JPH0729576A - Manufacture of electrode for fuel cell - Google Patents

Abstract

PURPOSE:To enhance the performance of the fuel cell comprising an electrode composed of a reactive layer and a gas supply layer, by providing a state of bond therebetween in which the both layers are partially permeated one into the other, unlike a conventional state of bond therebetween in which a line of bond is in the form of a straight line, and thereby uniformly supplying a gas into the catalyst in the reactive layer through the gas supply layer. CONSTITUTION:Catalyst, ion-conductive polymer solution, and water are mixed with each other to prepare a paste. When coating this paste onto a porous sheet fixed within a predetermined reactive-paste coating frame, this coating is performed while suction is being conducted from a rear-face side of the porous sheet. As a result, a state wherein the paste has been permeated into the porous sheet is obtained. Thereafter, the paste is desiccated and hardened, whereupon there is produced an electrode 1 wherein a reactive layer 2 consisting of the paste material and a gas supply layer 3 consisting of the porous sheet are bonded together in such a manner as to partially permeate one into the other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a fuel cell electrode, and more particularly to a method for manufacturing a fuel cell electrode by a coating method.

[0002]

2. Description of the Related Art In a fuel cell, a gas supply layer made of a porous material such as a carbon sheet is provided outside a reaction layer containing a catalyst so that the gas (hydrogen or oxygen) is uniformly diffused in the reaction layer. In order to improve the efficiency of the battery reaction by supplying it.

As a method for joining the reaction layer to the gas supply layer, a method in which pressure is applied from both sides is generally adopted. However, in the case of pressure contact, it was difficult to uniformly press the joint surface. Further, there is a drawback that the gas introduction path in the reaction layer is destroyed by the high pressure during the pressure contact, and the gas supply to the reaction layer is hindered.

In order to eliminate these drawbacks, JP-A-4-3
Japanese Patent No. 29264 proposes a method in which a paste containing mixed components forming a reaction layer is applied onto a gas supply layer, and the mixture is fired at a high temperature to join them.

[0005]

However, the reaction layer and the gas supply layer are divided into two parts in an orderly manner, regardless of whether they are joined by the pressure welding method or the firing method (FIG. 4).
It is difficult to supply gas evenly to all the catalysts in the reaction layer. That is, the activity of the catalyst located at a position away from the gas supply layer is reduced.

[0006]

DISCLOSURE OF THE INVENTION According to the present invention, in obtaining an electrode composed of a reaction layer and a gas supply layer, the bonding state between these layers is made good, and the gas supplied through the gas supply layer is supplied to the reaction layer. The purpose of the present invention is to disperse the catalyst evenly in almost all the catalysts therein, and to eliminate the bias of the activity of the catalysts in the reaction layer.

To achieve this object, the present invention employs a method for manufacturing a fuel cell electrode by a coating method. It has been conventionally proposed to manufacture a fuel cell or an electrode therefor by a coating method. For example, Japanese Patent Laid-Open No. 5-290
Japanese Patent Publication No. 05 discloses that an electrode-catalyst paste is applied by screen printing onto an electrolyte plate made of an ion-conductive polymer or the like to produce an electrode-electrolyte assembly. However, if the coating method is simply applied when the reaction layer is joined to the gas supply layer, then these layers become a structure in which these layers are properly divided into two, and the problem cannot be solved.

Therefore, the present invention adopts the coating method as a method for bonding the reaction layer to the gas supply layer, and at the time of coating, the reaction layer paste is gas-supplied by sucking from the side opposite to the bonding surface. It was completed by recalling that it was infiltrated into the layers.

That is, in the method for producing a fuel cell electrode according to the present invention, when a reaction layer made of a paste prepared by containing at least a catalyst, a solvent and water is formed on the gas supply layer, the reaction layer is applied from the back side of the gas supply layer. It is characterized in that the paste is permeated into the gas supply layer by forming it while sucking.

The depth of penetration of the paste into the gas supply layer is controlled by adjusting the pore size and suction strength of the gas supply layer.

The paste for coating can be prepared by using as a binder a solution of the same ion conductive polymer that constitutes the electrolyte of the fuel cell. The alcohol solvent content in the ion conductive polymer solution can be removed by a drying step after coating.

[0012] Preferably, the paste is heated and dried before the paste is applied to remove an arbitrary amount of the alcohol solvent content in the paste, and the paste is adjusted to have a viscosity suitable for application.

[0013]

When the paste for forming the reaction layer is applied to the porous sheet on which the gas supply layer is to be formed, the paste is applied while sucking from the side opposite to the application surface of the porous sheet. A state in which the porous sheet is at least partially penetrated is obtained.

[0014]

Example: Carbon black supporting a catalyst (Pt),
The ion conductive polymer (Nafion-registered trademark) solution and water were mixed at a ratio of 1: 13.3: 4.0, ultrasonically stirred for 15 minutes, and then maintained at 65 ° C for 1 hour under heating conditions to adjust the viscosity. Then, a coating paste is prepared.

This coating paste is applied onto a water-repellent sheet-like porous body (carbon sheet, metal foam, etc.) fixed in a coating frame, with the back surface of the porous sheet at that time. Apply while sucking from the side. This allows
The applied paste penetrates well into the porous sheet. The penetration depth of the paste into the porous body is controlled by adjusting the pore size and suction strength of the porous body.

