Fuel battery cell and method for designing fuel battery cell

Abstract

To provide a fuel battery cell that can improve durability of a membrane electrode joined body, and a method for designing a fuel battery cell.SOLUTION: A fuel battery cell comprises: a membrane electrode joined body that generates power by using reaction gas; a pair of gas diffusion layers that sandwich the membrane electrode joined body; and a pair of separators 14 that sandwich the membrane electrode joined body and the pair of gas diffusion layers. The gas diffusion layer has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less. The separator 14 has a groove 29 that has a branch part 31 and forms a channel 28 for supplying the reaction gas to the membrane electrode joined body. A value obtained by dividing the diameter D of an inscribed circle 33 of the branch part 31 in the groove 29 by a groove width W of a general part 32 other than the branch part 31 in the groove 29 is 2.5 or less.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a fuel cell and a method for designing a fuel cell.

Background Art

[0002] Conventionally, as a fuel cell, for example, the one shown in Patent Document 1 is known. Such a fuel cell has a configuration in which a membrane electrode assembly sandwiched between a pair of gas diffusion layers and supported by a frame member is sandwiched by a pair of separators. The separator is formed with a groove flow path for supplying a reaction gas to the membrane electrode assembly.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the fuel cell as described above, the groove flow path formed in the separator has a branch portion. Since the width of the branch portion in the groove flow path is wider than other portions in the groove flow path, the portion in contact with the branch portion in the gas diffusion layer is likely to bend. For this reason, the surface pressure of the portion in contact with the easily bendable portion of the gas diffusion layer in the membrane electrode assembly decreases, so it is likely to swell.

[0005] The membrane electrode assembly contracts and expands due to repeated drying and wetting. The portion where the surface pressure in the membrane electrode assembly decreases is likely to deform as it contracts and expands. Therefore, since the load applied to the portion where the surface pressure in the membrane electrode assembly decreases increases, there is a problem that the durability of the membrane electrode assembly decreases.

Means for Solving the Problems

[0006] Means for solving the above problems and their effects will be described below. The fuel cell for solving the above problems includes a membrane electrode assembly that generates electricity using a reaction gas, a pair of gas diffusion layers sandwiching the membrane electrode assembly, and a pair of separators sandwiching the membrane electrode assembly and the pair of gas diffusion layers. The gas diffusion layer has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less. The separator has a branch portion and a groove that forms a flow path for supplying the reaction gas to the membrane electrode assembly. The value obtained by dividing the diameter of the inscribed circle of the branch portion in the groove by the width of the general portion other than the branch portion in the groove is 2.5 or less.

[0007] Normally, the width of the branch portion in the groove is wider than that of the general portion, so the portion in contact with the branch portion in the gas diffusion layer is likely to bend. For this reason, the surface pressure of the portion in contact with the easily bendable portion of the gas diffusion layer in the membrane electrode assembly decreases, so it is likely to swell. The membrane electrode assembly contracts and expands due to repeated drying and wetting accompanying humidity changes during power generation. The portion with a reduced surface pressure in the membrane electrode assembly is likely to deform as it contracts and expands. As a result, the load applied to the portion with a reduced surface pressure in the membrane electrode assembly increases, so there is a problem that the durability of the membrane electrode assembly decreases.

[0008] Therefore, the inventor of the present application has found that by configuring as follows, a decrease in the durability of the membrane electrode assembly can be suppressed. That is, the gas diffusion layer has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less, and the value obtained by dividing the diameter of the inscribed circle of the branch portion in the groove of the separator by the width of the general portion other than the branch portion in the groove is set to 2.5 or less. Therefore, with the above configuration, the durability of the membrane electrode assembly can be improved.

