Bipolar plate for fuel cells, fuel cell stack with such bipolar plates, and vehicle with such a fuel cell stack

Abstract

In order to provide a bipolar plate for a fuel cell, providing an anode plate with an anode side and a coolant side, wherein a first structuring for forming an anode flow field is formed on the anode side, and a cathode plate with a cathode side and a coolant side, wherein a second structuring for forming a cathode flow field is formed on the cathode side; wherein structural elements, which are contacted by the coolant sides of the anode plate and the cathode plate, for forming a coolant flow field, are arranged between the anode plate and the cathode plate, which bipolar plate has an optimized pressure distribution in a fuel cell stack and increased stability in comparison with the prior art, it is proposed that the structural elements may be made of an elastic material and that the structural elements have a different height in different regions of the coolant flow field. A fuel cell stack and a vehicle are also disclosed.

Claims

1. A bipolar plate for a fuel cell, comprising: an anode plate with an anode side and a coolant side, wherein a first structuring for forming an anode flow field is formed on the anode side, and a cathode plate with a cathode side and a coolant side, wherein a second structuring for forming a cathode flow field is formed on the cathode side; wherein structural elements are arranged between the anode plate and the cathode plate to form a coolant flow field, wherein the structural elements comprise an elastic material and the structural elements have different heights in different regions of the coolant flow field when the bipolar plate is in an uninstalled state.

2. The bipolar plate according to claim 1, wherein the height of the structural elements is inversely proportional to the compressive stress in the regions of the coolant flow field.

3. The bipolar plate according to claim 1, wherein the anode plate and the cathode plate comprise metal or a conductive carbon-based material.

4. The bipolar plate according to claim 1, wherein the structural elements comprise an elastic polymer, wherein at least one structural element is electrically conductive.

5. The bipolar plate according to claim 1, wherein the structural elements are columnar.

6. The bipolar plate according to claim 1, wherein the first structuring of the anode plate and the second structuring of the cathode plate are positioned one above the other in the stack direction and overlap at least partially with the cross-sectional area of the structural elements.

7. The bipolar plate according to claim 1, wherein the structural elements are arranged in a regular or irregular manner.

8. The bipolar plate according to claim 1, wherein the structural elements are fixed to at least the anode plate or the cathode plate, or the structural elements are formed on at least one carrier plate, which is arranged to be adjacent either to the anode plate or to the cathode plate, wherein the carrier plate can be fixed to the anode plate or the cathode plate.

9. The bipolar plate according to claim 3, wherein the anode plate and the cathode plate comprise graphite or a composite material of graphite and carbon.

10. The bipolar plate according to claim 5, wherein the structural elements have a rectangular or oval cross section.

11. The bipolar plate according to claim 5, wherein the structurings of the anode plate and/or the cathode plate are columnar.

12. A fuel cell system comprising a stack between two end plates, wherein the stack includes alternately arranged membrane electrode assemblies and bipolar plates, wherein each of the bipolar plates includes: an anode plate with an anode side and a coolant side, wherein a first structuring for forming an anode flow field is formed on the anode side, and a cathode plate with a cathode side and a coolant side, wherein a second structuring for forming a cathode flow field is formed on the cathode side; wherein structural elements are arranged between the anode plate and the cathode plate to form a coolant flow field, wherein the structural elements comprise an elastic material and the structural elements have different heights in different regions of the coolant flow field when the bipolar plate is in an uninstalled state.

13. A vehicle comprising a fuel cell system comprising a fuel cell stack between two end plates, wherein the stack includes alternately arranged membrane electrode assemblies and bipolar plates, wherein each of the bipolar plates includes: an anode plate with an anode side and a coolant side, wherein a first structuring for forming an anode flow field is formed on the anode side, and a cathode plate with a cathode side and a coolant side, wherein a second structuring for forming a cathode flow field is formed on the cathode side; wherein structural elements are arranged between the anode plate and the cathode plate to form a coolant flow field, wherein the structural elements comprise an elastic material and the structural elements have different heights in different regions of the coolant flow field when the bipolar plate is in an uninstalled state.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) Embodiments of the invention are explained below in reference to the respective drawings. The following is shown:

(2) FIG. 1 is a schematic representation of a fuel cell stack;

(3) FIG. 2 is a perspective view of a detail of a bipolar plate;

(4) FIG. 3 is a sectional view of the detail of the bipolar plate according to FIG. 2;

(5) FIG. 4 is a sectional view of a detail of a bipolar plate;

(6) FIG. 5 is a perspective view of a detail of a cathode plate with structural elements arranged on a carrier plate;

(7) FIG. 6 is a plan view of structural elements with oval cross section on a carrier plate; and

(8) FIG. 7 is a plan view of structural elements with oval cross section on a carrier plate.

DETAILED DESCRIPTION

(9) FIG. 1 shows a schematic representation of a fuel cell stack, denoted overall by 100. The fuel cell stack 100 is part of a vehicle (not shown in 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.

