JP2000208153A - Solid polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact fuel cell with high performance and low cost by forming a separator from a metallic material, and integrally bonding a gas diffusion layer on the oxidizer gas supplying side to the separator opposed thereto. SOLUTION: Each of a gas diffusion layer 2 facing an oxidizer gas passage 5 and a separator 1 arranged in contact with the gas diffusion layer 2 is formed of stainless steel. The separator 1 is press molded into corrugated form, and the protruding parts of the separator 1 are bonded to the gas diffusion layer 2 in weld parts 10 by resistance welding. Although the surfaces of the gas diffusion layer 2 and separator 1 facing the oxidizer gas passage 5 are oxidized when an oxidizer gas is passed in the oxidizer gas passage 5 formed between the gas diffusion layer 2 and the separator 1, the contact resistance can be kept at a low value without being influenced by the oxidation since the gas diffusion layer 2 is bonded to the separator 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane for an electrolyte layer and supplying a reaction gas to obtain electric energy by an electrochemical reaction.

[0002]

2. Description of the Related Art FIG. 4 is a sectional view showing a basic structure of a conventional solid polymer electrolyte fuel cell stack. Membrane Electrode Assembly (MEA)
Is formed by bonding a catalyst layer containing a noble metal (mainly platinum) to both main surfaces of a solid polymer electrolyte membrane. Porous gas diffusion layers 2 are arranged on both surfaces of the catalyst layer to secure a gas diffusion path to the catalyst layer. The gas diffusion layer 2
May be formed integrally with the MEA by hot pressing. In this case, the ME including the gas diffusion layer 2 may be formed.
Called A. A corrugated separator 1 is disposed outside the gas diffusion layer 2, and an oxidizing gas flow path 5 extending in a direction perpendicular to the plane of the drawing between the concave portion of the corrugated separator 1 and the gas diffusion layer 2, and A fuel gas passage 6 is formed. A stack is formed by sequentially stacking the unit cells formed by the above components as shown in the figure. In the fuel cell, heat is generated along with power generation.
Cooling water for maintaining a predetermined temperature is provided between a corrugated separator 1 and a cooling water passage 7 formed between the separators 1.
Supplied to In addition, a seal 4 is interposed at the periphery of the stack, and plays a role of sealing the reaction gas and the cooling water for each layer. Although not shown in this figure, the stack also incorporates a manifold for distributing the reaction gas and the cooling water to each single cell.

In the above configuration, the separator 1
A conductive and gas-impermeable material such as a dense carbon material or a metal material is used. When the separator 1 is thick, the gas flow path may be formed by machining, but in order to reduce the weight of the stack, a thin plate as shown in FIG. In many cases, it is configured by combining components having the above.

[0004]

When a dense and hard carbon material that is conductive and gas impermeable is used, the corrugated separator 1 as shown in FIG. 4 cannot be formed. Therefore, a separator having the same function as that of FIG. 4 is formed by combining a component having a gas flow path function with a flat carbon separator substrate. However, with this configuration, the thickness of the separator becomes thicker than in the case where it is formed by press molding, so that there is a disadvantage that the stack cannot be miniaturized. Note that if a method of press-molding a flexible carbon sheet and forming a separator having a reaction gas flow path as shown in FIG. 4 is adopted, the thickness of the separator becomes thinner, which is effective in reducing the size of the stack. However, the separator formed by such a method is weak against a compressive force, and it is not easy to manufacture a separator having a compressive strength necessary for a stack configuration. In general, the use of a carbon material has a disadvantage that the cost is higher than the case of using a metal material.

On the other hand, if the separator 1 is formed using a conductive and gas-impermeable metal material, such as stainless steel or titanium, it is easy to form the separator 1 into a corrugated shape as shown in FIG. It is effective for miniaturization. However, when a stack is formed as shown in FIG. 4 using the separator 1 made of a metal material and a power generation operation is performed, the surface of the metal material is oxidized by oxygen in the oxidant gas supplied to the oxidant electrode. Therefore, the contact resistance between the separator 1 and the diffusion layer 2 increases. For this reason, when the operation is continued for a long time, the battery characteristics are deteriorated. Therefore, in order to avoid this increase in contact resistance, a method is generally used in which a metal material is plated with gold to suppress surface oxidation. However, this configuration has a disadvantage that the cost of the separator increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide an interposed separator having a small thickness.
In addition, an object of the present invention is to provide a compact, high-performance, and low-cost solid polymer electrolyte fuel cell that can be manufactured at low cost and that does not cause deterioration in characteristics due to oxidation even in the face of an oxidizing gas.

