JPH0697612B2 - Method for manufacturing fuel cell electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an electrode used in a solid polymer electrolyte type (SPE type) fuel cell.

[Conventional technology]

Although fuel cells are classified according to the type of electrolyte, fuel cells in which the electrolyte consists of solid polymer such as cation exchange membrane or anion exchange membrane are called solid polymer electrolyte type (SPE type: Solid Polymer Electolyte). Are distinguished from other fuel cells.

The electrode manufacturing method used in this SPE fuel cell includes
A method in which carbon powder and catalyst powder are mixed with polytetrafluoroethylene that functions as a binder and a water repellent and hot pressed together with a solid polymer electrolyte, and a catalyst metal is formed on the surface of the ion exchange membrane that becomes the solid polymer electrolyte by a chemical plating method. The method of precipitating is known, but in the latter case, the former hot pressing method is predominant because it is difficult to bond additional components such as carbon or oxide.

[Problems to be Solved by the Invention]

However, the electrode manufactured by the hot pressing method using the three components of carbon powder, platinum catalyst and polytetrafluoroethylene as raw materials has a problem that the porosity is low and the pore diameter is not constant. For this reason, there is a disadvantage in terms of efficiency and compactness, because pressure loss is large as an electrode material and it is necessary to separately form a gas flow path.

Therefore, an object of the present invention is to provide a method for producing a sheet-like SPE fuel cell electrode having carbon powder, a platinum catalyst and polytetrafluoroethylene as main components and having excellent porosity and a uniform pore size. There is a place to do it.

[Means for Solving the Problems]

The method for producing an electrode for a fuel cell according to the present invention to achieve the above object is a silicon carbide whisker having a surface coated with a carbon film on a component system consisting of carbon powder, a platinum catalyst and polytetrafluoroethylene (PTFE). Is added and kneaded, and the kneaded product is formed into a sheet, which is then heat-treated and ion-exchange resin treated.

As the carbon powder, conductive carbon black having a large specific surface area and a well-developed structure is preferably used. As the platinum catalyst, platinum black having a particle size of 0.5 to 1.0 μm is used. Polytetrafluoroethylene (PTFE) is a component that functions as a binder and a water repellent, and in the present invention, it can be used as a pore forming agent. Therefore, it is a desirable mode to selectively use polytetrafluoroethylene having a property of forming fibers by applying a shearing force. Examples of the polytetrafluoroethylene that can be made into fibers include Du Pont Mitsui Fluorochemical Co., Ltd.
Examples thereof include "Teflon K-10J" manufactured by Daikin Industries, Ltd., "Polyflon F-103" and "F-202" manufactured by Daikin Industries, Ltd.

Silicon carbide whiskers coated with a carbon film on the surface added to these component systems are silicon carbide whiskers such as phenol resin, high carbon resin resin such as furan resin, or a solution of pitch dissolved in an organic solvent. It can be formed by subjecting it to a dispersion in, for example, filtration, drying, and baking treatment in an inert atmosphere at a temperature range of about 1800 ° C.

The silicon carbide whiskers used should be as uniform in diameter and aspect ratio as possible.
It is preferable to select a property range of 0.3 to 0.6 μm and a length of 30 to 60 μm. The amount of silicon carbide whiskers coated with a carbon film on the surface is 100 to 300 with respect to the amounts of carbon powder, platinum catalyst and polytetrafluoroethylene.
It is desirable to set the content in the range of weight%, and if it is out of this range, the effect of improving the porosity decreases.

The above raw material components are put into a kneading device such as a kneader and kneaded while giving a sufficient shearing force. At this time, liquid paraffin, liquid polyethylene glycol or the like can be added as a kneading aid.

The kneaded product can be formed into a sheet by using a sheet forming means such as an ordinary papermaking method or a doctor blade method.

The formed sheet is then heat treated in an inert gas stream at a temperature of around 340 ° C. and pressed if necessary. This sheet is finally treated with an ion exchange resin. The ion exchange resin treatment is carried out by impregnating the sheet with a mixed solvent solution (Nafion solution) of styrene-divinylbenzenesulfonic acid powder, a lower aliphatic alcohol of perfluorocarbon sulfonic acid, and the like and water.

