen or an oxygen-containing gas mixture (e.g. air) is supplied to the cathode as a cathode operating medium via an open flow field on the cathode side of the bipolar plate, so that a conversion of O2 to O2 occurs with the receipt of electrons. 2- Reduction (1 / 2O2+2e - →O 2- ). At the same time, in the cathode chamber, oxygen anions react with protons transported via the membrane to form water (O 2- +2H +→H2O).

[0004] The fuel cell stack is supplied with its operating media, i.e. anode operating gas (e.g. hydrogen), cathode operating gas (e.g. air) and cooling medium, via main supply channels which penetrate the stack in its entire stacking direction and supply the operating media from it via the bipolar plates to the individual cells. For each operating medium, there are at least two such main supply channels, i.e. one for supplying and one for discharging the corresponding operating medium.

[0005] Typically, a bipolar plate consists of two interconnected half plates, each of which is structured on both sides. On the sides facing away from each other, a structure is required for transporting the operating medium, and on the sides facing each other, a structure is required for transporting the cooling medium. Here, the half plates must be coordinated with each other, because three separate transport paths must be provided by means of two half plates. This leads to additional boundary conditions, which reduce the flexibility of the design of the bipolar plate. In a typical embodiment, the half plates of the known bipolar plates are configured as contoured, wherein the contours are connected or interlaced into each other.

[0006] Fuel cells typically have end plates at their opposite stack ends, which are connected to one another by means of clamping devices as part of a clamping system. The clamping devices transmit tensile forces that pull the end plates toward one another and press, i.e., press the individual cells arranged between them against one another. Compression springs are also part of the clamping system in order to load the stack evenly and avoid damage thereto. Summary of the invention

[0007] The object of the present invention is to provide a bipolar plate which at least partially eliminates the disadvantages of bipolar plates which have these disadvantages in combination with compression springs.

[0008] This object is achieved by a bipolar plate according to the invention, a fuel cell stack and a vehicle having such a fuel cell stack.

[0009] The bipolar plate comprises an anode plate with an anode side and a cooling medium side, wherein a first structural part for constructing an anode flow field is constructed on the anode side. The bipolar plate further comprises a cathode plate with a cathode side and a cooling medium side, wherein a second structural part for constructing a cathode flow field is constructed on the cathode side. A structural element is arranged between the anode plate and the cathode plate to construct a cooling medium flow field, which contacts the cooling medium side of the anode plate and the cathode plate. According to the present invention, the structural element is made of an elastic material, and the structural element has different heights depending on in which area of ​​the cooling medium flow field it is arranged.

[0010] The pressure load on the bipolar plates or on the flow fields for reactants and cooling medium is not equal in all regions but varies, among other things, depending on the geometry of the flow paths and their position relative to the inflow or outflow region of the respective flow field.

[0011] In order to compensate for this difference, structural elements of different heights are arranged in zones, wherein in zones with a lower pressure load they have a greater height than structural elements in other zones with a higher pressure load.

[0012] According to the invention, a plurality of regions can be provided which can be provided with structural elements of different heights, depending on the specific design of the respective bipolar plate.

[0013] According to a preferred embodiment of the invention, three regions are provided, namely an inflow region, an outflow region and a transition region from the inflow region to the outflow region of the flow field, wherein the height of the structural element increases from the inflow region to the outflow region.

[0014] Depending on their height, the structural elements contact the cathode plate and / or the anode plate, wherein in the installed state in the fuel cell stack the cathode plate and the anode plate are contacted by all structural elements since they are clamped.

[0015] Furthermore, the structural element is used for an embedded spring in a fuel cell stack having a bipolar plate according to the invention in order to optimize the compression while at the same time increasing the structural rigidity.