[0009] A method for designing a fuel cell stack for solving the above problems, comprising a membrane electrode assembly that generates electricity using a reaction gas, a pair of gas diffusion layers sandwiching the membrane electrode assembly, and a pair of separators sandwiching the membrane electrode assembly and the pair of gas diffusion layers, wherein the gas diffusion layer has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less, the separator has a branch portion and a groove forming a flow path for supplying the reaction gas to the membrane electrode assembly, and the shape of the groove is designed such that the value obtained by dividing the diameter of the inscribed circle of the branch portion in the groove by the width of the general portion other than the branch portion in the groove is 2.5 or less.

[0010] Normally, the width of the branch portion in the groove is wider than that of the general portion, so the portion in contact with the branch portion in the gas diffusion layer is likely to bend. For this reason, the surface pressure of the portion in contact with the easily bendable portion of the gas diffusion layer in the membrane electrode assembly decreases, so it is likely to swell. The membrane electrode assembly contracts and expands due to repeated drying and wetting accompanying humidity changes during power generation. The portion with reduced surface pressure in the membrane electrode assembly is likely to deform as it contracts and expands. As a result, the load applied to the portion with reduced surface pressure in the membrane electrode assembly increases, so there is a problem that the durability of the membrane electrode assembly decreases.

[0011] Therefore, the inventor of the present application has found that by designing as follows, a decrease in the durability of the membrane electrode assembly can be suppressed. That is, the gas diffusion layer has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less, and the separator groove is designed such that the value obtained by dividing the diameter of the inscribed circle of the branch portion by the width of the general portion other than the branch portion in the groove is 2.5 or less. Therefore, the durability of the membrane electrode assembly can be improved by the above design method.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0013] Hereinafter, an embodiment will be described with reference to the drawings. <Fuel cell 11> As shown in FIG. 1, the fuel cell 11 has a rectangular plate shape and is stacked in a plurality to form a fuel cell stack (not shown). The fuel cell 11 includes a rectangular plate-shaped power generation unit 12, a pair of gas diffusion layers 13 having a rectangular sheet shape, and a pair of separators 14 having a rectangular plate shape. That is, the fuel cell 11 has a structure in which the power generation unit 12 sandwiched between a pair of gas diffusion layers 13 is sandwiched by a pair of separators 14 from the outside of the pair of gas diffusion layers 13.

[0014] In the following description, the long side direction, the short side direction, and the thickness direction in the fuel cell 11 are the long side direction X, the short side direction Y, and the thickness direction Z, respectively. The long side direction X, the short side direction Y, and the thickness direction Z are directions orthogonal to each other.

[0015] As shown in FIG. 1, among the pair of gas diffusion layers 13, one (cathode side) is the first gas diffusion layer 15, and the other (anode side) is the second gas diffusion layer 16. Among the pair of separators 14, one (cathode side) is the first separator 17, and the other (anode side) is the second separator 18.

[0016] The power generation unit 12 includes a resin-made frame member 19 having a rectangular plate shape, and a membrane electrode assembly 20 (MEA: Membrane Electrode Assembly) having a rectangular sheet shape supported by the frame member 19. The frame member 19 has a rectangular opening 21 at the central portion. The membrane electrode assembly 20 is adhered to the frame member 19 in a state of being disposed in the opening 21. That is, the membrane electrode assembly 20 is supported by the frame member 19 in a state of closing the opening 21.

[0017] A pair of gas diffusion layers 13 sandwich the membrane electrode assembly 20 supported in the opening 21 of the frame member 19 in the thickness direction Z. A pair of separators 14 sandwich the power generation unit 12 in the thickness direction Z from the outside of the pair of gas diffusion layers 13. The pair of gas diffusion layers 13 are set to have a thickness in the range of 0.12 mm or more and 0.25 mm or less, and to have a Young's modulus of 1800 MPa or more.

[0018] In the fuel cell 11, an oxidant gas containing oxygen is supplied to a portion on one side (cathode side) in the thickness direction Z of the membrane electrode assembly 20, and a fuel gas containing hydrogen is supplied to a portion on the other side (anode side) in the thickness direction Z of the membrane electrode assembly 20. Thereby, the fuel cell 11 generates power based on the electrochemical reaction of the oxidant gas and the fuel gas in the membrane electrode assembly 20. That is, in the membrane electrode assembly 20, power is generated using the oxidant gas and the fuel gas as reaction gases.

