JP2909539B1 - Gas diffusion electrode - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To provide a gas diffusion electrode which has high mechanical strength because the performance of the gas diffusion electrode is high, there is no deterioration of the performance, and hot pressing can be performed at a high temperature at the time of manufacturing, and the mechanical strength is large and each layer is difficult to peel off. provide. SOLUTION: In a gas diffusion electrode comprising a reaction layer and a gas supply layer, hydrophobic carbon black having an average particle size of 80 nm or less is scattered in a part of a space where metal fine particles having an average particle size of 600 nm or less are gathered. A reaction layer containing 20% to 45% by volume of polytetrafluoroethylene (PTFE) fine particles having a particle size of 300 nm or less;
m average particle size of 300 nm
A gas diffusion electrode comprising a gas supply layer containing the following PTFE fine particles in a volume ratio of 30% to 45%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas diffusion electrode used for electrolysis and fuel cells, and more particularly to a gas diffusion electrode which does not reduce the specific surface area of metal fine particles in a reaction layer when used as an oxygen cathode for salt electrolysis. .

[0002]

2. Description of the Related Art Gas diffusion electrodes have been used in various electrolysis and fuel cells, but recently, their use as oxygen cathodes in salt electrolysis has attracted attention. In this field, a gas diffusion electrode having a structure having two layers, a reaction layer and a gas supply layer, is usually used. However, a gas diffusion electrode having a structure as shown in FIG. In the electrode 11, the reaction layer 12 is made of silver fine particles and polytetrafluoroethylene (hereinafter referred to as “PTFE”) fine particles, and the gas supply layer 13 is made of a porous PTFE material. The gas diffusion electrode 11 composed of only silver and PTFE, having a structure in which such a metal net is arranged,
Since carbon black is not used, it is expected to have a long life. This electrode is composed of silver fine particles and PTF
A slurry obtained by self-assembling the mixture with E-dispersion with alcohol is applied to a silver screen or the like, and after drying, a surfactant is removed to form a reaction layer sheet. This reaction layer sheet and the PTFE fine powder layer serving as a gas supply layer were added at a rate of 10 kg /
The gas diffusion electrode was obtained by hot pressing at a pressure of 250 cm ² and a temperature of 250 ° C.

[0003]

By the way, in the gas diffusion electrode manufactured by the above-mentioned means, the gas supply layer obtained by hot pressing PTFE fine powder is made of PT.
Since the binding between the FE fine particles is weak, the mechanical strength is low, and the adhesion to the reaction layer is low. In addition, P
Since the crystallization of TFE proceeds, it is brittle and easily cracked. Therefore, when used as an oxygen cathode, there is a problem that there is a high possibility that a liquid leak will occur on the gas chamber side due to the liquid pressure. To solve this lack of strength, use PTFE
Heating above the melting point of 327 ° C. solves the problem of strength, but almost eliminates gas permeability and renders the gas supply layer useless. The present invention provides a gas diffusion electrode that has high mechanical strength because the performance of the gas diffusion electrode is high, and the performance is not deteriorated, and hot pressing can be performed at a high temperature during manufacturing, so that each layer has a large mechanical strength. It is intended for.

[0004]

The inventors of the present invention have studied the problems in the prior art, and found that the deterioration of the gas diffusion electrode using carbon black is caused by the hydrophilic carbon of the catalyst carrier used for forming the reaction layer. Previous studies have shown that black corrosion is the major cause, with little corrosion of hydrophobic carbon black. Therefore, the reaction layer is made of a mixture of a catalyst metal (silver) component, a hydrophobic carbon black and PTFE except for the hydrophilic carbon black, and the gas supply layer is made of a mixture of the hydrophobic carbon black and the PTFE.
It was studied to obtain a gas diffusion electrode by hot pressing the mixture with E. At that time, each of these substances is preferably composed of fine particles, and the range of the average particle diameter of each of these substances was examined. Further, as a result of studying the composition range of each substance, it was found that a gas diffusion electrode of the present invention having good performance and without deterioration could be obtained, and the present invention was reached.

