Bipolar Plates in Fuel Cell Stacks

Abstract

To provide a bipolar plate for a fuel cell, capable of appropriately maintaining moisture content in a cell.SOLUTION: There is provided a bipolar plate 70 for a fuel cell that is installed and operated while a stacking direction is horizontal. There are provided a cooling medium inlet side opening 61, an air inlet side opening 63, and a hydrogen outlet side opening 66 in the bipolar plate 70 on one side 22 of two sides facing each other in the left-right direction, and there are provided an air outlet side opening 64, a hydrogen inlet side opening 65 and a cooling medium outlet side opening 62 on another side 24. In the arrangement during operation, the hydrogen outlet side opening 66 of the bipolar plate 70 on the one side 22 is arranged vertically below the cooling medium inlet side opening 61 and the air inlet side opening 63, the air outlet side opening 64 on the another side 24 is arranged vertically below the cooling medium outlet side opening 62 and the hydrogen inlet side opening 65, and the cooling medium outlet side opening 62 is arranged vertically above the air outlet side opening 64 and the hydrogen inlet side opening 65.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] In a manner known per se, a fuel cell stack is an electrochemical device capable of converting chemical energy into electrical energy using a fuel, usually dihydrogen, and an oxidant, usually dioxygen or a gas containing dioxygen such as air, The product of this reaction is water with the accompanying release of heat and the production of electricity.

[0003] Fuel cell stacks can be used, for example, to power automobiles by providing power to electrical devices contained within the vehicle.

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

[0005] Referring to FIG. 1 which shows a cell 1 of a prior art fuel cell stack, such a cell 1 comprises a proton conducting electrolyte 2 sandwiched between two porous cathode and anode electrodes 3, 4, providing for the transfer of protons between these two electrodes 3, 4.

[0006] For this purpose, the electrolyte 2 can in particular be a polymeric proton exchange membrane having a thickness between 20 μm and 200 μm, the resulting stack being a PEM (short for "proton exchange membrane") stack or a PEMFC (short for "proton exchange membrane fuel cell") stack.

[0007] The assembly made of the electrolyte 2 and the 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. The first 6 and second bipolar plates 7 collect the electric current, distribute the oxidant and fuel to the electrodes 3, 4 and circulate a heat transfer fluid.

[0008] Typically used bipolar plates 6, 7 are made from a material that provides good corrosion resistance and electrical conductivity, such as a carbon-based material such as graphite, polymer impregnated graphite, or flexible graphite sheets that are shaped by machining or moulding.

[0009] It is also possible to manufacture the bipolar plates 6, 7 using metallic materials such as titanium, aluminum and iron-based alloys, including stainless steel, in which case the shaping of the bipolar plates can be achieved by pressing or stamping a small thickness sheet.

[0010] To ensure that the oxidant, fuel and heat transfer fluid are distributed to all the cells forming the stack, the second bipolar plate 7 has six openings 7a, 7b, 7c, 7d, 7e, 7f, of which three openings 7a, 7b, 7c are provided at the upper edge 8 of this plate 7 and the other three openings 7d, 7e, 7f are provided symmetrically at the lower edge 9 of this plate 7.

[0011] The first bipolar plate 6 is located in the same place as the bipolar plate 7. Although it has openings, only three upper openings 6a, 6b, 6c and one lower opening 6d are shown in FIG.

[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, thereby forming a manifold that allows fluid to flow through all of the cells that form the stack.

[0013] At each of these openings 7a, 7b, 7c, 7d, 7e, 7f, 6a, 6b, 6c, 6d, ducts (not shown) make it possible to supply or withdraw a heat transfer fluid, a fuel or an oxidant which flows over or through the surface of the plates 6, 7 or through fluid flow channels provided for this purpose.

