JPH06330366A - Electrode for electrolysis - Google Patents

Abstract

PURPOSE:To prevent the corrosion of an electrode base body and the peeling of catalytic coating film therefrom and to facilitate the recoating thereon by forming a water repellent synthetic resin layer, having the powder of an electrode catalytic material dispersed, on the electrode base body used under a corrosive environment. CONSTITUTION:A layer of a fluororesin as the water repellent synthetic resin made by dispersing the powder mainly containing iridium oxide as the electrode catalytic material is formed on the electrode base body such as titanium used for the electrolysis of salt water. In this case, the mixing ratio of the iridium oxide powder with the fluororesin is preferably (1:0.6)-(1:0.2) by weight ratio and the average particle diameter of the electrode catalytic material is preferably 1-10mum. It is preferable to enlarge surface area or roughen the surface by previously blast treating or etching, etc., of the surface of the base body to increase the adhesivility of the base body to the electrode coating film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic process involving the generation of oxygen, and more particularly to a method for producing an electrode which can be used as an anode in a corrosive environment in which titanium corrodes, such as in the presence of highly concentrated sulfuric acid or halogen such as fluorine. Is.

[0002]

2. Description of the Related Art In an industrial electrolysis typified by electrolysis of saline solution, an insoluble metal formed by forming a catalyst coating containing a platinum group metal oxide on an electrode substrate made of a thin film-forming metal such as titanium. Electrodes are widely used. Such an insoluble metal electrode has large corrosion resistance and can be stably used for a long period of time as an anode for generating chlorine. Also,
Recently, a titanium electrode coated with a noble metal catalyst has been used for an anode used for an electrode reaction in which oxygen is generated such as electrolysis in a sulfuric acid acidic bath or an aqueous solution of sulfates. In particular, the catalyst coating containing iridium oxide has the least amount of consumption and is the most excellent among the platinum group metal oxides. IrO ₂ and Ta ₂ are deposited on the titanium substrate.
Electrodes coated with a thermal decomposition method of O ₅ composite oxide are currently the center of development.

However, there is a problem that these electrodes cannot be electrolyzed in high-concentration sulfuric acid in a short time, and the catalyst coating falls off only by being immersed in sulfuric acid containing no dissolved oxygen. This is due to damage to the joint between the catalyst coating formed on the electrode and the titanium substrate. It is considered that the main cause of this damage is that the titanium substrate at the coating material-titanium joint portion is corroded and the catalyst coating is peeled off due to the infiltration of the electrolytic solution from the defects such as pinholes generated in the catalyst coating. Further, there is also a problem that titanium is corroded even in the presence of a fluoride ion-containing bath such as a chromium plating bath containing a silicofluoride, or a halogen other than chlorine such as iodide ion, and the electrode is damaged early.

On the other hand, as an anode for oxygen generation, there is also known one in which a thermoplastic resin having a high corrosion resistance and a catalyst substance are integrally formed instead of the method of forming a catalyst coating on an electrode substrate. For example, coating powdered lead dioxide with a thermoplastic resin,
An electrode formed by hot pressing this is Japanese Patent Publication No. 39-297.
No. 48 publication. In this electrode, it is necessary to increase the lead dioxide content in order to sufficiently secure the conductivity of the electrode substrate and the surface, but there is a problem that the mechanical strength of the electrode decreases when the lead dioxide content increases. is there. Further, an electrode formed by coating the surface of a thermoplastic resin particle with conductive particles and then hot-pressing is described in Japanese Patent Publication No. 3-6995. Since a mesh structure is formed by the conductive particles at this electrode, the electric resistance of the electrode may be large and the conductivity may be non-uniform. Bring about a decline. Further, these electrodes are excellent in corrosion resistance because they use lead dioxide or the like, but lead dioxide is not suitable as an electrode for oxygen generation because of large oxygen overvoltage.

Further, a resin-molded electrode using powder in which the surface of oxide particles of a thin film-forming metal such as titanium is coated with platinum group metal such as iridium or ruthenium as conductive particles is described in Japanese Patent Publication No. 3-6231. However, it has the same electrical and mechanical problems as the above electrodes. further,
Since all of these electrodes are manufactured by hot pressure molding, there is a possibility that mechanical damage such as cracks may be given to the conductive particles and the resin substrate during molding.

[0006]

DISCLOSURE OF THE INVENTION The present invention, in an electrode using a thin film-forming metal such as titanium as an electrode substrate, prevents corrosion of the electrode substrate in an environment in which the electrode substrate is corroded, and peels off the catalyst coating. It is an object of the present invention to provide an electrode that prevents the above-mentioned problems, and an object of the present invention is to provide an electrode that can be used as an anode for an oxygen generation reaction in which the deteriorated catalyst coating can be easily recoated.

