JP2010180441A - Gas diffusion electrode, method for producing the same and electrolyzing method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion electrode which is low in oxygen reduction pressure in the electrolyzing application of water or an aqueous alkali metal chloride solution, to provide a method for producing the gas diffusion electrode, and to provide an electrolyzing method using the gas diffusion electrode. <P>SOLUTION: The blending ratio between a silver catalyst and a conductive carrier is optimized, and the porosity in the electrode is increased. Concretely, in a gas diffusion electrode C using a conductive base material, a silver catalyst, a conductive carrier and a fluorine-containing resin, the gas diffusion electrode C in which the weight ratio of the silver catalyst/(the silver catalyst+the conductive carrier) lies in the range of 0.1 to 0.5, the porosity of the ones with the pore diameter of 0.01 to 10 μm is ≥60%, and also, the secondary particle size of silver particles on the surface of the conductive carrier is ≤1 μm is obtained, after contacting with a conductive carrier dispersion liquid containing a surfactant and a reducing substance and a water solution silver solution, by adding a fluorine-containing resin thereto, subjecting them to dispersing, mixing, solid-liquid separation, drying and pulverization so as to be powder, and molding the powder onto the conductive base material, and performing firing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas diffusion electrode used for electrolysis of water or electrolysis of an aqueous solution of alkali metal chloride such as salt, a method for producing the same, and an electrolysis method using the same.

  The water or alkali metal chloride aqueous solution electrolysis industry is a power intensive industry, and various technological developments have been made to save energy. As the water or alkali metal chloride aqueous solution electrolysis method, an ion exchange membrane method in which the cathode reaction is a hydrogen generation reaction is usually used. On the other hand, as an electrolysis method that is expected to save energy compared to the ion exchange membrane method, there is a gas diffusion electrolysis method using an oxygen reduction reaction for the cathode reaction, but the oxygen reduction overvoltage of the gas diffusion electrode is very high. It is insufficient for energy saving.

  The components of the electrolysis voltage mainly consist of a theoretical electrolysis voltage, a liquid resistance, a diaphragm resistance, an anode overvoltage, and a cathode overvoltage, and energy saving is to reduce the electrolysis voltage. In particular, the reduction in overvoltage depends on the electrode catalyst material and the electrode surface morphology, and so much research and development has been conducted on its improvement. For example, as a result of extensive research and development for reducing anode overvoltage, a dimensionally stable electrode [for example, DSE electrode (registered trademark) manufactured by Permerek Electrode Co., Ltd.] having low anode overvoltage and excellent durability has been completed. It is already used in a wide range of fields including the salt electrolysis industry.

  On the other hand, many proposals have been made regarding the reduction of the cathode overvoltage, that is, the oxygen reduction overvoltage of the gas diffusion electrode.

  The structure of the gas diffusion electrode is a laminated structure composed of a gas diffusion layer and a reaction layer, and a current collector for emphasizing and supplying electric power is embedded inside, and the electrode reaction is carried out by oxygen gas from the gas diffusion layer on the back of the electrode. Then, oxygen gas, water, and electrons react on the electrode catalyst inside the reaction layer on the front surface of the electrode to be reduced to hydroxide ions.

  Regarding the oxygen reduction overvoltage of the gas diffusion electrode, it is generally considered effective to reduce the overvoltage by improving the electrocatalytic activity, improving the reaction efficiency by making the catalyst fine and highly dispersed, and improving the gas diffusibility. Examples of the electrode catalyst include platinum and silver as highly active catalysts. However, inexpensive silver is preferably used, and a silver catalyst or a gas diffusion electrode to which a rare earth element is added is disclosed (for example, Patent Document 1 and Patent Document). 2).

  In addition to platinum and silver, a gas diffusion electrode using a perovskite type oxide as a catalyst is also disclosed (see, for example, Patent Document 3). On the other hand, a manufacturing method using the reverse micelle method is low overvoltage performance. Due to the high cost, it is not practical as an industrial process.

  Furthermore, fine particles having a primary particle diameter of the sub-micron of the catalyst are usually used for the dispersion state of the catalyst used in the gas diffusion electrode, but actually, these fine particles are secondary aggregates aggregated on the micro order. Therefore, it is difficult to disperse secondary aggregates to the primary particle level by mixing and dispersing raw materials in electrode production. As a result, the reaction efficiency of the catalyst particles inside the gas diffusion electrode is low because of low dispersibility. Had problems such as.