[0014] 2, which is a cross section along line II-II in Fig. 1, the cathode electrode 3 and the anode electrode 4 each have an active layer 10, which is the cathode reaction site, and an active layer 11, which is the anode reaction site, and also have respective diffusion layers 12, 13 interposed between the active layers 10, 11 and the corresponding bipolar plates 7, 6. The diffusion layers 12, 13 can be, for example, a paper substrate or a carbon fabric.

[0015] The diffusion layers 12,13 allow the diffusion of reactants such as dihydrogen and dioxygen, which flow through respective channels 14,15 formed by grooves in the respective bipolar plates 7,6.

[0016] In this manner, dihydrogen is supplied to the active layer 11 of the anode electrode 4 through the diffusion layer 13, and the following reaction occurs in this active layer 11: H2 → 2e - +2H + Similarly, oxygen is supplied to the active layer 10 of the cathode electrode 3 through the diffusion layer 12, and the following reaction occurs in the active layer 10: 1 / 2O2 + 2H + +2e - →H2O. These reactions are made possible by the presence of the membrane 2, which allows proton transfer from the active layer 11 of the anode 4 to the active layer 10 of the cathode 3.

[0017] In the case of fuel cell stacks cooled by liquids, and in particular in the case of low-temperature fuel cell stacks (also called "LT-PEM" for "low-temperature proton exchange membranes"), the bipolar plates extend in a vertical plane when the stack is in the use position. It is important to ensure uniform circulation of the fluids and to prevent both the accumulation of water in the manifolds and / or channels located below the plates and the trapping of dissolved gases in the manifolds and / or channels located below the plates.

[0018] Furthermore, the performance and service life of a system with a fuel cell stack depends heavily on the quality of the reactant transport 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 a good hydration level, and at the same time, the water needs to be accurately removed as much as possible from the porous parts of the electrodes so that the reactants can access the reaction sites. More specifically, a compromise needs to be reached between the drying-out of the membrane proton conductor at the gas inlet and the flooding of the electrodes 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 a use position, the plate having a first transverse edge and The fuel cell has a second transverse edge opposite the first transverse edge, an upper longitudinal edge, a lower longitudinal edge, a central region between the edges, a first opening for the inlet of a heat transfer fluid, a second opening for the recovery of the heat transfer fluid, a third opening for the inlet of an oxidant, in particular air, a fourth opening for the recovery of the oxidant, a fifth opening for the inlet of a fuel, in particular dihydrogen, and a sixth opening for the recovery of the fuel, the first opening, the third opening and the sixth opening being located at the first transverse edge. the second, fourth and fifth openings are provided on a second transverse edge and are axially arranged relative to one another; the plate has at least one distribution chamber, and in a vertical use position of the plate the sixth opening is arranged below the first and third openings, the fourth opening is arranged below the second and fifth openings and the second opening is arranged above the fourth and fifth openings.

[0020] 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 out of the ionomer that constitutes part of the active layer of the membrane. Furthermore, 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, i.e. when the stack is in the horizontal use position.

[0021] The particular arrangement of the second openings allows the natural escape of air bubbles trapped in the cooling circuit: in particular, when the plate is in a vertical position, air bubbles formed in this circuit are located at the top of the distribution chamber, which allows them to escape through the second openings located at the same height.

[0022] Surprisingly, the advantages gained by such an arrangement of the cooling circuits advantageously compensate for the imbalance in head losses caused by the lack of symmetry between the sixth and fifth openings.

[0023] According to one embodiment, in the vertical use position of the plate, the third opening is located above the first opening and the sixth opening.

[0024] Such a configuration makes it possible to prevent flooding of the anode compartment due to the relative placement of the fuel collector, while the countercurrent oxidant / fuel and cocurrent oxidant / heat transfer fluid situation homogenizes the operating conditions of the cell through better water management.

[0025] According to one embodiment, a distribution chamber is provided in the surface of the plate at the first transverse edge, the distribution chamber extending in particular facing at least the third opening, the first opening and the sixth opening.

[0026] According to one embodiment, a distribution chamber is provided in the surface of the plate at the second transverse edge, the distribution chamber in particular extending facing at least the second opening, the fifth opening and the fourth opening.

