JPH0992303A - Manufacture of solid polymer type fuel cell electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly apply an ion exchange resin solution to a conductive sheet preliminarily subjected to water repellent treatment by use of spin coating to exhibit high water repellency in an electrode, and manufacture a high durable electrode. SOLUTION: A catalyst layer 2 formed of carbon black of conductive powder, platinum of catalyst metal particle, and a water repelling agent is formed on the surface of a carbon sheet subjected to water repellent treatment, and placed on a rotating plate 3. While the rotating plate 3 is rotated at a prescribed speed, an ion exchange resin solution is dropped from a dropping device 6 arranged above the center of the catalyst layer 2, and after the dropping is ended, the rotating plate 3 is rotated at high speed. These application and drying are repeated, whereby the ion exchange resin solution can be uniformly applied to the whole surface of the conductive sheet, and the control of application quantity is also facilitated. Thus, high water repellency in electrode can be exhibited, and the durability of electrode can be also improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polymer electrolyte fuel cell electrode.

[0002]

2. Description of the Related Art In recent years, the importance of environmental and resource measures has been recognized, and there has been a strong demand for prevention of air pollution, in particular, prevention of global warming due to carbon dioxide emission, de-oiling, resource saving and high efficiency of energy supply. Therefore, in order to meet these demands, research is proceeding toward the practical application of fuel cells. Fuel cells have high power generation efficiency of 40 to 60%, and overall efficiency reaches 80% by recovering exhaust heat. It is desirable from the standpoint of resources such as natural gas, hydrogen, methanol, LPG, coal gasification gas, and environment. Be selectable,
Since it has advantages such as almost no pollution factor due to noise and exhaust gas, it is expected to be a new energy with less resource constraints and environmental load.

Fuel cells are classified into phosphoric acid type, molten carbonate type, solid electrolyte type, solid polymer type and the like according to the type of electrolyte. Among them, the polymer electrolyte fuel cell has a higher power density of 3 kW / m ² than other types, so it can be made smaller and lighter, and the electrolyte is a polymer ion exchange membrane (ion exchange resin membrane) at a low temperature (60 to 100 ° C.). ) Because it can be started quickly due to operation, it can be applied to portable and mobile power sources.

The polymer electrolyte fuel cell has a structure in which an ion exchange resin membrane as a solid electrolyte is sandwiched between a pair of electrodes and two electrodes are connected via a load. The principle of this polymer electrolyte fuel cell is to utilize the reverse reaction of electrolysis of water, and hydrogen (fuel) and the other (cathode) on one side (cathode side) of electrodes sandwiching an ion exchange resin membrane as a solid electrolyte. Hydrogen (fuel) is supplied by sending oxygen (air, oxidizer) to the (anode side) and connecting the two electrodes through a load.
It reacts with oxygen (air, oxidizer) to obtain water and electric energy. This reaction is called an electrochemical reaction.Hydrogen is ionized at the cathode, the ions move through the ion exchange resin membrane to the anode, and oxygen reacts with hydrogen ions at the anode and is released at the cathode. The electrons that have been moved through the external circuit are received to generate water.

An electrode of such a polymer electrolyte fuel cell is generally a porous conductive base material sheet such as a carbon sheet, and a conductive powder such as carbon powder formed on the surface of the base material sheet. It is composed of platinum as catalyst metal particles, polytetrafluoroethylene (PTFE) as a water repellent, and a porous catalyst layer made of an ion exchange resin. The platinum contained in the catalyst layer is for promoting the electrochemical reaction. In addition, the ion exchange resin contained in the catalyst layer is integrally bonded to the ion exchange resin membrane as the solid electrolyte sandwiched between the electrodes to improve the polarization characteristics by making the electrode reaction site three-dimensional. It is for making it. In addition, the water repellent contained in the catalyst layer improves the air permeability in the catalyst layer and promotes the contact between the conductive powder and a gas such as hydrogen or oxygen, and the electrode is soaked in water to inhibit gas diffusion. By preventing
This is for improving the durability as an electrode.

