Fuel cell

Abstract

To suppress the occurrence of damage to a membrane-electrode assembly and a gas diffusion layer in bonding a support body and the membrane-electrode assembly.SOLUTION: A fuel battery comprises: a membrane-electrode assembly having a first catalyst layer, a second catalyst layer and an electrolyte membrane disposed between the first catalyst layer and the second catalyst layer; a first gas diffusion layer laminated on the first catalyst layer and provided so that at least part of its peripheral edge extends beyond an outer peripheral edge of the membrane-electrode assembly; a second gas diffusion layer laminated on the second catalyst layer; a support body disposed around the membrane-electrode assembly; and a cover sheet arranged so as to bridge between the support body and at least one of the electrolyte membrane and first catalyst layer. In the fuel battery, the cover sheet has, on the side of at least one of the electrolyte membrane and first catalyst layer, a tiptoe part smaller than other parts of the cover sheet in thickness.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a fuel cell.

Background Art

[0002] Patent Document 1 discloses a structure in which an adhesive and a cover sheet are arranged so as to pass between a support frame and a membrane electrode assembly, and a gas diffusion layer is laminated on the cover sheet. Further, Patent Document 2 discloses a dummy resin member having a stepped surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional technology, when the cover sheet is arranged, there may be a problem that the membrane electrode assembly or the cover sheet itself is torn. This tear may lead to a leak of the reaction gas.

[0005] Therefore, in view of the above problems, an object of the present disclosure is to provide a fuel cell capable of suppressing the occurrence of breakage of a membrane electrode assembly or a gas diffusion layer in the joining of a support and a membrane electrode assembly.

Means for Solving the Problems

[0006] As a result of intensive studies, the inventor has obtained an idea that a space is generated at the tip of the cover sheet on the membrane electrode assembly side due to the thickness of the cover sheet, and this space is the cause of breakage of the membrane electrode assembly or the gas diffusion layer. And the technology of the present disclosure has been completed by specific means for solving this problem. Specifically, it is as follows.

[0007] The present application discloses a fuel cell including a membrane - electrode assembly having a first catalyst layer, a second catalyst layer, and an electrolyte membrane disposed between the first catalyst layer and the second catalyst layer; a first gas diffusion layer laminated on the first catalyst layer, with at least a part of the outer peripheral end portion provided beyond the outer peripheral end of the membrane - electrode assembly; a second gas diffusion layer laminated on the second catalyst layer; a support disposed around the membrane - electrode assembly; and a cover sheet disposed so as to span the support and at least one of the electrolyte membrane and the first catalyst layer, wherein the cover sheet is configured such that the tip portion on the side of at least one of the electrolyte membrane and the first catalyst layer is thinner than other portions of the cover sheet.

[0008] The tip portion may be configured to have an inclined surface that becomes thinner toward the tip.

Advantages of the Invention

[0009] According to the present disclosure, the space caused by the thickness of the cover sheet can be reduced without thinning the cover sheet (without reducing the strength of the cover sheet), and the occurrence of breakage (damage) of the membrane - electrode assembly and the cover sheet itself can be suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 8

Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0011] 1. Power generation unit cell FIGS. 1 to 3 show diagrams for explaining the power generation unit cell 10 according to one embodiment. The power generation unit cell 10 is a unit element for generating power by supplying hydrogen and oxygen (air), and a plurality of such power generation unit cells 10 are stacked to form a fuel cell. FIG. 1 is a plan view of the power generation unit cell 10, FIG. 2 is a diagram for explaining the layer structure in the power generation part 11 of the power generation unit cell 10, and FIG. 3 is a diagram for explaining the layer structure in the outer peripheral part 21 of the power generation unit cell 10.

