JP3238773B2 - Manufacturing method of electrode for electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode for electrolysis, and more particularly to an electrode suitable for electrolysis using a solid polymer electrolyte and a method for producing the same.

[0002]

2. Description of the Related Art A solid polymer electrolyte is used in an electrolytic cell or a fuel cell. Generally, an ion exchange membrane is used as a polymer solid electrolyte,
An electrode is formed directly on the surface of the ion exchange membrane, or the electrode is adhered to the ion exchange membrane. The electrolysis method of performing an aqueous solution electrolysis using an electrolytic cell using a polymer solid electrolyte initially allows the distance between the cathode and anode to approach the thickness of the ion exchange membrane, and almost eliminates ohmic loss due to the electrolyte. Attention was paid to the power saving effect, and much research and development was done.

However, almost the same effect can be obtained by simply contacting an electrode with an ion exchange membrane for the purpose of power saving, as actually seen in the electrolysis by the ion exchange membrane method of a saline solution. Due to the fact that it is difficult to produce a large-area electrode-solid-electrode-integrated electrode, little attention has been paid at present.

Therefore, an electrolytic cell using a solid polymer electrolyte has been put to practical use in an organic electrolysis apparatus or an ozone generation apparatus using electrolysis, which has problems such as corrosion and undesired side reactions occurring with ordinary metal electrodes. ing. A typical technique is a method of depositing an electrode catalyst metal such as a platinum group metal on the surface of an ion exchange membrane by electroless plating. This is because under conditions where the metal is stable as an electrode material,
That is, it has been applied to cathodes under acidic, neutral or alkaline conditions, and some have also been used as anodes.

[0005] This method is simple in the method of forming an electrode and is an effective method for forming an electrode on a solid polymer electrolyte. However, this method uses an alloy composed of two or more metals as an electrode catalyst or a compound. The use of a stable oxide electrode catalyst as an anode, particularly as an anode, has been limited to some substances. Further, baking of a powder of a catalyst substance such as an oxide together with a binder such as a fluororesin on an ion exchange membrane is also performed. In this method, it is possible to use metals, oxides or other compounds or mixtures as the catalytic material, but the catalyst used for this is usually
The use of a single metal, oxide or other powder has been limited.

An electrode using an oxide-based electrode catalyst material includes an electrode in which a composite oxide composed of a platinum group metal oxide and a titanium oxide is formed on a base of a thin film-forming metal such as titanium. Known as insoluble electrodes. These complex oxides form a complex oxide on the surface of a metal substrate by applying a solution containing a compound of a platinum group metal and a compound such as titanium on a substrate such as titanium and baking in a oxidizing atmosphere. Manufactured by the method. However, since the method of forming a composite oxide on the surface of a metal substrate is fired at a temperature of several hundred degrees, it cannot be applied to the formation of an electrode on the surface of an organic substance such as an electrode formed on a solid polymer electrolyte. It is.

Further, when fine particles of a composite oxide obtained by simply firing and pulverizing a solution of a metal compound forming a composite oxide are coated on a solid polymer electrolyte using a fluororesin or the like as a binder, The oxide fine particles do not have a uniform composition, and are not fine particles having excellent catalytic activity, and it is not possible to obtain an electrode of a polymer solid electrolyte having excellent electrochemical characteristics. It was also difficult to adjust according to the purpose of use of the electrode.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrode for a solid polymer electrolyte comprising a composite oxide having excellent electrochemical properties, and particularly to an electrode for a desired electrochemical reaction. An object of the present invention is to provide a method for manufacturing an electrode for a solid polymer electrolyte, which can arbitrarily control the characteristics of an electrode catalyst material.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a method of calcining a precipitate coprecipitated with an alkali from an aqueous solution containing a platinum group metal compound and at least one of a group 4 or group 5 metal compound. This is a method for producing an electrode for electrolysis in which fine particles of a substance are kneaded with a binder and applied to the surface of an ion exchange membrane. Further, the present invention is a method for producing an electrode for electrolysis, wherein the platinum group metal compound contains at least one compound selected from ruthenium chloride, ruthenic chloride, iridium chloride, and iridium chloride.

[0010] Further, there is provided a method for producing an electrode for electrolysis wherein the Group 4 metal compound contains at least one of a titanium compound and a tin compound.