The electrode of the above-mentioned conventional polymer electrolyte fuel cell is prepared, for example, by mixing carbon powder carrying platinum with a solvent solution of an ion exchange resin, and further by adding PTF as a water repellent agent.
E is added in the form of an aqueous suspension, the resulting mixture is kneaded to form a paste, and the paste is uniformly applied to the surface of a porous conductive substrate sheet such as a carbon sheet, and then dried. It can be manufactured by forming a catalyst layer on the surface of the substrate sheet.

[0007]

By the way, a water repellent such as PTFE is heated to about 350 to 380 ° C. to be melted,
High water repellency can be exhibited by making the granular structure into a chain structure by subsequent cooling and solidification. However, in the above-mentioned conventional method for manufacturing a polymer electrolyte fuel cell electrode in which PTFE as a water repellent is mixed in the paste for forming the catalyst layer, the above heat treatment for imparting high water repellency may be performed. Can not. That is, since the ion exchange resin component in the catalyst layer is thermally decomposed at a temperature of about 330 ° C., it cannot be heat-treated at about 350 ° C. or higher in order to impart high water repellency. Therefore, the electrode obtained by the above-mentioned conventional method cannot exhibit high water repellency, the reaction product water or the like wets the electrode, and gas diffusion is hindered, thus improving durability as an electrode. I can't.

Therefore, it is conceivable to apply an ion exchange resin solution to a conductive sheet which has been subjected to a water repellent treatment in advance. However, the ion exchange resin solution may be sprayed onto the surface of the conductive sheet or may be applied to the ion exchange resin solution. It is difficult to uniformly apply the ion exchange resin solution by the method of dipping the conductive sheet. The present invention has been made in view of the above circumstances, and a solid polymer capable of uniformly applying an ion exchange resin solution to a conductive sheet and exhibiting high water repellency to improve durability. It is a technical problem to be solved to provide a method for manufacturing a fuel cell electrode for a fuel cell.

[0009]

A method for producing a polymer electrolyte fuel cell electrode according to the present invention, which solves the above-mentioned problems, comprises a conductive material which contains a conductive component, catalytic metal particles and a water repellent agent and which has been subjected to a water repellent treatment. Spin coating treatment step of permeating the ion exchange resin into the conductive sheet by dropping a solution of the ion exchange resin as a solid polymer electrolyte on the surface near the center of the conductive sheet while rotating the conductive sheet. It is characterized by carrying out.

In the method of the present invention, a porous conductive sheet containing a conductive component, catalytic metal particles and a water repellent agent is subjected to a water repellent treatment in advance, and a spin coating method is applied to the water repellent treated conductive sheet. Then, since the solution of the ion exchange resin is permeated, sufficiently high water repellency can be exhibited. Further, by using the spin coating method, the ion exchange resin solution can be uniformly and thinly applied to the surface of the conductive sheet, and the ion exchange resin solution can be impregnated into the conductive sheet.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method for producing a polymer electrolyte fuel cell electrode of the present invention will be described below. (Water repellent treatment step) In the water repellent treatment step, a porous conductive sheet containing a conductive component, catalytic metal particles and a water repellent agent is subjected to a water repellent treatment.

This water repellent treatment is carried out by heating to an appropriate temperature depending on the type of water repellent used. For example,
Polytetrafluoroethylene (PTFE) as water repellent
When used, it is heated to about 350 to 380 ° C. As the conductive sheet, a sheet such as a carbon sheet or a carbon cloth foamed nickel paper on which platinum as a catalytic metal particle is supported, and a water repellent such as PTFE is impregnated and dried can be used. Further, as the conductive sheet, it is preferable to use one in which the concentration of the catalytic metal particles on one surface side is higher than that on the opposite surface side. When manufactured as a polymer electrolyte fuel cell, the concentration of catalytic metal particles on the surface side in contact with an ion exchange resin membrane as a polymer electrolyte sandwiched between a pair of electrodes is increased to improve electrochemical reactivity. Is to improve. For example, a porous conductive base material sheet containing a conductive component and a water repellent agent, and a porous catalyst layer formed on the surface of the base material sheet and containing conductive powder, catalytic metal particles and a water repellent agent. A conductive sheet composed of can be mentioned as a preferred embodiment. Note that it is also possible to use a single-layer conductive sheet having the above-described concentration gradient.