[0012] 1.1. Power generation part The power generation part 11 is a part that contributes to power generation in the part surrounded by a dotted line in FIG. 1, for example, and as shown in FIG. 2 representing the layer structure (a part of the A-A cross section) in the power generation part 11, a plurality of layers are stacked. In the power generation part 11 of the power generation unit cell 10, one side is a cathode (oxygen supply side) and the other side is an anode (hydrogen supply side) with the electrolyte membrane 12 interposed therebetween. On the cathode side, a cathode catalyst layer 13 (first catalyst layer), a cathode gas diffusion layer 14 (first gas diffusion layer), and a cathode separator 15 (first separator) are stacked in this order from the electrolyte membrane 12 side. On the anode side, an anode catalyst layer 16 (second catalyst layer), an anode gas diffusion layer 17 (second gas diffusion layer), and an anode separator 18 (second separator) are provided in this order. Note that the laminate of the electrolyte membrane 12, the cathode catalyst layer 13, and the anode catalyst layer 16 may be referred to as a membrane electrode assembly. The thickness of the membrane electrode assembly is typically about 0.4 mm, and the thickness of the power generation unit cell 10 in the power generation part 11 is typically about 1.3 mm. Each layer can be configured as known, for example, as follows.

[0013] 1.1a. Electrolyte membrane The electrolyte membrane 12 is a solid polymer thin film that exhibits good proton conductivity in a wet state. For example, it is composed of a fluorine-based ion exchange membrane. For example, a carbon-fluorine-based polymer can be used, and specifically, perfluoroalkylsulfonic acid-based polymers (Nafion (registered trademark)) and the like can be mentioned. The thickness of the electrolyte membrane 12 is not particularly limited, but it is 100 μm or less, preferably 50 μm or less, and more preferably 10 μm or less.

[0014] 1.1b. Cathode Catalyst Layer The cathode catalyst layer 13 is a layer containing a catalyst metal in a form in which the catalyst metal is supported on a carrier. For example, examples of the catalyst metal include Pt, Pd, Rh, or an alloy containing these. Examples of the carrier include a carbon carrier, and more specifically, carbon particles composed of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, and the like can be mentioned.

[0015] 1.1c. Anode Catalyst Layer The anode catalyst layer 16 is also a layer containing a catalyst metal in a form in which the catalyst metal is supported on a carrier, similar to the cathode catalyst layer 13. For example, examples of the catalyst metal include Pt, Pd, Rh, or an alloy containing these. Examples of the carrier include a carbon carrier, and more specifically, carbon particles composed of glassy carbon, carbon black, activated carbon, coke, natural graphite, artificial graphite, and the like can be mentioned.

[0016] 1.1d. Cathode Gas Diffusion Layer In this embodiment, the cathode gas diffusion layer 14 is a layer composed of, for example, a porous body having conductivity. More specific examples include a carbon porous body (carbon paper, carbon cloth, glassy carbon, etc.), a metal porous body (metal mesh, foamed metal), and the like. A microporous layer (MPL), which is a coated thin film applied to the cathode gas diffusion layer 14 on the cathode catalyst layer 13 side, may be provided. The MPL has functions of adjusting moisture by having water repellency or hydrophilicity as necessary. Typically, the MPL is mainly composed of a water-repellent resin such as polytetrafluoroethylene (PTFE) and a conductive material such as carbon black.

[0017] 1.1e. Anode gas diffusion layer The anode gas diffusion layer 17 is, for example, a layer composed of a porous body having conductivity. More specific examples include carbon porous bodies (carbon paper, carbon cloth, vitreous carbon, etc.), metal porous bodies (metal mesh, foamed metal), and the like.

[0018] 1.1f. Cathode separator The cathode separator 15 is a member that supplies a reaction gas (air in this embodiment) to the cathode gas diffusion layer 14, and has a plurality of grooves 15a on the surface facing the cathode gas diffusion layer 14, and these grooves function as reaction gas flow paths. The shape of the grooves is not particularly limited as long as the reaction gas can be appropriately supplied to the cathode gas diffusion layer 14, and a serpentine type in which a plate-like member is formed in a wave shape as in this embodiment can be mentioned. At that time, the plate thickness is typically 0.1 mm to 0.2 mm, and the height of the unevenness is typically about 0.5 mm. In the case of the serpentine type, grooves 15b are formed on the opposite side with the cathode separator 15 interposed therebetween between adjacent grooves 15a, and this functions as a cooling water flow path.

