JP3373140B2 - Gas diffusion electrode - Google Patents

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 suitable for use in electrolysis of an aqueous alkali chloride solution by an ion exchange membrane method, and particularly to a gas diffusion electrode having high strength and easy to manufacture.

[0002]

2. Description of the Related Art In electrolysis of an aqueous alkali chloride solution by an ion exchange membrane method, a gas diffusion electrode is used as an oxygen cathode for the cathode. Usually, the ion exchange membrane method electrolysis is performed in an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane which is a cation exchange membrane, and an aqueous sodium chloride solution is contained in an anode chamber having an anode of this electrolytic cell. The caustic soda aqueous solution is contained in the cathode part having the cathode, but in the type using the gas diffusion electrode as the cathode, the cathode part is a catholyte chamber containing the caustic soda aqueous solution between the ion exchange membrane and the gas diffusion electrode. And a gas diffusion electrode composed of a reaction layer and a gas supply layer, and an oxygen gas chamber. In the electrolysis cell having such a configuration, oxygen is generated on the gas diffusion electrode during electrolysis by energizing between the both electrodes of the gas diffusion electrode of the anode and the cathode part (which is composed of the gas diffusion electrode and the oxygen gas chamber). Since the reduction reaction occurs and the cathode potential rises, there is an advantage that the electrolysis voltage is significantly reduced.

The gas diffusion electrode provided in the cathode portion has a structure in which a reaction layer and a gas supply layer are laminated, and both the reaction layer and the gas supply layer are composed of a thin layer mainly composed of a porous body. Therefore, the gas diffusion electrode has air permeability as a whole. Carbon black is mainly used for the reaction layer, which is the electrolyte-side layer of the gas diffusion electrode, and the fine pores carry a catalyst made of a noble metal such as platinum, which is hydrophilic and allows the electrolyte to penetrate. It is a thing. On the other hand, the gas supply layer, which is a layer on the gas supply side, is composed of a water-repellent porous thin layer through which gas can pass but electrolyte does not leak. The water-repellent porous thin layer is usually formed mainly of fine particles of a fluororesin-based polymer having resistance to a redox reaction.

As shown in FIGS. 6 and 7, a conventional gas diffusion electrode is provided with a mesh-shaped power supply member 10 (also referred to as a wire mesh) on the surface of the gas supply layer 4 and / or on the surface of the gas supply layer 4, and the mesh-shaped power supply member. Current was supplied from 10 to the reaction layer 3 through the gas supply layer 4 (through a mesh-shaped power feeding body in the middle of the gas supply layer). However, since the hydrophobic gas supply layer 4 has a large electric resistance, the electrolysis voltage becomes large. When the size of the electrolytic cell is increased, the electrode area is increased, the internal resistance of the electrode is increased, and the power loss is increased as a resistance loss. Therefore, the present inventor first fills the gas chamber of the cathode part of the electrolytic cell with the conductive porous body to form the electrolytic cell frame of the cathode part (also referred to as a cathode outer frame) and the gas supply layer of the gas diffusion electrode. However, the contact resistance between the conductive porous body and the gas supply layer was as large as several Ω / cm ^2, and it was found that power feeding was practically impossible. Therefore, as shown in FIG. 7, a metal net was joined to the surface of the gas supply layer, the gas chamber was filled with a conductive porous body, and the metal net was brought into contact with the metal net to supply electric power. There is a drawback that the supply of gas is hindered due to the metal net joined to the surface of the gas supply layer. As described above, it cannot be said that the conventional technique is sufficient to supply the current to the gas diffusion electrode.

[0005]

As described above, it is possible to reduce the uniformity of gas supply when supplying gas from the gas chamber to the gas supply layer of the gas diffusion electrode and to reduce the resistance in supplying current to the gas diffusion electrode. As for the means for making the current distribution in the electrode uniform, satisfactory results have not been obtained by the conventional methods. The present inventor, as a result of diligent studies on these points, reduces the electrode overvoltage in the cathode reaction of oxygen, and in order to improve the current efficiency, when supplying gas from the gas chamber to the gas supply layer of the gas diffusion electrode. Gas supply uniformity,
In relation to the quality of the gas and the method of applying a current to the gas diffusion electrode, the gas chamber can be filled with a porous material that allows three-dimensional flow of gas, and the strength of the gas diffusion electrode is high. It was found that the above conditions must be met.