[0005] The present invention has solved the above-mentioned problems by the following means. (1) In a gas diffusion electrode composed of a reaction layer and a gas supply layer, hydrophobic carbon black having an average particle size of 80 nm or less is scattered in a part of a space where metal fine particles having an average particle size of 600 nm or less are gathered. 20% by volume of polytetrafluoroethylene (PTFE) fine particles with a diameter of 300 nm or less
And a reaction layer containing up to 45%, and a hydrophobic carbon black having an average particle diameter of 80 nm or less,
A gas diffusion electrode comprising a gas supply layer containing 30% to 45% by volume of TFE fine particles.

According to the present invention, the reaction layer does not contain the hydrophilic carbon black which causes deterioration, and the catalyst metal (for example, silver)
Component, a mixture of hydrophobic carbon black and PTFE, and the gas supply layer is made of a mixture of hydrophobic carbon black and PT.
The mixture with FE was hot-pressed at a temperature equal to or higher than the melting point of PTFE capable of obtaining high strength. The average particle size of the metal fine particles is preferably as small as possible, and the upper limit is 600 nm. If it is larger than this, the catalytic activity of the metal decreases. Although there is no particular lower limit in theory, a small one is difficult to manufacture and easily ignites, making it difficult to handle, so there is only a practical limitation. The reaction layer preferably contains 20 to 60% by volume of metal fine particles. The average particle size of the hydrophobic carbon black is preferably as small as possible, and the upper limit is 80 nm. The size is determined by a commercially available product. Although there is no particular lower limit in theory, there is a restriction that a small one is difficult to manufacture and easy to ignite and difficult to handle. The hydrophobic carbon black is preferably contained in the reaction layer in a volume ratio of 20 to 60%, and in the gas supply layer, 30 to 4% by volume.
Preferably, it is contained at 5%.

[0007] The average particle size of the PTFE fine particles is determined by the relationship in which they are mutually welded by hot pressing during production to form a matrix, and the average particle size is 300 nm or less. The lower limit is preferably 100 nm, but may be smaller. In order to form a matrix in order to maintain strength, it is necessary that a certain range of amounts be blended in each layer. The reaction layer needs to contain PTFE fine particles in a volume ratio of 20% to 45%, and preferably 25% to 40% in a volume ratio.
The gas supply layer needs to contain PTFE fine particles in a volume ratio of 30% to 45%, preferably 35% to 40% in a volume ratio. The reason that the ratio of the PTFE fine particles is larger than that of the reaction layer is that the inside of the gas supply layer needs to have high hydrophobicity in order to allow oxygen gas to pass therethrough. In the present invention, in the reaction layer, the average particle size of the metal fine particles and the average particle size of the hydrophobic carbon black are selected as described above. Therefore, when the metal fine particles, the hydrophobic carbon black and the PTFE dispersion are mixed, When the hydrophobic carbon black is scattered in the voids of the metal fine particles and is hot-pressed at a high temperature and high pressure together with the gas supply layer, the fine particles of the hydrophobic carbon black exist around the metal fine particles, so that the specific surface area of the metal fine particles Does not drop. Thereby, the electrode performance does not decrease. In addition, since hot pressing can be performed at a temperature equal to or higher than the melting point of PTFE, the strength and adhesion between the reaction layer and the gas supply layer increase.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, specifically, as shown in FIG. 1, a reaction layer 2 is composed of metal fine particles, hydrophobic carbon black and PTFE dispersion, and a gas supply layer 3 is composed of a hydrophobic layer. It is composed of a conductive carbon black and a PTFE dispersion. Here, first, the gas supply layer is made of, for example, acetylene black (hydrophobic carbon black).
And a PTFE dispersion to prepare a sheet. The average particle size of the acetylene black and the PTFE dispersion used is in the above range.
The method of producing the sheet is generally a roll method, but if a uniform sheet is obtained, the sheet may be produced by pressing powder.