  On the other hand, regarding the gas diffusibility of the gas diffusion electrode, a hot press was used as an electrode molding means and molding was performed at a high temperature and a high pressure. Therefore, the internal gap was small and the gas diffusibility was not sufficient.

  As described above, various gas diffusion electrodes have been proposed for the purpose of reducing the power consumption of the water or alkali metal chloride aqueous solution electrolysis industry, but high dispersion and high gas diffusibility of highly active catalysts have been proposed. A combined gas diffusion electrode has not been obtained.

JP-A-9-41181 JP 2007-70645 A JP 2003-288905 A

  An object of the present invention is to provide a gas diffusion electrode having a sufficiently low oxygen reduction overvoltage that can be used in water or alkali metal chloride aqueous solution electrolysis industry, a method for producing the gas diffusion electrode, and the gas diffusion electrode as a cathode. It is to reduce the power consumption of water or alkali metal chloride aqueous solution electrolysis industry.

  As a result of intensive studies to solve the above problems, the present inventors have optimized the mixing ratio of the silver catalyst and the conductive carrier, increased the porosity of the electrode, and highly dispersed the silver catalyst. In a gas diffusion electrode using a base material, a silver catalyst, a conductive carrier, and a fluororesin, the weight ratio of silver catalyst / (silver catalyst + conductive carrier) is in the range of 0.1 to 0.5, and pores A gas diffusion electrode having a high dispersion of a silver particle on a conductive support with a porosity of 60% or more having a diameter of 0.01 to 10 μm and a secondary particle diameter of 1 μm or less exhibits excellent oxygen reduction overvoltage performance. I found out.

  Furthermore, the gas diffusion electrode of the present invention is obtained by bringing a conductive carrier dispersion containing a surfactant and a reducing substance into contact with a water-soluble silver solution, and then adding a fluororesin, and dispersing, mixing, solid-liquid separation, and drying. When the pulverized powder is molded on a conductive substrate and baked, the gas diffusion electrode is obtained, and the gas diffusion electrode is used as a cathode in water or an aqueous alkali metal chloride solution. The present inventors have also found that the oxygen reduction overvoltage is extremely low and have completed the present invention. Hereinafter, the present invention will be described in detail.

  The gas diffusion electrode of the present invention is a gas diffusion electrode using a conductive substrate, a silver catalyst, a conductive carrier and a fluorine resin, and the weight ratio of silver catalyst / (silver catalyst + conductive carrier) is 0.1 to 0.1. 0.5, the porosity of the pore diameter of 0.01 to 10 μm is 60% or more, and the secondary particle diameter of the silver particles on the surface of the conductive support is 1 μm or less.

  For example, such a gas diffusion electrode is obtained by bringing a conductive carrier dispersion containing a surfactant and a reducing substance into contact with a water-soluble silver solution, and then adding a fluororesin and dispersing, mixing, solid-liquid separation, and drying. The pulverized powder can be produced by molding on a conductive substrate and firing, and when the gas diffusion electrode is used for electrolysis of water or an aqueous alkali metal chloride solution, the oxygen reduction overvoltage is excellent. Performance.

  Regarding the compounding ratio of the silver catalyst and the conductive carrier of the gas diffusion electrode of the present invention, the weight ratio of silver catalyst / (silver catalyst + conductive carrier) is preferably in the range of 0.1 to 0.5. When the blending ratio is less than 0.1, the ratio of the conductive carrier that forms pores increases and the porosity increases, but the silver catalyst amount itself is insufficient, and conversely, when it exceeds 0.5, pore formation occurs. In any case, the reduction of the oxygen reduction overvoltage becomes insufficient because the porosity decreases, such as a lack of the amount of the conductive carrier to be carried out, or pore clogging between the conductive carriers due to silver particles precipitated by wet reduction. In the production of the gas diffusion electrode described below, this raw material blending ratio is substantially maintained in the electrode composition after the production of the electrode.

  The role of the voids in the gas diffusion electrode is to increase the supply of oxygen gas, which is a reactant, and the diffusibility, so as to improve the efficiency of the oxygen reduction reaction.

  Regarding the pore diameter of the gas diffusion electrode, since the mean free path of oxygen gas is usually about 0.1 μm, when the pore diameter is 0.1 μm or less, oxygen molecules have a high frequency of collision with the pore walls, so-called Knudsen diffusion is dominant, and the diffusibility of oxygen gas is lowered. Conversely, when the pore diameter is increased, the gas diffusibility is improved. However, when the pore diameter exceeds 10 μm, pore clogging due to water permeation into the electrode, so-called flooding, is liable to occur.