[0016] In addition, the stack height of the fuel cell stack is reduced compared to the prior art, since the commonly used compression springs can be omitted. According to the prior art, these compression springs do not provide good control of the extrusion force on the active surface of the bipolar plate, wherein the resulting uneven stack compression can cause plate fractures. This is avoided by the bipolar plate according to the invention. In addition, weight can be saved by abandoning the compression springs. The deflection of the end plate is also minimized. In addition, it is particularly advantageous that the influence of the intrusion of the GDL / MEA can be minimized.

[0017] Furthermore, cost reductions can be achieved in the production of sheet metal, for example by dispensing with compression springs and by the possibility of using the form-in-place (FIP) method for mass production.

[0018] The bipolar plate according to the invention, apart from the structural elements, preferably consists of a conductive material, preferably a carbon-based material, preferably graphite or a composite material consisting of graphite and carbon. The use of metals is also provided.

[0019] The structural elements provided according to the invention preferably consist of an elastic, preferably electrically conductive polymer which is stable in the temperature range of fuel cell operation, wherein preferably at least one structural element is conductive.

[0020] Preferably, all structural elements consist of the same material, so that the elastic properties of the structural elements are adjusted in addition to the choice of material by their height.

[0021] The heights of the various structural elements are determined by the specific requirements in the respective area.

[0022] For example, in the case of a height of 1140um of the bipolar plate and a height of 440um of the cooling medium flow field, the height of the structural element can be 440um, 420um and 400um and a width of 500um. The height of the first and second structural parts is not determined by the height of the structural element. This can be in the range of 125um to 225um.

[0023] Preferably, silicone or siloxane is used, of which polydimethylsiloxane is particularly preferred.

[0024] The polymer preferably has an electrical conductivity of >100 S / cm. The electrical resistance is preferably 0.0008 Ωcm and the compression modulus is preferably 5 MPa.

[0025] The structural elements are arranged spaced apart from one another between the anode plate and the cathode plate, so that the coolant can flow through the coolant flow field of the bipolar plate with the lowest possible pressure loss.

[0026] For this purpose, the structural elements are designed in a cylindrical manner, preferably with a cross section which remains constant over the entire length of the individual structural elements, or else with a cross section which varies over the length, for example with a cross section which decreases in the middle of the structural element.

[0027] The structural elements can have cross-sectional areas of different sizes distributed over the surface of the bipolar plate in order to meet different requirements for the spring forces in different regions of the bipolar plate.

[0028] Preferably, the structural element has a rectangular or square cross section, which allows very simple production. A circular or elliptical cross section with one or two axes of symmetry is also preferred.

[0029] According to a particularly preferred embodiment of the bipolar plate according to the invention, the structural parts of the anode plate and the cathode plate are designed in such a way that at least the contact surfaces of the structural elements on the respective other sides of the anode plate and the cathode plate are at least partially covered by the structural parts in order to distribute the pressure over the entire stacking height.

[0030] As a result, the first structured part on the anode side and the second structured part and the structural element of the cathode plate are arranged directly one above the other in the stacking direction of the bipolar plates. Advantageously, damage to the bipolar plates can be avoided in this way.

[0031] The spatial design of the structures of the anode and cathode plates can otherwise be used without problems to optimize the flow conditions. Designs that are identical to the design of the structural elements are preferred.

[0032] A mixture of structural elements with different cross sections is also possible according to the invention.

[0033] The structural elements can be arranged regularly or irregularly in the coolant flow field under the configuration of the flow area in order to avoid pressure losses and to use the required spring forces in a demand-oriented manner. Preferably, the structural elements and optionally the structures form a grid pattern in the case of a regular arrangement.

[0034] The structural element is preferably fixed to at least the anode plate or the cathode plate, for example by adhesive bonding, wherein one-sided fixing can simplify the assembly of the bipolar plate and is usually sufficient. Here, fixing with the cathode plate that conducts the oxidizing medium is preferred.

[0035] According to a particularly preferred embodiment of the bipolar plate according to the invention, the structural element is provided arranged on at least one carrier plate. The at least one carrier plate preferably consists of the same material as the structural element and is preferably produced in one piece with the structural element.

