Bipolar plates for fuel cell stacks

Abstract

The present invention relates to a bipolar plate, a battery and a fuel cell group of a fuel cell group. When the battery group is in a use position, the plate extends in a vertical plane. In the vertical use position, the plate includes a first lateral edge, a second lateral edge opposite to the first lateral edge, upper and lower longitudinal edges, a central area between the edges, a first opening for an inlet of a heat transfer fluid, a second opening for collecting the heat transfer fluid, a third opening for an inlet of an oxidant, especially air, a fourth opening for collecting the oxidant, a fifth opening for an inlet of a fuel, especially hydrogen, and a sixth opening for collecting the fuel. The first, third and sixth openings are arranged in the first lateral edge and axially arranged with respect to each other, and the second, fourth and fifth openings are arranged in the second lateral edge and axially arranged with respect to each other. In the vertical use position of the plate: the sixth opening is below the first and third openings, the fourth opening is below the second and fifth openings, and the second opening is above the fourth and fifth openings.

Description

Technical Field

[0001] The invention relates to a bipolar plate for a fuel cell stack, a battery for a fuel cell stack comprising such a plate and a fuel cell stack comprising such a battery. The invention is particularly advantageously, but not exclusively, applicable to fuel cell stacks whose cells comprise bipolar plates which extend in a vertical plane when the stack is in the use position. Background Art

[0002] In a manner known per se, a fuel cell stack is an electrochemical device which allows chemical energy to be converted into electrical energy using a fuel (usually hydrogen) and an oxidant (usually oxygen or a gas containing oxygen such as air), the reaction product being water, while releasing heat and generating electricity.

[0003] The fuel cell stack may be used to power a motor vehicle, for example, by supplying power to electrical devices contained in the vehicle.

[0004] A fuel cell stack may consist of one or more cells.

[0005] refer to Figure 1 , which shows a cell 1 for a prior art fuel cell stack, such cell 1 comprises a proton-conducting electrolyte 2 sandwiched between two porous cathode electrodes 3 and an anode electrode 4 and providing proton transfer between these two electrodes 3 , 4 .

[0006] To this end, the electrolyte 2 may be a polymer proton exchange membrane, in particular a polymer proton exchange membrane having a thickness of 20 μm to 200 μm, and the resulting battery stack is a PEM (proton exchange membrane) or PEMFC (proton exchange membrane fuel cell) stack.

[0007] The assembly made of electrolyte 2 and two electrodes 3 , 4 forms a membrane electrode assembly (MEA) 5 , which is itself sandwiched between a first bipolar plate 6 and a second bipolar plate 7 which collect the electric current, distribute the oxidant and the fuel to the electrodes 3 , 4 and circulate a heat transfer fluid.

[0008] The bipolar plates 6 , 7 commonly used are made of a material providing good corrosion resistance and electrical conductivity, for example, a carbon-based material such as graphite, polymer-impregnated graphite, or a flexible graphite sheet formed by machining or molding.

[0009] It is also possible to use metallic materials such as titanium-based, aluminum-based and iron-based alloys, including stainless steel, for the production of the bipolar plates 6 , 7 . In this case, the forming / shaping of the bipolar plates can be achieved by pressing or stamping sheets of low thickness.

[0010] In order to ensure that the oxidant, fuel and heat transfer fluid are distributed to all the cells that make up the battery pack, the second bipolar plate 7 includes six openings 7a, 7b, 7c, 7d, 7e, 7f, of which three openings 7a, 7b, 7c are arranged on the upper edge 8 of the plate 7, and the other three openings 7d, 7e, 7f are arranged in a symmetrical manner on the lower edge 9 of the plate 7.

[0011] although Figure 1 Only three upper openings 6 a , 6 b , 6 c and one lower opening 6 d are shown, but the first bipolar plate 6 includes the same openings arranged at the same positions as on the bipolar plate 7 .

[0012] The openings 6a, 6b, 6c, 6d of the first bipolar plate 6 and the openings 7a, 7b, 7c, 7d, 7e, 7f of the second bipolar plate 7 are aligned to thereby form a manifold that allows fluid to flow through all the cells constituting the battery pack.

[0013] At each of these openings 7a, 7b, 7c, 7d, 7e, 7f, 6a, 6b, 6c, 6d, a duct (not shown) makes it possible to supply or collect a heat transfer fluid, a fuel or an oxidant flowing on the surface of the plates 6, 7, or flowing through the plates 6, 7, or flowing through fluid flow channels provided for this purpose.

