JP2009009768A - Method of manufacturing electrolyte membrane/membrane electrode assembly, and fuel cells - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an interface bonding capability between a catalyst layer and a water repellent layer with respect to an electrolyte membrane/membrane electrode assembly (MEA). <P>SOLUTION: A polymer electrolyte membrane 10 is sandwiched by catalyst layers 12, 16. Water-repellent layers 14 are formed on the surface of the catalyst layer 12, the surface coming in contact with the polymer electrolyte membrane 10, and on the surface of the opposite side thereof. Further, diffusion layers 18 are formed on the surface of the catalyst layer 16, the surface coming in contact with the electrolyte membrane 10 and on the surface on the opposite side thereof. The conductive powder that constitutes the water-repellent layers 14 is produced by means of a spray-dry method, while it is applied on the catalyst layer 12, which is subjected to thermo-compression bonding thereafter so as to form a water-repellent layer 14. The mean particle diameters of both the catalyst layer 12 and water-repellent layer 14 are set to 1 to 20 μm and 1 to 10 μm, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an electrolyte membrane / electrode assembly and a fuel cell, and more particularly to improvement of the interface between a catalyst layer and a water repellent layer.

  In the electrode of the polymer electrolyte fuel cell, platinum or the like is used as a catalyst for promoting the chemical reaction, and acetylene black is used to reduce the production cost by reducing the amount of platinum etc. while maintaining the power generation performance. There has been proposed a method for supporting conductive carbon particles such as a display.

  In Patent Document 1 shown below, Ketjen Black EC is dried while spraying a solution of an aqueous solution of chloroplatinic acid, reduced in a reducing gas atmosphere containing 4% of hydrogen gas, and subsequently sprayed with an aqueous solution of ruthenium chloride. And dried in a reducing gas atmosphere containing 4% hydrogen gas to carry 25% by weight of platinum particles and ruthenium particles on the surface of the conductive carbon particles to form catalyst-supported conductive carbon particles on the fuel electrode side. It is disclosed that a hydrogen ion conductive polymer electrolyte is bonded to this surface. The catalyst body is mixed with ethylene glycol in a nitrogen atmosphere to prepare a paste-like ink, which is applied to one side of the polymer electrolyte membrane by a screen printing method. The average particle diameter of the secondary particles of the catalyst body is 5 μm. Then, a carbon nonwoven fabric of conductive carbon particles is impregnated with an aqueous dispersion containing a fluororesin and then dried, and an ink in which conductive carbon powder and an aqueous solution in which PTFE fine powder is dispersed is mixed on one surface of the carbon nonwoven fabric. It is disclosed that a water-repellent layer is formed by coating using a screen printing method, and an electrolyte membrane / electrode assembly (MEA) is manufactured by thermocompression bonding so that the water-repellent layer is in contact with the catalyst layer. Has been.

JP 2003-242987 A

  As described above, conventionally, one surface of the carbon nonwoven fabric serving as the electrode diffusion layer is a water repellent layer, and the water repellent layer is brought into contact with the catalyst layer and bonded by thermocompression bonding. As a result, the gap between the catalyst particles and the water repellent layer is increased, or the contact resistance of the interface is increased. was there.

  An object of the present invention is to improve the adhesiveness at the interface between the catalyst layer and the water-repellent layer in the electrolyte membrane / electrode assembly, to suppress the gap, thereby improving the power generation characteristics.

  In the method for producing an electrolyte membrane / electrode assembly according to the present invention, a step of applying a catalyst layer powder on the electrolyte membrane, and applying a conductive layer powder made of a carbon resin mixed powder on the catalyst layer powder. It has the process and the process of thermocompression-bonding after application | coating.

  The present invention also provides a fuel cell having an electrolyte membrane and a catalyst layer, and sandwiching the electrolyte membrane between a pair of the catalyst layers, wherein the catalyst layer is electrically conductive on a side opposite to the side where the electrolyte membrane contacts. The conductive particle layer is formed by coating. In one embodiment of the present invention, the average particle diameter of either the catalyst layer or the conductive particle layer is 1 to 20 μm, and the other average particle diameter is 1 to 10 μm.