[0036] All structural elements can be arranged on a carrier plate, or they can also be arranged in regions on different carrier plates, that is to say all structural elements at a height are located on a single carrier plate. This advantageously reduces the manufacturing effort.

[0037] The carrier plate can be arranged in abutment with the anode plate or the cathode plate. This advantageous design allows for a substantially simplified assembly of the bipolar plate according to the invention. Even in this embodiment, bonding to at least the anode plate and the cathode plate can be achieved similarly to individual structural elements.

[0038] In addition to the provisions described above, the flow fields of the anode plates and cathode plates as well as the cooling medium flow fields can be designed individually independently of each other.

[0039] Another aspect of the invention relates to a fuel cell stack comprising a stack of membrane electrode assemblies and bipolar plates according to the invention arranged alternately between two end plates.

[0040] The invention further relates to a vehicle having a fuel cell system with a fuel cell stack according to the invention. The vehicle is preferably an electric vehicle, in which the electrical energy generated by the fuel cell system is used to supply an electric traction motor and / or a traction battery.

[0041] Further preferred embodiments of the invention result from the remaining features.

[0042] Unless otherwise indicated in the individual cases, the different embodiments of the invention mentioned in this application can be advantageously combined with one another. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Next, the present invention will be described in the following embodiments according to the accompanying drawings.

[0044] Figure 1 A schematic diagram of a fuel cell stack is shown;

[0045] Figure 2 A detail of a bipolar plate according to the invention is shown in a perspective view,

[0046] Figure 3 The cross-section diagram shows the Figure 2 Details of the bipolar plates,

[0047] Figure 4 A detail of a bipolar plate according to a second embodiment is shown in cross section,

[0048] Figure 5 A perspective view showing details of the cathode plate together with structural elements arranged on a carrier plate,

[0049] Figure 6 A top view shows a structural element with an elliptical cross section on a carrier plate, and

[0050] Figure 7 A structural element with an elliptical cross section according to a second embodiment is shown in a plan view on a carrier plate. DETAILED DESCRIPTION

[0051] Figure 1 A schematic diagram shows a fuel cell stack according to the invention, which is designated overall by 100. The fuel cell stack 100 is part of a vehicle (not shown in any more detail), in particular an electric vehicle, which has an electric traction motor which is supplied with electrical energy by the fuel cell stack 100.

[0052] The fuel cell stack 100 comprises a plurality of membrane electrode assemblies 10 and bipolar plates 12 which are arranged alternately on their planar sides (stacked). As a whole, a plurality of stacked single cells 11 thus form a fuel cell stack 100, wherein not only one of the single cells 11 but also the fuel cell stack 100 can be generally referred to as a fuel cell. The fuel cell stack 100 has end plates 18 on both sides. Anode and cathode chambers (not shown) are arranged between the bipolar plates 12 and the corresponding membrane electrode assemblies 10, which are limited by a surrounding seal 20. In particular, in order to establish the sealing function of the seal 20, the fuel cell stack 100 is pressed (pressed) against each other in the stacking direction S by means of a clamping system.

[0053] The clamping system comprises an outer clamping device 22 and elastic structural elements (not visible here) which are arranged in the coolant region of the bipolar plate 12. This will be explained in more detail below.

[0054] In order to form an external clamping force transmitted to the structural elements in the fuel cell stack 100, the elongated tension bodies 24 of the external clamping device 22 transmit the tensile force between the two end plates 18, so that the end plates 18 are pulled toward each other by means of the tension bodies 24. For this purpose, the tension bodies 24 extend in the stacking direction S of the fuel cell stack 100.

[0055] Figure 2 and 3 A bipolar plate 12 according to the invention is shown in different views according to a first embodiment. Each of the bipolar plates 12 is shown in detail.