[0014] Reference Figure 2 , the figure is along Figure 1 In the cross section taken along line II-II, each of the cathode electrode 3 and the anode electrode 4 includes respective active layers 10, 11 serving as sites for cathode reaction and anode reaction, respectively, and respective diffusion layers 12, 13 inserted between the active layers 10, 11 and the corresponding bipolar plates 7, 6, and the diffusion layers 12, 13 may be, for example, paper matrices or carbon fibers.

[0015] The diffusion layers 12 , 13 allow diffusion of reactants such as hydrogen and oxygen flowing through respective channels 14 , 15 formed by grooves opened in the respective bipolar plates 7 , 6 .

[0016] In this way, hydrogen is supplied to the active layer 11 of the anode electrode 4 via the diffusion layer 13, and the following reaction occurs in the active layer 11: 2 →2e - +2H + In the same manner, oxygen is supplied to the active layer 10 of the cathode electrode 3 via the diffusion layer 12, and the following reaction occurs in the active layer 10: 1 / 2O 2 +2H + +2e - →H 2O. These reactions are made possible by the presence of the membrane 2 , which allows the transfer of protons from the active layer 11 of the anode 4 to the active layer 10 of the cathode 3 .

[0017] In the case of a liquid-cooled fuel cell stack, in particular a low-temperature fuel cell stack (also called a "low-temperature proton exchange membrane (LT-PEM)"), the bipolar plates extend in a vertical plane when the stack is in the use position. It is important to ensure that the fluid circulates evenly and to prevent water from accumulating in the manifold and / or in the channels located in the lower part of the plates and to prevent dissolved gases from stagnating in the manifold and / or in the channels located in the lower part of the plates.

[0018] In addition, the performance and service life of a system equipped with a fuel cell stack depends largely on the quality of the delivery of the reactants and the management of the water produced by the reaction. The distribution of the reactants needs to be as uniform as possible, the membrane electrode assembly needs to maintain good hydration, and at the same time, as much water as possible needs to be removed accurately from the pores of the electrodes to allow the reactants to enter the reaction site. More specifically, a compromise must be made between the drying out of the proton conductor of the membrane at the gas inlet and the flooding of the electrode at the gas outlet. Summary of the invention

[0019] The present invention aims to effectively overcome these drawbacks by providing a bipolar plate for a fuel cell stack, the plate extending in a vertical plane when the stack is in the use position, the plate comprising, in the vertical use position, a first transverse edge, a second transverse edge opposite the first transverse edge, an upper longitudinal edge, a lower longitudinal edge, a central area arranged between these edges, a first opening for the inlet of a heat transfer fluid, a second opening for collecting the heat transfer fluid, a third opening for the inlet of an oxidant, in particular air, a fourth opening for collecting the oxidant, a fifth opening for the inlet of a fuel, in particular hydrogen, a sixth opening for collecting the fuel, the first, third and sixth openings being arranged in the first transverse edge and axially relative to each other, the second, fourth and fifth openings being arranged in the second transverse edge and axially relative to each other, the plate comprising at least one distribution chamber, characterised in that, in the vertical use position of the plate:

[0020] - the sixth opening is arranged below the first and third openings,

[0021] - the fourth opening is arranged below the second and fifth openings,

[0022] The second opening is arranged above the fourth and fifth openings.

[0023] Due to the increase in temperature of the heat transfer fluid as it flows through the cell, at the inlet of the cathode, the excess air promotes the drying of the ionomer that partially constitutes the active layer of the membrane. In addition, at the outlet of the cathode, the accumulation of water produced promotes flooding of the electrode. Thus, the invention makes it possible to promote the removal of water and the degassing of the heat transfer fluid without compromising the uniformity of the fluid distribution when the plates are in the vertical use position, that is, when the battery is in the horizontal use position.

[0024] The specific positioning of the second opening allows the bubbles trapped in the cooling circuit to escape naturally. Specifically, in the vertical position of the plate, the bubbles formed in the circuit are located in the upper part of the distribution chamber and can therefore escape via the second opening located at the same height.

[0025] Surprisingly, the advantages provided by this arrangement of the cooling circuit advantageously compensate for the imbalance in head losses caused by the lack of symmetry between the sixth and fifth openings.

[0026] According to one embodiment, in the vertical use position of the plate, the third opening is arranged above the first opening and the sixth opening.

[0027] Such a configuration allows preventing anode chamber flooding by the relative configuration / distribution of the fuel collection parts, while the oxidant / fuel countercurrent and oxidant / heat transfer fluid cocurrent flows homogenize the cell's operating conditions by better water management.