[0019] <Flow path configuration of the fuel cell 11> As shown in FIG. 1, at both ends of the fuel cell 11 sandwiching the membrane electrode assembly 20 in the long side direction X, that is, at both ends of the frame member 19 and the pair of separators 14 sandwiching the membrane electrode assembly 20 in the long side direction X, three rectangular through holes arranged in the short side direction Y are formed.

[0020] The three through holes at one end of the fuel cell 11 in the long side direction X are the oxidant gas supply hole 22, the cooling medium supply hole 23, and the fuel gas discharge hole 24. The three through holes at the other end of the fuel cell 11 in the long side direction X are the fuel gas supply hole 25, the cooling medium discharge hole 26, and the oxidant gas discharge hole 27. In this case, in the long side direction X, the oxidant gas supply hole 22 and the fuel gas supply hole 25 face each other, the cooling medium supply hole 23 and the cooling medium discharge hole 26 face each other, and the fuel gas discharge hole 24 and the oxidant gas discharge hole 27 face each other.

[0021] The fuel gas supply hole 25 constitutes the inlet side fuel gas manifold to which fuel gas is supplied in a fuel cell stack (not shown). The fuel gas discharge hole 24 constitutes the outlet side fuel gas manifold from which fuel gas is discharged in a fuel cell stack (not shown). The oxidant gas supply hole 22 constitutes the inlet side oxidant gas manifold to which oxidant gas is supplied in a fuel cell stack (not shown).

[0022] The oxidant gas discharge hole 27 constitutes the outlet side oxidant gas manifold from which oxidant gas is discharged in a fuel cell stack (not shown). Each of the above manifolds extends in the stacking direction (thickness direction Z) of the fuel cell 11 when the fuel cell stack (not shown) is configured.

[0023] An oxidant gas flow path is formed between the frame member 19 and the membrane electrode assembly 20 and the first separator 17 to allow the oxidant gas supplied from the oxidant gas supply hole 22 to flow to the oxidant gas discharge hole 27 via the membrane electrode assembly 20. A fuel gas flow path is formed between the frame member 19 and the membrane electrode assembly 20 and the second separator 18 to allow the fuel gas supplied from the fuel gas supply hole 25 to flow to the fuel gas discharge hole 24 via the membrane electrode assembly 20.

[0024] When a plurality of fuel cells 11 are stacked to form a fuel cell stack (not shown), a cooling medium flow path (not shown) is formed between a first separator 17 of one of two adjacent fuel cells 11 in the stacking direction (thickness direction Z) and a second separator 18 of the other. The cooling medium flow path (not shown) flows the cooling medium supplied from the cooling medium supply hole 23 to the cooling medium discharge hole 26.

[0025] <Separator 14> As shown in FIG. 1, since the first separator 17 and the second separator 18 have the same configuration, they will be described below as the separator 14. The first separator 17 and the second separator 18 are arranged so that they are front and back to each other in the fuel cell 11. The above-described oxidant gas flow path and fuel gas flow path will be described as a flow path 28 that supplies reaction gas to the membrane electrode assembly 20.

[0026] As shown in FIGS. 1 and 2, the flow path 28 is constituted by the front and back integrated concavo-convexities formed by pressing the separator 14. That is, a groove 29, which is a concave portion on the side of the membrane electrode assembly 20 in the concavo-convexity of the separator 14, forms the flow path 28. The convex portion on the side of the membrane electrode assembly 20 in the concavo-convexity of the separator 14 becomes a rib 30. The concavo-convexities constituting the flow path 28 and the rib 30 of the separator 14 in the present embodiment are substantially trapezoidal in cross-sectional view.