An object of the present invention is to eliminate the above-mentioned drawbacks in the conventional gas diffusion electrode, to have a compact structure, to uniformly supply the gas from the gas supply chamber to the gas diffusion layer, and to have extremely high resistance to supply power to the gas diffusion electrode. An object of the present invention is to provide an excellent gas diffusion electrode that can be made small, can be easily manufactured, can be made large, and has good current collecting efficiency.

[0007]

As a result of earnest studies, the present inventors have found that in order to reduce the electrode overvoltage in the cathode reaction of oxygen, the gas used for supplying gas from the gas chamber to the gas supply layer of the gas diffusion electrode is reduced. Focusing on the fact that the structure of the gas diffusion electrode is extremely important in relation to the uniformity of supply and the method of loading the current to the gas diffusion electrode, the present invention was studied by studying a configuration that can achieve those conditions at the same time. completed. The present inventor first fills the gas chamber on the back side of the gas diffusion electrode with a porous material to disperse the gas flow in the gas chamber, thereby making the gas supply to the gas supply layer of the gas diffusion electrode uniform. As a result, we have developed a technology to increase the current of the gas diffusion electrode. It has also been found that the filling of this porous material has a function of supporting the gas diffusion electrode and can increase the strength. Furthermore, when this porous body is composed of a conductor such as a metal, a technique has been developed to make the resistance of the gas diffusion electrode extremely low by bringing it into contact with the above-mentioned reticulated power supply body. Has also developed a technology for forming the metal porous body together and applied for a patent.

In the integral molding, since the gas supply layer raw material and the like are likely to enter the conductive porous body, conversely, the gas supply layer and the like are formed in the conductive porous body. The present invention has been reached on the basis of the idea of utilizing the body as a skeleton of a gas diffusion electrode. The gas diffusion electrode of the present invention used for the cathode part of the electrolytic cell of the ion exchange membrane method includes the case of having a configuration integrated with the gas chamber, and therefore, the gas diffusion electrode is a part of the gas chamber. May also include the part.

That is, the above object is achieved by the following gas diffusion electrode of the present invention. (1) A reaction layer is formed on one surface of the conductive porous body so that at least a part thereof is inside the conductive porous body,
A gas diffusion electrode, wherein the other surface side portion of the conductive porous body has no reaction layer and forms at least a part of the gas chamber in an exposed state. (2) A gas supply layer is formed in a layer shape on a part of the conductive porous body, and a reaction layer is laminated on one side of the conductive porous body in contact with the gas supply layer. A gas diffusion electrode, characterized in that the portion on the other surface side of the body does not have the gas supply layer and forms at least a part of the gas chamber in an exposed state. (3) Power is supplied to the gas diffusion electrode by contacting or joining the conductive porous body forming at least a part of the gas chamber in the exposed state with the electrolytic cell frame. Alternatively, the gas diffusion electrode according to (2).

The main point of the present invention is that the previously developed cathode portion is
Even if it is integrally molded, the gas diffusion electrode having the reaction layer and the gas supply layer and the conductive porous body (which is filled in the gas chamber) are separate bodies. As shown in FIG. 5, in the cathode portion, the gas diffusion electrode and the conductive porous body are integrated, and the conductive porous body serves as the base of the gas diffusion electrode. In other words, the conductive porous body diffuses the gas. It forms the skeleton of the electrode. With this structure, the porous body filled in the gas chamber is directly connected to the reaction layer, and since the porous body is in contact with the electrolytic cell frame (cathode outer frame), the resistance for supplying power to the gas diffusion electrode is not increased. It is extremely small. Of course, as an example of forming the cathode part using the gas diffusion electrode of the present invention, as shown in FIG. 5, a gas diffusion electrode prepared by using a conductive porous body as a base is provided with another porous body (which is conductive). It is preferable that the gas chamber is fitted into the outer frame of the cathode having the above (preferably), and a part of the conductive porous body and a porous body provided separately form the gas chamber.