The electroconductive sheet comprising the electroconductive substrate sheet and the catalyst layer can be manufactured and treated for water repellency, for example, as follows. First, the carbon sheet is immersed in PTFE dispersion (PTFE dispersed in water at a ratio of about 30 to 60 wt%) for about 20 to 30 seconds,
Then, it is dried at 80 ° C. for 30 minutes. And 35
By heating at a temperature of about 0 to 380 ° C. for about 5 to 30 minutes, a water repellent carbon sheet (conductive substrate sheet) is obtained. On the other hand, platinum is added to carbon black at 10 to 40 wt%
Supported and PTFE dispersion (PTFE
Dispersed in water at a ratio of about 30 to 60 wt%)
Are mixed and dried under the condition of 80 ° C. × 48 hours to obtain a mixed powder of carbon black and PTFE. An ethanol solvent such as Serna SE604 (trade name, manufactured by Chukyo Yushi Co., Ltd.) is mixed with this mixed powder and kneaded to obtain a paste. The obtained paste is uniformly applied to the surface of the above-mentioned water repellent carbon sheet by a doctor blade method or the like, and is applied in vacuum 1
By drying under the condition of time, a porous catalyst layer composed of conductive powder, catalytic metal particles and a water repellent is formed on the surface of the carbon sheet. Then, the catalyst layer is subjected to water repellent treatment by heating at a temperature of about 350 to 380 ° C. for about 5 to 30 minutes.

The carbon sheet is dipped in PTFE dispersion, and the paste of carbon black, PTFE and ethanol solvent is uniformly applied to the surface of the dried carbon sheet, which is then dried 3
The carbon sheet and the catalyst layer may be simultaneously subjected to water repellent treatment by heating at a temperature of about 50 to 380 ° C. Also,
The platinum as the catalytic metal particles can be supported after forming the catalyst layer on the carbon sheet.

The thickness of the carbon sheet and the catalyst layer is
Although not particularly limited, the thickness of the carbon sheet as the conductive substrate sheet may be about 90 to 360 μm, and the thickness of the catalyst layer may be about 5 to 20 μm. (Spin coating process) In the spin coating process,
By rotating a conductive sheet that has been subjected to water repellent treatment as described above, by dropping a solution of an ion exchange resin as a solid polymer electrolyte on the surface near the center of the conductive sheet,
An ion exchange resin is impregnated into the conductive sheet.

The type of ion exchange resin is not particularly limited, but when it is produced as a polymer electrolyte fuel cell,
It is preferable to use the same kind of ion exchange resin as the ion exchange resin membrane as the solid electrolyte sandwiched between the pair of electrodes. For example, Aciplex (ss-910) (manufactured by Asahi Kasei Corp., trade name), an ion exchange resin solution such as a Nafion solution can be used. These ion exchange resin solutions are used after being appropriately diluted with ethanol, isopropyl alcohol, or the like.

The spin coating treatment conditions are not particularly limited, but the ion exchange resin solution dropped on the surface near the center of the rotating conductive sheet is instantaneously centrifuged by the peripheral force of the conductive sheet. It is preferable that the rotation speed is such that it spreads over and the excess ion-exchange resin solution is scattered around. If the rotation speed is too slow, it becomes difficult to uniformly apply the ion exchange resin solution to the entire surface of the conductive sheet, and the amount of the ion exchange resin that permeates the conductive sheet becomes excessive, which is not preferable. Since the ion exchange resin is an electric resistance component, an excessive amount of the ion exchange resin causes a decrease in battery performance.

Specifically, the rotation speed is preferably such that about 50 to 90 wt% of the dropped ion exchange resin solution is scattered around. More specifically, the rotation speed when dropping the ion exchange resin solution is 300 to 1000 rpm.
And the rotation speed after dropping the ion exchange resin solution is 5
It is preferable to set it to about 00 to 3000 rpm. In this way, the rotation speed at the time of dropping the ion-exchange resin solution and the rotation speed after dropping are changed because if the rotation speed is too fast at the time of dropping, the liquid is repelled by the conductive sheet and does not spread well. This is because. The rotation time after dropping the ion exchange resin solution can be about 2 to 10 seconds.