[0007]

In order to achieve the above object, according to the present invention, there is provided a solid polymer electrolyte membrane, and two catalyst layers disposed on both main surfaces of the solid polymer electrolyte membrane.
It has two gas diffusion layers made of a conductive porous material disposed on the outer surfaces of these two catalyst layers, and two separators having gas flow paths disposed outside these two gas diffusion layers. In a solid polymer electrolyte fuel cell configured using a single cell, (1) a separator is formed of a metal material, and a gas diffusion layer on the oxidant gas supply side and a separator facing the same are integrally joined. For example, joining is performed by a resistance welding method.

(2) Alternatively, the separator is formed of a metal material, a thermoplastic resin film is provided on the surface of the separator, and the separator is integrally joined to the gas diffusion layer on the oxidant gas supply side by heating. .

(3) Further, the thermoplastic resin film of the above (2) is formed of a conductive thermoplastic resin. (4) Alternatively, the separator is formed of a resin material containing carbon fibers and having conductivity, that is, a carbon fiber reinforced resin having carbon fibers exposed on the surface.

As described in (1) above, if the metal separator and the gas diffusion layer on the oxidant gas supply side are joined by the resistance welding method, the resistance of the joint does not increase even if the surface of the metal separator is oxidized. Therefore, the battery characteristics do not deteriorate. Further, since the separator is made of metal, it can be easily formed into a corrugated shape by pressing, and a thin separator can be obtained.

Further, according to the above (2), the oxidation of the surface of the metal separator is suppressed by the thermoplastic resin coating applied to the surface, so that the contact resistance between the separator and the gas diffusion layer is reduced. Is prevented from increasing. In the case of (3), since the thermoplastic resin film has conductivity, the contact resistance is reduced.

According to the above (4), the carbon fiber reinforced resin can obtain a sufficiently low contact resistance as a separator if an appropriate amount of carbon fiber is exposed on the surface. Further, since carbon is not oxidized, there is no deterioration in characteristics even when used for a long time. Further, by selecting a resin to be used, it is possible to form a required shape while maintaining gas impermeability.

[0013]

FIG. 1 is a sectional view of a single cell showing a first embodiment of a solid polymer electrolyte fuel cell according to the present invention.

In this configuration, the gas diffusion layer 2 facing the oxidizing gas flow path 5 and the separator 1 disposed in contact with the gas diffusion layer 2 are both made of stainless steel. The separator 1 is formed into a corrugated shape by press molding in the same manner as in the conventional example shown in FIG. 4, and the protruding portion of the separator 1 and the gas diffusion layer 2 are joined at the welding portion 10 by resistance welding. Is a feature of this configuration. When the oxidizing gas flows through the oxidizing gas passage 5 formed between the gas diffusion layer 2 and the separator 1, the surfaces of the gas diffusion layer 2 and the separator 1 facing the oxidizing gas passage 5 oxidize. However, since the gas diffusion layer 2 and the separator 1 are joined, the contact resistance is maintained at a low value without being affected by oxidation.

When the separator 1 is made of stainless steel and the gas diffusion layer 2 is made of a carbon material, the gas diffusion layer 2 is welded in an inert gas atmosphere to separate the gas diffusion layer 2 from the separator 1.
A method of embedding and joining the inside of the substrate may be used.

Embodiment 2 FIG. 2 is a sectional view of a single cell showing a second embodiment of the solid polymer electrolyte fuel cell according to the present invention. The feature of this configuration is that a protective coating 11 made of nylon is disposed on the surface of the separator 1 facing the oxidizing gas flow path 5, and the gas diffusion layer facing the oxidizing gas flow path 5 is provided through the protective coating 11. 2 and the separator 1 are joined. That is, in the present configuration, when the separator 1 made of stainless steel is press-formed, the protective film 11 made of nylon is adhered to the surface of the separator 1, and the separator 1 with the protective film 11 adhered thereto is overlapped with the gas diffusion layer 2. The gas diffusion layer 2 is put into the protective coating 11 by hot pressing, and the separator 1 and the gas diffusion layer 2 are brought into a state of exhibiting good electric conductivity of 10 [mΩ / cm ² ] or less, and then cooled. The method of joining both is used. In this configuration, even if the oxidizing gas flows through the oxidizing gas flow path 5, the contact resistance of the joining portion is not affected, and the separator 1 is not oxidized.

