JPH10340731A - Solid polymer-based electrolyte type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide superior battery output properties of a solid polymer-based electrolyte type fuel cell by adjusting the wettability of an ion-exchange fluoro polymer solvent-containing solution with a carbon-supporting body on which a catalytically active particle is carried and improving the utilization factor of the catalyst and the ion conductivity. SOLUTION: A solid polymer-based electrolyte type fuel cell is constituted of electrodes and solid polymer electrolytic substance members, and each of the electrodes comprises a carbon supporting body for supporting a particle having catalytically active property, a catalytic layer formed by immobilizing a mixture of a solvent having 5 degree or smaller contact angle to the carbon supporting body to support a catalytically active particle and a solid polymer electrolytic substance on the carbon supporting body, and a diffusion layer contacting the catalytic layer and each of the membranes is jointed to the electrodes to compose a membrane-electrode jointed body. Consequently, the contact surface area of the catalytic particle and the electrolytic substance is kept wide, and the utilization factor of the catalytically active particle and ion conductivity are improved and superior battery output can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a membrane electrode assembly comprising a gas diffusion electrode produced from catalytically active particles for directly generating electric energy from a fuel and an oxidant, and an ion exchange membrane. The present invention relates to a solid polymer electrolyte fuel cell, and more particularly to a membrane electrode assembly using an ion exchange membrane having improved ion conductivity and utilization of catalytically active particles in a catalyst layer containing a solid polymer electrolyte. is there.

[0002]

2. Description of the Related Art In a solid polymer electrolyte fuel cell, a cathode and an anode of a gas diffusion electrode which are disposed opposite to each other, and the electrolyte which is interposed between the electrodes while being in contact with both electrodes, are substantially retained. A plurality of unit cells each composed of a membrane electrode assembly composed of an ion exchange membrane that selectively allows ions to pass without passing through the battery, and a plurality of unit cells are alternately stacked via a bipolar plate provided with a gas flow unit. Have been. In this fuel cell, a fuel gas such as hydrogen and an oxidant such as oxygen are supplied to an anode side or a cathode side of a gas diffusion electrode, respectively. Oxidizing agent is electrocatalytically reduced at the same time as oxidation
Electric power is generated by converting chemical reaction energy directly into electrical energy.

A gas diffusion electrode is formed on a carbon support on which a catalyst such as platinum, ruthenium, rhodium, iridium, tin, molybdenum, or an alloy thereof is supported, on the surface of an ion exchange membrane of perfluorovinyl ether and tetrafluoroethylene. It has a catalyst layer to which a perfluorocarbon sulfonic acid resin membrane made of a copolymer is fixed. The catalyst layer is designed to facilitate contact with the fuel gas and the oxidizing gas,
Usually, it is supported on a diffusion layer of a porous substrate such as carbon paper. While the catalyst-supporting carbon material is originally a hydrophobic material, the solid polymer electrolyte solution used as the ion exchange polymer has conventionally contained a fluorosulfonic acid polymer in a solution of a hydrocarbon solvent and water,
Contains about 25% to 45% of water. Therefore, the contact angle of the electrolyte solution with respect to the carbon support of the electrode has been increased. That is, on the catalyst-supporting carbon support, the wettability to the electrolyte solution of the portion where the catalyst particles such as platinum are not deposited and the portion where the catalyst particles are deposited is reduced,
The catalyst is not sufficiently covered by the electrolyte comprising the ion-exchanged fluoropolymer. Here, the contact angle is represented by an angle between a tangent drawn on the droplet surface at a point where the surface of the droplet of the electrolyte solvent intersects the surface of the solid carbon support and the surface of the carbon support.

Since the catalyst constituting the electrode is not sufficiently covered with the electrolyte, the utilization efficiency of the catalyst is affected, and the electrochemical reaction with the fuel gas and the oxidizing gas supplied to the electrode is efficient and stable. Therefore, the output characteristics of the battery cannot be obtained.

[0005]

However, due to the necessity of dissolving the ion-exchanged fluoropolymer and the requirement based on the affinity for water, as described above, the solvent solution of the ion-exchanged fluoropolymer is, for example, propanol, ethanol or butanol. A mixed solution of alcohol and water was used. That is, for the solvent solution of the ion-exchanged fluoropolymer, the wettability of the carbon support on which the catalytically active particles are supported has not been adjusted for the purpose of improving the catalyst use efficiency and maintaining the ion exchange performance. Was. Thus, the ion-exchanged fluoropolymer can be dissolved by methods known in the art, a polymer solution for forming the ion-exchanged fluorine film or membrane can be produced, and the wetting of the carbon support carrying the catalytically active particles can be achieved. There is a need for a solvent that can also improve the properties.