This is a method for producing an electrode for electrolysis in which a fluororesin is used as a binder, kneaded with fine particles of a fired product, applied to an ion exchange membrane and sintered.

The composite oxide of the electrode catalyst used for the electrode for electrolysis according to the present invention is obtained by coprecipitating the electrode catalyst as a hydrate and a hydroxide by adding an alkali to a mixed solution of salts constituting the electrode catalyst. A coprecipitate comprising uniform fine particles is produced, and the coprecipitate is heated and calcined to form a uniform solid solution or an oxide comprising a mixture. In the oxide thus obtained, a plurality of metal oxides constituting the electrode catalyst are homogeneously mixed, and exhibit an effect as the electrode catalyst.

Hereinafter, a method for producing an electrode catalyst will be described.
In the electrode catalyst for chlorine generation, in order to control the chlorine generation potential and the oxygen generation potential, use ruthenium oxide or a mixture of ruthenium oxide and iridium oxide as a catalyst substance, and add tin or titanium oxide to it. Good. Specifically, an aqueous hydrochloric acid solution of ruthenium chloride or a mixture of ruthenium chloride and iridium chloride, an aqueous hydrochloric acid solution of an inorganic compound such as titanium tetrachloride or titanium trichloride, or an organic compound such as orthotetrabutyl titanate, or a mixture of alcohol and hydrochloric acid An aqueous solution of an alkali such as aqueous ammonia is added dropwise while stirring a solution containing the solution as a solvent at a predetermined ratio, and the acid is neutralized. When approaching the neutralization point, titanium and ruthenium, or ruthenium and iridium, gradually co-precipitate as hydroxides or hydrates. Still further, the ammonia water is continuously dropped to make it slightly alkaline. Next, after the dropping of the aqueous ammonia is stopped, stirring is continued for a while, and the mixture is allowed to stand for 2 to 4 hours in order to grow floc of the precipitate as it is. Thereafter, the precipitate and the solution are separated by filtration with a glass filter or the like, and the coprecipitate is washed with water. When ammonia water is used as the alkali, the ammonia can be easily removed in the subsequent baking step, but when neutralized with an alkali solution containing a metal alkali, it is sufficient to completely remove the alkali metal salt. Need to be cleaned.

The washed precipitate is first air-dried and then fired in a weakly oxidizing or inert atmosphere such as in air. The temperature is suitably from 350 to 500 ° C. and is adjusted according to the type of the electrode catalyst, but is preferably from about 70 to 120 minutes. Thereby, an oxide composite is obtained. Although the state varies depending on the composition, it is characterized in that it is a solid solution, a mixture, or a mixture thereof, all of which are crystalline. If the generated electrode catalyst is in the form of a lump, it is pulverized into fine particles and then used as an electrode material.

The particle size of the electrode catalyst is preferably from 1 to 100 μm, particularly preferably from 5 to 30 μm.
The particles are kneaded with a binder and applied to the surface of the ion exchange membrane. As the binder, a fluororesin is preferably used, and an aqueous suspension of polytetrafluoroethylene is preferably used. When a fluororesin is used as the binder, the electrodes are formed by kneading the particles, applying the particles to the surface of the ion exchange membrane, and sintering the particles. The ion exchange membrane should be roughened by blasting using glass beads or the like in advance, or the surface should be activated using sodium or hydrogen peroxide to improve the adhesion to the kneaded material. Is desirable. The electrode applied to the surface of the ion exchange membrane is heated and sintered in an oven at a temperature of 150 to 250 ° C. or sintered while being pressed by a hot press. A current collector is closely attached to the electrode surface of the ion exchange membrane and used for electrolysis.

[0016]

An electrode for electrolysis using a composite oxide is used as an electrode catalyst for a solid polymer electrolyte. An alkali is added to a mixed solution of a mixture of salts forming the electrode catalyst, and the electrode catalyst is hydrated or hydroxylated. Coprecipitate as a solid product, produce a fine and uniformly mixed coprecipitate, and heat and sinter the coprecipitate to form a uniform solid solution or an oxide composed of a mixture, which has an excellent effect as an electrode catalyst. Thus, an electrode having an arbitrary composition can be obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments of the present invention. Example 1 Iridium chloride (IrCl ₃ ) was used as a platinum group metal salt, and tantalum chloride (TaCl ₅ ) was used as a group 5 metal salt.
Was used to prepare a coprecipitated mixture by the following method.
After suspending tantalum chloride in 35% hydrochloric acid, it is heated and boiled and held for 1 hour while evaporating a part of water and hydrochloric acid. After repeating twice adding pure water and hydrochloric acid and boiling again,
The same amount of water was added to prepare a hydrochloric acid solution containing 50 g / l of tantalum. Iridium chloride was dissolved therein by heating to obtain a mixed solution of iridium 100 g / l and tantalum 50 g / l.

