Powder Catalyst Material, Method for Producing Same and Electrode for Solid Polymer Fuel Cell Using Same

Abstract

The battery performance of a solid polymer fuel cell is enhanced by improving a three-phase interface. A catalyst carrier conductive material 10, solid polymer electrolyte 20 and 30, and a good solvent and a poor solvent with respect to the solid polymer electrolyte are mixed so as to prepare an ink in which at least part of the solid polymer electrolyte is colloidalized. The ink is then dried to produce a powder catalytic material 40, which is applied to an electrolyte membrane or a gas diffusion layer, thereby forming a catalyst layer of an electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conceptual chart of a membrane-electrode assembly (MEA) in a solid polymer fuel cell.

FIG. 2 schematically shows an example of a method for preparing a powder catalytic material according to the invention.

FIG. 3 shows a graph illustrating the battery performance of fuel battery cells according to Examples 1 and 2 and a Comparative Example.

FIG. 4 shows a graph illustrating the battery performance of a fuel battery cell according to Example 3.

In the drawings, numeral 1 designates an electrolyte membrane, 2 designates a catalyst layer, 3 designates a gas diffusion layer, 4 designates a membrane-electrode assembly (MEA), 10 designates a solid polymer electrolyte, 20 designates a solid polymer electrolyte dissolved in a solvent, 30 designates a solid polymer electrolyte existing in the solvent in the form of a colloid, and 40 designates a powder catalytic material obtained by drying.

BEST MODES FOR CARRYING OUT THE INVENTION

The invention will be hereafter described by way of examples thereof.

EXAMPLE 1

Ink A was prepared with the mixture ratio (% by weight) shown in Table 1 in the following order. First, a liquid mixture of a catalyst carrier conductive material (60 wt % Pt/C), a solid polymer electrolyte, water (dielectric constant 78.5), and propylene glycol (good solvent; dielectric constant 32.0) was prepared (a conceptual chart is shown in FIG. 2a). While stirring the liquid mixture, cyclohexanol (poor solvent; dielectric constant 15.0) was added. After stirring for approximately 30 minutes, an ink in which part of the electrolyte was colloidalized was obtained (a conceptual chart is shown in FIG. 2b). The ink was then dried with a spray dryer under the conditions consisting of a solution delivery rate of 10 cc/min, spray pressure of 0.1 MPa, and a drying temperature of 80° C., thereby preparing a powder catalytic material (a conceptual chart is shown in FIG. 2c). In FIGS. 2a to 2c, numeral 10 designates the catalyst carrier conductive material, 20 designates the solid polymer electrolyte dissolved in the solvent, 30 designates the solid polymer electrolyte existing in the solvent in the form of a colloid, and 40 designates the powder catalytic material obtained by drying.

TABLE 1
[Ink A]
catalyst carrier conductive material 1
solid polymer electrolyte        0.4
water                            4
propylene glycol                 2.5
cyclohexanol                     6
(cyclohexanol + water)/          4.0
propylene glycol

The prepared powder catalytic material was applied to both sides of the electrolyte membrane to 0.20 mg/cm2 and 0.50 mg/cm2 by spray coating. The material was then fixed by a roll press machine under conditions of 160° C. and 30 kgf/cm, thereby preparing a solid polymer fuel cell electrode.

Using this solid polymer fuel cell electrode, a fuel cell was made, and its cell performance was evaluated in terms of the relationship between current density and voltage. The result is shown in FIG. 3, where ink A is indicated by symbol (-⋄-).

EXAMPLE 2

An ink was prepared in the same way as in Example 1 with the exception that the order of preparation was such as follows. Namely, a liquid mixture of catalyst carrier conductive material (60 wt % Pt/C), water, propylene glycol (good solvent), and cyclohexanol (poor solvent) was prepared, to which a solid polymer electrolyte solution was added while stirring. The mixture was then stirred for 30 minutes, whereby an ink in the form of colloid was obtained.

Thereafter, the ink was dried in the same way as in Example 1 so as to prepare a powder catalytic material. Using the thus prepared powder catalytic material in a solid polymer fuel cell electrode, a fuel battery cell was made. Its battery performance was then evaluated in terms of the relationship between current density and voltage. The result of the evaluation is shown in FIG. 3, where ink B is indicated by symbol (-▭-).

COMPARATIVE EXAMPLE 1

An ink was prepared in the same way as in Example 1 with the exception that no cyclohexanol (poor solvent) was added. The ink was then allowed to stand for 30 minutes, whereupon no colloidalization of the electrolyte was observed.