After the application is completed while sucking, the coating is dried at room temperature for about 1 hour to dry and remove the alcohol solvent in the Nafion solution, and the reaction layer formed by the printing paste is placed on the gas supply layer made of a porous sheet. To be laminated. As described above, since the coating paste is dried and solidified in a state of being permeated into the porous sheet, in the electrode 1 thus obtained, the reaction layer 2 partially joins the gas supply layer 3 and is bonded. The state is obtained (Fig. 1). As is apparent from this joined state, the substantial thickness of the reaction layer 2 can be reduced without reducing the amount of catalyst supported in the reaction layer 2, and the size can be reduced. Further, since the reaction layer 2 has a structure in which it is entangled with the gas supply layer 3, the bonding surface area of these is increased as compared with the bonding between flat surfaces, and the resistance value of the electrode is reduced.

As described above, two electrodes having the same structure were prepared, and an ion conductive polymer (Nafion) 4 serving as an electrolyte was sandwiched between these electrodes 1 and 1 and hot pressed (10).
0 kg / cm ² , 130 ° C., 90 seconds),
A unit cell 5 composed of an electrode, an electrolyte and an electrode is manufactured (FIG. 2).

FIG. 3 is a comparison diagram of the battery voltage (V) -current density (A / cm ² ) curves in the unit cells according to the present invention and the prior art. From this comparative diagram, it can be seen that the current density of the electrodes of the unit cell according to the present invention is significantly improved as compared with the conventional unit cell in which the reaction layer and the gas supply layer in the electrode are joined by hot pressing. I understand.

In the coating paste, a solution of Nafion having the same composition as the ion conductive polymer used in the electrolyte is used as the binder of the catalyst. This means that in the fuel cell manufactured by using the electrode of the present invention, the ion conductive polymer is present not only in the electrolyte but also in the electrodes in contact with both sides of the ion conductive polymer, thereby improving the cell performance and coating paste. It is possible to simplify the drying process of.

That is, in the coating paste of the present invention, a solvent having a low boiling point and a high volatility (mainly alcohol) is used as a solvent for the resin, and ethylene glycol, which has been conventionally used for adjusting the viscosity of the coating paste, is used. Does not contain solvents such as glycerin.

The prepared coating paste is, for example, 65
The paste is dried under the condition of 1 ° C. for 1 hour, whereby a part of the alcohol in the resin solution of the ion conductive polymer is removed by drying, and the paste has a predetermined viscosity. The viscosity of the paste can be freely adjusted by changing the drying treatment conditions at this time, and the paste viscosity suitable for application (for example, 5 to 5).
2,000 poise).

The paste thus obtained is applied to the porous sheet while being sucked by a pressure reducing means such as an aspirator or a rotary pump, and the obtained electrode is left at room temperature for about 1 hour. By performing such room temperature drying, the alcohol remaining in the ion conductive polymer solution can be completely removed. Therefore, the problem of deterioration of the electrode performance due to the solvent content in the coating paste remaining in the electrode does not occur in the present invention.

The ionic conductive polymer used for the electrolyte is generally weak to heat, and its decomposition temperature is around 150 ° C., but actually, it is thermally deteriorated by heating and drying at around 130 ° C. to deteriorate the ionic conductivity. However, in the present invention, a drying treatment temperature of about 65 ° C. for adjusting the paste viscosity is sufficient, and the paste solidification after obtaining the electrode can be carried out at room temperature. There is no thermal deterioration and the desired battery performance is not impaired.

[0024]

According to the present invention, the gas is evenly supplied to the catalyst in the reaction layer through the gas supply layer to activate the catalyst, so that the performance of the electrode is improved in both the fuel electrode and the air electrode. Is greatly improved.

On the other hand, since the thickness of the reaction layer is thin, it is not necessary to add a water repellent agent to the reaction paste, and the electrode performance is improved.

Further, although the present invention manufactures an electrode by a coating method, since the same ion conductive polymer as that used in the electrolyte is used as a binder in the coating paste, the ion conductive property of the entire battery is improved. In addition, since the solvent does not contain a solvent such as ethylene glycol or glycerin, the solvent performance does not deteriorate due to the solvent remaining in the electrode.

Further, since the paste containing neither solvent nor water repellent is used, the paste can be dried at room temperature, and thermal deterioration of the ion conductive polymer can be avoided.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a bonded state of a reaction layer and a gas supply layer in an electrode manufactured according to the present invention.

FIG. 2 is a schematic diagram showing a unit cell manufactured using the electrode of FIG.

FIG. 3 is a diagram showing the performance of the unit cell of FIG. 2 in comparison with a conventional example.

FIG. 4 is a schematic view showing a joined state of a reaction layer and a gas supply layer in an electrode according to a conventional example.

[Explanation of symbols]

 1 Electrode 2 Reaction Layer 3 Gas Supply Layer 4 Ion Conductive Polymer 5 Single Cell

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirohiko Ozeki 10 Takane, Fujii-cho, Anjo City, Aichi Prefecture Aisin AW Co., Ltd. (72) Masataka Ueno 10 Takane, Fujii-cho, Anjo City, Aichi Prefecture Aisin・ AW Co., Ltd.

Claims (4)

[Claims] 1. When forming a reaction layer composed of a paste prepared by containing at least a catalyst, a solvent and water on a gas supply layer, the paste is formed by sucking from the back side of the gas supply layer. A method of manufacturing an electrode for a fuel cell, which is characterized in that the gas supply layer is permeated. 2. The paste is prepared by using the same ion conductive polymer solution as a binder to form an electrolyte of a fuel cell, and the alcohol solvent component in the ion conductive polymer solution is removed by drying in the drying step. The method for manufacturing an electrode for a fuel cell according to claim 1, wherein 3. The method for producing a fuel cell electrode according to claim 2, wherein the drying step is performed at room temperature. 4. The viscosity of the paste is adjusted by heating and drying the paste before forming a reaction layer of the paste to remove an arbitrary amount of the alcohol solvent in the paste. Alternatively, the method of manufacturing an electrode for a fuel cell according to 3).