When the cathode part is formed using the gas diffusion electrode of the present invention, the following types of forms can be adopted. a) As shown in FIG. 1, the conductive porous body 2 is used as a substrate, and a gas permeable and hydrophobic gas supply layer 4 is formed in a layer on a part of the inside thereof, and on the gas supply layer 4, The surface is provided with a reaction layer 3 which is water-permeable and carries a catalyst.
The exposed portion 6 of the lower conductive porous body 2 where the gas supply layer is not provided serves as a portion forming a gas chamber. In FIG. 1, in order to show that the conductive porous body 2 is also present in the gas supply layer 4, the filler on the left side of the gas supply layer 4 is removed to expose the filled portion 5 of the conductive porous body 2. The result is shown. A part of the filling portion 5 also exists in the reaction layer 3.

B) As shown in FIG. 2, the conductive porous body 2 is a gas-permeable and hydrophobic material with the conductive porous body 2 as a substrate, leaving an exposed portion 6 in the form of a thin layer below the porous body 2. Which is formed as a permeable gas supply layer 4 and is provided with a reaction layer 3 having a water-permeable catalyst supported on the surface side opposite to the exposed exposed portion of the thin layer. In this type of cathode part, another conductive porous body 7 is combined with the gas diffusion electrode 1, and the exposed portion 6 in the thin layer of the porous body 2 and another conductive porous body 7 form a gas chamber. FIG. 2 also shows the filling portion 5 on the left side. c) As shown in FIG. 3, a conductive porous body 2 is used as a substrate, and a reaction layer 3 having water permeability and carrying a catalyst is formed on or (part of one side) of the porous body 2. What will be. Of course, when the gas diffusion electrode including the porous body exemplified in b) and c) is fitted into the cathode outer frame to form the cathode portion, there is no porous body in the gas chamber without combining other conductive porous bodies 7. It can also be used in the state.

As the conductive porous body of the present invention, a metal porous body is preferable, and examples thereof include a porous body of nickel or silver, and a continuous foamed body of plastic such as polyurethane plated with nickel, or plastic. Alternatively, the continuous foamed body may be plated with nickel and then sintered to form a nickel porous body. Further, it may be a carbon porous body or one plated with nickel. This conductive porous body not only gives strength to the gas diffusion electrode, but also acts as a current collector, and has a larger contact area with the electrode material than in the case of a mesh-shaped power feeding body such as a conventional wire mesh. A wire net may be used as the conductive porous body of the present invention.

The thickness of the conductive porous body is 0.01 to 10 m.
It is preferably m. Further, the installation mode of the gas supply layer and the like exemplified in the above a), b), and c) provided in the porous body differs depending on whether the gas supply layer is conductive or non-conductive, and the gas supply layer is conductive. When the gas supply layer is non-conductive, the conductive porous body does not have to reach the reaction layer by penetrating the gas supply layer, and the conductive porous body penetrates the gas supply layer when the gas supply layer is non-conductive. It is preferable to reach the reaction layer. That is, power can be supplied to the reaction layer by exposing the conductive porous body on the surface of the gas supply layer and providing the reaction layer on the exposed conductive porous body. Further, the conductive porous body may penetrate through the reaction layer and be exposed from the surface of the reaction layer to the catholyte compartment.

A gas supply layer provided in the conductive porous body
As an installation mode of the gas diffusion electrode without a gas supply layer
May be liquid-permeable, and as shown in FIG.
As the gas supply layer is not installed in the conductive porous body,
Water-repellent gas chamber is formed by water-repellent treatment of the porous material itself
However, a cathode may be formed by providing a reaction layer on it.
There is no gas supply layer installed like this example
Gas using a conductive porous body provided only with a reaction layer
When supplying hydrogen, prevent leakage of catholyte from the reaction layer
That is, at least one surface (gas chamber side) of the conductive porous body
The surface has a molecular weight of 3 × 10 by the rubbing method.^FiveFrom
0.5 x 10^FourUp to low molecular weight fluoropolymer
Can be achieved by Low molecular weight on the surface
Rubbing the fluorine resin is not possible with PTFE (polytetrafluor
Polyethylene) tape or other sheet of resin
Achieved by rubbing the powder. Molecular weight is 3 ×
10 ^FiveTo 0.5 x 10^FourLow molecular weight
Examples of the base resin include LUB manufactured by Daikin Industries, Ltd.
Product name Ron L-2, or Central Glass Co., Ltd.
Low-priced Cefral Lube 1
An example is a molecular weight tetrafluoroethylene resin.