[0056] The bipolar plate 12 includes two individual plates, namely an anode plate 30 and a cathode plate 40. The anode plate 30 has an anode side 31 and a cooling medium side 32, which points toward the cathode plate 40. The cathode plate 40 has a cathode side 41 and a cooling medium side 42 pointing toward the anode plate 30. In order to construct a cooling medium flow field 50, elastic structural elements 51a, 51b, 51c are arranged on the cooling medium sides 32, 42 between the anode plate 30 and the cathode plate 40, respectively, which have different heights h. In the inflow area A for the cooling medium, the height h of the structural element 51a is less than the height of the structural element 51c in the outflow area C, and in the transition area B, the height h of the structural element 51b is between the heights of the other structural elements 51a and 51c.

[0057] In the unassembled state, only the structural element 51c contacts the anode plate 30 and the cathode plate 40 in the outflow region C. In the assembled state, all structural elements 51a, 51b, 51c contact the anode plate 30 and the cathode plate 40, since the corresponding fuel cell stack 100 is clamped, thus compensating for height differences between the structural elements 51a, 51b, 51c.

[0058] The structural elements 51 a , 51 b , 51 c are cylindrical and have a square cross section. They are evenly distributed and thus form flow paths 52 in the form of a grid, through which a coolant can flow in the longitudinal and transverse direction with respect to the main axis of the bipolar plate 12 .

[0059] On the anode side 31 and cathode side 41 facing away from the coolant flow field 50, a first structural part 33 or a second structural part 43 is provided, both of which are designed and structured similarly to the structural elements 51a, 51b, 51c of the coolant flow field 50, and the anode flow field 34 and the cathode flow field 44. This means that they are cylindrical with a square cross section. In addition, they are structured for the flow paths 35, 45 of the two reaction media, wherein they are Figures 2 to 4 In the stacking direction S, the structural elements 51a, 5b, 51c coincide with each other.

[0060] The different sizes of the structural elements 51a, 51b, 51c in the center of the cathode plate 40 as opposed to at the edge are attributable only to the illustrated cross section of the bipolar plate 12 and have no technical significance. It is of course basically possible for the structural elements 51a, 51b, 51c to be differently dimensioned and unevenly distributed. To simplify the assembly of the bipolar plate 12, the structural elements 51a, 51b, 51c are fixed, preferably adhesively bonded, at least to the coolant side 42 of the cathode plate 40.

[0061] Figure 4 A detail of a bipolar plate 12 according to a second embodiment is shown in cross section again. In this embodiment, the structural elements 51a, 51b, 51c are formed in one piece with a carrier plate 53, which rests with its flat side on the coolant side 42 of the cathode plate 40. The use of this carrier plate 53 significantly simplifies the assembly of the bipolar plate 12. In this variant, fixing can also be achieved, for example, by gluing the carrier plate 53 or the structural elements 51a, 51b, 51c.

[0062] exist Figure 5 , another variant is shown in which the side of the carrier plate 53 carrying the structural elements 51a, 51b, 51c is placed on the coolant side 42 of the cathode plate 40. The anode plate 30 (not shown) is mounted on the cathode plate 40 according to the arrangement of the carrier plate 53 together with the structural elements 51a, 51b, 51c to complete the bipolar plate 12.

[0063] Figure 6 and 7 The carrier plate 53 is shown together with the structural elements 51a, 51b, 51c mounted thereon, i.e. an elliptical cross section with two axes of symmetry ( Figure 6 ) and a cross section with an axis of symmetry ( Figure 7). This embodiment is used to optimize the flow of the cooling medium. The cross section can also be selected as the first structural part 33 and / or the second structural part 43.

[0064] Unless otherwise indicated, these embodiments relate equally to all embodiments.