The ink was then dried with a spray dryer under the conditions consisting of a solution delivery rate of 10 cc/min, spray pressure of 0.1 MPa, and drying temperature of 80° C., thereby preparing a powder catalytic material. Thereafter, a fuel battery cell was prepared using the powder catalytic material in a solid polymer fuel cell electrode in the same way as in Example 1. Its battery performance was evaluated in terms of the relationship between current density and voltage. The result is shown in FIG. 3, where Comparative Example 1 is indicated by symbol (-∘-).

[Analysis]

The graph in FIG. 3 shows that the cells according to Examples 1 and 2 possess higher battery performance than that of the Comparative Example, thus indicating the validity of the present invention.

EXAMPLE 3

Inks C, D, and E were prepared with the mixture ratios (% by weight) shown in Table 2 in the same order as in Example 1. By stirring each ink for approximately 30 minutes, an ink in which part of the electrolyte was colloidalized was obtained. Each of the inks was dried with a spray dryer in the same way as in Example 1, thereby making a powder catalytic material.

	TABLE 2
		Ink C	Ink D	Ink E
	Catalyst carrier conductive	1	1	1
	material
	Solid polymer electrolyte	0.4	0.4	0.4
	Water	4	4	4
	Propylene glycol	4	4	4
	Cyclohexanol	6	4	2
	(Cyclohexanol + Water)/	2.5	2	1.5
	Propylene glycol

The prepared powder catalytic material was applied to both sides of the electrolyte membrane to 0.20 mg/cm2 and 0.50 mg/cm2 by spray coating. The material was then fixed by a roll press machine under the same conditions as in Example 1, thereby preparing a solid polymer fuel cell electrode.

Using this solid polymer fuel cell electrode, a fuel cell was made, and its cell performance was evaluated in terms of the relationship between current density and voltage. The result is shown in FIG. 4.

[Analysis]

The graph in FIG. 4 shows that while the fuel battery cells using inks C and D have substantially the same battery performance, the battery performance of the fuel battery cell using ink E is somewhat inferior. This shows that it is particularly effective in the present invention when the value of (poor solvent including water)/(good solvent) is 2 or more.

Claims

1. A method for manufacturing a powder catalytic material, comprising the steps of mixing at least a catalyst carrier conductive material, a solid polymer electrolyte, and a good solvent and a poor solvent with respect to said solid polymer electrolyte, thereby preparing an ink in which at least part of said solid polymer electrolyte is colloidalized, and drying said ink so as to obtain a powder catalytic material.

2. A method for manufacturing a powder catalytic material, comprising the steps of mixing at least a catalyst carrier conductive material, a solid polymer electrolyte, and a good solvent with respect to said solid polymer electrolyte, adding a poor solvent with respect to said solid polymer electrolyte to the mixture, thereby preparing an ink in which at least part of said solid polymer electrolyte is colloidalized, and drying said ink so as to obtain a powder catalytic material.

3. A method for manufacturing a powder catalytic material, comprising the steps of mixing at least a catalyst carrier conductive material, and a good solvent and a poor solvent with respect to a solid polymer electrolyte, adding a solid polymer electrolyte to the mixture, thereby preparing an ink in which at least part of said solid polymer electrolyte is colloidalized, and drying said ink so as to obtain a powder catalytic material.

4. The method for manufacturing a powder catalytic material according to any one of claims 1 to 3, wherein, in the solution in which said catalyst carrier conductive material, said solid polymer electrolyte, and said good solvent and said poor solvent with respect to said solid polymer electrolyte are mixed, the value of poor solvent/good solvent is 2 or more.

5. The method for manufacturing a powder catalytic material according to any one of claims 1 to 3, wherein said poor solvent has a dielectric constant of 15 or less, or 35 or more.

6. The method for manufacturing a powder catalytic material according to any one of claims 1 to 3, wherein said good solvent comprises one or more kinds selected from propylene glycol, ethylene glycol, (iso, n-) propyl alcohol, and ethyl alcohol, and wherein said poor solvent comprises one or more kinds selected from water, cyclohexanol, n-butyl acetate, n-acetic acid, n-butylamine, methyl amyl ketone, and tetrahydrofuran.

7. A solid polymer fuel cell electrode produced by applying the powder catalytic material obtained by the manufacturing method according to any one of claims 1 to 3 to an electrolyte membrane or a gas diffusion layer.

8. A powder catalytic material for a solid polymer fuel cell composed of a catalyst carrier conductive material and a solid polymer electrolyte, wherein said solid polymer electrolyte is integrally attached to said catalyst carrier conductive material in a coagulated state.