Direct oxidation fuel cell and method for operating direct oxidation fuel cell system

Abstract

A direct oxidation fuel cell includes at least one unit cell. The at least one unit cell includes an anode, a cathode, and a hydrogen-ion conductive polymer electrolyte membrane interposed between the anode and the cathode. The anode includes: a catalyst layer in contact with the polymer electrolyte membrane; and a diffusion layer. The diffusion layer includes: a porous composite layer containing a water-repellent binding material and an electron-conductive material; a first conductive porous substrate provided on the anode-side separator side of the porous composite layer; and a second conductive porous substrate provided on the catalyst layer side of the porous composite layer.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A is a schematic view of an anode diffusion layer according to the present invention in which the diffusion of fuel is illustrated;

FIG. 1B is a schematic view of an anode diffusion layer in a comparative example in which the diffusion of fuel is illustrated;

FIG. 2 is a schematic longitudinal sectional view of a unit cell of a fuel cell in one embodiment of the present invention;

FIG. 3 is a schematic sectional view showing the structure of the main part of the anode diffusion layer of the unit cell;

FIG. 4 is a block diagram showing the structure of a fuel cell system in one embodiment of the present invention; and

FIG. 5 is a schematic longitudinal sectional view showing the structure of a device for measuring methanol permeation flux.

Claims

1. A direct oxidation fuel cell comprising at least one unit cell, said at least one unit cell comprising an anode, a cathode, a hydrogen-ion conductive polymer electrolyte membrane interposed between said anode and said cathode, an anode-side separator with a flow channel for supplying and discharging a fuel to and from said anode, and a cathode-side separator with a gas flow channel for supplying and discharging an oxidant gas to and from said cathode, wherein said anode comprises: a catalyst layer in contact with said polymer electrolyte membrane; and a diffusion layer, andsaid diffusion layer comprises: a porous composite layer comprising a water-repellent binding material and an electron-conductive material; a first conductive porous substrate provided on an anode-side separator side of said porous composite layer; and a second conductive porous substrate provided on a catalyst layer side of said porous composite layer.

2. The direct oxidation fuel cell in accordance with claim 1, wherein a flux of the fuel permeating through said first conductive porous substrate and said porous composite layer is less than a flux of the fuel permeating through said second conductive porous substrate.

3. The direct oxidation fuel cell in accordance with claim 1, wherein said porous composite layer has a substantially flat surface to which said second conductive porous substrate is joined, so that the water-repellent binding material and the electron-conductive material of said porous composite layer are kept from getting into said second conductive porous substrate.

4. The direct oxidation fuel cell in accordance with claim 1, wherein said water-repellent binding material is composed mainly of fluorocarbon resin.

5. The direct oxidation fuel cell in accordance with claim 1, wherein said electron-conductive material is composed mainly of conductive carbon black.

6. The direct oxidation fuel cell in accordance with claim 1, wherein said first conductive porous substrate and said second conductive porous substrate contain a water-repellent binding material.

7. The direct oxidation fuel cell in accordance with claim 6, wherein said water-repellent binding material is composed mainly of fluorocarbon resin.

8. A method for operating a direct oxidation fuel cell system comprising: the fuel cell of claim 1; a fuel tank connected to an inlet of the anode of said fuel cell by a fuel supply path; a fuel discharge path connected to an outlet of the anode of said fuel cell; an oxidant supply source connected to an inlet of the cathode of said fuel cell by an oxidant supply path; and an oxidant discharge path connected to an outlet of the cathode of said fuel cell, said method comprising operating said fuel cell system such that the amount of the fuel supplied to the anode of said fuel cell is 1.1 to 2.2 times the amount of the fuel consumed by power generation of said fuel cell.

9. The method for operating a direct oxidation fuel cell system in accordance with claim 8, wherein said fuel is methanol or a methanol aqueous solution, andsaid method comprises operating said fuel cell system at a fuel concentration and a cell temperature such that a flux of the fuel permeating through said first conductive porous substrate and said porous composite layer is 0.6×10−4 to 1.5×10−4 mol/(cm2·min).

10. The method for operating a direct oxidation fuel cell system in accordance with claim 8, wherein said fuel is methanol or a methanol aqueous solution, andsaid method comprises operating said fuel cell system at a fuel concentration and a cell temperature such that a flux of the fuel permeating through said second conductive porous substrate is 4.5×10−4 to 8.0×10−4 mol/(cm2·min).