  According to the present invention, conductive layer powder such as a water repellent layer is applied and formed in contact with the catalyst layer, so that the particle diameter of both layers at the interface is controlled, the adhesion at the interface is improved, and the gap is suppressed. Can do. Moreover, the power generation performance as a fuel cell can be improved by improving the adhesiveness in an interface.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In FIG. 1, the structure of the electrolyte membrane / electrode assembly (MEA) of this embodiment is shown. Catalyst layers 12 and 16 are formed on the cathode surface side (air electrode side) and anode surface side (fuel electrode side) of the polymer electrolyte membrane 10 that selectively transports hydrogen ions, respectively. The polymer electrolyte membrane 10 is sandwiched. A conductive layer, more specifically, a water repellent layer 14 is formed on the cathode-side catalyst layer 12, that is, on the surface of the two surfaces of the catalyst layer 12 that is not in contact with the polymer electrolyte membrane 10. Further, a diffusion layer 18 is formed on the catalyst layer 16 on the anode surface side, that is, on the surface of the two surfaces of the catalyst layer 16 that is not in contact with the polymer electrolyte membrane 10. The polymer electrolyte membrane 10, the catalyst layers 12 and 16, the water repellent layer 14, and the diffusion layer 18 constitute an electrolyte membrane / electrode assembly (MEA).

  In the present embodiment, the water repellent layer is not formed by water repellent treatment of a part of the carbon non-woven fabric to form a water repellent layer, and the water repellent layer is brought into contact with the catalyst layer 12 and bonded by thermocompression bonding. The water-repellent layer powder constituting 14 is applied and formed on the catalyst layer 12 and then thermocompression bonded to fix the water-repellent layer 14 on the catalyst layer 12. This eliminates a gap at the interface between the catalyst layer 12 and the water repellent layer 14, suppresses water accumulation at the interface between the catalyst layer 12 and the water repellent layer 14, and contact resistance at the interface between the catalyst layer 12 and the water repellent layer 14. To improve power generation characteristics.

  In this embodiment, since the water-repellent layer powder is applied and formed on the catalyst layer 12, the interface between the catalyst layer 12 and the water-repellent layer 14 becomes a particle interface (an interface between particles), eliminating gaps and adhesiveness. Can be improved. The catalyst layer powder in the present embodiment is, for example, platinum black or catalyst-supporting carbon, and the average particle diameter thereof can be about 1 to 20 μm, and the average particle diameter of the water repellent layer powder can be about 1 to 10 μm. The average particle size of the catalyst layer powder may be 1 to 10 μm, and the average particle size of the water repellent layer powder may be about 1 to 20 μm. The ratio of the average particle diameter of the catalyst layer powder to the water repellent layer powder is within a certain range, for example, (average particle diameter of water repellent layer powder) / (average particle diameter of catalyst layer powder) is 1/20. It may be set to be within the range of 20, which can reduce the interfacial gap.

  The catalyst layer powder and the water repellent layer powder in the present embodiment can be produced by any method, but may be produced by, for example, a spray drying method. The average particle size of the catalyst layer powder and the water repellent layer powder can be controlled relatively easily by spray drying.

  In this embodiment, the water-repellent layer 14 is formed on the cathode-side catalyst layer 12 that is the air electrode, and the diffusion layer 18 similar to the conventional one is formed on the anode-side catalyst layer 16 that is the fuel electrode. However, a water repellent layer may be formed on the anode-side catalyst layer 16 by the same method as the water repellent layer 14.

<Example 1>
(1) Preparation of catalyst layer powder Solute and solvent were mixed according to the following composition and dispersed by various mills, ultrasonic waves, or the like. The produced slurry was spray-dried using a spray drying apparatus to produce catalyst layer powder.
50 wt% Pt / C 2.0 (weight ratio)
Electrolyte 1.0 (weight ratio)
Water 48.5 (weight ratio)
Ethanol 48.5 (weight ratio)

(2) Preparation of water repellent layer powder Solute and solvent were mixed according to the following composition and dispersed by various mills, ultrasonic waves, or the like. The produced slurry was spray-dried using a spray drying apparatus to produce a carbon resin mixed powder used for the water repellent layer 14.
Acetylene black 0.5 (weight ratio)
PVDF 0.5 (weight ratio)
NMP 99 (weight ratio)

(3) Application The produced catalyst layer powder was applied on the cathode surface side so that the platinum content was 0.5 mg / cm ² on the polymer electrolyte membrane 10. Next, the produced water-repellent layer powder was applied onto the catalyst layer powder so as to be 3 mg / cm ² .