[0027] The groove 29 that forms the flow path 28 in the separator 14 has a branch portion 31 that branches from one to two. The plurality of grooves 29 that form a plurality of flow paths 28 in the separator 14 extend in parallel at regular intervals. Ribs 30 are formed between the grooves 29 in the separator 14. In the separator 14, the groove 29 on one surface constitutes the rib 30 on the other surface, and the rib 30 on one surface constitutes the groove 29 on the other surface.

[0028] The separator 14 is made of a material such as a metal such as aluminum, titanium, stainless steel, or a carbon fiber reinforced plastic (CFRP; Carbon Fiber Reinforced Plastics).

[0029] <Detailed Configuration of Groove 29 of Separator 14> As shown in FIGS. 1 to 3, the groove 29 of the separator 14 has a branch portion 31 and a general portion 32 which is a portion other than the branch portion 31. The groove 29 of the separator 14 is set such that the value obtained by dividing the diameter D of the inscribed circle 33 of the branch portion 31 by the groove width W of the general portion 32 is 2.5 or less. That is, the groove 29 of the separator 14 is set such that the diameter D of the inscribed circle 33 of the branch portion 31 is 2.5 times or less the groove width W of the general portion 32.

[0030] For example, when the groove width W is 1, the diameter D is set to 2.5 or less. When the groove width W is 0.9, the diameter D is set to 2.25 or less. When the groove width W is 0.8, the diameter D is set to 2.0 or less. In all of these examples, (diameter D / groove width W) = (2.5 / 1) = (2.25 / 0.9) = (2.0 / 0.8) = 2.5. The value of (diameter D / groove width W) in this example is set to about 1.7 as an example.

[0031] Next, the reason for setting the value of (diameter D / groove width W) described above to 2.5 or less will be explained. As shown in FIGS. 3 to 5, as a quality required for improving the durability of the membrane electrode assembly 20, the amount of deflection T of the gas diffusion layer 13 in the groove 29 when the gas diffusion layer 13 is brought into contact with the separator 14 is known from experimental results to be 21 μm or less. From the graph in FIG. 5, the amount of deflection T becomes 21 μm or less when the contact rate C of the gas diffusion layer 13 with respect to the region including the branch portion 31 and the rib 30 sandwiching the branch portion 31 in the separator 14 is 0.48 or more.

[0032] The contact rate C is obtained by (L1 + L2) / L. In FIG. 4, L1 and L2 indicate the contact portions (ribs 30) of the gas diffusion layer 13 in the separator 14, M indicates the non-contact portion (branch portion 31) of the gas diffusion layer 13 in the separator 14, and L indicates the sum of L1, L2, and M.

[0033] When the contact ratio C is 0.48, the value of (diameter D / groove width W) is 2.5. Therefore, by setting the value of (diameter D / groove width W) to 2.5 or less, the contact ratio C becomes 0.48 or more. That is, by setting the value of (diameter D / groove width W) to 2.5 or less, the amount of deflection T becomes 21 μm or less.

[0034] As shown in FIGS. 3, 6, and 7, it is preferable that the side surface 34 at the branch portion 31 of the groove 29 of the separator 14 is inclined at an angle B of 25° or more and less than 90° with respect to the thickness direction Z of the separator 14. The side surface 34 is located at the crotch position between the two grooves 29 branched at the branch portion 31.

[0035] The reason for setting the angle B to 25° or more is that, as shown in the graph of FIG. 7, when the angle B is 25° or more, the value of (diameter D / groove width W) becomes 2.5 or less. On the other hand, the reason for setting the angle B to less than 90° is that when the angle B is 90°, the side surface 34 at the branch portion 31 disappears. The angle B in this example is set to about 35° as an example.

[0036] As shown in FIGS. 3 and 8, it is preferable that the branch angle A at the branch portion 31 of the groove 29 of the separator 14 is in the range of 30° or more and 90° or less. The reason for setting the branch angle A to 30° or more and 90° or less is that, as shown in the graph of FIG. 8, when the branch angle A is in the range of 30° or more and 90° or less, the value of (diameter D / groove width W) becomes 2.5 or less. The branch angle A in this example is set to about 40° as an example.