As the fine metal particles used in the reaction layer, platinum group metals, gold, silver, alloys and oxides thereof can be used. Specifically, a combination of inexpensive silver fine particles, acetylene black and PTFE dispersion can be used. The average particle size of each substance is in the above-mentioned range. These are dispersed in an aqueous solution to which a surfactant is added, self-organized with alcohol, and water is removed.
The reaction layer is placed on the gas supply layer 3 by applying or spraying the slurry on the gas supply layer 3. After drying, the surfactant was removed, and then the current collector silver mesh 4
Is laminated on the reaction layer 2 or the gas supply layer 3 side, and hot-pressed to manufacture the gas diffusion electrode 1.

FIG. 1 shows that the silver net 4 of the current collector is provided in the reaction layer 2, and FIG. 2 shows that the silver net 4 is provided on the gas supply layer 3 side.
In addition, since the conductivity of the metal net is small because the cross-sectional area of the conductor is small, if it is desired to increase the conductivity, the material of the gas supply layer is introduced from one side of the thin plate-shaped conductive porous body. By pressing (slurry) and drying, the gas supply layer 3 having the conductive porous body as a skeleton can be formed. If the gas diffusion electrode 1 is arranged so that this conductive porous body is brought into contact with another conductive porous body (not shown) in the gas chamber, high conductivity can be provided.
When a conductive porous body having a size including the entire gas chamber is used, since the gas diffusion electrode is supported by the conductive porous body, the overall strength increases,
Further, since the conductivity is further improved and the gas flow is disturbed in the gas chamber, there is an advantage that the gas supply to the gas diffusion electrode is made uniform.

[0011]

The present invention will be described below in detail with reference to examples. However, the present invention is not limited to only these examples.

Example 1 Hydrophobic carbon black (No. 6: average particle size 50n)
m, manufactured by Denki Kagaku Kogyo Co., Ltd.) (6 parts by weight) (the same applies hereinafter), 160 parts of 10% Triton as a surfactant is added, and the mixture is dispersed with an ultrasonic dispersing machine. PTFE dispersion D-1 (average particle size 300 nm, manufactured by Daikin Industries, Ltd.) 4
Parts, and disperse and mix. Add ethanol 5
Add 00 parts and self-organize. After filtration and drying, solvent naphtha is added and rolled to form a gas supply layer sheet having a thickness of 0.5 mm and dried. Hydrophobic carbon black (No. 6: average particle size 50 nm,
160 parts of 10% Triton as a surfactant is added to 6 parts of Denki Kagaku Kogyo Co., Ltd., and dispersed by an ultrasonic dispersing machine. 3 parts of silver fine particles (Ag-3010, average particle size 110 nm, manufactured by Mitsui Kinzoku Mining Co., Ltd.) are added, and the mixture is dispersed with an ultrasonic dispersing machine.
This was mixed with PTFE dispersion D-1 (average particle size 30).
0 nm, manufactured by Daikin Industries, Ltd.) and stirring.
After mixing, 400 parts of ethanol is added and the mixture is stirred to form a self-organized product. The precipitate at the time of self-assembly was filtered with a filter paper having a pore size of 0.8 μm to obtain a slurry.

The slurry is added to the above-mentioned gas supply layer sheet for 20 minutes.
Apply evenly with a thickness of 0 microns. After drying, the surfactant is removed from the sheet with an extractor using ethyl alcohol. Furthermore, after drying at 100 ° C., 50 mesh,
Spread a silver mesh of 0.1 mm thickness on the reaction layer side,
Hot pressing was performed at a pressure of 0 kg / cm ² for 60 seconds to obtain a silver-carrying gas diffusion electrode. The amount of silver fine particles used in this electrode was 420 g / m ² . This electrode has a tensile strength of 10 times or more and a peel strength of the reaction layer and the gas supply layer of 10 times or more as compared with a gas diffusion electrode in which the gas supply layer is made of only PTFE.
More than doubled. When the oxygen reduction performance of this electrode was measured, it was found to be 0.76 V (vs. R) at 30 A / dm ^2.
HE). As the current collector, a silver net, a silver-plated nickel net, or a silver-plated foamed nickel is preferably used.

