Cell for fuel cell and method for designing cell for fuel cell

Abstract

The invention provides a single cell of a fuel cell and a method for designing the single cell of the fuel cell, which can improve the durability of a membrane electrode assembly. A single cell of a fuel cell is provided with a membrane electrode assembly, a pair of gas diffusion layers that sandwich the membrane electrode assembly, and a pair of separators that sandwich 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 groove having a branch portion. The groove forms a flow path for supplying a 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 in the groove is 2.5 or less.

Description

Technical Field

[0001] The present disclosure relates to a single cell of a fuel cell and a method for designing the single cell of the fuel cell. Background Art

[0002] Currently, as a single cell of a fuel cell, for example, a single cell shown in Japanese Unexamined Patent Application Publication No. 2022-182067 is known. Such a single cell includes a membrane electrode assembly sandwiched between a pair of gas diffusion layers, a frame member that supports the membrane electrode assembly, and a pair of separators that sandwich the membrane electrode assembly. A groove flow path for supplying a reaction gas to the membrane electrode assembly is formed in the separator. Summary of the Invention

[0003] Problems to be Solved by the Invention

[0004] Among them, in the single 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 of the gas diffusion layer in contact with the branch portion is likely to be deflected. Therefore, the portion of the membrane electrode assembly in contact with the portion of the gas diffusion layer that is likely to be deflected is likely to swell due to a decrease in surface pressure.

[0005] The membrane electrode assembly contracts and expands due to repeated drying and wetting. The portion of the membrane electrode assembly where the surface pressure has decreased is likely to be deformed along with the contraction and expansion. Thus, the load applied to the portion of the membrane electrode assembly where the surface pressure has decreased becomes large, and there is a problem of reduced durability of the membrane electrode assembly.

[0006] Means for Solving the Problems

[0007] A single cell of a fuel cell according to one aspect of the present disclosure includes: a membrane electrode assembly configured to generate electricity using a reaction gas; a pair of gas diffusion layers that sandwich the membrane electrode assembly; and a pair of separators that sandwich the membrane electrode assembly and the pair of gas diffusion layers, the gas diffusion layer having a Young's modulus of 1800 MPa or more, a thickness of 0.12 mm or more and 0.25 mm or less, the separator having a groove, the groove being a groove having a branch portion and forming a flow path for supplying the reaction gas to the membrane electrode assembly, and 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 being 2.5 or less.

[0008] In a method for designing a single cell of a fuel cell according to an aspect of the present disclosure, the single cell includes a membrane electrode assembly configured to generate electricity using reaction gases, 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 design method includes: setting the Young's modulus of the gas diffusion layer to 1800 MPa or more; setting the thickness of the gas diffusion layer to 0.12 mm or more and 0.25 mm or less; designing the separator to have a groove, where the groove is a groove having a branch portion and forms a flow path for supplying the reaction gases to the membrane electrode assembly; and designing the shape of the groove 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 FIG. is an exploded perspective view of a single cell according to an embodiment.

[0010] Figure 2 FIG. is a schematic cross-sectional view showing a main part of the separator.

[0011] Figure 3 FIG. is a schematic top view showing a main part of the separator.

[0012] Figure 4 FIG. is a cross-sectional view taken along line 4-4 when the gas diffusion layer is in contact with the separator of Figure 3 FIG.

[0013] Figure 5 FIG. is a coordinate diagram showing the positional relationship between the amount of deflection of the gas diffusion layer and the contact ratio of the gas diffusion layer.

[0014] Figure 6 FIG. is Figure 3 a cross-sectional view taken along line 6-6 of FIG.

[0015] Figure 7 FIG. is a coordinate diagram showing the relationship between the value of diameter / groove width and the angle.

[0016] Figure 8 FIG. is a coordinate diagram showing the relationship between the value of diameter / groove width and the branch angle. DETAILED DESCRIPTION

[0017] Hereinafter, an embodiment will be described with reference to the drawings.

[0018] <Fuel cell single cell 11>

[0019] As shown in Figure 1As shown, the single cell 11 of the fuel cell is in the shape of a rectangular plate, and a fuel cell stack (not shown) is formed by stacking a plurality of them. The single cell 11 includes a rectangular plate-shaped power generation unit 12, a pair of gas diffusion layers 13 in the shape of rectangular sheets, and a pair of separators 14 in the shape of rectangular plates. That is, the single cell 11 has a structure in which the power generation unit 12 sandwiched by the pair of gas diffusion layers 13 is clamped from the outside of the pair of gas diffusion layers 13 by the pair of separators 14.

[0020] In the following description, the long side direction, the short side direction, and the thickness direction in the single cell 11 are respectively set as the long side direction X, the short side direction Y, and the thickness direction Z. The long side direction X, the short side direction Y, and the thickness direction Z are orthogonal to each other.