  Therefore, the larger the number of pores having a pore diameter of 0.01 to 10 μm, the better because oxygen gas diffusion proceeds better. The larger the number of pores, the larger the porosity.

  As for the porosity of the gas diffusion electrode, the porosity of the gas diffusion electrode of the present invention must be 60% or more with a pore diameter of 0.01 to 10 μm. The reason for this is that when the amount is less than 60%, the amount of oxygen in the gap is insufficient with respect to the reaction consumption, resulting in insufficient oxygen inside the electrode, resulting in insufficient reduction of the oxygen reduction overvoltage. is there.

  About the dispersion state of the silver particle inside the gas diffusion electrode of this invention, it is essential that the secondary particle diameter of the silver particle on an electroconductive support | carrier is 1 micrometer or less. When the secondary particle diameter of the silver particles is 1 μm or more inside the electrode, the effective reaction surface area with oxygen gas is reduced, so that the reaction efficiency with the oxygen gas-silver catalyst is lowered. Become.

  The gas diffusion electrode of the present invention is obtained by, for example, molding a powder obtained by dispersing, mixing, solid-liquid separation, drying, and pulverizing a silver catalyst, a conductive carrier, and a fluororesin in an aqueous surfactant solution onto a conductive substrate. Any manufacturing method may be used as long as a gas diffusion electrode having a porosity of 60% or more can be obtained.

  Hereinafter, in the gas diffusion electrode using the conductive substrate, the silver catalyst, the conductive carrier, and the fluorine resin provided by the present invention, the silver catalyst / (silver catalyst + conductive carrier) weight ratio is 0.1 to 0. A specific method for producing a gas diffusion electrode that is in the range of 0.5, the porosity of the electrode is 60% or more, and the secondary particle diameter of the silver particles on the conductive support is 1 μm or less will be described.

  Examples of the conductive substrate used in the present invention include nickel, iron, copper, titanium, and stainless steel alloy, and nickel having excellent corrosion resistance against an alkaline solution is particularly preferable. The shape of the conductive substrate is not particularly limited, and may generally be a shape that matches the electrode of the electrolytic cell. For example, a flat plate, a curved plate, or the like can be used.

  In addition, the conductive substrate used in the present invention is preferably a perforated plate, and for example, expanded metal, punch metal, and net can be used.

  The surfactant of the present invention only needs to be able to uniformly disperse each raw material, and examples thereof include ether type, ester type, ether ester type, alcohol ethoxylate, etc. For example, Triton X-100 which is a nonionic surfactant is used. What is necessary is just to disperse | distribute to the used aqueous solution. In addition, if an ultrasonic dispersion process is performed, it can disperse | distribute efficiently.

  The conductive carrier of the present invention is a material having hydrophobicity in order to prevent electrical conductivity, pore formation and pore clogging due to water penetration into the electrode, so-called flooding, such as acetylene black, ketjen black And hydrophobic carbon such as carbon black and graphite.

  The reducing substance of the present invention may be any substance that can reduce silver ions in a water-soluble silver solution to metallic silver, and examples thereof include hydrogen, hydrazine, borohydrides, saccharides, ascorbic acid, formalin, and tartaric acid. .

  Next, for the conductive carrier dispersion containing the surfactant and the reducing substance, the concentration of the surfactant is preferably the minimum amount that can be dispersed, and can be exemplified by 2 to 10% by weight. It is sufficient that the amount of the silver ion in the water-soluble silver solution is equal to or more than that which can be reduced. Further, when the concentration of the conductive carrier is higher than 10% by weight, the dispersion may not be stirred, so the concentration is preferably 10% by weight or less, more preferably 5% by weight or less. .

  Examples of the water-soluble silver solution of the present invention include water-soluble silver salts such as silver nitrate, silver acetate, silver sulfate, silver chloride, and silver carbonate. These are present as silver ions in an aqueous solution, but an aqueous ammonia solution is added. In addition, they may be present as complex ions such as silver ammonium ions.

  The method of contacting the conductive carrier dispersion of the present invention with the water-soluble silver solution is a method of adding the conductive carrier dispersion to the water-soluble silver solution under stirring or adding the water-soluble silver solution to the conductive carrier dispersion. The silver ions are reduced by the contact between the silver ions in the water-soluble silver solution and the reducing substance, and the precipitated metallic silver can be supported on the conductive carrier.

