JPH07118322B2 - Gas diffusion electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of a gas diffusion electrode used in a fuel cell, a secondary battery or the like.

(Prior Art) Conventionally, as a gas diffusion electrode, a gas diffusion electrode composed of Pt, hydrophilic carbon black, water repellent carbon black, and polytetrafluoroethylene was added to a reaction layer composed of water repellent carbon black and polytetrafluoroethylene. Some are made by combining layers.

When this gas diffusion electrode is used in, for example, 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 reaction or the supply gas diffuses and permeates the gas diffusion layer.

(Problems to be Solved by the Invention) By the way, in the conventional gas diffusion electrode described above, since the hydrophilic part and the water repellent part in the reaction layer are dispersed in a lump form, the passage area and gas through which the electrolytic solution permeates The diffusing passage area is narrow, and therefore the contact area between the electrolyte and the gas is small, so that the current that can be passed or taken out per unit area of the electrode is small.

Therefore, the present invention is intended to provide a gas diffusion electrode having a large contact area between an electrolytic solution and a gas, a reaction progressing in a short time, and a high electrode reaction efficiency.

(Means for Solving Problems) The gas diffusion electrode of the present invention for solving the above problems is
The fine hydrophilic part and the water-repellent part are formed of a reaction layer which is fibrous in the layer thickness direction and is randomly dispersed with both ends exposed on both sides.

(Operation) As described above, in the gas diffusion electrode of the present invention, fine hydrophilic parts and / or water repellent parts are randomly dispersed in a fibrous shape in the thickness direction. The passage area through which the gas permeates and the passage area through which the gas diffuses are extremely large. Therefore, the contact area between the electrolytic solution and the gas is large, and the reaction is actively performed.

(Example) An example of the gas diffusion electrode of the present invention will be described with reference to FIGS. 1 and 2. In the gas diffusion electrode 1, the hydrophilic portion 2 and the hydrophilic portion 3 having an average thickness of 2 μ are formed in a fibrous shape in the layer thickness direction. And the hydrophilic part 2 is composed of hydrophilic carbon black and polytetrafluoroethylene, and the water-repellent part 3 is composed of water-repellent carbon black and poly. It is composed of tetrafluoroethylene.

There are two methods for making this gas diffusion electrode 1. One of them will be described with reference to FIGS. Average particle size 390
Å Hydrophilic carbon black, polytetrafluoroethylene powder with an average particle size of 0.3μ and water were mixed at a ratio of 7.5: 2.5: 40 to give ductility, and then extruded to obtain a hydrophilic wire rod having a diameter of 1 mm of 500 On the other hand, water-repellent carbon black with an average particle size of 420Å, polytetrafluoroethylene powder with an average particle size of 0.3μ, and water were made at 7: 3: 4.
It is mixed at a ratio of 0 to give ductility and then extruded to make 500 water-repellent wires with a wire diameter of 1 mm. Next, as shown in FIG. 3a, 500 water-repellent wires 5 and 500 water-repellent wires 6 are mixed and bundled.
Next, this is extruded to form a reaction layer wire 7 having a wire diameter of 1 mm as shown in FIG. 3b. Next, as shown in FIG. 3c, about 1200 wire bundles for the reaction layer are bundled and crimped, and the length is 100 mm and the width is 100 mm.
A reaction layer strip 8 having a rectangular cross section is produced. Then, the reaction layer strip 8 is sliced to a thickness of 0.2 mm as shown in FIG. After that, the reaction layer material 9 is 280 ° C 180
Heat for 1 minute to dry, remove water as solvent,
A gas diffusion electrode 1 composed of the reaction layer 4 shown in FIG. 2 is produced.

Next, another method for manufacturing the gas diffusion electrode 1 will be described with reference to FIGS. Mixing hydrophilic carbon black with an average particle size of 390Å, water repellent carbon black with an average particle size of 420Å, polytetrafluoroethylene powder with an average particle size of 0.3μ and solvent naphtha at a ratio of 6: 4: 4: 50 And then extruded, as shown in Fig. 4a, the reaction layer wire 7'having a wire diameter of 1 mm.
make. Next, as shown in FIG. 4b, about 1200 pieces of the reaction layer wires 7'are bundled and crimped to form a reaction layer strip 8'having a rectangular cross section of 100 mm in length and 100 mm in width. Next, this reaction layer strip 8'is sliced to a thickness of 0.2 mm as shown in FIG. After that, this reaction layer material 9'is made into 28
The mixture is heated at 0 ° C. for 180 minutes to be dried, the solvent naphtha as a solvent is removed, and the gas diffusion electrode 1 composed of the reaction layer 4 shown in FIGS.

The gas diffusion electrode 1 formed of the reaction layer 4 formed by either of the above two methods also has a fine hydrophilic portion 2 and a water repellent portion 3 in the thickness direction which are fibrous and both ends thereof are exposed on both sides. Since they are dispersed at random, the passage area through which the electrolytic solution permeates and the passage area through which the gas diffuses are also extremely large when used for, for example, fuel cell. Therefore, the contact area between the electrolytic solution and the gas is large, and the reaction is actively performed.

Although the gas expansion electrode 1 of the above embodiment is composed of only the reaction layer 4, a catalyst such as platinum may be supported on the hydrophilic portion 2 if necessary, and a gas may be provided on one surface of the reaction layer 4. A diffusion layer may be provided, and a current collector may be attached to the reaction layer 4.

Further, in the above example, hydrophilic carbon black, water repellent carbon black, polytetrafluoroethylene, and solvent naphtha were mixed at the same time, but hydrophilic carbon black, polytetrafluoroethylene powder, and solvent naphtha were mixed separately. Alternatively, it may be dried, pulverized and then mixed with the solvent naphtha.

Further, in the above-mentioned embodiment, the material for extrusion is processed and bundled to form the reaction layer strip, but it may be processed by rolling and laminated to form the reaction layer strip.

(Effects of the Invention) As can be seen from the above description, the gas diffusion electrode of the present invention has an extremely large passage area through which the electrolytic solution permeates, and an extremely large passage area through which the gas diffuses. Is large, each reaction is actively carried out, and the reaction is completed in a short time. Therefore, the electrolytic reaction efficiency is high, and the current that can be passed and the current that can be taken out per unit area of the electrode are extremely large.

[Brief description of drawings]

FIG. 1 is a perspective view of a gas diffusion electrode of the present invention, FIG. 2 is a partially enlarged perspective view, and FIGS. 3A to 3D are diagrams showing a unidirectional process for producing the gas diffusion electrode of the present invention, and FIG. FIGS. 3A to 3C are diagrams showing steps of another method for producing the gas diffusion electrode of the present invention. 1 ... Gas diffusion electrode, 2 ... Hydrophilic part, 3 ... Water repellent part, 4
…… Reaction layer.

Claims (1)

[Claims] 1. A gas diffusion electrode comprising a reaction layer in which fine hydrophilic portions and / or water repellent portions are fibrous in the layer thickness direction and are randomly dispersed with both ends exposed on both sides.