[0021] As Figure 1 shown, in the pair of gas diffusion layers 13, one side (cathode side) is set as the first gas diffusion layer 15 and the other side (anode side) is set as the second gas diffusion layer 16. In the pair of separators 14, one side (cathode side) is set as the first separator 17 and the other side (anode side) is set as the second separator 18.

[0022] The power generation unit 12 includes a resin-made frame member 19 in the shape of a rectangular plate and a membrane electrode assembly 20 (MEA: Membrane Electrode Assembly) in the shape of a rectangular sheet supported by the frame member 19. The frame member 19 has a rectangular opening 21 in the central part. The membrane electrode assembly 20 is bonded 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.

[0023] The pair of gas diffusion layers 13 clamp the membrane electrode assembly 20 in a state of being supported in the opening 21 of the frame member 19 along the thickness direction Z. The pair of separators 14 clamp the power generation unit 12 from the outside of the pair of gas diffusion layers 13 along the thickness direction Z. The thickness of the pair of gas diffusion layers 13 is set in the range of 0.12 mm or more and 0.25 mm or less, and the Young's modulus is set to 1800 MPa or more.

[0024] In the single cell 11, an oxygen-containing oxidant gas is supplied to a part on one side (cathode side) in the thickness direction Z of the membrane electrode assembly 20, and a hydrogen-containing fuel gas is supplied to a part on the other side (anode side) in the thickness direction Z of the membrane electrode assembly 20. Thus, the single cell 11 generates electricity 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, the oxidant gas and the fuel gas are used as reaction gases to generate electricity.

[0025] <Flow path structure of single cell 11>

[0026] As Figure 1 shown, at both ends of the membrane electrode assembly 20 in the long side direction X of the single cell 11, that is, at both ends of the frame member 19 and the pair of separators 14 across the membrane electrode assembly 20 in the long side direction X, three rectangular through-holes arranged along the short side direction Y are formed respectively.

[0027] The three through-holes at one end of the single cell 11 in the long side direction X are provided as an oxidant gas supply hole 22, a cooling medium supply hole 23, and a fuel gas discharge hole 24. The three through-holes at the other end of the single cell 11 in the long side direction X are provided as a fuel gas supply hole 25, a cooling medium discharge hole 26, and an oxidant gas discharge hole 27. In this case, in the long side direction X, the oxidant gas supply hole 22 is aligned with the fuel gas supply hole 25, the cooling medium supply hole 23 is aligned with the cooling medium discharge hole 26, and the fuel gas discharge hole 24 is aligned with the oxidant gas discharge hole 27.

[0028] The fuel gas supply hole 25 constitutes an inlet side fuel gas manifold for supplying fuel gas in a fuel cell stack (not shown). The fuel gas discharge hole 24 constitutes an outlet side fuel gas manifold for discharging fuel gas in a fuel cell stack (not shown). The oxidant gas supply hole 22 constitutes an inlet side oxidant gas manifold for supplying oxidant gas in a fuel cell stack (not shown).

[0029] The oxidant gas discharge hole 27 constitutes an outlet side oxidant gas manifold for discharging oxidant gas in a fuel cell stack (not shown). Each of the above manifolds extends along the stacking direction (thickness direction Z) of the single cell 11 when forming a fuel cell stack (not shown).

[0030] An oxidant gas flow path is formed between the frame member 19, the membrane electrode assembly 20, and the first separator 17, through which the oxidant gas supplied from the oxidant gas supply hole 22 flows through the membrane electrode assembly 20 to the oxidant gas discharge hole 27. A fuel gas flow path is formed between the frame member 19, the membrane electrode assembly 20, and the second separator 18, through which the fuel gas supplied from the fuel gas supply hole 25 flows through the membrane electrode assembly 20 to the fuel gas discharge hole 24.

[0031] In the case where a plurality of single cells 11 are stacked to form a fuel cell stack (not shown), a cooling medium flow path (not shown) is formed between the first separator 17 of one of the two adjacent single cells 11 and the second separator 18 of the other in the stacking direction (thickness direction Z). The cooling medium flow path (not shown) allows the cooling medium supplied from the cooling medium supply hole 23 to flow to the cooling medium discharge hole 26.

[0032] <Separator 14>

[0033] As Figure 1 shown, the first separator 17 and the second separator 18 have the same structure as each other. Therefore, the following description will be made with the separator 14. The first separator 17 and the second separator 18 are arranged in the single cell 11 with their front and back sides facing each other. The above-described oxidant gas flow path and fuel gas flow path will be described as the flow path 28 for supplying reaction gas to the membrane electrode assembly 20.