From the viewpoint of coating the ion exchange resin solution more uniformly on the entire surface of the conductive sheet and further reducing the permeation thickness of the ion exchange resin into the conductive sheet to reduce the electrical resistance, the spin is performed. It is preferable that the coating treatment be repeated, and that a solution having a low concentration of the ion exchange resin be first applied and dried, and then a solution having a high concentration of the ion exchange resin be repeatedly applied and dried. This is because if the solution having a high concentration of the ion exchange resin is first applied suddenly, the solution does not spread well over the entire surface of the conductive sheet. Specifically, an ethanol solution having a concentration of the ion exchange resin of 0.5 to 1 wt% is applied by the first spin coating treatment, dried at about 50 to 80 ° C. for about 20 to 30 minutes, and then the ion exchange resin is dried. Concentration is 2-3 wt%
Of ethanol solution, and 2 at 50-80 ℃
It is preferable to repeat drying for about 0 to 30 minutes 4 to 5 times.

Further, when the polymer electrolyte fuel cell is manufactured, the concentration of the ion exchange resin on the surface side in contact with the ion exchange resin membrane as the solid polymer electrolyte sandwiched between the pair of electrodes is high. preferable. When manufactured as a polymer electrolyte fuel cell, the larger the bonding area between the ion exchange resin membrane as the solid polymer electrolyte and the ion exchange resin in the electrode, the better the polarization characteristics due to the three-dimensionalization of the electrode reaction site. This is because From such a viewpoint, as the conductive sheet, a porous conductive base material sheet containing a conductive component and a water repellent, and a conductive powder, catalytic metal particles and water repellent formed on the surface of the base material sheet. Which is composed of a porous catalyst layer containing an agent, is uniformly coated with a paste of carbon black, PTFE and an ethanol-based solvent on the surface of a conductive base material sheet, and after drying, 350
It is preferable to use a conductive sheet having a two-layer structure obtained by heating at a temperature of about 380 ° C. According to such a manufacturing method, it is possible to obtain a structure in which the catalyst layer has a denser structure than that of the base material sheet. If the surface of the catalyst layer is coated with an ion exchange resin solution, ion exchange is performed. This is because the resin solution can be prevented from penetrating into the base material sheet side.

As described above, in this embodiment, since the ion-exchange resin solution is permeated into the water-repellent conductive sheet by the spin coating method, high water repellency of the electrode is ensured and the durability of the electrode is improved. be able to. Moreover, since the spin coating method is used, the ion exchange resin solution can be uniformly applied to the entire surface of the conductive sheet, and the amount of application can be easily controlled. Furthermore, by appropriately diluting the ion exchange resin solution and performing spin coating in several times, the ion exchange resin component can be evenly applied to the entire surface of the conductive sheet, and the ion exchange into the conductive sheet is performed. The permeation thickness of the resin can be made thinner to suppress an increase in electric resistance due to the ion exchange resin component.

[0022]

EXAMPLES Hereinafter, the method for producing a polymer electrolyte fuel cell electrode of the present invention will be specifically described with reference to examples. A carbon sheet (trade name: trading card, manufactured by Toray Industries, Inc.) having a film thickness of 180 μm and 12 cm × 12 cm is dipped in a PTFE dispersion (PTFE dispersed in water at a ratio of 30 wt%) for about 30 seconds, and then 80 ° C. × It was dried under the condition of 30 minutes. Then, the carbon sheet (conductive base material sheet) which has been subjected to water repellent treatment by heating at a temperature of 380 ° C. for 30 minutes
1 was obtained.

On the other hand, 20 wt% of platinum is added to carbon black.
% Supported 8.9 g, PTFE dispersion (PTFE dispersed in water at a ratio of 60 wt%)
5.1 g was mixed and dried at 80 ° C. for 48 hours to obtain a mixed powder of carbon black and PTFE. Serna SE604 (made by Chukyo Yushi Co., Ltd., trade name)
90 g of the above ethanol-based solvent was mixed and kneaded to obtain a paste. The obtained paste was uniformly applied to the surface of the water-repellent treated carbon sheet 1 by a doctor blade method, and dried under vacuum for 1 hour to obtain carbon black as conductive powder and catalyst metal particles. A porous catalyst layer 2 made of platinum and PTFE as a water repellent was formed on the surface of the carbon sheet 1. And 3
The catalyst layer 2 was subjected to water repellent treatment by heating at a temperature of about 80 ° C. for 30 minutes. The thickness of the catalyst layer 2 is 10 μm.

