JPH0766809B2 - Raw material powder for gas diffusion electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is used in fuel cells, secondary batteries, electrochemical reactors, anodes for plating, etc., and reacts at the three-phase interface of gas, electrolyte, and catalyst. The present invention relates to a raw material powder that is a raw material of a gas diffusion electrode that causes a phenomenon.

(Prior Art) As a raw material powder for forming a gas diffusion electrode, a mixture of hydrophilic carbon black carrying a conventional catalyst, polytetrafluoroethylene fine powder and water repellent carbon black has been used. It was

(Problems to be Solved by the Invention) By the way, in the gas diffusion electrode made of the above-mentioned mixed powder, the catalyst supported on the hydrophilic carbon black is released and aggregated and condensed during a relatively short period of use. As a result, the dispersion density of the catalyst becomes coarse, and even if the electrolytic solution permeates or the gas diffuses and permeates, it only contacts the surface of the aggregated condensed catalyst, not the internal catalyst, so it is effective. There are few working catalysts. Therefore, the amount of current that can be passed per unit weight of the catalyst is small, and the efficiency is extremely low.

In addition, the deterioration of the catalyst due to the liberation and flow of the catalyst is quick, and the life of the gas diffusion electrode is short.

Therefore, the present invention is intended to provide a raw material powder for producing a gas diffusion electrode in which the catalyst is not liberated from the hydrophilic carbon black.

(Means for Solving the Problems) The raw material powder for gas diffusion electrode of the present invention for solving the above problems is a fine powder formed by coating a hydrophilic carbon black carrying a catalyst with an ion exchange resin. , Polytetrafluoroethylene fine powder and water-repellent carbon black are mixed.

(Function) When a gas diffusion electrode is made of the raw material powder having the above-mentioned constitution, the catalyst supported on the hydrophilic carbon black is not separated from the hydrophilic carbon black even if it is used for a long time because the ion exchange resin is coated. . Therefore, the catalyst does not aggregate and condense, but remains dispersed in a uniform and fine manner, and the dispersion density of the catalyst is fine, and when the electrolyte permeates or gas diffuses and permeates, the cations hardly permeate the ion exchange resin. The catalyst is actively contacted with any catalyst. Thus, the amount of current that can be passed per unit weight of the catalyst is increased, and the efficiency is remarkably improved.

(Example 1) An example of the raw material powder for a gas diffusion electrode of the present invention will be described. An average particle size of 42 with platinum fine powder having an average particle size of 30Å
0 Å hydrophilic carbon black is coated with ion exchange resin, Nafion (trade name) in this example, with a thickness of 0.05μ, polytetrafluoroethylene fine powder with an average grain size of 0.3μ, and average grain It is made by mixing water-repellent carbon black fine powder with a diameter of 420Å at a ratio of 3: 4: 3.

The raw material powder of the mixed fine powder of Example 1 was placed on a base plate in a thickness of 0.45 mm, pressed and bound to a thickness of 0.1 m.
A gas diffusion electrode consisting of m reaction layers was made.

When the gas diffusion electrode thus produced was used as an air electrode in a fuel cell containing 20% sulfuric acid as an electrolyte, the platinum fine powder supported on the hydrophilic carbon black in the air electrode remained for 1000 hours. Not released from the hydrophilic carbon black, the ion-exchange resin prevents the platinum fine powder from condensing and condensing.
The platinum fine powder was dispersed uniformly and finely, and the dispersion density of the platinum fine powder was fine. Therefore, as a result of the cations permeating the ion-exchange resin and contacting most of the platinum fine powder in the infiltrated electrolytic solution, a vigorous reaction is carried out, resulting in a current that can flow per unit weight of the platinum fine powder that is higher than that of the conventional one. It is about 1.5 times more, and the efficiency is remarkably improved.

In the above embodiment, the catalyst is platinum, but the catalyst is not limited to this, and other precious metals or their alloys, base metals or their alloys may be used.

Further, the hydrophilic carbon black coated with Nafion in the above examples is obtained by diluting liquid Nafion with alcohol, mixing the hydrophilic carbon black with this, and then removing the solvent by evaporation.

(Effects of the Invention) As can be seen from the above description, according to the positive electrode raw material powder of the gas diffusion electrode of the present invention, the catalyst is not released from the hydrophilic carbon black during use, and therefore the catalyst does not aggregate and condense. While finely dispersed, a large amount of current can be passed per unit weight of the catalyst, and a gas diffusion electrode having extremely high efficiency can be obtained.

Claims (1)

[Claims] 1. A fine powder obtained by coating a hydrophilic carbon black carrying a catalyst with an ion exchange resin,
A raw material powder for a gas diffusion electrode, which is a mixture of polytetrafluoroethylene fine powder and water-repellent carbon black without a catalyst.