[0034] As Figure 1 and Figure 2 shown, the flow path 28 is constituted by concavo-convex portions that are integral with the front and back sides formed by stamping the separator 14. That is, the concave portion, i.e., the groove 29, on the side of the membrane electrode assembly 20 in the concavo-convex portions of the separator 14 forms the flow path 28. The convex portion on the side of the membrane electrode assembly 20 in the concavo-convex portions of the separator 14 becomes the rib 30. The concavo-convex portions constituting the flow path 28 and the rib 30 of the separator 14 in the present embodiment are substantially trapezoidal in a cross-sectional view.

[0035] The groove 29 forming the flow path 28 in the separator 14 has a branch portion 31 that branches from one into two. The plurality of grooves 29 forming the plurality of flow paths 28 in the separator 14 extend in parallel at a constant interval. 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.

[0036] The separator 14 is made of a material such as metal (e.g., aluminum, titanium, stainless steel) or carbon fiber reinforced plastic (CFRP; Carbon Fiber Reinforced Plastics).

[0037] <Detailed Structure of the Groove 29 of the Separator 14>

[0038] As Figures 1 to 3 shown, the groove 29 of the separator 14 has a branch portion 31 and a general portion 32 that 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.

[0039] 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 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 approximately 1.7 as an example.

[0040] Next, the basis for setting the value of (diameter D / groove width W) to 2.5 or less will be described.

[0041] As Figures 3 to 5 shown, as a quality required to improve the durability of the membrane electrode assembly 20, according to the experimental results, the deflection amount T of the gas diffusion layer 13 in the groove 29 when the gas diffusion layer 13 contacts the separator 14 is 21 μm or less. According to Figure 5 the coordinate diagram, the deflection amount T becomes 21 μm or less when the contact rate C of the gas diffusion layer 13 with respect to the region of the separator 14 including the rib 30 including the branch portion 31 and the clamping branch portion 31 is 0.48 or more.

[0042] The contact rate C is obtained by (L1 + L2) / L. In Figure 4 , L1 and L2 represent the contact portions (ribs 30) of the gas diffusion layer 13 in the separator 14, M represents the non-contact portion (branch portion 31) of the gas diffusion layer 13 in the separator 14, and L represents the sum of L1, L2, and M.

[0043] Moreover, the value of (diameter D / groove width W) when the contact rate C is 0.48 becomes 2.5. Therefore, by setting the value of (diameter D / groove width W) to 2.5 or less, the contact rate C becomes 0.48 or more. That is, by setting the value of (diameter D / groove width W) to 2.5 or less, the deflection amount T becomes 21 μm or less.

[0044] As Figure 3 , Figure 6 and Figure 7 shown, it is preferable that the side surface 34 of 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 in the branch portion 31.

[0045] The basis for setting the angle B to 25° or more is that according to Figure 7From the coordinate diagram, when the angle B is more than 25°, the value of (diameter D / channel width W) becomes 2.5 or less. On the other hand, the reason for setting the angle B to be less than 90° is that when the angle B is 90°, the side surface 34 of the branch portion 31 no longer exists. In this example, the angle B is set to about 35° as an example.

[0046] As Figure 3 and Figure 8 shown, the branch angle A of the branch portion 31 of the groove 29 of the separator 14 is preferably in the range of 30° or more and 90° or less. The reason for setting the branch angle A to be 30° or more and 90° or less is that according to Figure 8 the coordinate diagram, when the branch angle A is in the range of 30° or more and 90° or less, the value of (diameter D / channel width W) becomes 2.5 or less. In this example, the branch angle A is set to about 40° as an example.

[0047] Thus, the design method of the single cell 11 includes: setting the thickness of the gas diffusion layer 13 to be 0.12 mm or more and 0.25 mm or less; setting the Young's modulus of the gas diffusion layer 13 to be 1800 MPa or more; and designing the shape of the groove 29 of the separator 14 so that the value of (diameter D / channel width W) becomes 2.5 or less, the branch angle A becomes 30° or more and 90° or less, and the angle B becomes 25° or more and less than 90°.

[0048] <Function of the Embodiment>

[0049] When generating power by the single 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 to the single 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.

[0050] On the other hand, when the fuel gas is supplied from the fuel gas supply hole 25 to the single 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. Moreover, the single 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. In addition, through power generation, water is generated on the cathode side of the membrane electrode assembly 20.

[0051] Here, in the groove 29 of the separator 14 of the plurality of single cells 11 constituting the fuel cell stack, the branch portion 31 in the groove 29 has a width wider than that of the general portion 32, so the portion of the gas diffusion layer 13 in contact with the branch portion 31 is likely to be deflected. Therefore, the portion of the membrane electrode assembly 20 in contact with the portion of the gas diffusion layer 13 that is likely to be deflected is likely to swell due to a decrease in surface pressure.