The mixture was stirred while a 5% aqueous sodium hydroxide solution was added dropwise. Precipitation started around pH 8, and at pH 12, the liquid portion became colorless and a black precipitate was deposited. In this state, the floc was left standing for 24 hours to allow the floc to grow sufficiently, and then the supernatant was removed and washed thoroughly with pure water. As a result, although a small amount of chloride ions remained in the floc, the amount of added sodium became 0.1% or less of the floc weight. The precipitate was then washed with N
o. After filtration through 4 filter papers (manufactured by Toyo Roshi Kaisha, Ltd.), the mixture was fired in a ceramic crucible at 450 ° C. for 1 hour. After cooling, it was ground in an agate mortar. Observation of this powder with an X-ray microanalyzer revealed that iridium and tantalum were uniformly distributed.

The solid content of polytetrafluoroethylene is adjusted to 3
The obtained powder was mixed and kneaded with an aqueous suspension containing 0% by weight so that the weight ratio of powder: polytetrafluoroethylene powder was 1: 2, and the surface was roughened by glass bead blasting. A coating film having a thickness of 10 μm was formed on the surface of the ion exchange membrane (Nafion 117 manufactured by DuPont) by a doctor blade method. An aluminum foil is placed on the surface of the coating film, and a pressure of 15
The treatment was performed at 250 ° C. for 15 minutes at 0 kg / cm ² . Thereafter, the aluminum foil was dissolved with hydrochloric acid to form electrodes.

An expanded metal of platinum-plated titanium was used as a power supply for the electrodes. 60 ° C, 15
It showed a potential of 1.45 V with respect to a standard hydrogen electrode at a current density of 50 A / dm ² in 0 g / l sulfuric acid. This potential was about 100 mV lower than that of the iridium oxide-based insoluble metal electrode, and it was expected that the electrode was active and worked effectively three-dimensionally. Also,
Upon continuous electrolysis, electrolysis was possible at 200 A / dm ² even after 4000 hours of use.

Comparative Example 1 From the mixed solution of iridium and tantalum of Example 1, the solvent was evaporated to dryness and then calcined to produce an oxide by thermal decomposition. As a result of observation of the oxide with an X-ray microanalyzer, a slight distribution of Ir and Ta was observed, and 4% of residual chlorine relative to the amount of metal was observed.

Next, an electrode was prepared in the same manner as in Example 1, and an expanded metal of platinum-plated titanium was used as a power feeder for the electrode at 50 ° C. in 150 g / l sulfuric acid at 60 ° C. ^At a current density of ^2, the voltage was 1.55 V with respect to the standard hydrogen electrode. Further, when electrolysis was performed at a current density of 200 A / dm ² , iridium almost disappeared in 2500 hours, and it was impossible to continue the electrolysis.

[0023]

Example 2 An aqueous hydrochloric acid solution was prepared by mixing ruthenium chloride RuCl ₃ and titanium tetrachloride TiCl ₄ in a molar ratio of 3: 7.

The metal concentration of the solution was 100 g / l.
The solution was neutralized by dropwise addition of aqueous ammonia while being heated to 60 ° C. Almost the entire amount was precipitated up to pH 10, and the liquid portion became colorless and transparent. This was allowed to stand overnight, washed with pure water, filtered, and fired. The firing temperature was 400 ° C. Using this as an electrode material, an electrode was produced in the same manner as in Example 1. The chlorine generation potential was measured under the same conditions as in Example 1 except that the electrolytic solution was a saline solution of 200 g / l. The potential was 1.32 V against a standard hydrogen electrode at a current density of 30 A / dm ² .

A two-chamber electrolytic cell was assembled using the ion exchange membrane coated with the electrode substance as a diaphragm. On the anode side,
As a current collector, a platinum-plated titanium expanded metal was adhered to the electrode material. A nickel expanded metal as a cathode was adhered to the opposite side of the ion exchange membrane.

