Membrane electrode assembly for use in solid polymer electrolyte fuel cell

Abstract

The present invention provides a membrane electrode assembly for use in a solid polymer electrolyte fuel cell which assembly can attain an excellent electric power generation performance both under low-humidity conditions and under high-humidity conditions. The membrane electrode assembly includes: a solid polymer electrolyte membrane 2 having proton conductivity; a cathode electrode catalyst layer 3 disposed on one side of the solid polymer electrolyte membrane 2; an anode electrode catalyst layer 4 disposed on the other side of the solid polymer electrolyte membrane 2; and two gas diffusion layers 5 and 6 disposed on a side of the cathode electrode catalyst layer 3 and a side of the anode electrode catalyst layer 4, respectively, both these sides facing away from the solid polymer electrolyte membrane 2; wherein the gas diffusion layer 6 in the anode side is smaller in contact angle to water than the gas diffusion layer 5 in the cathode side. The membrane electrode assembly also includes at least two coating layers 11a and 11b different in properties from each other between the gas diffusion layer 5 and the cathode electrode catalyst layer 3, and at least two coating layers 12a and 12b different in properties from each other between the gas diffusion layer 6 and the anode electrode catalyst layer 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a configuration of a membrane electrode assembly of an embodiment of the present invention;

FIG. 2 is a schematic sectional view illustrating a configuration of a fuel cell using the membrane electrode assembly shown in FIG. 1; and

FIG. 3 is a schematic sectional view illustrating a configuration of another membrane electrode assembly of the embodiment of the present invention.

Claims

1. A membrane electrode assembly for use in a solid polymer electrolyte fuel cell, the membrane electrode assembly comprising: a solid polymer electrolyte membrane having proton conductivity;a cathode electrode catalyst layer disposed on one side of the solid polymer electrolyte membrane;an anode electrode catalyst layer disposed on the other side of the solid polymer electrolyte membrane;two gas diffusion layers disposed on a side of the cathode electrode catalyst layer and a side of the anode electrode catalyst layer, respectively, both these sides facing away from the solid polymer electrolyte membrane;wherein the gas diffusion layer in the anode side is smaller in contact angle to water than the gas diffusion layer in the cathode side.

2. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 1, wherein the gas diffusion layer in the cathode side is formed of an untreated carbon paper.

3. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 1, wherein the gas diffusion layer in the cathode side is formed of a carbon paper subjected to a water repellent treatment.

4. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 1, wherein the gas diffusion layer in the anode side is formed of a carbon paper subjected to a hydrophilization treatment.

5. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 4, wherein the hydrophilization treatment is carried out by impregnating the carbon paper with an aqueous solution of a metal oxide and by thereafter heat treating the thus impregnated carbon paper.

6. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 5, wherein the metal oxide is titanium oxide.

7. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 1, wherein the gas diffusion layer in the anode side has a contact angle to water falling within a range from 0 to 20°.

8. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 1, the membrane electrode assembly comprising at least two coating layers different in properties from each other between each of the gas diffusion layers and the electrode catalyst layer pairing therewith.

9. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 8, wherein the coating layers different in properties from one another are formed by coating different pastes each obtained by mixing a carbon powder, a binder and an organic solvent and by thereafter heat treating the coated layer, wherein the carbon powders in the different pastes are different from one another.

10. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 9, wherein each of the carbon powders comprises at least one type of carbon powder selected from carbon black and vapor grown carbon.

11. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 9, wherein the binder is a resin selected from a water-repellent resin and an ion conducting polymer.

12. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 11, wherein the water-repellent resin is polytetrafluoroethylene.

13. The membrane electrode assembly for use in a solid polymer electrolyte fuel cell according to claim 9, wherein the organic solvent is selected from the group consisting of ethylene glycol, tetrafluoroethylene-tetrafluoropropylene copolymer, and N-methyl-2-pyrrolidone.