[0052] The membrane electrode assembly 20 contracts and expands due to the repeated drying and wetting accompanied by the humidity change caused by power generation. The portion of the membrane electrode assembly 20 where the surface pressure is reduced is likely to be deformed along with the contraction and expansion. As a result, the load applied to the portion of the membrane electrode assembly 20 where the surface pressure is reduced becomes large, so there is a problem that the durability of the membrane electrode assembly 20 is reduced.

[0053] In view of this, in the single cell 11 of the present embodiment, the gas diffusion layer 13 is configured to be a member having a Young's modulus of 1800 MPa or more, 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 set to 2.5 or less.

[0054] Therefore, according to the description of the <detailed structure of the groove 29 of the separator 14> above, the amount of deflection T of the gas diffusion layer 13 in the groove 29 when the gas diffusion layer 13 is in contact with the separator 14 becomes 21 μm or less. Thus, the deformation of the portion of the membrane electrode assembly 20 corresponding to the branch portion 31 is suppressed, and therefore the load applied to this portion is also reduced. As a result, the durability of the membrane electrode assembly 20 is improved, and further, the durability of the single cell 11 is improved.

[0055] <Effect of the Embodiment>

[0056] According to the embodiment described in detail above, the following effects can be achieved.

[0057] (1) The single cell 11 includes a membrane electrode assembly 20 that generates power using reaction gases, a pair of gas diffusion layers 13 that sandwich the membrane electrode assembly 20, and a pair of separators 14 that sandwich the membrane electrode assembly 20 and the pair of gas diffusion layers 13. The Young's modulus of the gas diffusion layer 13 is 1800 MPa or more, and the thickness is 0.12 mm or more and 0.25 mm or less. The separator 14 has a groove 29, and the groove 29 has a branch portion 31 and forms a flow path 28 for supplying reaction gases 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.

[0058] With the above structure, according to the description of <Function of the Embodiment> above, the durability of the membrane electrode assembly 20 can be improved.

[0059] (2) In the single cell 11, the branch angle A of the branch portion 31 of the groove 29 is 30° or more and 90° or less, and the side surface 34 of 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.

[0060] With the above structure, according to the description of <Detailed Structure of the Groove 29 of the Separator 14> above, the durability of the membrane electrode assembly 20 can be further improved.

[0061] <Modification Example>

[0062] The above embodiment can be implemented with the following modifications. In addition, the above embodiment and the following modification examples can be implemented in combination with each other within the scope without technical contradictions.

[0063] · The branch angle A of the branch portion 31 of the groove 29 does not necessarily need to be 30° or more and 90° or less.

[0064] · The side surface 34 of the branch portion 31 of the groove 29 does not necessarily need 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.

[0065] · The flow path 28 may also be formed by the groove 29 formed by machining the separator 14.

Claims

1. A single cell of a fuel cell, wherein: The fuel cell has: A membrane electrode assembly configured to generate 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 Young's modulus of the gas diffusion layer is 1800 MPa or more, and the thickness is 0.12 mm or more and 0.25 mm or less, The separator has a groove having a branch portion and forming a flow path for supplying the reaction gas to the membrane electrode assembly. A value obtained by dividing a diameter of an inscribed circle of the branch portion in the groove by a width of a general portion of the groove other than the branch portion is 2.5 or less.

2. The fuel cell according to claim 1, wherein: The branch angle of the branch portion of the groove is greater than or equal to 30° and less than or equal to 90°, The side surfaces of the branch portions of the groove are inclined at an angle of not less than 25° and less than 90° with respect to the thickness direction of the separator.

3. A method for designing a single cell of a fuel cell, wherein: The single cell includes a membrane electrode assembly configured to generate 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 design method comprises: The Young's modulus of the gas diffusion layer is set to be greater than 1800 MPa; The thickness of the gas diffusion layer is set to be greater than or equal to 0.12 mm and less than or equal to 0.25 mm; The separator is designed to have a groove, wherein the groove is a groove having a branch portion and forms a flow path for supplying the reaction gas to the membrane electrode assembly; and The shape of the groove is designed so that a value obtained by dividing a diameter of an inscribed circle of the branch portion in the groove by a width of a general portion of the groove other than the branch portion is 2.5 or less.

4. The method for designing a single cell of a fuel cell according to claim 3, wherein: The design method of a single cell of the fuel cell comprises: The shape of the groove is designed so that the branch angle of the branch portion of the groove is greater than 30° and less than 90°, and the side surface of the branch portion of the groove is inclined at an angle of greater than 25° and less than 90° relative to the thickness direction of the partition.

Images