As the ion exchange resin solution, Aci
Plex (ss-910) (manufactured by Asahi Kasei Corp., trade name, ion exchange resin component 5 wt%, ethanol 47.5 wt%,
Water (47.5 wt%) diluted with ethanol 8 times and Aciplex (ss-910) diluted 2 times were prepared. The carbon sheet 1 having the catalyst layer 2 formed thereon was placed on the rotary plate 3 so that the catalyst layer 2 was on the upper surface. The rotary plate 3 is connected to a rotation drive device (not shown) having a rotation speed control function and is rotatable at a predetermined rotation speed. A curtain 4 is disposed around the rotary plate 3 to prevent the dropped ion-exchange resin solution from scattering around, and the ion-exchange resin solution hitting the curtain 4 is located below the rotary plate 3. It is designed to be collected in the collecting container 5 installed in the.

Then, while rotating the rotary plate 3 at a rotation speed of 400 rpm, the Aciplex (ss-910) from the dropping device 6 arranged above the central position of the catalyst layer 2 is rotated.
5 times what was diluted with 8 times was dripped. After dropping,
The rotary plate 3 was rotated at a rotation speed of 1000 rpm for 5 seconds. Then, it dried at 80 degreeC for 30 minutes. Next, the rotating plate 3
While rotating the catalyst at a rotation speed of 400 rpm, the catalyst layer 2
From the dropping device 6 arranged above the central position of the
5 ml of double diluted lex (ss-910)
It was dropped. After the dropping was completed, the rotary plate 3 was rotated at a rotation speed of 1000 rpm for 5 seconds. Then, it dried at 80 degreeC for 30 minutes. And this Aciplex (ss-910)
Was diluted two times, and coating and drying were repeated 5 times in total.

Solid polymer fuel thus obtained
The battery electrode consists of an ion exchange resin impregnated in the catalyst layer 2.
Minute (solid content) 144 cm²64-67m for all electrodes
It became g. This is Aciplex (ss-910)
Undiluted solution of 0.01 ml / cm ²When applied at a ratio of
Which is included in the catalyst layer 2 of the polymer electrolyte fuel cell.
The amount is suitable as an on-exchange resin component.

A solid polymer fuel cell was produced from the obtained solid polymer fuel cell electrode by a conventional method, and hydrogen,
When the discharge characteristics were examined by performing a single cell test under the condition of 1 ata (normal pressure) for both air, it was 0.3 in the case of the conventional electrode.
In contrast to W / cm ² (0.75 A / cm ² hour), the electrode of this example has 0.38 W / cm ² (0.75 A / c ² ).
m ² o'clock), and may improve significantly discharge characteristics were confirmed.

The ion exchange resin solution recovered by the curtain 4 in the recovery container 5 can be reused.

[0029]

As described above in detail, in the method for producing a polymer electrolyte fuel cell electrode according to the present invention, the ion-exchange resin is impregnated into a conductive sheet which has been subjected to a water-repellent treatment by a spin coating method. Therefore, high water repellency in the electrode can be exhibited, and an electrode with high durability can be manufactured. Further, by using the spin coating method, the solution of the ion exchange resin can be uniformly and thinly applied to the surface of the conductive sheet, and the application amount can be easily controlled.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically illustrating a method for manufacturing a polymer electrolyte fuel cell electrode according to this embodiment.

[Explanation of symbols]

In the figure, 1 is a carbon sheet as a conductive substrate sheet,
2 is a catalyst layer, 3 is a rotating plate, 4 is a curtain, 5 is a collection container, and 6 is a dropping device.

Claims (1)

[Claims] 1. A solid polymer electrolyte as a solid polymer electrolyte on the surface near the center of the conductive sheet while rotating a water-repellent porous conductive sheet containing a conductive component, catalytic metal particles and a water repellent agent. A method for producing a polymer electrolyte fuel cell electrode, which comprises performing a spin coating treatment step of infiltrating the ion exchange resin into the conductive sheet by dropping the solution of the ion exchange resin.