[0019] Also, as can be seen from FIG. 1, the cathode separator 15 has an air inlet hole A at a position extending from the power generation unit 11 to the outside and at one end side in the direction in which the grooves 15a and 15b extend. in , a cooling water inlet hole W in , a hydrogen outlet hole H out are provided, and an air outlet hole A is provided at a position on the other end side in the direction in which the grooves 15a and 15b extend. out , a cooling water outlet hole W out , a hydrogen inlet hole H inis provided. Here, the groove 15a communicates with the air inlet hole A in , the air outlet hole A out , and the groove 15b communicates with the cooling water inlet hole W in , the cooling water outlet hole W out .

[0020] The material constituting the cathode separator 15 may be any material that can be used as a separator for the power generation unit cell, and may be a gas-impermeable conductive material. Examples of such materials include dense carbon obtained by compressing carbon to make it gas-impermeable, and a pressed metal plate, etc.

[0021] 1.1g. Anode separator The anode separator 18 is a member that supplies the reaction gas (hydrogen) to the anode gas diffusion layer 17, and has a plurality of grooves 18a on the surface facing the anode gas diffusion layer 17, and these grooves function as reaction gas flow paths. The shape of the grooves is not particularly limited as long as the reaction gas can be appropriately supplied to the anode gas diffusion layer 17, and a serpentine type as in this embodiment can be mentioned. At that time, the plate thickness is typically 0.1 mm to 0.2 mm, and the height of the unevenness is typically about 0.4 mm. In the case of a serpentine type, grooves 18b are formed on the opposite side across the anode separator 18 between adjacent grooves 18a, and this functions as a cooling water flow path.

[0022] Further, as can be seen from FIG. 1, in the anode separator 18, at a position extending from the power generation unit 11 to the outside, at a part on one end side in the direction in which the grooves 18a and 18b extend, there are provided an air inlet hole A in , a cooling water inlet hole W in , a hydrogen outlet hole H out , and at a part on the other end side in the direction in which the grooves 18a and 18b extend, there are provided an air outlet hole A out , a cooling water outlet hole W out , a hydrogen inlet hole H in . Here, the groove 18a communicates with the hydrogen inlet hole H in , the hydrogen outlet hole H out , and the groove 18b communicates with the cooling water inlet hole Win , the cooling water outlet hole W out is in communication with.

[0023] The material constituting the anode separator 18 may be any material that can be used as a separator for the power generation unit cell, and may be a gas-impermeable conductive material. Examples of such materials include dense carbon obtained by compressing carbon to make it gas-impermeable, and a pressed metal plate, etc.

[0024] 1.1 h. Power generation by the power generation unit As is well known, power generation is performed as follows by the power generation unit cell 10 described above. The hydrogen inlet hole H in The hydrogen supplied from the groove 18a of the anode separator 18 passes through the anode gas diffusion layer 17 and is decomposed into protons (H + ) and electrons (e - ) at the anode catalyst layer 16. The protons pass through the electrolyte membrane 12, and the electrons pass through the conductive wire connected to the outside, and each reaches the cathode catalyst layer 13. The remaining hydrogen is discharged from the hydrogen outlet hole H out . Oxygen (air) is supplied to the cathode catalyst layer 13 from the air inlet hole A in through the groove 15a of the cathode separator 15 and the cathode gas diffusion layer 14. At the cathode catalyst layer 13, water (H2O) is generated by protons, electrons, and oxygen. The generated water and the remaining air pass through the cathode gas diffusion layer 14 and reach the groove 15a of the cathode separator 15 and are discharged from the air outlet hole A out . In the power generation unit cell 10, the flow of electrons passing through the conductive wire connected to the outside from the anode catalyst layer 16 is utilized as an electric current.

[0025] Also, by arranging adjacent power generation unit cells 10 such that the anode separator 18 of one power generation unit cell 10 adjacent to the cathode separator 15 of the other power generation unit cell 10 overlaps, a cooling water flow path is formed by the groove 15b of the cathode separator 15 and the groove 18b of the anode separator 18. For this cooling water flow path, the cooling water inlet hole Win Cooling water is supplied from , and the supplied cooling water cools the power generation unit cell 10 and is discharged from the cooling water outlet hole W. out It is discharged from.