[0028] According to one embodiment, the distribution chamber is arranged on the surface of the plate on the first lateral edge, the distribution chamber extending in particular at least facing the third, first and sixth opening.

[0029] According to one embodiment, the distribution chamber is arranged on the second lateral edge on the surface of the plate, the distribution chamber extending in particular at least facing the second, fifth and fourth openings.

[0030] This configuration makes it possible to balance the head losses (between the inlet and the collector) without having to design the distribution chamber specifically to balance the fluid flows. Thus, the volume of the plate and the head losses are reduced.

[0031] According to one embodiment, the distribution chamber comprises a pattern of protrusions, in particular bumps or lines consisting of solder, to promote uniformity in the distribution of the fluid.

[0032] According to one embodiment, the plate comprises flow channels arranged in a central area, in particular on a surface of the plate, for example in the form of corrugations of the surface.

[0033] According to one embodiment, the flow channel extends along the longitudinal axis of the plate.

[0034] This configuration makes it possible to reduce the volume of the plate while maintaining good uniformity in the distribution of the fluid.

[0035] According to one embodiment, each opening comprises a hole extending through the thickness of the plate.

[0036] Another subject of the invention is a cell for a fuel cell stack, in particular for a proton exchange membrane fuel cell stack, comprising two bipolar plates and a membrane electrode assembly as described above, the plates being arranged to cooperate with each other and with the membrane electrode assembly sandwiched between the two plates.

[0037] According to one embodiment, the membrane electrode assembly contains no catalyst in the distribution chamber.

[0038] Another subject of the invention is a fuel cell stack, in particular a proton exchange membrane fuel cell stack, comprising at least one cell as described above.

[0039] According to one embodiment, the battery pack comprises:

[0040] - an inlet manifold for a heat transfer fluid, intended to be connected to the heat transfer fluid inlet, to allow the fluid to flow through the first openings;

[0041] - an inlet manifold for the oxidant, intended to be connected to the oxidant inlet, to allow the oxidant to flow through the third opening; and

[0042] - an inlet manifold for fuel, intended to be connected to the fuel inlet, to allow the fuel to flow through the fifth opening. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The invention will be better understood by reading the following description and studying the accompanying drawings, which are given by way of illustration only and do not limit the invention in any way.

[0044] Figure 1 A prior art battery is schematically shown;

[0045] Figure 2 is along Figure 1 II-II axis of the graph; and

[0046] Figure 3 is a front view of a bipolar plate for a battery according to the present invention.

[0047] In the various figures, the same reference numerals are used for the same, similar or analogous elements. DETAILED DESCRIPTION

[0048] The battery for a fuel cell stack according to the present invention is combined with Figure 1 and 2 The battery consists of two Figure 3The bipolar plate 70 of the type shown and the reference Figure 1 and Figure 2 The two bipolar plates 70 are arranged to cooperate with each other so that the membrane electrode assembly is sandwiched between the two plates 70 .

[0049] A fuel cell stack according to the invention comprises a group of cells such as those described above.

[0050] Reference Figure 3 The cross-section of the bipolar plate 70 of the present invention is rectangular. In an exemplary embodiment, the length of the bipolar plate is greater than about twice its width.

[0051] When the battery pack is in the use position, the bipolar plate 70 extends in a vertical plane and includes a first lateral edge 22 , a second lateral edge 24 opposite the first lateral edge 22 , an upper longitudinal edge 20 , a lower longitudinal edge 26 , and a central region 30 disposed between the edges 20 , 22 , 24 , 26 .

[0052] The bipolar plate 70 comprises a third opening 63 for the inlet of the oxidant, which is arranged in the first lateral edge 22 .

[0053] An introduction channel 50 for introducing an oxidant is opened in the plate 70 to allow the oxidant to be introduced from the third opening 63 into the distribution chamber 42 for distributing the oxidant, which is arranged in the plate 70 on the first lateral edge 22 .

[0054] The distribution chamber 42 for distributing the oxidant includes a ridge or line made of solder, which makes it possible to promote the uniformity of the distribution of the oxidant introduced thereby, so that the oxidant flows through the central region 30, and more specifically, the cathode electrode of the membrane electrode assembly close to one surface of the bipolar plate 70. The distribution chamber 42 extends vertically over the entire height of the central region 30.