[0037] In this way, as a design method of the fuel cell 11, a gas diffusion layer 13 having a thickness of 0.12 mm or more and 0.25 mm or less and a Young's modulus of 1800 MPa or more is used, and in the separator 14, the value of (diameter D / groove width W) is 2.5 or less, and the branch angle A is 30° or more and 90° or less, and the angle B is 25° or more and less than 90°, and the shape of the groove 29 is designed.

[0038] <Operation of the Embodiment> When power generation is performed by the fuel cell 11, an oxidant gas is supplied from the oxidant gas supply hole 22, and a fuel gas is supplied from the fuel gas supply hole 25. When the oxidant gas is supplied from the oxidant gas supply hole 22 in the fuel cell 11, the oxidant gas is diffused by the first gas diffusion layer 15 while flowing through the oxidant gas flow path toward the oxidant gas discharge hole 27, and is supplied to the cathode side surface of the membrane electrode assembly 20.

[0039] On the other hand, when the fuel gas is supplied from the fuel gas supply hole 25 in the fuel cell 11, the fuel gas is diffused by the second gas diffusion layer 16 while flowing through the fuel gas flow path toward the fuel gas discharge hole 24, and is supplied to the anode side surface of the membrane electrode assembly 20. Then, the fuel cell 11 generates power based on the electrochemical reaction in the membrane electrode assembly 20 between the oxidant gas supplied to the cathode side surface in the membrane electrode assembly 20 and the fuel gas supplied to the anode side surface in the membrane electrode assembly 20. Note that, on the cathode side in the membrane electrode assembly 20 due to power generation, generated water is produced.

[0040] Here, since the width of the branch portion 31 in the groove 29 of the separator 14 of the plurality of fuel cells 11 constituting the fuel cell stack is wider than that of the general portion 32, the portion of the gas diffusion layer 13 in contact with the branch portion 31 is likely to bend. For this reason, the surface pressure of the portion in contact with the easily bendable portion of the gas diffusion layer 13 in the membrane electrode assembly 20 decreases, so that it is likely to swell.

[0041] The membrane electrode assembly 20 contracts and expands due to repeated drying and wetting accompanying the humidity change due to power generation. The portion where the surface pressure has decreased in the membrane electrode assembly 20 is likely to deform as it contracts and expands. As a result, since the load applied to the portion where the surface pressure has decreased in the membrane electrode assembly 20 increases, there is a problem that the durability of the membrane electrode assembly 20 decreases.

[0042] In this regard, in the fuel cell 11 of the present embodiment, the gas diffusion layer 13 has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less, and the value obtained by dividing the diameter D of the inscribed circle 33 of the branch portion 31 in the groove 29 of the separator 14 by the groove width W of the general portion 32 other than the branch portion 31 in the groove 29 is configured to be 2.5 or less.

[0043] Therefore, according to the description of the <detailed configuration of the groove 29 of the separator 14> described above, the amount of deflection T of the gas diffusion layer 13 in the groove 29 when the gas diffusion layer 13 is brought into contact with the separator 14 is 21 μm or less. Accordingly, the deformation of the portion corresponding to the branch portion 31 in the membrane electrode assembly 20 is suppressed, so that the load applied to the portion is also reduced. As a result, the durability of the membrane electrode assembly 20 is improved, and thus the durability of the fuel cell 11 is improved.

[0044] <Effects of the embodiment> According to the embodiment described in detail above, the following effects are exhibited. (1) The fuel cell 11 includes a membrane electrode assembly 20 that generates electricity using a reaction gas, a pair of gas diffusion layers 13 sandwiching the membrane electrode assembly 20, and a pair of separators 14 sandwiching the membrane electrode assembly 20 and the pair of gas diffusion layers 13. The gas diffusion layer 13 has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less. The separator 14 has a branch portion 31 and a groove 29 that forms a flow path 28 for supplying a reaction gas to the membrane electrode assembly 20. The value obtained by dividing the diameter D of the inscribed circle 33 of the branch portion 31 in the groove 29 by the groove width W of the general portion 32 other than the branch portion 31 in the groove 29 is 2.5 or less.