[0026] 1.2. Outer peripheral part The outer peripheral part 21 is the outer peripheral part of the power generation unit cell 10 outside the power generation part 11 surrounded by a dotted line in FIG. 1, and as shown in FIG. 3 representing the layer structure (B-B cross section) in the outer peripheral part 21, a plurality of layers are laminated.

[0027] 1.2a. Structure of the outer peripheral part As can be seen from FIG. 3, in this embodiment, the outer peripheral part 21 has at least a part thereof configured as follows. The end faces of the electrolyte membrane 12, the anode catalyst layer 16, and the anode gas diffusion layer 17 are laminated so as to be generally at the same position, and the end face of the cathode catalyst layer 13 is laminated so as to be at a position recessed (receded) from the end face of the electrolyte membrane 12. Further, the end face of the cathode gas diffusion layer 14 is at a position protruding (advanced) from the end face of the electrolyte membrane 12 and extends to a position overlapping the support 23 in a plan view of the power generation unit cell 10 (viewpoint from the direction of FIG. 1, line of sight in the direction indicated by arrow L in FIG. 3). The support 23 will be described later.

[0028] The cathode separator 15 and the anode separator 18 are arranged in the outer peripheral part 21 so as to sandwich the above-described layers in the same manner as the electrode part 11 therebetween. Also, the end faces of the cathode separator 15 and the anode separator 18 extend so as to protrude from the end faces of the membrane electrode assembly, the cathode gas diffusion layer 14, and the anode gas diffusion layer 17, and the support 23 is arranged between the cathode separator 15 and the anode separator 18 at the extended part. Note that in the outer peripheral part 21, since flow paths are not required for both the cathode separator 15 and the anode separator 18, the grooves 15a and 18a are not formed (however, as can be seen from FIG. 3, it does not prevent the formation of grooves in part).

[0029] A cover sheet 22 is disposed so as to span between an end of a surface of the support 23 facing the cathode side and an end of a surface of the membrane electrode assembly facing the cathode side. The cover sheet 22 will be described later.

[0030] 1.2b. Support The above-described support 23 functions as a sealing member that seals between the cathode separator 15 and the anode separator 18 in the outer peripheral portion 21 of the power generation unit cell 10. The support 23 includes a base material 23a and adhesive layers 23b disposed on both surfaces (the surface facing the cathode side and the surface facing the anode side) of the base material 23a. By adhering the adhesive layers 23b to the cathode separator 15 and the anode separator 18, the inside of the power generation part 11 is sealed. Therefore, the distance between the cathode separator 15 and the anode separator 18 is bent so as to change depending on the layer sandwiched therebetween. As can be seen from FIG. 3, in the portion where only the support 23 is disposed, the distance is narrowed in part, and the support 23 is sandwiched and fixed between the cathode separator 15 and the anode separator 18.

[0031] The base material 23a is made of a thermoplastic resin material having electrical insulation and airtightness and a relatively high melting point. Examples of such materials include crystalline polymers, more specifically, engineering plastics. Examples of engineering plastics include polyethylene naphthalate-based resins (PEN) and polyethylene terephthalate-based resins (PET). The thickness of the base material 23a is not particularly limited, but is preferably 0.05 mm or more and 0.25 mm or less.

[0032] The adhesive layer 23b may be any known material as long as it has adhesiveness in the adhered state. Examples include modified polyolefins obtained by introducing functional groups (such as maleic anhydride and epoxy) into polyolefins to impart adhesiveness.

[0033] As can be seen from FIG. 3, such a support 23 is arranged such that its end face faces the end faces of the membrane electrode assembly and the anode gas diffusion layer 17 with a gap S therebetween, and extends toward the side opposite to the power generation unit 11. This gap S can absorb dimensional changes due to linear expansion of the support 23, the membrane electrode assembly, etc., and can suppress the occurrence of damage due to expansion and contraction.

[0034] 1.2c. Cover sheet As described above, the cover sheet 22 is arranged so as to bridge the end of the surface of the support 23 facing the cathode side and the end of the surface of the membrane electrode assembly facing the cathode side. FIG. 4 shows an enlarged view focusing on the periphery where the cover sheet 22 is arranged in FIG. 3.