[0055] Flow channels 44 for the circulation of the oxidant are arranged on the surface of the plate 70 and on one side of the plate in the central region 30 to allow the circulation of the oxidant. These flow channels 44 extend along the longitudinal axis of the plate 70 and open into another distribution chamber 42 for distributing the oxidant, located on the second transverse edge 24.

[0056] The bipolar plate 70 also includes fourth openings 64 disposed in the second lateral edge 24 for collecting oxidant.

[0057] Collection channels 54 for collecting oxidants are made in the plate 70 to allow the oxidants to be collected from the distribution chambers 42 located on the second transverse edge in the fourth openings 64. These collection channels 54 thus make it possible to collect the oxidants that have flowed through the flow channels 44 and have been distributed by the distribution chambers 42.

[0058] exist Figure 3 In the figure, only one surface of the plate 70 can be seen, and on this surface, the distribution chamber 42 for distributing the oxidant, the flow channels 44, the introduction channels 50 and the collection channels 54 can be seen.

[0059] When the battery pack is assembled, the third openings 63 for the inlet of the oxidant and the fourth openings 64 for collecting the oxidant of all the plates overlap and form a manifold that transports the oxidant through the battery pack. The manifold extends along an axis orthogonal to the width of the plate 70 when the battery pack is in the use position.

[0060] The bipolar plate 70 comprises a first opening 61 arranged in the first lateral edge 22 for the inlet of a heat transfer fluid.

[0061] Similarly, an introduction channel for introducing a heat transfer fluid is provided in the plate 70 to allow the heat transfer fluid to be introduced from the first opening 61 into a distribution chamber arranged in the plate 70 on the first lateral edge. The distribution chamber comprises a ridge or line made of solder, which is capable of promoting the uniformity of the distribution of the heat transfer fluid introduced thereby, so that the heat transfer fluid flows in the central region 30 within the bipolar plate 70. Advantageously, the distribution chamber for distributing the heat transfer fluid can be formed by a pattern complementary to the pattern applied to the distribution chamber for distributing the oxidant or the fuel. The distribution chamber extends vertically over the entire height of the central region 30.

[0062] Flow channels (not shown) for circulating the heat transfer fluid are arranged in the central zone 30 to allow the fluid to circulate. These channels extend along the longitudinal axis of the plate 70 and open into distribution chambers located on the second transverse edge for distributing the heat transfer fluid.

[0063] The bipolar plate 70 also comprises second openings 62 for collecting the heat transfer fluid, which are arranged in the second lateral edge 24 .

[0064] Collecting channels for collecting the heat transfer fluid are made in the plate 70 to allow the heat transfer fluid to be collected from the distribution chambers located on the second transverse edge into the second openings 62. These collecting channels thus make it possible to collect the heat transfer fluid that has flowed through the flow channels and has been distributed by the distribution chambers for distributing the heat transfer fluid.

[0065] When the battery pack is assembled, the first openings 61 for the inlet of the heat transfer fluid and the second openings 62 for collecting the heat transfer fluid of all the plates overlap and form a manifold that conveys the heat transfer fluid through the battery pack. The manifold extends along an axis orthogonal to the width of the plates 70 when the battery pack is in the use position.

[0066] The bipolar plate 70 includes a fifth opening 65 arranged in the second lateral edge 24 for fuel inlet.

[0067] Similarly, an introduction channel for introducing fuel is opened in the plate 70 to allow the fuel to be introduced from the fifth opening 65 into a distribution chamber for distributing the fuel arranged in the plate 70 on the second lateral edge 24 .

[0068] The distribution chamber for distributing the fuel comprises a ridge or line made of solder, which makes it possible to promote the uniformity of the distribution of the fuel introduced thereby, so that the fuel flows through the central region 30, and more specifically through the anode electrode of the membrane electrode assembly close to the other surface of the bipolar plate 70. The distribution chamber extends vertically over the entire height of the central region 30.

[0069] Flow channels for fuel circulation are arranged on the surface of the plate 70 and on the other side of the plate in the central area 30 to allow fuel circulation. These flow channels extend along the longitudinal axis of the plate 70 and open into another distribution chamber located on the first transverse edge 22 for distributing fuel.

[0070] The bipolar plate 70 also includes a sixth opening 66 disposed in the first lateral edge 22 for collecting fuel.

[0071] Collecting channels for collecting fuel are made in the plate 70 to allow the fuel to be collected in the sixth openings 66 from the distribution chambers situated on the first transverse edge 22. These collecting channels thus make it possible to collect the fuel flowing through the flow channels and distributed by the distribution chambers.