  Next, a fluorine-based resin is added. The fluorine-based resin has a binder function for binding silver and a conductive carrier and has a water repellency for preventing flooding. As the fluororesin used, for example, a powder or dispersion (dispersion) of polytetrafluoroethylene (PTFE), tetrafluoroethylene copolymer (FEP), (PFE), etc. can be used, and the amount added is a binder. It is sufficient if water repellency can be imparted to prevent the function and flooding. For example, the weight ratio of fluororesin / conductive carrier is preferably about 0.2 to 2.

  After the raw materials are mixed in this manner, filtration and cleaning of the surfactant are performed to recover the gas diffusion electrode raw material powder. In order to perform filtration and washing efficiently, particles are aggregated in advance using alcohol. The alcohol to be used is not particularly limited, and examples thereof include ethanol, methanol, butanol and the like, and ethanol may be used for general purposes. The filtered and washed product is dried and then pulverized using a pulverizing mixer or mill to obtain a gas diffusion electrode raw material powder.

  Next, a gas diffusion electrode is produced using the gas diffusion raw material powder. The production method is to mold the gas diffusion raw material powder on the conductive substrate. The method is a press method using a mold, a hot press that heats simultaneously with the molding, and the kneaded raw material powder is molded with a roll molding machine. However, there is no particular limitation as long as the porosity of the obtained gas diffusion electrode having a pore diameter of 0.01 to 10 μm is 60% or more.

  Next, the molded product is fired for the purpose of improving the strength and decomposing the remaining surfactant. The firing temperature is such that the melting point of the fluororesin is around 250 ° C. and the decomposition temperature of the surfactant is about 220 ° C. Therefore, the firing temperature is preferably in the range of 200 ° C. to 350 ° C., and the firing time is from 5 minutes to It is preferable to carry out for about 20 minutes.

  The gas diffusion electrode of the present invention obtained in this way can be used as an oxygen reduction electrode in the electrolysis of an aqueous solution of alkali metal chloride such as water or sodium chloride, and a low oxygen overvoltage can be obtained. By using the electrode, the energy required for electrolysis can be easily reduced.

  The gas diffusion electrode of the present invention has a low oxygen reduction overvoltage, and when used for electrolysis of an aqueous solution of alkali metal chloride such as water or salt, the required energy can be greatly reduced.

The ring cell structure made from Teflon (trademark) used by the measurement of oxygen reduction overvoltage is shown.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  In addition, each evaluation was implemented by the method shown below.

(Oxygen reduction overvoltage evaluation cell)
The produced gas diffusion electrode was cut out and attached to a cell as shown in FIG. 1 for evaluation. The measurement cell has a ring cell structure made of Teflon (registered trademark), and the gas diffusion electrode is supplied to the back surface of the electrode through the oxygen gas supply pipe while keeping the gas tightness by the O-ring. It is a structure supplied through a platinum wire-platinum mesh.

(Oxygen reduction overvoltage evaluation)
In the oxygen reduction overvoltage evaluation, pure oxygen gas was supplied at a rate of 100 ml / min, and the electrolyte was a 32 wt% sodium hydroxide aqueous solution (capacity: about 1 L), a platinum plate as a counter electrode, temperature 90 ° C., current Electrolysis was performed under conditions of a density of 6 kA / m ^{2 and} measurement was performed by a current interrupter method.

(Pore volume evaluation)
The pore structure was measured by measuring a pore volume of 0.003 μm to 400 μm using a mercury porosimeter (manufactured by Shimadzu Corporation: Autopore 9510) using a mercury intrusion method, and the ratio of the pore volume of 0.01 to 10 μm was used as the porosity. Asked.

(Secondary particle size)
The cross section of the produced gas diffusion electrode was measured from a secondary electron reflection image by a scanning electron microscope (JEOL Datum Co., Ltd., JSM-6390 type, magnification: 20000, 10000 times), and the particle diameter of 100 silver particles was measured. A simple average value was measured for the purpose.

Example 1
As an electroconductive carrier, 3 g of acetylene black (manufactured by Cabot: CX-72R) was added to 200 ml of an aqueous solution of a nonionic surfactant (Triton X-100) adjusted to 2% by weight, and ultrasonic dispersion was performed for about 10 minutes. 3 ml of an aqueous solution of% hydrazine was added.

  Next, an aqueous silver nitrate solution (0.14 mol / L-100 ml) is added at a rate of 5 ml / min while stirring the conductive carrier dispersion, and the mixture is stirred for 30 minutes to add metal silver fine particles to the surface of the conductive carrier. Precipitated. The weight ratio of silver catalyst / (silver catalyst + conductive support) was 0.33.