[0035] One end of the cover sheet 22 is arranged to cover the surface end of the cathode side of the support 23, and the other end is arranged to cover at least one of the surface ends of the electrolyte membrane 12 and the cathode catalyst layer 13 on the membrane electrode assembly side (in this embodiment, the cover sheet is arranged to cover both surface ends of the electrolyte membrane 12 and the cathode catalyst layer 13). Thereby, the cathode and the anode can be appropriately separated at the outer peripheral portion 21. Therefore, the cover sheet 22 is arranged between the membrane electrode assembly and the cathode gas diffusion layer 14 at the end on the membrane electrode assembly side.

[0036] A material that does not permeate the reaction gas of the fuel cell is used for the cover sheet 22. As a member that does not permeate the reaction gas, for example, a film-like member made of a resin such as polypropylene, polyphenylene sulfide, polyethylene naphthalate, nylon, ethylene vinyl alcohol copolymer, etc. can be adopted. In particular, nylon 11, nylon 12, nylon 9T, and ethylene vinyl alcohol can be mentioned from the viewpoints of hydrolysis resistance and adhesion to the electrolyte membrane. In addition, additives having an amide group, an epoxy group, a hydroxyl group, etc. may be added to improve the adhesiveness to the electrolyte membrane 12.

[0037] Here, the cover sheet 22 is adhered from the adhesive layer 23b of the support 23 at the portion where it overlaps the support 23. On the other hand, for the portion where the cover sheet 22 overlaps the membrane electrode assembly, an adhesive layer is provided on the cover sheet 22 and adhered as necessary. However, when nylon is used as the cover sheet 22, the cover sheet and the membrane electrode assembly can be adhered by thermocompression bonding, so the adhesive layer is not necessary.

[0038] Also, at the end of the cover sheet 22 facing the membrane electrode assembly side, there is a tip portion 22a configured to be thinner than other portions. FIG. 5 shows an enlarged view focusing on the portion of the tip portion 22a, which is the portion indicated by V in FIG. 4.

[0039] As can be seen from FIG. 5, in this embodiment, the tip portion 22a has an inclined surface 22b that becomes thinner toward the tip, and this inclined surface 22b has a concave curved shape. Thereby, the tip portion 22a can reduce the size of the space A, and it becomes possible to solve the problem. Details will be described later.

[0040] Here, the thickness of the cover sheet 22 is not particularly limited, and it is preferably 60 μm or less at the tip of the tip portion 22a, and preferably thicker than 60 μm at portions other than the tip portion 22a. By making the portion other than the tip portion 22a thicker than 60 μm, the strength of the cover sheet 22 can be increased, and the occurrence of problems such as tearing can be suppressed. Also, by making the tip portion 22a 60 μm or less at the tip, the size of the space A can be more reliably reduced.

[0041] 2. Effects, etc. When one end side of the cover sheet is disposed between the cathode gas diffusion layer and the membrane electrode assembly, a space is generated at the portion indicated by A in FIG. 5 due to the thickness of the cover sheet. This tends to increase as the cover sheet is thicker. And the inventor has found that the larger this space A is, the more likely it is to cause damage to the membrane electrode assembly and the cathode gas diffusion layer. On the one hand, the cover sheet requires a certain thickness for sealing as described above. Therefore, the space A tends to become large inevitably. On the other hand, according to the present disclosure, the tip portion 22a acts to fill at least a part of the space A, reducing the size of this space A, thereby reducing the possibility of damage to the membrane electrode assembly and the cathode gas diffusion layer and suppressing the leakage of the reaction gas due to the damage.

[0042] 3. Other forms Other exemplary forms regarding the outer peripheral portion will be described below. 3.1. Other exemplary form 1 FIG. 6 shows a diagram for explaining another example of the form of the outer peripheral portion. FIG. 6 is a diagram from the same perspective as FIG. 4. In the example of FIG. 6, the end face of the cathode catalyst layer 13 is also positioned at the same position as the end face of the electrolyte membrane 12. In this case, there is no portion where the cover sheet 22 is laminated on the electrolyte membrane 12, and it is laminated on the cathode catalyst layer 13. Even in such a form, the same effects as described above can be achieved.