As a result of various studies on the above-mentioned problems, the present inventor has found that the contact ratio of the solution in which the ion-exchanged fluoropolymer is dissolved to the carbon support is determined by the mixing ratio of the alcohol and water in the alcohol-water mixed solution. Adjusting the angle to improve its wettability to the carbon support,
As a result, they found that the output characteristics of the battery were improved, and completed the present invention. The solid polymer electrolyte fuel cell of the present invention comprises a carbon support supporting particles exhibiting catalytic activity, a solvent having a contact angle of not more than 5 degrees with respect to the carbon support supporting the catalyst active particles, and a solid polymer electrolyte. A diffusion electrode comprising a catalyst layer formed by fixing the mixture on the carbon support using the mixture, a diffusion layer in contact with the catalyst layer, and a solid electrode which is joined to the electrode to form a membrane electrode assembly. And a molecular electrolyte membrane. A solid polymer electrolyte fuel cell according to a second invention of the present application is characterized in that the solid polymer electrolyte in the first invention is a perfluorosulfonic acid polymer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An electrode of a solid polymer electrolyte fuel cell according to the present invention is constituted by the catalyst layer and the diffusion layer. This catalyst layer is formed by coating, spraying or other methods known in the art with an ink composition of a catalyst comprising platinum on a carbon support and a solution of a perfluorocarbon sulfonic acid resin dissolved in a solvent. Obtained by coating on a diffusion layer such as carbon paper or carbon cloth or on an ion exchange membrane, or previously coated with a carbon powder carrying a catalyst such as platinum using a method known in the art. It can be obtained by applying or spraying the fluoropolymer solution on an object. The carbon support supporting the platinum group metal is a carbon powder particle having a particle diameter of 0.01 to several μm. In this case, the polymer electrolyte fuel cell of the present invention is required to use a catalyst layer having a thickness of about 1 to 50 μm. In the present invention, the catalyst particles,
Desirably, from about 0.01 mg / cm ² to about 1 mg / cm ² and more is deposited in the catalyst layer.

The component having a functional group of the ion exchange membrane serving as the solid polymer electrolyte of the present invention has a fluorinated polymer as a skeleton, and the functional group may be any one of a sulfonic acid group, a carboxylic acid group and a phosphoric acid group. One having one or a plurality is included. Generally, a perfluorocarbon sulfonic acid resin made of a copolymer of perfluorovinyl ether and tetrafluoroethylene is suitably used.
It is also possible to use a perfluoroolefin such as hexafluoropropylene, chlorotrifluoroethylene or perfluoroalkoxyvinyl ether instead of tetrafluoroethylene which is a monomer constituting the fluorocarbon polymer having a functional group. After the copolymerization, if necessary, it can be converted into a proton-transporting functional group by post-treatment such as hydrolysis.
The exchange capacity of a component having a functional group is defined as the number of moles of the functional group per gram, and is usually measured by a titration method.
Generally, the exchange capacity of the component having a functional group is 0.8 to 2
Meq / g, preferably 0.9 to 2 meq / g
g. If it is less than 0.8 meq / g, the resistance is increased and the performance is reduced. If it is more than 2 meq / g, the strength of the film as a structure is greatly reduced. As the perfluorocarbon sulfonic acid resin ion exchange polymer, there is NAFION (registered trademark) solution of I. D. Du Pont de Nemours and Company, USA.

In the present invention, the polymer concentration in the ion-exchanged fluoropolymer solution is generally about 1% by weight to 10% by weight.
% By weight, and the solution is prepared from a fluoropolymer which is a copolymer of perfluorovinyl ether and tetrafluoroethylene and a novel solvent. Preparation of the solution
It is as follows. A mixture of water and an organic solvent and a fluoropolymer, for example, a mixture of perfluorovinyl ether and tetrafluoroethylene copolymer are added to a container such as a shaking tube at a temperature in the range of about 180 to 250 ° C.
Contact for at least 0.5 hours. The contacting is effected, usually with stirring, by shaking or shaking the closed pressure vessel. By cooling, an ion-exchanged fluoropolymer is obtained.

The solution of the ion exchange fluoropolymer is
The polymer is dissolved in an alcohol solution, such as propanol or isopropyl alcohol, or other alcohols,
For example, it is dissolved in a solution with ethanol or butanol. In the present invention, an organic solvent obtained by mixing at least one or a plurality of water-soluble organic solvents such as methanol, propanol, isopropanol, butyl alcohol, isobutyl alcohol, methoxyethanol, methoxypropanol, ethoxyethanol, and methyl ethyl ketone is used. Can also. The mixing ratio of the water-soluble organic solvent and water is such that the organic solvent is 80% by weight to 10% by weight.
0% by weight, 0% to 20% by weight of water, preferably 85% to 100% by weight of an organic solvent, and 0% by weight of water
To 15% by weight, particularly preferably 90 to 90% by weight of the organic solvent.
-100, water is 0-10. The contact angle of the mixed solvent with the carbon support is in the range of 5 ° or less. When the amount of the organic solvent in the mixed solvent is less than 80% by weight, the contact angle of the mixed solvent to the carbon support exceeds 5 °, and the contact angle in each case decreases with the amount of the organic solvent contained. Tends to be large. When this contact angle exceeds 5 °, it was found that the contact area between the ion-exchange polymer solution and the catalyst particles sharply decreased, and the ionic conductivity decreased.

