JPH0665036B2 - Gas diffusion electrode and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas diffusion electrode used for a fuel cell, a secondary battery, an electrochemical reactor, an anode for plating, etc., and a method for producing the same.

(Prior Art) Conventionally, as a gas diffusion electrode, a reaction layer having a hydrophilic portion and a water repellent portion made of platinum, hydrophilic carbon black, and polytetrafluoroethylene was used. There is one formed by joining the water-repellent gas diffusion layers.

When this gas diffusion electrode is used in a fuel cell or the like, the electrolytic solution permeates the reaction layer, but does not permeate the gas diffusion layer, but only the gas generated by the catalytic reaction or the supply gas diffuses and permeates the gas diffusion layer. is there.

(Problems to be Solved by the Invention) By the way, the reaction layer of the gas diffusion electrode is formed by adhering a platinum catalyst to hydrophilic carbon black and mixing and binding with polytetrafluoroethylene. The portion does not necessarily have a structure through which the electrolytic solution can permeate, and the platinum catalyst portion through which the electrolytic solution can permeate and the gas diffusion passage do not have a structure in which they are uniformly and finely adjacent to each other. Therefore, some platinum catalysts in the reaction layer do not come into contact with the electrolytic solution and do not contribute to the reaction,
In addition, the contact area between the electrolyte and the gas diffusion passage is not sufficient,
The catalyst performance is low. That is, the conventional gas diffusion electrode has a problem that the reaction area ratio of the platinum catalyst per unit area and the contact area between the electrolytic solution and the gas diffusion passage are small, and therefore the current that can be passed per unit area of the gas diffusion electrode is small. is there.

Therefore, the present invention is intended to improve the catalytic performance by bringing all the platinum catalyst in the reaction layer into contact with the electrolytic solution and increasing the contact area between the electrolytic solution and the gas diffusion passage.

(Means for Solving Problems) The gas diffusion electrode of the present invention for solving the above problems is
Platinum group metal or its oxide or both, hydrophilic carbon black, hydrophilic component consisting of polytetrafluoroethylene and water-repellent part consisting of water repellent carbon black and polytetrafluoroethylene are alternately layered. It is composed of a reaction layer formed by binding the formed powder to a sheet.

The production method of the present invention for producing a gas diffusion electrode having such a structure is a hydrophilic sheet formed by mixing and rolling hydrophilic carbon black, polytetrafluoroethylene and a solvent, water-repellent carbon black and polytetrafluoroethylene. After pressing a water-repellent sheet prepared by mixing and rolling a solvent and rolling multiple times to make a multilayer sheet, the solvent in the multilayer sheet is removed by heating, and then the multilayer sheet is crushed to powder. Then, the powder is pressed into a flat plate or mixed with a solvent and rolled to form a material sheet, and in the latter case, the solvent in the material sheet is removed by heating, and then the hydrophilicity of the powder in the material sheet is increased. The platinum group compound solution is impregnated in the conductive portion, and then the material sheet is heated to decompose the platinum group compound solution, and the platinum group metal or its oxide or both are adhered to the hydrophilic portion of the powder to prevent reaction. It is characterized in forming a layer.

(Function) In the gas diffusion electrode of the present invention configured as described above, the fine powder forming the reaction layer has a structure in which hydrophilic portions and water repellent portions are alternately layered. When used in a fuel cell, etc., the electrolytic solution permeates the entire hydrophilic portion of all the fine powder, the electrolytic solution contacts most of the platinum catalyst, and the contact area between the electrolytic solution and the gas diffusion passage is large. Will be orders of magnitude larger. Therefore, the gas diffusion electrode of the present invention has a remarkably large electric current per unit area.

(Example) An example of a gas diffusion electrode and a method for manufacturing the same of the present invention will be described with reference to the drawings.

The gas diffusion electrode 1 of the present invention shown in FIG. 1 has an average particle size of 50Å
Platinum, hydrophilic carbon black with an average particle size of 450Å and polytetrafluoroethylene with an average particle size of 0.3μ in a ratio of 0.7: 7: 3 with a thickness of 1.0μ hydrophilic part 2 and an average particle size of 420Å
The water-repellent carbon black and the water-repellent portion 3 having a thickness of 1.0 μ and composed of polytetrafluoroethylene having an average particle diameter of 0.3 μ in a ratio of 7: 3 are alternately layered in 10 layers to have an average particle diameter of 10 μ.
100mm wide, 100mm long, 0.1mm thick
Of the reaction layer 5 formed into the sheet of FIG.