(10) The fuel cell stack 100 comprises a plurality of membrane electrode assemblies 10 and bipolar plates 12 alternately arranged (stacked) next to each other on their flat sides. Overall, several stacked individual cells 11 thus form the fuel cell stack 100, wherein both one of the individual cells 11 and the fuel cell stack 100 can generally be called a fuel cell. The fuel cell stack 100 has end plates 18 on both end sides. Between the bipolar plates 12 and the respective membrane electrode assemblies 10, anode and cathode chambers (not shown) are arranged, which are delimited by circumferential seals 20. In order to produce the sealing function of the seals 20, among other things, the fuel cell stack 100 is pressed in the stack direction S by means of a tensioning system.

(11) The tensioning system comprises an outer tensioning device 22 along with elastic structural elements which are not visible here and are arranged in the coolant region of the bipolar plates 12. These are described in more detail below.

(12) In order to build external stress, which is transmitted to the structural elements in the fuel cell stack 100, elongated tensile bodies 24 of the outer tensioning devices 22 transfer tensile forces between the two end plates 18, such that the end plates 18 are pulled toward one another by means of the tensile bodies 24. To this end, the tensile bodies 24 extend in a stack direction S of the fuel cell stack 100.

(13) FIGS. 2 and 3 show a bipolar plate 12 according to a first embodiment in different views. A detail of the bipolar plate 12 is shown in each case.

(14) The bipolar plate 12 here comprises two individual plates, an anode plate 30 and a cathode plate 40. The anode plate 30 has an anode side 31 and a coolant side 32 facing the cathode plate 40. The cathode plate 40 has a cathode side 41 and a coolant side 42 facing the anode plate 30. In order to form a coolant flow field 50, elastic structural elements 51a, 51b, 51c which have a different height h are arranged between the anode plate 30 and the cathode plate 40 on the coolant side 32, 42 in each case. In the inflow region A for the coolant, the height h of the structural elements 51a is smaller than that of the structural elements 51c in the outflow region C, and the height h of the structural elements 51b in the transition region B is between those of the other structural elements 51a and 51c.

(15) In the uninstalled state, only the structural elements 51c in the outflow region C contact the anode plate 30 and the cathode plate 40.

(16) In the installed 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 braced so that there is compensation for a difference in height between the structural elements 51a, 51b, 51c.

(17) The structural elements 51a, 51b, 51c are columnar and have a square cross section. They are distributed uniformly and thus form flow paths 52 in the form of a grid, through which a coolant can flow in the longitudinal and transverse directions relative to a main axis of the bipolar plate 12.

(18) On the anode side 31 and the cathode side 41 facing away from the coolant flow field 50, a first structuring 33 and a second structuring 43 respectively are provided, which are both designed analogously to the structural elements 51a, 51b, 51c of the coolant flow field 50 and form an anode flow field 34 and a cathode flow field 44. That is to say, they are columnar with a square cross section. In addition, they form flow paths 35, 45 for the two reaction media, wherein such flow paths in FIGS. 2 to 4 are congruent in the stack direction S with the structural elements 51a, 51b, 51c.

(19) The deviating sizes of the structural elements 51a, 51b, 51c in the center of the cathode plate 40 in contrast to those at the edges are only attributed to the shown section of the bipolar plate 12 and have no technical significance. Of course, it is possible in principle to dimension the structural elements 51a, 51b, 51c differently and to distribute them unevenly. In order to facilitate the mounting of the bipolar plate 12, the structural elements 51a, 51b, 51c are fixed, such as glued, at least to the coolant side 42 of the cathode plate 40.

(20) FIG. 4 again shows a detail of a bipolar plate 12 according to a second embodiment in section. With such embodiment, the structural elements 51a, 51b, 51c are integrally formed with a carrier plate 53, which rests with the flat side on the coolant side 42 of the cathode plate 40. The use of this carrier plate 53 significantly facilitates the mounting of the bipolar plate 12. With this variant as well, fixing can be carried out, for example, by gluing the carrier plate 53 or the structural elements 51a, 51b, 51c.

(21) The other variant with which the side of the carrier plate 53 carrying the structural elements 51a, 51b, 51c rests on the coolant side 42 of the cathode plate 40 is shown in FIG. 5. The anode plate 30, which is not shown, is applied to the cathode plate 40 after arranging the carrier plate 53 with the structural elements 51a, 51b, 51c, in order to complete the bipolar plate 12.

(22) FIGS. 6 and 7 each show a carrier plate 53 with structural elements 51a, 51b, 51c applied thereto, such structural elements having an oval cross section with two axes of symmetry (FIG. 6) and a cross section with one axis of symmetry (FIG. 7). Such embodiments serve to optimize the flow conditions of a coolant. Such cross sections can also be selected as first structuring 33 and/or second structuring 43.

(23) Unless explicitly stated, the statements equally relate to all embodiments.

(24) This application claims priority to German patent application no. 10 2019 205 564.8, filed Apr. 17, 2019, which is hereby incorporated herein by reference in its entirety.

(25) In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.