JP2007026719A - Method for forming catalyst layer of fuel cell, and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst layer forming method for forming a catalyst layer on a solid polymer electrolyte membrane for a fuel cell that reduces costs by reducing platinum useless for contributing to reaction. <P>SOLUTION: The fuel cell catalyst layer forming method forms a catalyst layer 5 by spraying porous carbon particles 1 supporting platinum on a surface of a solid polymer electrolyte membrane 4 to form a first layer 5a, further spraying the porous carbon particles 1 supporting platinum and nonporous carbon particles 2 supporting platinum simultaneously to form a second layer 5b, and further spraying the nonporous carbon particles 2 supporting platinum to form a third layer 5c, so that the amount of platinum included in the catalyst layer 5 decreases with distance from the solid polymer electrolyte membrane 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a catalyst layer forming method for forming a catalyst layer on a solid polymer electrolyte membrane of a fuel cell, and in particular, a fuel that changes the amount of platinum contained in the catalyst layer so as to decrease with increasing distance from the solid polymer electrolyte membrane. The present invention relates to a battery catalyst layer forming method and a membrane electrode assembly formed by the method.

  In a fuel cell of a solid polymer fuel cell, a catalyst layer is formed on both sides of a solid polymer electrolyte membrane, and a gas diffusion layer is formed on the outer side thereof. A plurality of fuel cells thus formed are further stacked to constitute a fuel cell stack. In this fuel cell stack, it is necessary to constantly apply a fastening pressure in the stacking direction in order to reduce the electrical contact resistance of the components and to maintain the gas sealing performance.

  However, when the fastening pressure is constantly applied, there is a possibility that the carbon paper or carbon cloth needle-like projections constituting the gas diffusion layer penetrate to the polymer electrolyte membrane and cause a micro short circuit.

  In view of this, a fuel cell has been proposed in which the catalyst layer is multilayered to prevent the needle-like protrusions from entering (see Patent Document 1).

In this conventional example, in the multi-layered catalyst layer, the layer on the side in contact with the solid polymer electrolyte membrane is made a dense layer to prevent a micro short circuit, and the layer on the side in contact with the gas diffusion layer is made a dense layer. Bondability with the gas diffusion layer is improved.
JP 2003-303596 A

  The general catalyst layer is mainly composed of carbon particles carrying platinum as a catalyst. Of the platinum in this catalyst, platinum in the portion closest to the solid polymer electrolyte membrane contributes most to the reaction, and the solid polymer. As the distance from the electrolyte membrane increases, the reaction tends not to contribute.

  However, in the conventional fuel cell manufacturing method described above, the amount of platinum is not changed although the catalyst layer is multi-layered. There was a problem that the cost increased.

  In order to solve the above-described problems, a fuel cell catalyst layer forming method according to the present invention is a fuel cell catalyst layer forming method in which a catalyst layer is formed on a solid polymer electrolyte membrane of a fuel cell, wherein the solid state The first layer is formed by spraying porous carbon particles carrying platinum on the surface of the polymer electrolyte membrane. The porous carbon particles carrying platinum on the first layer and the non-platinum carrying platinum. The catalyst layer is formed by spraying the porous carbon particles simultaneously to form the second layer, and spraying the non-porous carbon particles carrying platinum on the second layer to form the third layer. It is characterized by forming.

  Further, the membrane electrode assembly according to the present invention is a membrane electrode assembly in which a catalyst layer is formed on both surfaces of a solid polymer electrolyte membrane, and the catalyst layer is made of platinum on the surface of the solid polymer electrolyte membrane. A first layer formed by spraying supported porous carbon particles, a porous carbon particle supporting platinum on the first layer, and a non-porous carbon particle supporting platinum; And a third layer formed by spraying carbon particles having a non-porous structure carrying platinum on the second layer.

In the fuel cell catalyst layer forming method according to the present invention, since the catalyst layer is formed by laminating three layers having different platinum amounts, the platinum amount of the catalyst layer is increased on the side closer to the solid polymer electrolyte membrane, The catalyst layer can be formed so as to decrease as the distance from the solid polymer electrolyte membrane increases, thereby reducing the amount of platinum that does not contribute to the reaction and thereby reducing the cost. Further, since the catalyst layer is formed of carbon particles having a porous structure, the hydrogen gas permeability is good and the output of the fuel cell can be improved. Also, in the membrane electrode assembly according to the present invention, the catalyst layer has Since it is formed by laminating three layers with different platinum amounts, the catalyst layer should be formed so that the platinum amount is close to the solid polymer electrolyte membrane and decreases as the distance from the solid polymer electrolyte membrane increases. This can reduce the amount of platinum that does not contribute to the reaction, thereby reducing the cost. Furthermore, since the catalyst layer is formed of porous carbon particles, the hydrogen gas permeability is good and the output of the fuel cell can be improved.