The main constituent materials of the reaction layer are a catalyst made of a precious metal such as platinum, a mixture of fine particles of hydrophilic carbon and fine particles of water-repellent carbon, a small amount of fluororesin fine particles and binder particles connecting these fine particles. . The main constituent materials of the gas supply layer are water-repellent carbon fine particles, fluororesin fine particles, and binder particles connecting these fine particles.

As a method of providing the gas supply layer in the conductive porous body, the water repellent carbon fine particles, the fluororesin fine particles and the binder particles and other particles, which are the main constituent materials, are put into the porous body by a vibration method. , A method of forming a gas supply layer by heating and sintering, or mixing water-repellent carbon black, water and powdered polytetrafluoroethylene to prepare a slurry, and then applying this slurry to a conductive porous body on one side. (Or both sides), a method of removing the dispersant from the slurry before or after drying, if necessary, followed by drying and sintering.

As a method of partially providing the gas supply layer in the conductive porous body, the powder of the gas supply layer constituting material is put in a part, for example, half of the conductive porous body, and the remaining part is made of, for example, calcium carbonate. A water-repellent treatment gas chamber can be prepared by putting a powder of a soluble salt in water as described above, pressing it, and then dissolving and removing the salt such as calcium carbonate.
Further, together with the powder of the gas supply layer constituting material in the conductive porous body, after partially filling the powder of a soluble salt in water such as calcium carbonate in the direction in which the liquid flows and pressing, the salt is dissolved and removed, A liquid-permeable gas diffusion electrode can be prepared by partially allowing the catholyte to pass through the gas supply layer. In the present invention, the water-repellent carbon black in the gas supply layer constituent material may not be used.

In the gas diffusion electrode of the present invention, in the general case shown in FIG. 1, gas is supplied to the gas chamber side rather than the gas supply layer so that the gas chamber is filled with a conductive porous body. It has a portion where the conductive porous body is exposed without being covered with a layer, and this portion serves as a portion forming a gas chamber. When this gas diffusion electrode is installed in the cathode part, the part where the conductive porous body is exposed is installed in the gas chamber, and in the gas diffusion electrode developed earlier, a separate conductive porous body is placed in the gas chamber. The same structure as when loaded can be formed, and in this case, a similar effect can be obtained. In such a gas diffusion electrode, a gas is uniformly transmitted three-dimensionally, so that a large overvoltage does not occur during electrolysis. Further, this gas diffusion electrode does not need to be provided with a current collector as in the conventional case. The current applied to the gas diffusion electrode can be evenly and efficiently applied to the entire surface. Because of such characteristics, when salt water is electrolyzed in an electrolytic cell using the gas diffusion electrode of the present invention, electrolysis can be performed with an extremely low electrolysis voltage and current efficiency.

In the production of this gas diffusion electrode, a conductive porous body is filled and molded with a substance for forming a gas supply layer, and then compacted if necessary and sintered to complete. When carbon black is not used, for example, when only silver fine particles and fluororesin are used for molding at room temperature, the pressing pressure is 20 to 60 kg / cm ² , and the sintering is 200 to
Perform at 300 ° C. When molding is performed by a hot press, the press temperature is 150 to 300 ° C and the pressure is 1 to 5 kg.
/ Cm ² is preferable. When using carbon black, it is desirable to press at 50 kg / cm ² , 380 ° C. for 1 minute. When the material for the gas supply layer or the material for the reaction layer is sludge, and when the sludge is applied or pressed into the conductive porous body to fill and mold the electrode layer, it is used to disperse from the sludge at this molding stage. The dispersant is washed and removed, and then sintered to complete the process. Surfactants are usually used as the dispersant used to make the slurry. As the surfactant to be used, any of nonionic, anionic and cationic surfactants can be used alone or in combination, but the nonionic surfactant is preferred. Further, the surfactant may be contained in a material used for manufacturing an electrode, for example, a suspension solution of polytetrafluoroethylene, or the like.