(4) Fixing After the water-repellent layer powder is applied and formed on the catalyst powder, the catalyst layer powder and the water-repellent layer powder are fixed by applying a heat pressure of 140 ° C. and 3 MPa for 4 minutes. A catalyst layer 12 and a water repellent layer 14 were formed on the electrolyte membrane 10. Further, the catalyst layer 16 was formed on the anode surface side of the electrolyte membrane by a transfer method so that the platinum content was 0.2 mg / cm ² .

(5) Formation of diffusion layer A diffusion layer 18 was formed on the catalyst layer on the anode surface side, and both electrodes were sandwiched between a porous body and a separator to produce a fuel cell.

<Comparative Example 1>
In the above Example 1, a catalyst layer was formed on the catalyst layer 12 on the cathode side using a catalyst layer transfer roll having the same composition as the catalyst layer powder used in Example 1, and a fuel cell was produced.

  FIG. 2A shows a cross-sectional electron micrograph of Example 1, and FIG. 2B shows a cross-sectional electron micrograph of Comparative Example 1. In both figures, the positions of the electrolyte membrane 10, the catalyst layer 12, and the water repellent layer 14 are shown. In Example 1, both the catalyst layer 12 and the water repellent layer 14 are formed by coating, and the adhesion at the interface between the two layers is improved.

  FIG. 3 shows the cell voltage and resistance when power is generated at the cell cooling water inlet temperature of 70 degrees and the humidification temperature of 60 degrees for the fuel cells produced in Example 1 and Comparative Example 1. The cell of Example 1 has a higher cell voltage and lower resistance than the cell of Comparative Example 1. Moreover, even at high current density, power was generated without causing flooding (inhibition of gas diffusion due to excessive moisture).

  As described above, in the cell of Example 1, it was confirmed that the adhesiveness at the interface between the catalyst layer 12 and the water repellent layer 14 was improved and the power generation characteristics were improved.

It is a block diagram of an electrolyte membrane / electrode assembly (MEA). It is typical sectional drawing of an Example. It is typical sectional drawing of a comparative example. It is a graph which shows the cell voltage and resistance of an Example and a comparative example.

Explanation of symbols

  10 polymer electrolyte membrane, 12 catalyst layer (cathode side), 14 water repellent layer, 16 catalyst layer (anode side), 18 diffusion layer, 20 electrolyte membrane / electrode assembly.

Claims (8)

Applying a catalyst layer powder on the electrolyte membrane;
Applying a conductive layer powder on the catalyst layer powder;
A process of thermocompression bonding after application;
A method for producing an electrolyte membrane / electrode assembly, comprising: The method of claim 1, wherein
The method for producing an electrolyte membrane / electrode assembly, wherein the catalyst layer powder has an average particle size of 1 to 20 μm, and the conductive layer powder has an average particle size of 1 to 10 μm. The method according to claim 1,
The method for producing an electrolyte membrane / electrode assembly, wherein the conductive layer is a water repellent layer. An electrolyte membrane;
A catalyst layer;
A fuel cell in which the electrolyte membrane is sandwiched between a pair of the catalyst layers,
The fuel cell, wherein the layer on the opposite side of the catalyst layer to the side in contact with the electrolyte membrane is a conductive particle layer. An electrolyte membrane;
A catalyst layer;
A fuel cell in which the electrolyte membrane is sandwiched between a pair of the catalyst layers,
A conductive particle layer is disposed on the side of the catalyst layer opposite to the side where the electrolyte membrane contacts,
One of the catalyst layer and the conductive particle layer has an average particle diameter of 1 to 20 μm, and the other has an average particle diameter of 1 to 10 μm. The fuel cell according to claim 5, wherein
An average particle size of the catalyst layer is 1 to 20 μm, and an average particle size of the conductive particle layer is 1 to 10 μm. The fuel cell according to any one of claims 4 to 6,
The fuel cell, wherein the conductive particle layer is a water repellent layer. The fuel cell according to any one of claims 4 to 7,
The fuel cell, wherein the particles constituting the catalyst layer and the particles constituting the conductive particle layer are produced by a spray drying method.

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