[0065] List of Reference Numerals

[0066] 100 fuel cell stacks

[0067] 10 Thin Film Electrode Assembly

[0068] 11 single battery

[0069] 12 Bipolar Plates

[0070] 18 End Plate

[0071] 20 Seals

[0072] 22 Clamping device

[0073] 24 Slender pulling body

[0074] 30 Anode Plate

[0075] 31 Anode side

[0076] 32 Cooling medium side

[0077] 33 First structural part

[0078] 34 Anode flow field

[0079] 35 Flow Path

[0080] 40 cathode plate

[0081] 41 cathode side

[0082] 42 Cooling medium side

[0083] 43 Second structure part

[0084] 44 Anode flow field

[0085] 45 Flow Path

[0086] 50 Cooling medium flow field

[0087] 51a,b,c Structural elements

[0088] 52 Flow Path

[0089] 53 Loading plate

[0090] A Inflow area

[0091] B Transition zone

[0092] C outflow area

[0093] S Stacking direction

Claims

1. A bipolar plate (12) for a fuel cell, comprising: An anode plate (30) with an anode side (31) and a cooling medium side (32), wherein a first structure (33) for constructing an anode flow field (34) is constructed on the anode side (31), and a cathode plate (40) with a cathode side (41) and a cooling medium side (42), wherein a second structure (43) for constructing a cathode flow field (44) is constructed on the cathode side (41), wherein a second structure (43) for constructing a cathode flow field (44) is constructed between the anode plate (30) and the cathode plate (40) A cooling medium flow field (50) is provided with structural elements (51a, 51b, 51c), characterized in that the structural elements (51a, 51b, 51c) are made of elastic material, and the structural elements (51a, 51b, 51c) have different heights in different areas of the cooling medium flow field (50), wherein the height (h) of the structural elements (51a, 51b, 51c) is inversely proportional to the pressure load in the area of ​​the cooling medium flow field (50).

2. The bipolar plate (12) according to claim 1, characterized in that: The anode plate (30) and the cathode plate (40) are made of metal or conductive carbon-based material.

3. The bipolar plate (12) according to claim 1, characterized in that: The anode plate (30) and the cathode plate (40) are made of graphite or a composite material consisting of graphite and carbon.

4. The bipolar plate (12) according to any one of claims 1 to 3, characterized in that: The structural elements (51a, 51b, 51c) are made of an elastic polymer, wherein at least one structural element (51a, 51b, 51c) is electrically conductive.

5. The bipolar plate (12) according to any one of claims 1 to 3, characterized in that: The structural elements (51a, 51b, 51c) are cylindrical and arranged at a distance from each other.

6. The bipolar plate (12) according to any one of claims 1 to 3, characterized in that: The structural elements (51a, 51b, 51c) are cylindrical and have a rectangular or elliptical cross section and are arranged spaced apart from one another, and the structural parts (33, 43) of the anode plate (30) and / or the cathode plate (40) are cylindrical.

7. The bipolar plate (12) according to any one of claims 1 to 3, characterized in that: The first structural portion (33) of the anode plate (30) and the second structural portion (43) of the cathode plate (40) are positioned overlapping each other in the stacking direction (S) and at least partially overlap with the cross section of the structural element (51a, 51b, 51c).

8. The bipolar plate (12) according to any one of claims 1 to 3, characterized in that: The structural elements (51a, 51b, 51c) are arranged regularly or irregularly when forming the flow path (52).

9. The bipolar plate (12) according to any one of claims 1 to 3, characterized in that: The structural elements (51a, 51b, 51c) are fixed at least to the anode plate (30) or the cathode plate (40), or the structural elements (51a, 51b, 51c) are constructed on at least one carrier plate (53) which is arranged in contact with the anode plate (30) or the cathode plate (40), wherein the carrier plate can be fixed to the anode plate (30) or the cathode plate (40).

10. A fuel cell stack (100) comprising a stack of membrane electrode assemblies (10) and bipolar plates (12) according to any one of claims 1 to 9, arranged alternately between two end plates (18).

11. A vehicle with a fuel cell system having a fuel cell stack (100) according to claim 10.

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