[0027] This configuration allows for balancing of pressure losses (between the inlet and the collector) so that the distribution chambers do not need to be specially designed to balance the fluid flow, thus reducing plate bulk and pressure losses.

[0028] According to one embodiment, the distribution chamber has a protruding pattern, particularly solder bumps or lines, to promote uniform distribution of the fluid.

[0029] According to one embodiment, the plate has flow channels in the central region, in particular provided on the surface of the plate, for example in the form of corrugations on said surface.

[0030] According to one embodiment, the flow channels extend in the longitudinal axis of the plate.

[0031] Such a configuration makes it possible to reduce the bulk of the plates while retaining good uniformity in the distribution of the fluids.

[0032] According to one embodiment, each opening comprises a hole passing through the thickness of the plate.

[0033] Another subject of the invention is a cell of a fuel cell stack, in particular a proton exchange membrane fuel cell stack, the cell comprising two bipolar plates as described above and a membrane electrode assembly, the plates being arranged to cooperate together and the membrane electrode assembly being sandwiched between the plates.

[0034] According to one embodiment, the membrane electrode assembly is free of catalyst in the distribution chamber.

[0035] 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.

[0036] According to one embodiment, the stack comprises: a heat transfer fluid inlet manifold connected to the heat transfer fluid inlet and adapted to allow fluid to flow through the first opening; an oxidant inlet manifold connected to the oxidant inlet and adapted to allow the oxidant to flow through the third opening; a fuel inlet manifold connected to the fuel intake and adapted to allow fuel to flow through the fifth opening; Equipped with.

[0037] The invention will be better understood on reading the following description and on studying the accompanying drawings, which are given purely by way of example and which do not limit the invention in any way. [Brief description of the drawings]

[0038] [Figure 1] FIG. 1 is a schematic diagram showing a prior art cell. [Diagram 2]FIG. 2 is a view along axis II-II of FIG. 1. [Diagram 3] FIG. 2 is a front view of a bipolar plate of a cell according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Identical, similar or analogous elements retain the same reference numbers from one drawing to another.

[0040] A cell of a fuel cell stack according to the invention is of the type described with reference to Figures 1 and 2. This cell comprises two bipolar plates 70 of the type shown in Figure 3 and a membrane electrode assembly of the same type as that described with reference to Figures 1 and 2. The bipolar plates 70 are cooperatively arranged together such that the membrane electrode assembly is sandwiched between the plates 70.

[0041] A fuel cell stack according to the present invention comprises a stack of cells as described above.

[0042] Referring to FIG. 3, the cross-sectional shape of the bipolar plate 70 of the present invention is rectangular. In the exemplary embodiment, the length of the bipolar plate 70 is approximately twice its width.

[0043] When the stack is in the use position, the bipolar plate 70 extends in a vertical plane and has a first transverse edge 22, a second transverse edge 24 opposite the first transverse 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.

[0044] The bipolar plate 70 has a third opening 63 for the inlet of oxidant, provided at the first transverse edge 22 .

[0045] A channel 50 for the introduction of an oxidant is formed in the plate 70, which makes it possible to introduce the oxidant through the third opening 63 into the chamber 42 for distribution of the oxidant provided in the first transverse edge 22 of the plate 70.

[0046] The oxidant distribution chamber 42 has solder bumps or lines, which make it possible to promote uniform distribution of the oxidant thus introduced, so that it flows through the central region 30, and more particularly through the cathode electrode of the membrane electrode assembly abutting one face of the bipolar plate 70. The distribution chamber 42 extends vertically over the entire height of the central region 30.

[0047] Flow channels 44 for the circulation of the oxidant are provided on one side of the surface of the plate 70, in the central region 30, thereby allowing the circulation of the oxidant. These flow channels 44 extend along the longitudinal axis of the plate 70 and open into another chamber 42 for the distribution of the oxidant, located at the second transverse edge 24.

