JPS6364266A - Raw material powder for gas diffusion electrode - Google Patents

Abstract

PURPOSE:To eliminate the separation or flow of a catalyst, by mixing a micropowder which consists of a hydrophile carbon black coated with an ion exchange resin, a polyethylene tetrafluoride micropowder, and a water-repellent carbon black. CONSTITUTION:A micropowder which consists of a hydrophile carbon black carrying platinum micropowder, coated with an ion exchange resin, a polyethylene tetrafluoride micropowder, and a water-repellent carbon black micropowder are mixed at the ratio 3:4:3. Thereby, a raw material powder to produce a gas diffusion electrode, in which no catalyst is separated from the hydrophile carbon black micropowder in the operation, and no catalyst flow-out from the polyethylene tetrafluoride or the water-repellent carbon black, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to raw material powder that is a material for gas diffusion electrodes used in fuel cells, secondary batteries, electrochemical reactors, plating anodes, and the like.

(Conventional technique) The raw material powder used to make gas diffusion electrodes is conventionally made of hydrophilic carbon black that supports a catalyst, or catalyst fine powder, polytetrafluoroethylene fine powder, and water-repellent carbon black. A mixture of these has been used.

(Problems to be Solved by the Invention) By the way, during a relatively short period of use, the gas diffusion electrode made from the above-mentioned mixed powder can cause the catalyst supported on the hydrophilic carbon blank to be liberated, aggregated, and condensed. The catalyst interposed between the polytetrafluoroethylene fine powder and the water-repellent carbon blank flows and collects and condenses. As a result, the dispersion density of the catalyst becomes low, and even if the electrolyte penetrates or the gas diffuses and permeates, it will only contact the surface of the aggregated and condensed catalyst.
Since it does not come into contact with the internal catalyst, there is less catalyst to work effectively. Therefore, the current that can be passed per unit weight of the catalyst is small,
This is extremely inefficient.

Furthermore, the life of the gas diffusion electrode is shortened due to deterioration due to nitrogen separation and flow of the catalyst.

Therefore, in the present invention, the catalyst can be converted from hydrophilic carbon black or polytetrafluoroethylene. &t5
) end and ↑0 between the aqueous carbon black and La 'L)
J Original F for making a gas diffusion electrode that does not shatter
It is intended to provide a 'l costume.

(Means for Solving the Problems) In order to solve the above problems, the raw material powder for gas diffusion electrodes of the present invention is a hydrophilic carbon blank carrying a catalyst or a catalyst 'Ri F'tl powder, and an ion exchange resin. It is a mixture of a fine powder coated with polytetrafluoroethylene, a fine powder of polytetrafluoroethylene, and water-repellent carbon black.

(Function) When a gas diffusion electrode is made from the raw material powder with the above configuration, the catalyst supported on the hydrophilic carbon black is coated with an ion exchange resin, so even if used for a long period of time, the catalyst supported on the hydrophilic carbon black will be Moreover, the catalyst coated with ion-exchange resin is polytetrafluoroethylene fine powder or i
Ω It remains between the aqueous carbon blacks and does not flow. Therefore, the catalyst does not collect and condense, but remains uniformly and finely dispersed, and the dispersion density of the catalyst is low. When the power 7 liquid permeates or the gas diffuses mA, cations and ions are transferred to the ion exchange resin. It permeates through and comes into contact with most of the catalysts, and the reaction takes place actively. In this way, a large amount of current can be passed per unit weight of the catalyst, resulting in a marked improvement in efficiency.

In addition, deterioration due to catalyst release and flow S: is prevented.
The life of the gas diffusion type ( ) is significantly longer.

(Example 1) An actual example of the raw material powder for gas diffusion electrodes of the present invention will be described. A fine powder formed by coating a hydrophilic carbon blank with an average particle size of 420 mm on which platinum fine powder with an average particle size of 30 mm is supported, and coated with an ion exchange resin (trade name: Nafion in this example) to a thickness of 0.05 μm. It is made by mixing polytetrafluoroethylene fine powder with an average particle size of 0.3μ and fine aqueous carbon black powder with an average particle size of 420 IΩ in a ratio of 3:4:3.

(Example 2) Thirty platinum fine powders are coated with an ion exchange resin, in this example Nafion (trade name), to a thickness of 00 μm, and polytetrafluorocarbons with an average particle size of 0 and 3 μm are coated. It is made by mixing ethylene chloride fine powder and an aqueous carbon blank with an average particle size of 420 tΩ in a ratio of 4:4:3.

The raw material powders of the mixed fine powders of Example 1.2 were each placed on a base plate to a thickness of 0.45 IIm, and pressed and bonded to form a gas diffusion electrode consisting of a reaction layer of 0.1 mm thickness. Had made.

The gas diffusion electrodes made in this way were used as air electrodes, respectively.
When used in a fuel cell with a 20% sulfuric acid electrolyte, the platinum fine powder supported on the hydrophilic carbon blank in the air electrode was 1
Even after 1,000 hours, the hydrophilic carbon blank still shows &
Without Wfl, the ion exchange resin prevented the agglomeration and condensation of the fine platinum powder, and the fine platinum powder remained uniformly and finely dispersed, and the dispersion density of the fine platinum powder was maintained. Therefore, in the permeated electrolyte, the cations permeate through the ion exchange resin and come into contact with most of the platinum fine powder, resulting in an active reaction.
The current that can be passed per unit weight of fine platinum powder is 1.5 times higher than that of conventional products, significantly improving efficiency.

Furthermore, since deterioration due to release and flow of the platinum fine powder was prevented, the life of the gas diffusion electrode was approximately twice as long as that of conventional electrodes.

Although the catalyst is platinum in the above embodiments, it is not limited to this, and may be other noble metals or alloys thereof, base metals, or alloys thereof.

In addition, the hydrophilic carbon black coated with Nafion in Examples described above was obtained by diluting liquid Nafion with alcohol, mixing it with aqueous carbon black, and then removing the solvent by evaporation.

(Effects of the Invention) As can be seen from the above explanation, according to the gas diffusion electrode positive raw material powder of the present invention, the catalyst may be released from the hydrophilic carbon blank during use, or the catalyst may be released from the hydrophilic carbon blank or from polytetrafluoroethylene or 1B aqueous carbon blank. Therefore, the catalyst does not aggregate and condense, and remains uniformly and finely dispersed, allowing a large current to flow per unit weight of catalyst, making it possible to obtain a highly efficient gas diffusion electrode. can.

In addition, there is no separation or flow of the catalyst, so deterioration of function can be suppressed and a long-life gas diffusion electrode can be obtained.

Claims (1)

[Claims] A fine powder formed by coating hydrophilic carbon black or catalyst fine powder supporting a catalyst with an ion exchange resin;
A raw material powder for gas diffusion electrodes, which is a mixture of polytetrafluoroethylene fine powder and water-repellent carbon black.