FUEL CELL STACK COMPRISING VARIABLE BIPOLAR PLATES

Abstract

A fuel cell stack is provided comprising membrane electrode assemblies and bipolar plates for supplying the membrane electrode assemblies with operating media and coolant, wherein a first bipolar plate comprises flow pathways having path depths that are different from path depths of corresponding flow pathways of a second bipolar plate. Moreover, a vehicle with a fuel cell system having such a fuel cell stack is provided.

Claims

1. A fuel cell stack, comprising: a stack of membrane electrode assemblies and bipolar plates situated in alternating manner between two end plates, wherein the bipolar plates each comprise an anode plate having an anode side and a coolant side, a cathode plate having a cathode side and a coolant side, a plurality of electrode-side flow pathways having path depths, and a plurality of coolant-side flow pathways having path depths, and wherein: a first one of the bipolar plates comprises at least one anode-side flow pathway having a path depth, which is different from a path depth of at least one anode-side flow pathway of a second one of the bipolar plates; the first one of the bipolar plates comprises at least one cathode-side flow pathway having a path depth, which is different from a path depth of at least one cathode-side flow pathway of the second one of the bipolar plates; and/or the first one of the bipolar plates comprises at least one coolant-side flow pathway having a path depth, which is different from a path depth of at least one coolant-side flow pathway of the second one of the bipolar plates.

2. The fuel cell stack according to claim 1, wherein the first bipolar plate is situated in a first stack direction closer to a first end plate of the fuel cell stack than the second bipolar plate is, and at least one of the coolant-side flow pathways of the first bipolar plate has a lesser depth than a depth of at least one of the coolant-side flow pathways of the second bipolar plate.

3. The fuel cell stack according to claim 1, wherein the first bipolar plate is situated in a first stack direction closer to a first end plate of the fuel cell stack than the second bipolar plate is and at least one of the cathode-side flow pathways of the first bipolar plate has a greater depth than a depth of at least one of the cathode-side flow pathways of the second bipolar plate.

4. The fuel cell stack according to claim 1, wherein the bipolar plates comprise anode-side structural elements for forming the anode-side flow pathways, and cathode-side structural elements for forming the cathode-side flow pathways, and wherein: the first bipolar plate comprises at least one anode-side structural element having a height which is different from a height of at least one anode-side structural element of the second bipolar plate; and/or the first bipolar plate comprises at least one cathode-side structural element having a height which is different from a height of at least one cathode-side structural element of the second bipolar plate.

5. The fuel cell stack according to claim 1, wherein the bipolar plates comprise coolant-side structural elements for forming the coolant-side flow pathways, and wherein the first bipolar plate comprises at least one coolant-side structural element having a height which is different from a height of at least one coolant-side structural element of the second bipolar plate.

6. The fuel cell stack according to claim 5, wherein the coolant-side structural elements are formed as columns.

7. The fuel cell stack according to claim 5, wherein the coolant-side structural elements have a rectangular or oval cross section.

8. The fuel cell stack according to claim 4, wherein the anode-side structural elements are connected to the anode plate and/or the cathode-side structural elements are connected to the cathode plate.

9. The fuel cell stack according to claim 4, wherein the anode-side structural elements are connected by an anode-side carrier plate to the anode plate and/or the cathode-side structural elements are connected by a cathode-side carrier plate to the cathode plate.

10. The fuel cell stack according to claim 5, wherein the coolant-side structural elements are connected to both the anode plate and to the cathode plate.

11. The fuel cell stack according to claim 5, wherein the coolant-side structural elements are part of a coolant-side carrier plate.

12. A vehicle having a fuel cell system that comprises a fuel cell stack, the fuel cell stack including: a stack of membrane electrode assemblies and bipolar plates situated in alternating manner between two end plates, wherein the bipolar plates each comprise an anode plate having an anode side and a coolant side as well as a cathode plate having a cathode side and a coolant side as well as a plurality of electrode-side flow pathways having path depths and a plurality of coolant-side flow pathways having path depths, and wherein: a first one of the bipolar plates comprises at least one anode-side flow pathway having a path depth, which is different from a path depth of at least one anode-side flow pathway of a second one of the bipolar plates; the first one of the bipolar plates comprises at least one cathode-side flow pathway having a path depth, which is different from a path depth of at least one cathode-side flow pathway of the second one of the bipolar plates; and/or the first one of the bipolar plates comprises at least one coolant-side flow pathway having a path depth, which is different from a path depth of at least one coolant-side flow pathway of the second one of the bipolar plates.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0038] Embodiments of the invention are explained with the aid of the corresponding drawings.

[0039] FIG. 1 shows a schematic representation of a fuel cell stack.

[0040] FIG. 2 shows in perspective view from above, a bipolar plate of a fuel cell stack in a first embodiment.

[0041] FIG. 3 shows in a sectional view, the bipolar plate of FIG. 2.

[0042] FIG. 4 shows in a schematic side view, a fuel cell stack showing the position of a first bipolar plate and a second bipolar plate.

[0043] FIG. 5 shows in a sectional view, a bipolar plate of a fuel cell stack in a second embodiment.

[0044] FIG. 6 shows in a front view, structural elements having a basically oval cross section on a carrier plate for a bipolar plate of a fuel cell stack.

DETAILED DESCRIPTION

[0045] FIG. 1 shows in a schematic representation a fuel cell stack designated overall as 100. The fuel cell stack 100 is part of a vehicle, especially an electric vehicle, having an electric traction motor which is supplied with electrical energy by the fuel cell stack 100.