[0043] 3.2. Other exemplary form 2 FIG. 7 shows a diagram for explaining another example of the form of the outer peripheral portion. FIG. 7 is a diagram from the same perspective as FIG. 5. In the example of FIG. 7, the tip portion 22a becomes thinner stepwise with respect to the other portion. Even in such a form, the same effects as described above can be achieved.

[0044] 3.3. Other exemplary form 3 FIG. 8 shows a diagram for explaining another example of the form of the outer peripheral portion. FIG. 8 is a diagram from the same perspective as FIG. 5. In the example of FIG. 8, the tip portion 22a has a linear inclined surface 22d. Even in such a form, the same effects as described above can be achieved.

[0045] 4. Fuel cell The fuel cell 30 is a member formed by stacking a plurality (about 50 to 400) of the above-described power generation unit cells 10, and collects electric power from the plurality of power generation unit cells 10. The outline of its configuration is shown in FIG. 9. The fuel cell 30 includes a stack case 31, an end plate 32, a plurality of power generation unit cells 10, a current collector plate 34, and a biasing member 35.

[0046] The stack case 31 is a housing that houses the stacked plurality of power generation unit cells 10, the current collector plate 34, and the biasing member 35 inside. In this embodiment, the stack case 31 is in the shape of a rectangular cylinder with one end open and the other end closed, and a plate-like piece projects from the edge of the opening to the side opposite to the opening along the edge of the opening, forming a flange 31a.

[0047] The end plate 32 is a plate-like member that closes the opening of the stack case 31. The end plate 32 is fixed to the stack case 31 so as to cover the stack case 31 with bolts, nuts, etc. at the overlapping portion with the flange 31a of the stack case 31.

[0048] The power generation unit cell 10 is as described above. A plurality of such power generation unit cells 10 are stacked. At this time, the anode separator 18 of the power generation unit cell 10 adjacent to the cathode separator 15 of one power generation unit cell 10 is arranged so as to overlap. Then, by overlapping the groove 15b of the cathode separator 15 and the groove 18b of the anode separator 18, a cooling water flow path is formed.

[0049] The current collector plate 34 is a member that collects electric power from the stacked power generation unit cells 10. Therefore, the current collector plate 34 is arranged at each of one end and the other end of the stack of power generation unit cells 10, with one being the positive electrode and the other being the negative electrode. Terminals (not shown) are connected to this current collector plate 34 so that it can be electrically connected to the outside.

[0050] The biasing member 35 is housed inside the stack case 31 and applies a pressing force in the stacking direction to the stack of power generation unit cells 10. Examples of the biasing member include a disc spring.

[0051] 5. Others In the above description, each member on the cathode side was described as "first" and each member on the anode side as "second", but it may be the reverse, and the same effect can be achieved by replacing the cathode side with "second" and the anode side with "first".

Explanation of Reference Numerals

[0052] 10 Power generation unit cell 11 Power generation section 12 Electrolyte membrane 13 Cathode catalyst layer 14 Cathode gas diffusion layer 15 Cathode separator 16 Anode catalyst layer 17 Anode gas diffusion layer 18 Anode separator 21 Outer peripheral portion 22 Cover sheet 22a Tip portion 23 Support 23a Base material 23b Adhesive layer 30 Fuel cell

Claims

1. A membrane electrode assembly comprising a first catalyst layer, a second catalyst layer, and an electrolyte membrane disposed between the first catalyst layer and the second catalyst layer; A first gas diffusion layer laminated on the first catalyst layer, at least a part of the outer peripheral end portion of which is provided beyond the outer peripheral end of the membrane electrode assembly; A second gas diffusion layer laminated on the second catalyst layer; A support disposed around the membrane electrode assembly; A cover sheet disposed so as to pass between the support and at least one of the electrolyte membrane and the first catalyst layer, The cover sheet is configured such that the tip portion on the side of at least one of the electrolyte membrane and the first catalyst layer is thinner than other portions of the cover sheet. A fuel cell.

2. The fuel cell according to claim 1, wherein the tip portion has an inclined surface that becomes thinner toward the tip.

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