A method of manufacturing the gas diffusion electrode 1 having such a structure will be described. First, as shown in FIG. The width is 100m, which is obtained by mixing in a ratio of 1: 1.8 and solvent naphtha in a ratio of 1: 1.8 and rolling and molding.
m, length 3 m, thickness 2 mm hydrophilic sheet 6 and average particle size 4
20 Å water repellent carbon black and polytetrafluoroethylene with an average particle size of 0.3μ are mixed in a ratio of 7: 3, and solvent naphtha is mixed in a ratio of 1: 1.8. A water-repellent sheet 7 having a thickness of 3 m and a thickness of 2 mm is overlapped and rolled to a thickness of 2 mm as shown in FIG. 2b, then this is cut into two pieces, and as shown in FIG. After rolling to a thickness of 2 mm as shown in Fig. D, and then repeating this lap rolling process 10 times to make a multilayer sheet 8 as shown in Fig. 2e, heat it up to 280 ° C and remove the solvent in the multilayer sheet 8. After removing the naphtha, the multilayer sheet 8 is crushed to prepare a powder 4 having an average particle size of 10 μ as shown in Fig. 2f, and then the powder 4 is mixed with the solvent naphtha at a ratio of 1: 1.8 and then rolled. Mold and form a material sheet 9 with a width of 100 mm, a length of 100 mm and a thickness of 0.2 mm as shown in Fig. 2g. Then 280 ℃
To remove the solvent naphtha in the raw material sheet 9 and then apply chloroplatinic acid solution to the surface of the raw material sheet 9 to impregnate the hydrophilic portion 2 of the powder 4 as shown in FIG. 2h. After that, the material sheet 9 is heated at 200 ° C. for 60 minutes to decompose the solution, and further reduced in hydrogen at 200 ° C. for 60 minutes so that platinum is attached to the hydrophilic part 2 and the reaction layer 5
Then, a gas diffusion electrode 1 was obtained.

When the gas diffusion electrode 1 of the embodiment thus produced is used in a fuel cell or the like, the electrolytic solution does not penetrate into the water repellent portion 3 of the powder 4 constituting the reaction layer 5 shown in FIG. It penetrates only into the hydrophilic portion 2 having the catalyst, and most of the platinum catalyst is in contact with the electrolytic solution. Therefore, the platinum catalyst in the reaction layer 5 almost contributes to the catalytic reaction.

Although the gas diffusion electrode 1 of the above-described embodiment is composed of only the reaction layer 5, in some cases, a water repellent gas diffusion layer of water repellent carbon black and polytetrafluoroethylene is bonded to the reaction layer 5. Or, by joining a gas diffusion layer that can hold an electrolyte or a water repellent carbon paper,
It may be used as a gas diffusion electrode.

When the water-repellent gas diffusion layer, the gas diffusion layer capable of holding an electrolytic solution, the water-repellent carbon paper, and the like are joined, the surface of the material sheet 9 is coated with a chloroplatinic acid solution to make the powder 4 hydrophilic. It may be performed before the impregnation of the flexible portion 4a.

Further, although solvent naphtha was used as the solvent in the examples, the solvent is not limited to this, and may be water, ethanol, isopropyl alcohol, or a hydrocarbon such as n-butane.

(Effects of the Invention) As can be seen from the above description, in the gas diffusion electrode of the present invention, the fine powder forming the reaction layer has a hydrophilic portion having a platinum catalyst and a water-repellent portion alternately layered. Since it has a structure, the contact area between the electrolytic solution and the gas diffusion passage is extremely large, and most of the platinum catalyst comes into contact with the electrolytic solution, and the catalytic performance is extremely high. There is an excellent effect that the current is large.

Further, according to the method for manufacturing a gas diffusion electrode of the present invention, there is an advantage that the above excellent gas diffusion electrode can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a partially enlarged sectional view showing an embodiment of a gas diffusion electrode of the present invention, and FIGS. 2A to 2H are views showing steps of a method for manufacturing the gas diffusion electrode.

Claims (2)

[Claims] 1. A hydrophilic portion comprising a platinum group metal and / or an oxide thereof, hydrophilic carbon black and polytetrafluoroethylene, and a water repellent portion comprising water repellent carbon black and polytetrafluoroethylene. , A gas diffusion electrode comprising a reaction layer formed in a sheet shape by alternately binding layered powders. 2. A hydrophilic sheet formed by mixing and rolling hydrophilic carbon black, polytetrafluoroethylene and a solvent, and a water repellent sheet formed by mixing and rolling water-repellent carbon black, polytetrafluoroethylene and a solvent. After pressing and rolling multiple times to make a multilayer sheet, heat to remove the solvent in the multilayer sheet, then crush this multilayer sheet to make powder, and then use this powder as a raw material sheet Then, the hydrophilic part of the powder in the material sheet is impregnated with the platinum group compound solution, and then the material sheet is heated to decompose the platinum group compound solution to decompose the platinum group metal or its oxide or both. Is attached to the hydrophilic portion of the powder to form a reaction layer, which is a method for producing a gas diffusion electrode.