[0046] The fuel cell stack 100 comprises a plurality of membrane electrode assemblies 10 and bipolar plates 12 arranged in a row (stacked) in alternating manner at their flat sides. Thus, multiple stacked individual cells 11 form the fuel cell stack 100 overall, while both one of the individual cells 11 and also the fuel cell stack 100 can generally be called a fuel cell. The fuel cell stack 100 has end plates 18 on either side. Between the bipolar plates 12 and the respective membrane electrode assemblies 10 there are arranged anode and cathode spaces, not shown, being bounded by encircling seals 20. In order to ensure the sealing function of the seals 20, among other things, the fuel cell stack 100 is compressed (press-fitted) in the stack direction S by means of a clamping system.

[0047] The clamping system comprises an outer clamping device 22, as well as elastic structural elements of the bipolar plates 12, not visible here. These shall be further described in the following.

[0048] In order to create an external clamping which is transmitted to the structural elements in the fuel cell stack 100, lengthwise tension elements 24 of the outer clamping devices 22 pass on tension forces between the two end plates 18, so that the end plates 18 are pulled together by means of the tension elements 24. For this, the tension elements 24 extend in a stack direction S of the fuel cell stack 100. In this way, sizeable pressures are created inside the stack.

[0049] FIGS. 2 and 3 show a bipolar plate 12 in a first embodiment in various views. Each time one detail of the bipolar plate 12 is shown.

[0050] 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, pointing toward the cathode plate 40. The cathode plate 40 has a cathode side 41 and a coolant side 42 pointing toward the anode plate 30. In order to form a coolant flow field 50, coolant-side structural elements 51 are arranged each time on the coolant side 32, 42 between the anode plate 30 and the cathode plate 40, each of them contacting the anode plate 30 and the cathode plate 40. The structural elements 51 are in the form of columns and have a square cross section. These are evenly distributed and thus form flow pathways 52 in the shape of a lattice network, through which a coolant can flow in the lengthwise and transverse direction, relative to a principal axis of the bipolar plate 12.

[0051] Anode-side structural elements 33 and cathode-side structural elements 43 are provided on the anode side 31 and cathode side 41 facing away from the coolant flow field 50, both of them being configured similar to the coolant-side structural elements 51 of the coolant flow field 50 and forming an anode flow field 34 and a cathode flow field 44, respectively. That is, they are in the form of columns with a square cross section. This does not rule out the structural elements having a different form of cross section. The bipolar plate 12 comprises at least one anode-side flow pathway 35 having a path depth TA. Furthermore, the bipolar plate 12 comprises cathode-side flow pathways 45 having a path depth TK. Moreover, the bipolar plate 12 comprises coolant-side flow pathways 52 having a path depth TC. FIG. 4 now shows the relative arrangement of a first bipolar plate 12.1 and a second bipolar plate 12.2. The first bipolar plate 12.1 comprises at least one anode-side flow pathway TA having a path depth TA, which is different from the path depth TA of at least one anode-side flow pathway 35 of the second bipolar plate 12.2. Furthermore, the first bipolar plate 12.1 may comprise at least one cathode-side flow pathway 45 having a path depth TK, which differs from the path depth TK of at least one cathode-side flow pathway TK of the second bipolar plate 12.2. Moreover, the first bipolar plate 12.1 may comprise at least one coolant-side flow pathway 52 having a path depth TC, which differs from the path depth TC of at least one coolant-side flow pathway TC of a second bipolar plate 12.2.

[0052] The first bipolar plate 12.1 is situated closer in a first stack direction S1 to a first end plate 12.1 of the fuel cell stack 100 than to the second bipolar plate 12.2, as can likewise be seen from FIG. 4. At least one of the coolant-side flow pathways 52 of the first bipolar plate 12.1 may have a lesser depth TC than the depth TC of at least one of the coolant-side flow pathways 52 of the second bipolar plate 12.2. This makes possible better control of the heat removal. The first stack direction S1 here designates the direction from the middle level M of the stack to the first end plate 18.1. A second stack direction S2 the direction from the middle level M of the stack to the second end plate 18.2.

[0053] The anode-side structural elements 33 have a height HA. The cathode-side structural elements 43 have a height HK. The coolant-side structural elements 51 have a height HC. The heights HA, HK, HC correspond respectively to the depths TA, TK, TC.

[0054] FIG. 5 in turn shows a detail of a bipolar plate 12 according to second configuration in cross section. In this configuration, the structural elements 51 form a single piece with a carrier plate 56, which lies by its flat side against the coolant side 42 of the cathode plate 40. The use of this carrier plate 56 makes the assembly of the bipolar plate 12 much easier. Also in this variant a gluing of the carrier plate 56 or the structural elements 51 can be done. Moreover, in this embodiment the anode-side structural elements 33 are formed as a single piece with an anode-side carrier plate 36, which lies by its flat side against the anode side 31 of the anode plate 30. The use of this carrier plate 36 further makes the assembly of the bipolar plate 12 much easier. Moreover, in this embodiment the cathode-side structural elements 43 are also formed as a single piece with a cathode-side carrier plate 46, which lies by its flat side against the cathode side 41 of the cathode plate 40. The use of this carrier plate 46 further makes the assembly of the bipolar plate 12 much easier. Thus, viewed as a whole, the embodiment shown in FIG. 6 differs from the embodiment shown in FIGS. 2 and 3 in that the structural elements 33, 43, 51 are placed not directly, but rather by means of carrier plates 36, 46, 56, on the anode plate 30 or on the cathode plate 40.

[0055] Unless otherwise explicitly stated, the remarks pertain equally to all of the embodiments.

[0056] Again, aspects of the various embodiments described above can be combined to provide further embodiments. 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.