  Examples of the method for forming a catalyst layer of a fuel cell according to the present invention will be described below. First, the structure of a membrane electrode assembly (MEA) constituting the fuel cell will be described with reference to FIG.

  As shown in FIG. 3, the membrane electrode assembly 14 includes a solid polymer electrolyte membrane 16 for permeating hydrogen ions, an anode electrode 17 disposed on the anode side of the solid polymer electrolyte membrane 16, and a cathode side. And a cathode electrode 18 disposed on the substrate.

  Further, the anode electrode 17 is composed of an anode catalyst layer 17a and a gas diffusion layer 17b, and the cathode electrode 18 is composed of a cathode catalyst layer 18a and a gas diffusion layer 18b.

  Separators are arranged on both surfaces of the membrane electrode assembly 14 thus configured to constitute a single fuel cell, and a plurality of single fuel cell cells are stacked to constitute a fuel cell stack.

Next, an embodiment of the present invention will be described with reference to the drawings. 1 is a diagram illustrating a method for forming a catalyst layer of a fuel cell according to a first embodiment.

  As shown in FIG. 1, in the fuel cell catalyst layer forming method of this embodiment, a zeolite-structured carbon particle 1 and platinum-supported normal carbon particles 2 are fed from a nozzle 3 to a solid polymer electrolyte. The catalyst layer 5 is formed by spraying on the surface of the membrane 4. Each of the carbon particles 1 and 2 is prepared as a catalyst ink by being dispersed in the polymer electrolyte solution, and sprayed onto the surface of the solid polymer electrolyte membrane 4 to be applied.

  First, only the zeolite-structured carbon particles 1 carrying platinum on the surface of the solid polymer electrolyte membrane 4 are sprayed from the nozzle 3 to form the first layer 5a. Next, the zeolite-structured carbon particles 1 supporting platinum and the normal carbon particles 2 supporting platinum are simultaneously sprayed from the nozzle 3 on the first layer 5a to form the second layer 5b. Furthermore, the catalyst layer 5 is formed by spraying only the normal carbon particles 2 carrying platinum on the second layer 5b to form the third layer 5c.

  As described above, when the carbon particles 1 having the porous structure and the carbon particles 2 having the non-porous structure are sprayed from the same nozzle 3, a plurality of carbon particles can be controlled and sprayed. And the thickness of the coating layer can be controlled.

  Since the zeolite-structured carbon particles 1 supporting platinum have a porous structure having many pores inside the particles, the surface area is increased and more platinum can be supported. In this example, the carbon particles having a zeolite structure are described as an example. However, carbon particles having other structures can be used as long as the carbon particles have a porous structure capable of supporting more platinum than ordinary carbon particles. It may be.

  Further, the normal carbon particles 2 supporting platinum may be non-porous carbon particles as long as the amount of platinum that can be supported is smaller than that of zeolite structure carbon particles.

  Thus, since the zeolite-structured carbon particles 1 can carry more platinum than the normal carbon particles 2, among the three layers forming the catalyst layer 5, the zeolite-structured carbon particles 1 are formed only of the zeolite-structured carbon particles 1. In addition, the amount of platinum in the first layer 5a is the largest, the amount of platinum in the second layer 5b is then increased, and the amount of platinum in the third layer 5c formed of only normal carbon particles 2 is the smallest.

  For example, the platinum amount of the first layer 5a with a large amount of platinum is 0.3 mg / cm 2, and the platinum amount of the third layer 5c with a small amount of platinum is 0.1 mg / cm 2. Thus, the catalyst layer 5 is formed such that the amount of platinum increases on the side closer to the solid polymer electrolyte membrane 4 and the amount of platinum decreases as the distance from the solid polymer electrolyte membrane 4 increases. Usually, in the catalyst layer 5, the portion of platinum close to the solid polymer electrolyte membrane 4 contributes most to the reaction, and as the distance from the solid polymer electrolyte membrane 4, the platinum does not contribute to the reaction. By increasing the amount of platinum on the side closer to the distance and decreasing the amount of platinum as it goes away, it is possible to reduce the amount of platinum that does not contribute to the reaction and reduce costs.

