JPH0326909B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a gas diffusion electrode that has a long life and low electrical resistance. [Prior Art] Conventionally, as in JP-A No. 48-55333, a dispersion of carbon powder and a dispersion of a water-repellent binder are mixed, and particles of the binder are attached to the carbon powder. There has been a method for manufacturing gas electrodes in which carbon powder, a fixing agent, and a catalyst material are combined into one body through alkali treatment and heat treatment. Further, as in JP-A-49-41830, polytetrafluoroethylene (PTFE) powder was used as both a binder and a water repellent. [Problems to be Solved by the Invention] Water repellency of gas diffusion electrodes is an important problem in air batteries and the like in terms of storage characteristics, discharge under high temperature and high humidity, and the like. If the amount of PTFE is increased, the gas permeability of the gas diffusion electrode will deteriorate and the operating voltage will decrease. Furthermore, since the activated carbon itself was not water-repellent because it only contained PTFE powder, it did not have good long-term storage properties. Another manufacturing method was to dissolve a liquid or solid water repellent in a solvent and impregnate the activated carbon, and then evaporate the solvent, but the water repellent covered the entire surface of the activated carbon, increasing the electrical resistance of the electrodes and causing a discharge. The operating voltage has become low. Furthermore, when the amount of water repellent is reduced, a sufficient water repellent effect cannot be obtained. The present invention provides water repellency to the gas diffusion electrode without deteriorating its electrical resistance and contact ability by welding water-repellent fine particles to the surface of activated carbon in a strong and stable state, thereby improving long-term storage characteristics. . [Means for solving the problems] The manufacturing method of the present invention will be explained. First, activated carbon or activated carbon adsorbed with a catalyst is dispersed in water, an aqueous dispersion of water-repellent fine particles is diluted with water, and an appropriate amount of this dispersion is dropped. Adjust the amount to be dropped as needed. Next, while reducing the pressure of the above mixed liquid and removing minute air bubbles existing on the surface of the activated carbon, the surface of the activated carbon is impregnated with water-repellent fine particles,
Overdry. Next, the activated carbon is heated at a temperature higher than its melting point to melt and partially fuse the water-repellent particles to the surface of the activated carbon. Thereafter, the water-repellent activated carbon and water-repellent fine particles are mixed, formed into a sheet using a roller, a nickel net is crimped onto the sheet, and a water-repellent film is further crimped onto the sheet to produce a gas diffusion electrode. [Function] In the present invention, air bubbles adsorbed on the activated carbon surface are removed by reduced pressure and heated, so water-repellent fine particles can be uniformly and firmly fused to the activated carbon surface, making it resistant to battery vibration and temperature shock. It becomes stronger and the reaction area with air is expanded, so it can be used with large currents.
This improves long-term storage. [Example] An example of the present invention will be described. First, 100 g of activated carbon adsorbed with a catalyst is dispersed in 1 part of water, and then a 60% by weight aqueous dispersion of PTFE having a diameter of 0.01 to 50 μ is diluted 10 times with water, and 100 ml of the solution is added dropwise to the activated carbon dispersion. The amount of this dripping is based on the weight ratio of PTFE solid content to activated carbon, assuming that activated carbon is 100.
Good results are obtained between 0.1:100 and 40:100.
The amount is appropriately adjusted within the above range depending on the type of activated carbon used. Next, add the above mixture to 40Torr~
Stir for 15 minutes under a reduced pressure of 100 Torr to remove minute air bubbles on the surface of activated carbon.
Impregnate with PTFE particles and overdry. Further, the activated carbon is heated for 15 minutes at a temperature of 380°C to 400°C, which is higher than the melting point of PTFE, to melt and weld a portion of the PTFE to the surface of the activated carbon. The fusion does not cover the entire surface of the activated carbon, but only partially makes the activated carbon water repellent, so that a sufficient surface area remains for the oxygen reduction catalyst to act on. 80% by weight of activated carbon and PTFE powder treated with water repellency in this way
20% by weight, formed into a sheet using a roller, crimped with a nickel net, and further crimped with a PTFE film to produce a gas diffusion electrode. PR44 type air cell [A] according to the present invention was prototyped using the above gas diffusion electrode, and for comparison, the same type of air was mixed at normal pressure and manufactured using a gas diffusion electrode without heating at a temperature higher than the melting point. Battery [B]
We also prototyped the same type of air cell [C] using a gas diffusion electrode made by dissolving PTFE in kerosene and mixing it with activated carbon to evaporate the kerosene. Table 1 shows the open circuit voltage of the initial batteries [A], [B], and [C], the internal resistance of the batteries, the discharge capacity up to 0.9 V, and the operating voltage at 60% discharge. Table 2 shows the discharge capacity and discharge operating voltage of the battery after it was stored for one month at a temperature of 45° C. and a humidity of 60% with the air holes open for comparison.

【table】

[Table] From the results in Tables 1 and 2, the product of the present invention has water-repellent fine particles fused to it, but the results after storage are superior to the conventional products [B] and [C] in both discharge capacity and discharge operating voltage. You can see that In the above example, PTFE was used as the water-repellent fine particles.
Although we have described a gas diffusion electrode using fluoroethylene, excellent results can also be obtained using the same manufacturing method using other fluorocarbon resins such as copolymers of tetrafluoroethylene and hexafluoropropylene. Can be done. [Effects] As described above, when the gas diffusion electrode of the present invention is used in an air battery, the internal resistance of the battery is small and it can withstand high current use, and even after storage, it maintains excellent characteristics such as discharge operating voltage and discharge capacity. Obtainable.

Claims (1)

[Claims] 1 Activated carbon or activated carbon that has adsorbed a catalyst and a water-repellent fine particle dispersion are mixed under reduced pressure, dried, and heated at a temperature higher than the melting point of the fine particles, so that the water-repellent fine particles are partially fused to the surface of the activated carbon. A method for manufacturing a gas diffusion electrode, characterized by dressing the gas diffusion electrode.