[0048] The bipolar plate 70 also has a fourth opening 64 provided at the second transverse edge 24 for the withdrawal of oxidant.

[0049] Channels 54 for the recovery of the oxidant are formed in the plate 70, making it possible to recover the oxidant from the distribution chambers 42 located at the second transverse edge, in the fourth openings 64. These recovery channels 54 thus make it possible to recover the oxidant that flows through the flow channels 44 and that has been distributed by the distribution chambers 42.

[0050] In FIG. 3, only one side of the plate 70 is visible, on which the chamber 42 for distribution of the oxidant, the flow channel 44, the input channel 50 and the recovery channel 54 are visible.

[0051] When the stack is assembled, the third openings 63 for oxidant inlet and the fourth openings 64 for oxidant withdrawal of all the plates overlap to form a manifold that carries oxidant through the stack. When the stack is in the use position, the manifold extends along an axis perpendicular to the width of the plates 70.

[0052] The bipolar plate 70 has a first opening 61 provided at the first transverse edge 22 for the inlet of a heat transfer fluid.

[0053] Likewise, channels for the introduction of heat transfer fluid are provided in the plate 70, making it possible to introduce the heat transfer fluid through the first openings 61 into distribution chambers provided at a first transverse edge of the plate 70. The distribution chambers may have solder bumps or lines, which facilitate an even distribution of the heat transfer fluid thus introduced, so that it flows within the central region 30 of the bipolar plate 70. The chambers for distribution of the heat transfer fluid can advantageously be formed according to a pattern complementary to the pattern applied to the chambers for distribution of the oxidant or fuel. The distribution chambers extend vertically over the entire height of the central region 30.

[0054] Flow channels (not shown) for the circulation of a heat transfer fluid are provided in the central region 30, thereby allowing the circulation of the fluid. These channels extend along the longitudinal axis of the plate 70 and open into chambers for the distribution of the heat transfer fluid located at the second transverse edge.

[0055] The bipolar plate 70 also has a second opening at the second transverse edge 24 for the withdrawal of the heat transfer fluid 62 .

[0056] Channels for the withdrawal of heat transfer fluid are formed in the plate 70, making it possible to withdraw the heat transfer fluid from the distribution chambers located at the second transverse edge, in the second openings 62. These withdrawal channels thus make it possible to withdraw the heat transfer fluid that flows through the flow channels and that has been distributed by the heat transfer fluid distribution chambers.

[0057] When the stack is assembled, the first openings 61 for the inlet of heat transfer fluid and the second openings 62 for the return of heat transfer fluid of all the plates overlap to form a manifold that carries heat transfer fluid through the stack. When the stack is in the use position, the manifold extends along an axis perpendicular to the width of the plates 70.

[0058] The bipolar plate 70 has a fifth opening 65 for the inlet of fuel located at the second transverse edge 24 .

[0059] Similarly, a channel for the introduction of fuel is formed in the plate 70, making it possible to introduce fuel through the fifth opening 65 into a fuel distribution chamber provided in the second transverse edge 24 of the plate 70.

[0060] The fuel distribution chamber has solder bumps or lines that can promote uniform distribution of the fuel thus introduced, so that the fuel flows through the central region 30, and more particularly through the anode electrode of the membrane electrode assembly that abuts the other face of the bipolar plate 70. The distribution chamber extends vertically over the full height of the central region 30.

[0061] Flow channels for the circulation of fuel are provided on one side of the surface of the plate 70, in the central region 30, thereby allowing the circulation of fuel. These flow channels extend along the longitudinal axis of the plate 70 and open into another chamber for the distribution of fuel located at the first transverse edge 22.

[0062] The bipolar plate 70 also has a sixth opening 66 at the first transverse edge 22 for the return of fuel.

[0063] Fuel recovery channels are formed in the plate 70, making it possible to recover fuel from the distribution chambers located at the first transverse edge 22, in the sixth openings 66. These recovery channels thus make it possible to recover the fuel that flows through the flow channels and that has been distributed by the distribution chambers.