[0045] With the above configuration, the durability of the membrane electrode assembly 20 can be improved from the description of the <operation of the embodiment> above. (2) In the fuel cell 11, the branch angle A at the branch portion 31 of the groove 29 is 30° or more and 90° or less, and the side surface 34 at the branch portion 31 of the groove 29 is inclined at an angle B of 25° or more and less than 90° with respect to the thickness direction Z of the separator 14.

[0046] With the above configuration, the durability of the membrane electrode assembly 20 can be further improved based on the description of the <detailed configuration of the groove 29 of the separator 14>. <Modification example> The above embodiment can be implemented with the following modifications. Also, the above embodiment and the following modification examples can be implemented in combination with each other as long as they do not technically conflict.

[0047] · The branching angle A at the branching portion 31 of the groove 29 does not necessarily have to be 30° or more and 90° or less. · The side surface 34 at the branching portion 31 of the groove 29 does not necessarily have to be inclined at an angle of 25° or more and less than 90° with respect to the thickness direction Z of the separator 14.

[0048] · The flow path 28 may be formed by the groove 29 formed by machining the separator 14.

Explanation of reference numerals

[0049] 11… Fuel cell 12… Power generation unit 13… Gas diffusion layer 14… Separator 15… First gas diffusion layer 16… Second gas diffusion layer 17… First separator 18… Second separator 19… Frame member 20… Membrane electrode assembly 21… Opening 22… Oxidant gas supply hole 23… Cooling medium supply hole 24… Fuel gas discharge hole 25… Fuel gas supply hole 26… Cooling medium discharge hole 27… Oxidant gas discharge hole 28… Flow path 29… Groove 30… Rib 31… Branching portion 32… General portion 33… Inscribed circle 34… Side surface A… Branching angle B… Angle C… Contact rate D… Diameter T… Amount of deflection W… Groove width X… Long side direction Y… Short side direction Z… Thickness direction

Claims

1. A fuel cell comprising a membrane electrode assembly that generates electricity using a reaction gas, a pair of gas diffusion layers sandwiching the membrane electrode assembly, and a pair of separators sandwiching the membrane electrode assembly and the pair of gas diffusion layers, wherein: the gas diffusion layer has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less; the separator has a branch portion and a groove that forms a flow path for supplying the reaction gas to the membrane electrode assembly; a fuel cell, characterized in that a value obtained by dividing the diameter of the inscribed circle of the branch portion in the groove by the width of the general portion other than the branch portion in the groove is 2.5 or less.

2. a branch angle in the branch portion of the groove is 30° or more and 90° or less; The fuel cell according to claim 1, wherein side surfaces in the branch portion of the groove are inclined at an angle of 25° or more and less than 90° with respect to the thickness direction of the separator.

3. A method for designing a fuel cell comprising a membrane electrode assembly that generates electricity using a reaction gas, a pair of gas diffusion layers sandwiching the membrane electrode assembly, and a pair of separators sandwiching the membrane electrode assembly and the pair of gas diffusion layers, wherein: the gas diffusion layer has a Young's modulus of 1800 MPa or more and a thickness of 0.12 mm or more and 0.25 mm or less; the separator has a branch portion and a groove that forms a flow path for supplying the reaction gas to the membrane electrode assembly; A method for designing a fuel cell, characterized in that the shape of the groove is designed such that a value obtained by dividing the diameter of the inscribed circle of the branch portion in the groove by the width of the general portion other than the branch portion in the groove is 2.5 or less.

4. a branch angle in the branch portion of the groove is 30° or more and 90° or less; The method for designing a fuel cell according to claim 3, characterized in that the shape of the groove is designed such that side surfaces in the branch portion of the groove are inclined at an angle of 25° or more and less than 90° with respect to the thickness direction of the separator.

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