Example 2 Hydrophobic carbon black (No. 6, average particle size: 50 n)
m, 10% Triton 20 in 6 parts
Add 0 parts and disperse with an ultrasonic disperser. This is PTF
4 parts of E-dispersion D-1 (average particle size: 300 nm, manufactured by Daikin Industries, Ltd.) are added and dispersed and mixed. 50 parts of ethanol is added to the dispersion to self-assemble. After filtering and drying this, solvent naphtha was added and rolled to create a 2.5 mm thick gas supply layer sheet.
dry. To 6 parts of hydrophobic carbon black (No. 6: average particle diameter 50 nm, manufactured by Denki Kagaku Kogyo Co., Ltd.), 200 parts of 10% Triton is added as a surfactant, and the mixture is dispersed with an ultrasonic disperser. Silver fine particles (Ag-301, manufactured by Mitsui Kinzoku Mining Co., Ltd.)
(0, average particle size: 110 nm), and dispersed by an ultrasonic dispersing machine. PTFE dispersion D-1
(Average particle size: 300 nm, manufactured by Daikin Industries, Ltd.) 2.5 parts was added, and the mixture was stirred and mixed. Then, 300 parts of ethanol was added, and the mixture was self-organized by stirring. This precipitate was filtered through a filter paper having a pore diameter of 0.8 μm and dried.

[0015] Solvent naphtha is added thereto and rolled to form a reaction layer sheet having a thickness of 0.5 mm, which is thinned to 0.7 mm together with the gas supply layer sheet described above. The surfactant is removed from the combined sheet with an extractor using ethyl alcohol. After drying at 100 ° C., a 50-mesh, 0.19-mm-thick silver mesh is laid on the gas supply layer side,
Hot pressing was performed at 370 ° C. and a pressure of 50 kg / cm ² for 60 seconds to obtain a silver-carrying gas diffusion electrode. When the oxygen reduction performance of this electrode was measured, it was 0.77 at 30 A / dm ² .
V (vs. RHE) high performance was obtained.

[0016]

According to the present invention, the fine particles of hydrophobic carbon black can be scattered in the voids of the fine metal particles despite the use of fine metal particles such as silver fine particles which are easy to sinter. Even if hot pressing is performed at a high temperature and a high pressure, the specific surface area of the metal fine particles does not decrease, and thus the electrode performance does not decrease. Since the gas diffusion electrode can be hot-pressed at a temperature equal to or higher than the melting point of PTFE, the strength and adhesion between the reaction layer and the gas supply layer are dramatically increased.

[Brief description of the drawings]

FIG. 1 shows a schematic cross-sectional view of one example of a gas diffusion electrode of the present invention.

FIG. 2 shows a schematic sectional view of another example of the gas diffusion electrode of the present invention.

FIG. 3 shows a schematic sectional view of a conventional gas diffusion electrode.

[Description of Signs] 1 gas diffusion electrode 2 reaction layer 3 gas supply layer 4 silver mesh 11 gas diffusion electrode 12 reaction layer 13 gas supply layer

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C25B 11/03 C25B 11/04 H01M 4/86

Claims (1)

(57) [Claims] In a gas diffusion electrode comprising a reaction layer and a gas supply layer, hydrophobic carbon black having an average particle size of 80 nm or less is scattered in a part of a space where metal fine particles having an average particle size of 600 nm or less are gathered, A reaction layer containing 20% to 45% by volume of polytetrafluoroethylene fine particles having an average particle size of 300 nm or less, and a polytetrafluoroethylene fine particle having an average particle size of 300 nm or less are added to hydrophobic carbon black having an average particle size of 80 nm or less. 30% to 45%
%. A gas diffusion electrode comprising a gas supply layer containing up to 10%.