[0064] When the stack is assembled, the fifth opening 65 for fuel inlet and the sixth opening 66 for fuel return of all plates overlap to form a manifold that conveys fuel through the stack. When the stack is in the use position, the manifold is 1 / 100th of a width of the plate 70. The axis extends perpendicular to the axis of the axial direction.

Claims

1. A bipolar plate (70) for a fuel cell stack, comprising: the plate (70) extending in a vertical plane when the stack is in a use position; In the vertical use position, The plate (70) comprises: A first transverse edge (22); a second transverse edge (24) opposite the first transverse edge (22); A longitudinal upper edge (20); A lower longitudinal edge (26); a central region (30) provided between said edges (20, 22, 24, 26); a first opening (61) for the inlet of a heat transfer fluid; a second opening (62) for the withdrawal of said heat transfer fluid; a third opening (63) for the inlet of an oxidant, in particular air; a fourth opening (64) for recovery of the oxidant; a fifth opening (65) for the inlet of a fuel, in particular dihydrogen; A sixth opening (66) for recovery of said fuel; having the first opening (61), the third opening (63) and the sixth opening (66) are provided in the first transverse edge (22) and are axially disposed relative to one another; the second opening (62), the fourth opening (64), and the fifth opening (65) are provided in the second transverse edge (24) and are axially disposed relative to one another; The plate (70) has at least one distribution chamber (42); In the vertical use position of the plate: the sixth opening (66) is disposed below the first opening (61) and the third opening (63); the fourth opening (64) is disposed below the second opening (62) and the fifth opening (65); The second opening (62) is above the fourth opening (64) and the fifth opening (65). Located in the second opening (62) is disposed at an upper end of the second transverse edge (24); the first opening (61) or the third opening (63) is located at an upper end of the first transverse edge (22); the fourth opening (64) is disposed at a lower end of the second transverse edge (24); A bipolar plate, characterized in that said sixth opening (66) is located at the lower end of said first transverse edge (22).

2. 2. The plate (70) according to claim 1, characterized in that in the vertical use position of the plate, the third opening (63) is arranged above the first opening (61) and the sixth opening (66).

3. 3. A plate (70) according to claim 1 or 2, characterized in that the distribution chamber (42) is provided in the surface of the plate (70) at the first transverse edge (22), the distribution chamber (42) extending in particular facing at least the third opening (63), the first opening (61) and the sixth opening (66).

4. A plate (70) according to any one of claims 1 to 3, wherein the distribution chambers (42) have a protruding pattern, in particular solder bumps or lines, to promote uniform distribution of the fluid.

5. A plate (70) according to any one of claims 1 to 4, characterized in that in the central region (30) the plate (70) has flow channels (44) provided in the surface of the plate (70), for example in the form of corrugations in said surface.

6. 6. The plate (70) of claim 5, wherein the flow channels (44) extend in a longitudinal axis of the plate (70).

7. A plate (70) according to any one of the preceding claims, wherein each opening (61, 62, 63, 64, 65, 66) comprises a hole passing through the thickness of the plate (70).

8. A cell of a fuel cell stack, in particular a proton exchange membrane fuel cell stack, characterized in that it comprises two bipolar plates (70) according to any one of claims 1 to 7 and a membrane electrode assembly, said plates (70) being arranged to cooperate together and said membrane electrode assembly being sandwiched between said plates (70).

9. A fuel cell stack, in particular a proton exchange membrane fuel cell stack, comprising at least one cell according to claim 8.

10. a heat transfer fluid inlet manifold connected to a heat transfer fluid inlet and intended to allow fluid to flow through said first opening (61); an oxidant inlet manifold connected to an oxidant intake and intended to allow oxidant to flow through said third opening (63); a fuel inlet manifold connected to a fuel intake and intended to allow fuel to flow through said fifth opening (65); The fuel cell stack according to claim 9, comprising:

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