In the production of the reaction layer in the gas diffusion electrode of the present invention, a method of filling a catalyst having an electrocatalytic action and a sludge from the electrode constituent material into the pores of the conductive porous body so as not to dry is used. To be At that time, the slurry is uniformly filled in the conductive porous body to form a gas diffusion electrode layer having a required thickness. As the activation catalyst mixed in the reaction layer of the gas diffusion electrode of the present invention, the following catalysts are suitable, and the catalyst obtained in the steps shown therein can be used. Platinum black: A step of adhering a catalyst salt such as a platinum salt on the surface of a catalyst carrier such as carbon black, and heating and reducing with hydrogen in an inert gas atmosphere to obtain platinum black. Reduced silver: Silver fine particles adhered to carbon black by adhering a catalyst salt such as silver nitrate on the surface of a catalyst carrier such as hydrophilic carbon black, drying the powder at 80 ° C., heating and reducing at 150 ° C. with hydrogen. And the process.

The Teflon dispersion used as one of the constituent materials for the reaction layer and the gas supply layer of the gas diffusion electrode of the present invention is preferably Teflon Dispersion 30J manufactured by Mitsui Fluorochemical Co., Ltd., for example. With the new technology of the various items described in detail above and the integrated manufacturing method of the present invention using a new material, good workability is achieved in simple steps,
It becomes possible to continuously and efficiently manufacture a large gas diffusion electrode.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

1. Production of conductive porous body 200 mm (length) x 300 mm (width) x 2 mm (thickness)
Rigid polyurethane foam (porosity 50 ppI (number of bubbles /
Inch)) plate with nickel chloride 5μ
A nickel porous body (porosity 50 ppI) obtained by electrolessly plating to a thickness of m is used as a current collector.
This is further plated with 5 μm of silver. 2. Production of electrode material Composition i) Catalyst: fine silver powder average particle size 0.1 μm ii) Hydrophilic carbon black (AB-7; Denka black): Average particle size 400Å iii) Water repellent carbon black (No. 6; Denka) Black): Average particle size 500Å iv) Polytetrafluoroethylene suspension polymerization liquid (Polyflon dispersion, D-1; manufactured by Daikin Industries, Ltd.): Average particle size 0.3 μm Dispersant: Triton X-100

Preparation of Sludge-1 Preparation of Sludge for Gas Supply Layer PTFE (dispersion, D-1; manufactured by Daikin Industries) and water-repellent carbon black (No. 6, average particle size)
500Å, prototype, manufactured by Denki Kagaku Kogyo) in weight ratio of 2: 3
Was mixed and dispersed in 100 parts by weight of an aqueous solution containing 20% of Triton X-100, and filtered to obtain a slurry. -2 Preparation of sludge for reaction layer Silver fine particles (average particle size 0.1 μm, manufactured by Mitsui Mining & Smelting) and P
TFE (dispersion, D-1; manufactured by Daikin Industries, Ltd.)
And hydrophilic carbon black (AB-11, average particle size 4
00Å, manufactured by Denki Kagaku Kogyo) and water-repellent carbon black (No. 6, average particle size of 500Å, manufactured by Denki Kagaku Kogyo) were mixed at a weight ratio of 3: 1: 1: 1 (100).
(Parts by weight) was dispersed and mixed in 100 parts by weight of an aqueous solution containing 20% of Triton X-100, and filtered to obtain a slurry.

3. Filling of the gas supply layer slurry into the conductive porous body The gas supply layer slurry was uniformly pushed into the conductive porous body from one side thereof. It was dried at 80 ° C. for 2 hours. 4. Application of Reaction Layer Sludge to Conductive Porous Body The reaction layer slurry is applied onto the gas supply layer of the conductive porous body on which this gas supply layer is formed, dried at 80 ° C. for 2 hours, and then a surfactant is added with alcohol. Triton X-100 was removed, dried again, pressed at a pressure of 50 kg / cm ² , and then 350 ° C.
And sintered for 10 minutes to obtain a gas diffusion electrode. The gas diffusion electrode was filled in the outer frame of the cathode to form a cathode part.