Electrolysis was carried out while circulating 200 g / l of a saline solution in the anode compartment of the electrolytic cell and adding pure water so that the concentration of sodium hydroxide generated in the cathode compartment became 12% by weight. Electrolysis could be continued without any problem for more than an hour. Also, the current efficiency was able to maintain 93%.

Example 3 A mixture of iridium chloride and ruthenium chloride in a molar ratio of 1: 1 was dissolved in 5% hydrochloric acid at 60 ° C. An equal amount of alcohol was added to the obtained solution, and the mixture was heated and boiled for 12 hours in a round-bottom flask equipped with a reflux condenser to remove about 50% of the contained chlorine. Orthotetrabutyl titanate was added to the obtained solution so that the molar ratio of ruthenium and iridium: titanium was 1: 1.
The solution was heated to 60 ° C. and neutralized by dropwise addition of aqueous ammonia with stirring. Precipitation of the coprecipitate started when the pH of the solution was 8, and after the precipitation of the coprecipitate was completed, excess ammonia water was added dropwise. After stirring was continued for 30 minutes, the mixture was allowed to cool. The precipitate was filtered off with filter paper and air-dried. When the air-dried product was heated at 450 ° C. for 30 minutes in an air stream, a rutile-type powder having good crystallinity was obtained.

This powder was ground in the same manner as in Example 1,
The mixture was kneaded with an aqueous suspension of polytetrafluoroethylene, and applied on the surface of an ion exchange membrane (Nafion 902 manufactured by DuPont) in the same manner as in Example 1 to form an anode. On the obtained anode, an expanded metal of titanium plated with platinum was attached as a current collector, and on the opposite side of the ion exchange membrane, an electrolytic cell with an expanded metal of nickel was assembled, and an anode chamber side was assembled. , A 200 g / l saline solution was circulated, and the cathode compartment side was filled with a 25% by weight aqueous sodium hydroxide solution to perform electrolysis. During the electrolysis, pure water was added so that the concentration of sodium hydroxide was 30% by weight. The electrolysis temperature was 85 ° C., and the current density was 40 A / dm ² . The electrolysis voltage was extremely stable at 3.1 to 3.15 V, and the oxygen in chlorine on the anode chamber side was 0.6% by volume.

Comparative Example 2 An oxide of iridium, ruthenium or titanium having the same composition as in Example 3 was prepared by direct thermal decomposition from an aqueous alcohol solution of iridium chloride, ruthenium chloride and ortho-tetrabutyl titanate. The crystallinity of the product was not good, and an electrolytic cell similar to that of Example 3 was produced using the obtained oxide.
Although it was almost the same as 5 to 3.15 V, the oxygen concentration in the generated chlorine was 2.5% by volume, and sufficient selectivity as an electrode for chlorine generation could not be obtained.

[0031]

As an electrode catalyst for a solid polymer electrolyte,
An electrode for electrolysis using a composite oxide was added to a mixed solution of a mixture of salts constituting an electrode catalyst, alkali was added, and the electrode catalyst was coprecipitated as a hydrate or a hydroxide, and finely and uniformly mixed. By producing a coprecipitate and heating and sintering the coprecipitate to form a uniform solid solution or an oxide composed of a mixture, it is possible to obtain an electrode of any composition excellent in effect as an electrode catalyst, An electrode for a polymer solid electrolyte having a low electrolysis voltage and a long electrode life can be obtained.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (4)

(57) [Claims] 1. A precipitate co-precipitated with an alkali from an aqueous solution containing a platinum group metal compound and at least one of a group 4 or group 5 metal compound and calcining the particles of the calcined product together with a binder. And applying it to the surface of an ion exchange membrane. 2. The method for producing an electrode for electrolysis according to claim 1, wherein the platinum group metal compound contains at least one compound selected from ruthenium chloride, ruthenic chloride, iridium chloride, and iridium chloride. 3. The group 4 metal compound is a titanium compound,
The method for producing an electrode for electrolysis according to claim 1, comprising at least one kind of a tin compound. 4. The method for producing an electrode for electrolysis according to claim 1, wherein a fluororesin is used as a binder and the ion exchange membrane is sintered.