[Action]

The fine fibrous silicon carbide whiskers added as a raw material component in the present invention function to form pores in the tissue,
The carbon film of the surface layer contributes to improving the performance of the electrode. In particular, when fibrous polytetrafluoroethylene is used, this promotes the formation of pores by the above-mentioned silicon carbide whiskers by forming fibers by the shearing force in the kneading process, and strengthens the porous structure by the mutual entanglement phenomenon. Exert the action. Further, when the polytetrafluoroethylene is made into fibers, carbon black adheres to the surface of the fibers to form a net, which also serves to increase conductivity.

Through these synergistic effects, a highly functional sheet electrode having excellent porosity and uniform particle size is formed.

Further, the obtained sheet has appropriate flexibility, which is advantageous in terms of cell assembly.

〔Example〕

 Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 6 (1) 50 g of silicon carbide whiskers having a diameter of 0.3 to 0.6 μm and a length of 30 to 60 μm were mixed with a phenol resin [manufactured by Gunei Chemical Co., Ltd.,
The mixture was added to 500 ml of an ethanol solution of "PGA-4508", sufficiently stirred and dispersed, filtered, and dried at 100 to 150 ° C for 2 hours. Then, this was baked in an argon gas stream for 30 minutes to carbonize the resin component and form a carbon film on the surface.

The changing conditions of each example are as shown in Table 1.

(2) 25 g of silicon carbide whiskers coated with a carbon film on the above-mentioned surface was used as conductive carbon black [Tokai Carbon Co., Ltd., "Toker Black"] 8.0 g, particle size 0.5 to 1.0 μ.
2.5 g of m of platinum black and 2.0 g of polytetrafluoroethylene [manufactured by Daikin Industries, Ltd., "Polyflon F-104"] were added to 100 ml of ethanol, and the mixture was kept for 5 minutes while applying ultrasonic waves to uniformly mix them. The mixture was put into a small kneader, and 25 g of liquid paraffin and liquid polyethylene glycol were added as auxiliary agents and kneaded. At this stage, polytetrafluoroethylene was made into fibers.

The auxiliary agent was once extracted and removed with toluene, disassembled with a Carter mixer, and again thoroughly dispersed in 200 ml of ethanol by ultrasonic waves. Then, the dispersion was paper-made using a 35 μm nylon net to form a sheet. This sheet is 50-80
After drying at ℃, it was heat-treated for about 1 hour in a temperature range of 330 to 350 ℃ in an argon stream, and further pressed to form a sheet having a length and width of 100 mm and a thickness of 0.15 mm.

This sheet was immersed in a 5% aqueous solution of perfluorocarbon sulfonic acid containing a lower aliphatic alcohol and dried at a temperature of 100 ° C. or lower to produce an electrode for SPE fuel cell.

The characteristics and cell performance of each electrode thus obtained are shown in Table 2.

Comparative Examples 1 and 2 Two kinds of SPE-type fuels were prepared by using the same conductive carbon black (25.0 g), platinum black powder (2.5 g) and polytetrafluoroethylene (6.2 g) as component systems, and the subsequent steps were the same as those of the examples. A battery electrode was created.

The characteristics and cell performance of this electrode are also shown in Table 2.

[Effects of the Invention] According to the present invention, a sheet-like solid polymer electrolyte type (SPE type) fuel cell electrode having a high porosity and a uniform pore size, high strength and moderate flexibility can be easily produced. It becomes possible to do. Therefore, since the gas diffusivity is systematically excellent, a high degree of battery efficiency can be obtained without providing a gas flow path.

Claims (2)

[Claims] 1. A silicon carbide whisker having a surface coated with a carbon film is added to a component system composed of carbon powder, a platinum catalyst and polytetrafluoroethylene (PTFE) and kneaded.
A method for producing an electrode for a fuel cell, which comprises heat-treating the kneaded material into a sheet, and then subjecting it to heat treatment and ion exchange resin treatment. 2. The method for producing an electrode for a fuel cell according to claim 1, wherein polytetrafluoroethylene having a property of being made into fibers by applying a shearing force is used.