[0072] When the battery pack is assembled, the fifth openings 65 for fuel inlet and the sixth openings 66 for collecting fuel of all the plates overlap and form a manifold that delivers the fuel through the battery pack. The manifold extends along an axis orthogonal to the width of the plate 70 when the battery pack is in the use position.

Claims

1. A bipolar plate (70) for a fuel cell stack, wherein when the fuel cell stack is in a use position, the bipolar plate (70) extends in a vertical plane; in the vertical use position, the bipolar plate (70) comprises a first transverse edge (22), a second transverse edge (24) opposite to the first transverse edge (22), an upper longitudinal edge (20), a lower longitudinal edge (26), a central area (30) arranged between the first transverse edge (22), the second transverse edge (24), the upper longitudinal edge (20) and the lower longitudinal edge (26), a first opening (61) for an inlet of a heat transfer fluid, a second transverse edge (24) for collecting the heat transfer fluid, and a first opening (61) for an inlet of a heat transfer fluid. The bipolar plate (70) comprises a first opening (61), a second opening (62), a third opening (63) for an oxidant inlet, a fourth opening (64) for collecting the oxidant, a fifth opening (65) for an oxidant inlet, and a sixth opening (66) for collecting the fuel; the first opening (61), the third opening (63) and the sixth opening (66) are arranged in the first lateral edge (22) and are arranged axially relative to each other, the second opening (62), the fourth opening (64) and the fifth opening (65) are arranged in the second lateral edge (24) and are arranged axially relative to each other, the bipolar plate (70) comprises at least one distribution chamber (42), characterized in that, In the vertical use position of the bipolar plate: - the sixth opening (66) is arranged below the first opening (61) and the third opening (63), - the fourth opening (64) is arranged below the second opening (62) and the fifth opening (65), - the second opening (62) is arranged above the fourth opening (64) and the fifth opening (65), The third opening (63) is arranged above the first opening (61) and the sixth opening (66).

2. The bipolar plate (70) according to claim 1, characterized in that: The oxidant is air and / or the fuel is hydrogen.

3. The bipolar plate (70) according to claim 1 or 2, characterized in that: The distribution chamber (42) is arranged on the surface of the bipolar plate (70) on the first lateral edge (22).

4. The bipolar plate (70) according to claim 3, characterized in that: The distribution chamber (42) extends toward at least the third opening (63), the first opening (61), and the sixth opening (66).

5. The bipolar plate (70) according to claim 1 or 2, characterized in that: The dispensing chamber (42) includes a pattern of protrusions to promote uniformity in fluid dispensing.

6. The bipolar plate (70) according to claim 5, characterized in that: The protruding pattern is a bump or line made of solder.

7. The bipolar plate (70) according to claim 1 or 2, characterized in that: The bipolar plate (70) includes flow channels (44) disposed in the central region (30).

8. The bipolar plate (70) according to claim 7, characterized in that: The flow channels are arranged on the surface of the bipolar plate (70) in the central region.

9. The bipolar plate (70) according to claim 8, characterized in that: The flow channels are in the form of corrugations of the surface.

10. The bipolar plate (70) according to claim 7, characterized in that: The flow channel (44) extends along a longitudinal axis of the bipolar plate (70).

11. The bipolar plate (70) according to claim 1 or 2, characterized in that: Each of the first opening (61), the second opening (62), the third opening (63), the fourth opening (64), the fifth opening (65), and the sixth opening (66) comprises a hole extending through the thickness of the bipolar plate (70).

12. A battery for a fuel cell stack, characterized in that: The cell comprises a membrane electrode assembly and two bipolar plates (70) according to any one of the preceding claims, the two bipolar plates (70) being arranged to cooperate together, wherein the membrane electrode assembly is sandwiched between the two bipolar plates (70).

13. A fuel cell stack comprising at least one cell according to claim 12.

14. The fuel cell stack according to claim 13, characterized in that: The fuel cell stack is a proton exchange membrane fuel cell stack.

15. The fuel cell stack according to claim 13 or 14, characterized in that: The fuel cell stack comprises: - an inlet manifold for a heat transfer fluid, intended to be connected to the heat transfer fluid inlet, to allow the heat transfer fluid to flow through the first openings (61); - an inlet manifold for the oxidant intended to be connected to the oxidant inlet to allow the oxidant to flow through the third opening (63); and - an inlet manifold for fuel intended to be connected to the fuel inlet to allow the fuel to flow through the fifth openings (65).

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