  In addition, since the carbon particles 1 having a zeolite structure are porous, they have good hydrogen gas permeability and are effective in improving the output of the fuel cell. Furthermore, the effect of improving the bonding force with the solid polymer electrolyte membrane 4 can also be expected.

  Thus, after forming the catalyst layer 5 on one surface of the solid polymer electrolyte membrane 4, the catalyst layer 5 is further formed on the other surface. Then, a gas diffusion layer 6 is formed on the outer side to form a membrane electrode assembly 7 as shown in FIG.

  Thus, in the catalyst layer forming method of the fuel cell of the present embodiment, the catalyst layer 5 is formed by laminating three layers having different platinum amounts. Therefore, the platinum amount of the catalyst layer 5 is a solid polymer. The catalyst layer 5 can be formed so as to increase on the side closer to the electrolyte membrane 4 and decrease with distance from the solid polymer electrolyte membrane 4, thereby reducing the amount of platinum that does not contribute to the reaction and reducing the cost. Can do. Further, since the catalyst layer 5 is formed by the carbon particles 1 having a porous structure, the hydrogen gas permeability is good and the output of the fuel cell can be improved.

  In the fuel cell catalyst layer forming method of the present embodiment, the porous carbon particles 1 and the non-porous carbon particles 2 are sprayed from the same nozzle 3, so that a plurality of carbon particles are It can be controlled and sprayed, and the gradient of platinum amount and the thickness of the coating layer can be controlled.

  Furthermore, the membrane electrode assembly produced by the fuel cell catalyst layer forming method of this example is formed by laminating three layers having different platinum amounts, so that the catalyst layer has a solid platinum amount. It can be formed so as to increase on the side closer to the polymer electrolyte membrane and decrease with distance from the solid polymer electrolyte membrane, thereby reducing the amount of platinum that does not contribute to the reaction and reducing the cost. Furthermore, since the catalyst layer is formed of carbon particles having a porous structure, the hydrogen gas permeability is good and the output of the fuel cell can be improved.

  The fuel cell catalyst layer forming method of the present invention has been described based on the illustrated embodiments. However, the present invention is not limited to this, and the configuration of each part is an arbitrary configuration having the same function. Can be replaced by something.

It is a figure for demonstrating the catalyst layer formation method of the fuel cell which concerns on Example 1 of this invention. 1 is a cross-sectional view showing the structure of a fuel cell produced by a method for forming a catalyst layer of a fuel cell in Example 1. FIG. It is sectional drawing which shows the structure of a membrane electrode assembly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Carbon particle of zeolite structure 2 ... Normal carbon particle 3 ... Nozzle 4, 16 ... Solid polymer electrolyte membrane 5 ... Catalyst layer 5a ... 1st layer 5b ... 2nd layer 5c ... 3rd layer 6 ... Gas diffusion layer 7 , 14 ... Membrane electrode assembly 17 ... Anode electrode 17a ... Anode catalyst layer 17b, 18b ... Gas diffusion layer 18 ... Cathode electrode 18a ... Cathode catalyst layer

Claims (3)

A method for forming a catalyst layer of a fuel cell, comprising forming a catalyst layer on a solid polymer electrolyte membrane of a fuel cell, comprising:
The first layer is formed by spraying porous carbon particles supporting platinum on the surface of the solid polymer electrolyte membrane, and the porous carbon particles supporting platinum and platinum are supported on the first layer. The second layer is formed by simultaneously spraying the nonporous structure carbon particles, and the third layer is formed by spraying the nonporous structure carbon particles supporting platinum on the second layer. A method for forming a catalyst layer for a fuel cell, comprising forming a layer.   The method for forming a catalyst layer of a fuel cell according to claim 1, wherein the porous carbon particles carrying platinum and the non-porous carbon particles carrying platinum are sprayed from the same nozzle. . A membrane electrode assembly in which catalyst layers are formed on both sides of a solid polymer electrolyte membrane,
The catalyst layer includes a first layer formed by spraying carbon particles having a porous structure supporting platinum on the surface of the solid polymer electrolyte membrane, and a porous structure supporting platinum on the first layer. A second layer formed by simultaneously spraying carbon particles of non-porous structure supporting platinum and non-porous structure carbon particles supporting platinum, and spraying carbon particles of non-porous structure supporting platinum on the second layer A membrane electrode assembly, comprising: a third layer formed by:

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