Example 2 To a 12 × 28 cm square plate composed of 5 μm silver-plated 50 ppI foamed nickel porous body, ethanol was first added to Lubron to form a paste, which was coated on the foamed nickel plate to form a gas supply layer. 3 parts of fine silver particles (Mitsui Metal Co., Ltd., 3010, average particle size 0.11 μm) and 1 part of rublon, which are to be formed and then become a reaction layer, are kneaded with ethanol to form a paste,
Apply from above to a thickness of 200 μm, 10 kg / cm
^A gas supply layer and a reaction layer are formed by pressing at a pressure of ² and pushing it inside. By this operation, the reaction layer and the silver-plated nickel foam plate come into contact with each other. Dry at 80 ° C for 3 hours, press at room temperature at a pressure of 40 kg / cm ² for 60 seconds, and
An electrode was obtained by heat-treating at 10 ° C. for 10 minutes and cooling. When the oxygen reduction performance of this electrode was measured, it was 30 A
A high performance of 0.79 V (vs. RHE) at / dm ² was obtained. The contact resistance between the back surface of the electrode and the silver-plated foam nickel plate in the gas chamber showed a small value of 1 mΩ / cm ² or less.

[0028]

INDUSTRIAL APPLICABILITY The gas diffusion electrode of the present invention has a low electric resistance and is used as an oxygen cathode in an electrolytic cell comprising a cation exchange membrane to electrolyze salt water at an extremely low electrolysis voltage and current efficiency. can do. Also,
Since an electrode having high strength can be obtained and the porous body portion which becomes the portion of the gas chamber can be integrally formed and obtained, a large-sized gas diffusion electrode can be efficiently manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an example of a gas diffusion electrode of the present invention.

FIG. 2 is a cross-sectional explanatory view showing another example of the gas diffusion electrode of the present invention.

FIG. 3 is an explanatory sectional view showing a gas diffusion electrode of the present invention having only a reaction layer.

FIG. 4 is a cross-sectional explanatory view showing an example of a cathode part in which the gas diffusion electrode of the present invention is installed.

FIG. 5 is a cross-sectional explanatory view showing another example of the cathode part in which the gas diffusion electrode of the present invention is installed.

FIG. 6 shows a cross-sectional explanatory view of a conventional gas diffusion electrode having a reticulated power supply member inside.

FIG. 7 shows a cross-sectional explanatory view of a conventional gas diffusion electrode having a reticulated power supply inside and on the surface.

[Explanation of symbols]

1 gas diffusion electrode 2 Conductive porous body 3 reaction layers 4 gas supply layer 5 filling part 6 exposed part 7 Conductive porous body 8 Reticulated power supply 9 Cathode outer frame 10 Reticulated power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Choichi Furuya 2-14 Nakamura-cho, Kofu-shi, Yamanashi (56) Reference JP-A-5-287571 (JP, A) JP-A-8-302493 (JP, A) ) JP-A-6-212469 (JP, A) JP-A-8-283980 (JP, A) JP-A-10-110285 (JP, A) JP-A-10-158877 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (3)

(57) [Claims] 1. A reaction layer is formed on one surface of a conductive porous body such that at least a part thereof is inside the conductive porous body, and a portion on the other surface side of the conductive porous body has no reaction layer. A gas diffusion electrode, wherein at least a part of a gas chamber is formed in an exposed state. 2. A gas supply layer is formed as a layer on a part of the conductive porous body, and a reaction layer is laminated on one side of the conductive porous body in contact with the gas supply layer. A gas diffusion electrode, characterized in that the portion on the other surface side of the porous body does not have the gas supply layer and forms at least a part of the gas chamber in an exposed state. 3. The gas diffusion electrode is supplied with power by contacting or joining the conductive porous body forming at least a part of the gas chamber in the exposed state with the electrolytic cell frame. The gas diffusion electrode according to claim 1 or claim 2.