[0011]

Embodiments of the present invention will be described below. (Embodiment) A mixed solvent of ethyl alcohol / water having a contact angle with the carbon support of 1.8 degrees was applied to an electrode (0.5 mg / cm ² of platinum supported on the carbon support) manufactured by E-TEK. Made by Dupont in the United States that selectively permeates protons and protons
The FION (registered trademark) solution is applied, for example, by brushing or spraying, and after being sufficiently dried, the electrode layer and an ion exchange membrane composed of a copolymer of perfluorovinyl ether and tetrafluoroethylene have already been subjected to hydrolysis. Finished 50 µm thick NAFION manufactured by DuPont
(Registered trademark) NF112, 135 ° C, 50k
The electrode layer and the membrane were thermocompression-bonded under the conditions of g / cm ² and 2 minutes to produce a membrane / electrode assembly. This membrane electrode assembly has a serpentine type groove fixed inside, and the electrode area is 25 cm ^2.
The experimental fuel cell using a carbon block and a surface heater is operated at 50 ° C. by supplying hydrogen gas as a fuel gas and oxygen as an oxidant gas from an external source at 50 ° C., respectively. Measure the voltage and current density of the electrode assembly. The results are reported in FIG.

Comparative Example An electrode manufactured by E-TEK (platinum supported on carbon support 0.5 mg / cm ² ) was mixed with a mixed solvent of propyl alcohol / water having a contact angle of 38 degrees with the carbon-supported substrate. A solution of NAFION (registered trademark) manufactured by Dupont, USA, which selectively transmits protons, was applied and dried sufficiently in the same manner as in the example. Made NAFION
(Registered trademark) NF112, 135 ° C, 50k
The electrode layer and the membrane were thermocompression-bonded under the conditions of g / cm ² and 2 minutes to produce a membrane / electrode assembly. The obtained membrane electrode assembly is fixed in an experimental fuel cell in the same manner as in the example, and the voltage and current density of the membrane electrode assembly are measured. The results are reported in FIG.

FIG. 1 shows the voltage-current characteristics of the membrane electrode assemblies according to the examples of the present invention and the comparative example. The current-voltage curve of the membrane / electrode assembly using the solvent of the example of the present invention was as shown by curve A, and the battery voltage was 0.38 V at a current density of 2 A / cm ² . On the other hand, the current-voltage curve of the membrane electrode assembly of the comparative example is as shown by curve B, and the current density was 2 A /
In cm ² , the battery voltage was 0.2 V.

FIG. 1 shows that the contact angle of the solvent of the solid polymer electrolyte solution constituting the solid polymer electrolyte fuel cell with respect to the catalyst-supporting carbon support is adjusted so that the catalyst particles of the present invention are sufficiently covered with the electrolyte. The molecular electrolyte fuel cell was found to be superior in the cell output to the conventional solid polymer electrolyte fuel cell in which the contact angle was not adjusted. It has been found that the effects of the present invention can be obtained by using a solid polymer electrolyte solution using a solvent whose contact angle with the catalyst-supporting carbon support is 5 ° or less.

[0015]

As described above, according to the present invention, when the solid polymer electrolyte of the catalyst layer constituting the membrane electrode assembly is formed so as to be in contact with the carbon support substrate carrying the catalytically active particles, By adjusting the contact angle of the solid polymer electrolyte solution with respect to the carbon support substrate, the solid polymer electrolyte is fixed to the carbon support, and as a result, the area of the catalyst active particles in the catalyst layer is increased. By improving utilization efficiency and ionic conductivity, excellent battery output characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 shows a carbon support for supporting catalytically active particles exhibiting conductivity in the electrode layer of a membrane electrode assembly of a solid polymer electrolyte fuel cell, and the carbon of a solvent of a solid polymer electrolyte solution forming a catalyst layer. 5 is a graph showing a contact angle with respect to a support and a change in current-voltage characteristics of a fuel cell.

Claims (2)

[Claims] 1. A method for preparing a carbon support using a mixture of a carbon support for supporting particles exhibiting catalytic activity, a solvent having a contact angle of not more than 5 degrees with the carbon support for supporting the catalyst active particles, and a solid polymer electrolyte. An electrode comprising a catalyst layer formed by fixing on a support, a diffusion layer in contact with the catalyst layer, and a solid polymer electrolyte membrane which is joined to the electrode to constitute a membrane electrode assembly. A solid polymer electrolyte fuel cell characterized by the above-mentioned. 2. The solid polymer electrolyte fuel cell according to claim 1, wherein the solid polymer electrolyte is a perfluorosulfonic acid polymer.