Note that a protective coating 11 is shown on the opposite surface of the separator 1 disposed on the side facing the fuel gas flow path 6, and this protective coating 11 is provided on the lower side of the unit cell shown in FIG. It is joined to the gas diffusion layer facing the oxidant gas flow path.

Embodiment 3 FIG. 3 is a sectional view of a single cell showing a solid polymer electrolyte fuel cell according to a third embodiment of the present invention. The feature of this configuration is that the separator 1A is formed of carbon fiber reinforced resin. That is,
The separator 1A is formed by dispersing short carbon fibers having a length of about 1 mm in a matrix of an epoxy resin, and the dispersed carbon fibers impart electrical conductivity. The higher the density of the carbon fiber, the higher the electrical conductivity. However, if the density is too high, gas may permeate. Therefore, the density of the gas fiber must be determined in consideration of the gas permeability.

In this configuration, since the separator 1A is formed of a carbon fiber reinforced resin, the separator 1A is not oxidized even if the oxidant gas flows through the oxidant gas flow path 5, so that the joint 1A is not oxidized. The contact resistance is not affected.

[0020]

As described above, according to the present invention, the solid polymer electrolyte membrane, the two catalyst layers disposed on both main surfaces of the solid polymer electrolyte membrane, and the outer surfaces of these two catalyst layers Two gas diffusion layers made of a conductive porous material disposed on,
In a solid polymer electrolyte fuel cell configured using a single cell having two separators provided with gas flow passages disposed outside these two gas diffusion layers, (1) the separator is formed of a metal material Then, the gas diffusion layer on the oxidizing gas supply side and the separator facing the gas diffusion layer are joined by, for example, a resistance welding method, or a thermoplastic resin film is provided on the surface of the separator, and heated to be joined to the gas diffusion layer. And so on, so that the separator is thin and can be manufactured at a low cost, and furthermore, the deterioration in characteristics due to oxygen in the oxidizing gas is avoided, so that the separator is compact and has high performance. In addition, a low-cost solid polymer electrolyte fuel cell can be obtained.

(2) Even if the separator is formed of a carbon fiber reinforced resin having carbon fibers exposed on the surface, similarly, deterioration in characteristics due to oxygen in the oxidizing gas is avoided, so that the separator is compact and has high performance. It is suitable as a low-cost and solid polymer electrolyte fuel cell.

[Brief description of the drawings]

FIG. 1 is a sectional view of a single cell showing a first embodiment of a solid polymer electrolyte fuel cell according to the present invention.

FIG. 2 is a sectional view of a single cell showing a second embodiment of the solid polymer electrolyte fuel cell according to the present invention;

FIG. 3 is a sectional view of a single cell showing a third embodiment of the solid polymer electrolyte fuel cell according to the present invention;

FIG. 4 is a cross-sectional view showing a basic configuration of a stack of a conventional solid polymer electrolyte fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1A Separator 2 Gas diffusion layer 3 Membrane electrode assembly (MEA) 4 Seal 5 Oxidant gas flow path 6 Fuel gas flow path 10 Weld part 11 Protective coating

Claims (5)

[Claims] 1. A solid polymer electrolyte membrane, two catalyst layers disposed on both main surfaces of the solid polymer electrolyte membrane, and a conductive porous material disposed on outer surfaces of the two catalyst layers. In a solid polymer electrolyte fuel cell configured using a single cell having two gas diffusion layers, and two separators having gas channels arranged outside the two gas diffusion layers, A solid polymer electrolyte fuel cell, wherein the separator is formed of a metal material, and the gas diffusion layer on the oxidant gas supply side and the separator facing the gas diffusion layer are integrally joined. 2. The solid polymer electrolyte fuel cell according to claim 1, wherein the joining between the gas diffusion layer and the separator is performed by a resistance welding method. 3. The solid polymer electrolyte according to claim 1, wherein the bonding between the gas diffusion layer and the separator is performed by bonding with a thermoplastic resin film provided on the surface of the separator. Type fuel cell. 4. The solid polymer electrolyte fuel cell according to claim 3, wherein said thermoplastic resin film is a conductive thermoplastic resin film. 5. A solid polymer electrolyte membrane, two catalyst layers disposed on both main surfaces of the solid polymer electrolyte membrane, and a conductive porous material disposed on the outer surfaces of the two catalyst layers. In a solid polymer electrolyte fuel cell configured using a single cell having two gas diffusion layers, and two separators having gas channels arranged outside the two gas diffusion layers, A solid polymer electrolyte fuel cell, wherein the separator contains carbon fiber and is formed of a resin material having conductivity.