  Next, 1.25 g of PTFE dispersion (Mitsui DuPont Fluorochemicals: 31J) was added and stirred, then ethanol was added to agglomerate, suction filtration, washing and drying were performed, and the dried powder was pulverized with a mixer, and silver-conductive A conductive carrier-fluorine resin powder was prepared.

Next, a silver expanded mesh (3 × 3 cm) was laid using a mold, and 2 g of the crushed powder was molded at a molding pressure of 9.8 × 10 ⁶ Pa (100 kg / cm ² ).

  The molded body was fired in a box-type muffle furnace (model KM-600 manufactured by Advantech Toyo Co., Ltd., internal volume 27 L) at 300 ° C. for 15 minutes under an air flow to produce a gas diffusion electrode of the present invention.

  Next, measurement results of the oxygen reduction overvoltage and pore volume of the gas diffusion electrode are shown in Table 1, and a series of gas diffusion electrodes were prepared and evaluated twice.

Example 2
The same operation as in Example 1 was carried out except that the ratio between the conductive carrier and the silver powder was changed. The results evaluated by the above method are shown in Table 1, and a series of gas diffusion electrodes were prepared and evaluated twice.

比較例１
導電性担体と銀粉末の割合を変化させた以外は、実施例１と同様の操作で実施した。上記の方法で評価した結果を表２に示した。

Comparative Example 1
The same operation as in Example 1 was performed except that the ratio of the conductive carrier and the silver powder was changed. The results of evaluation by the above method are shown in Table 2.

Comparative Example 2
Nonionic surfactant (Triton X-) in which 3 g of acetylene black (manufactured by Cabot: CX-72R) and 1.5 g of silver powder (manufactured by Fukuda Metal Foil Industry: AgC-H) were adjusted to 2% by weight as conductive carriers. 100) The solution was added to 200 ml of an aqueous solution and subjected to ultrasonic dispersion for about 10 minutes. The Ag / (Ag + C) weight ratio is 0.33.
Next, 1.25 g of PTFE dispersion (Mitsui DuPont Fluorochemicals: 31J) was added and stirred, then ethanol was added to agglomerate, suction filtration, washing and drying were performed, and the dry powder was pulverized with a mixer. The same operation as in Example 1 was performed. The results of evaluation by the above method are shown in Table 2.

Comparative Examples 3-7
The same operation as in Comparative Example 2 was performed except that the ratio of the conductive carrier and the silver powder was changed. The results of evaluation by the above method are shown in Table 2.

Comparative Example 8
The same operation as in Example 1 was performed except that the electrode molding method was hopless at 380 ° C. and a pressure of 4.9 × 10 ² Pa (50 kg / m ² ) for 1 minute. The results of evaluation by the above method are shown in Table 2.

実施例１〜２の結果より、本発明が提供するガス拡散電極は酸素還元過電圧が低い、優れた特性を有することが明らかである。

From the results of Examples 1 and 2, it is clear that the gas diffusion electrode provided by the present invention has excellent characteristics with low oxygen reduction overvoltage.

  On the other hand, by comparison with the results of Comparative Examples 1 to 8, as in the gas diffusion electrode of the present invention, the silver catalyst / (silver catalyst + conductive support) weight ratio is in the range of 0.1 to 0.5, The effect of the present invention cannot be obtained unless the porosity of the pore diameter of 0.01 to 10 μm is 60% or more and the secondary particle diameter of the silver particles on the surface of the conductive support is 1 μm or less. Is clear.

A: Platinum wire B: Oxygen gas supply pipe C: Gas diffusion electrode D: O-ring E: Platinum mesh

Claims (3)

In a gas diffusion electrode using a conductive base material, a silver catalyst, a conductive carrier and a fluororesin, the weight ratio of silver catalyst / (silver catalyst + conductive carrier) is 0.1 to 0.5, and pores A gas diffusion electrode in which a porosity of 0.01 to 10 μm in diameter is 60% or more, and a secondary particle diameter of silver particles on the surface of the conductive support is 1 μm or less. After contacting the conductive carrier dispersion containing the surfactant and the reducing substance with the water-soluble silver solution, the fluororesin is added, and the dispersed, mixed, solid-liquid separated, dried and pulverized powder is added to the conductive group. The method for producing a gas diffusion electrode according to claim 1, wherein the gas diffusion electrode is molded and fired on a material. A method for electrolyzing water or an aqueous alkali metal chloride solution using the gas diffusion electrode according to claim 1.

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