[0007]

The present invention is a method for producing an electrode for oxygen generation in which a water-repellent polymer resin layer in which fine particles of an electrode catalyst substance are dispersed is formed on a thin film-forming metal substrate such as titanium. That is, according to the present invention, the conventional oxygen-generating electrode based on titanium or the like is damaged, and the base is damaged at the joint between the catalyst coating and the base due to corrosion or passivation of the titanium base, resulting in the inability to energize. Focusing on the appearance of locations, peeling of the catalyst coating from the electrode substrate, etc., the main reason for this is that the electrolytic solution penetrates from defective portions such as pinholes generated in the catalyst coating, The catalyst coating is made impermeable to the electrolytic solution to prevent damage to the substrate such as titanium.

The electrode substrate used in the electrode of the present invention is preferably a thin film-forming metal such as titanium or its alloy from the viewpoint of corrosion resistance against oxidizing use environment when used as an anode, and has a plate shape. The shape is desirable. In order to enhance the adhesion of this substrate to the electrode coating, blasting,
It is preferable to use one that has been subjected to etching treatment or the like to increase its surface area and roughen the surface.

On the other hand, the electrode catalyst that covers the electrode substrate is
It is preferable to use fine particles of iridium oxide, which have excellent oxygen generation characteristics in an electrolytic solution containing sulfuric acid and the like. The fine particles of iridium oxide can be obtained by thermal decomposition, pulverization, or the like of an aqueous solution of iridium chloride in an oxygen-containing atmosphere. The average particle size of the fine particles is preferably about 1 μm to 10 μm in order to sufficiently maintain the conductivity in the film and to uniformly disperse the particles, and if the particle size is 1 μm or less, the particles in the film cannot be sufficiently joined, and If it is 10 μm or more, the powder cannot be uniformly dispersed in the coating liquid.

The water-repellent synthetic resin layer used for the catalyst coating of the present invention is preferably a fluororesin having high water repellency and corrosion resistance, particularly polytetrafluoroethylene resin. It is preferable to use an aqueous dispersion of these fluorine-based synthetic resins, and the fine particles used for the electrode catalyst are mixed in the aqueous dispersion to form a coating solution. It is suitable that the mixing ratio of the catalyst fine particles and the fluorine-based synthetic resin is approximately 1: 0.6 to 0.2 (weight ratio). If the ratio of the resin is too large, the conductivity becomes poor, and if it is too small, the substrate is protected. And the retention of powder are reduced. This coating solution is coated on the above substrate,
Drying is performed at -60 ° C for 30 to 60 minutes, and then firing is performed at the softening point of the resin or higher for 1 to 2 hours to fix the coating. By repeating the steps from coating to baking or from coating to drying to form a multilayer film, the uniformity of the film and the protective property of the substrate are improved, but if the number of layers is too large, the conductivity decreases. Layers are preferred.

[0011]

In the electrode of the present invention, since the electrode catalyst coating in which the electrode catalyst is dispersed in the highly water-repellent fluororesin is formed on the electrode substrate, the electrolytic solution does not reach the joint between the electrode substrate and the electrode catalyst coating. It can be used as an anode even in the corrosive environment of the electrode substrate such as titanium, and there is no mutual diffusion between the electrode and the catalyst coating, which is seen when the electrode catalyst coating is formed on the metal substrate by thermal decomposition. It is very easy to peel off the coating during coating.

[0012]

EXAMPLES The present invention will be described below with reference to examples. Example 1 A solution prepared by dissolving 5 g of iridium chloride in 60 ml of pure water was used.
After heat treatment in air at 480 ° C. for 15 to 18 minutes, pulverization was performed for 2 hours, this was repeated twice, and finally heat treatment was performed at 480 ° C. for 15 minutes. An iridium oxide powder having an average particle size of 5 μm was obtained. This powder was mixed with an aqueous polytetrafluoroethylene dispersion (Teflon 30J, manufactured by Mitsui DuPont Fluorochemicals) so that the solid content of iridium oxide: polytetrafluoroethylene was 1: 0.6 (weight ratio), and ultrasonically dispersed. A coating solution was prepared.

35 mm × 35 mm × 3 mm for the electrode substrate
A titanium plate having a diameter of 3 mm and a length of 150 mm welded to the titanium plate was used, and after sandblasting as pretreatment, etching was performed in boiling hydrochloric acid for 20 minutes. The coating solution was coated on the substrate so that the solid content was 32 mg, dried at 60 ° C. for 30 minutes, and then at 350 ° C. for 1 minute.
Firing was performed for a time to prepare a catalyst layer-covered electrode.

The electrode potential was 1.02 V when the electrode potential was measured at a current density of 5 A / dm ² in a sulfuric acid having a concentration of 150 g / l and a sulfuric acid mercuric acid electrode as a reference electrode at room temperature. In addition, the obtained electrode,
When the immersion test was performed for 215 hours in 6M sulfuric acid at 40 ° C. which was degassed with argon, no change was observed on the electrode surface. Then 150g of this electrode
/ L sulfuric acid in an electrolyte solution at 40 ° C as an anode 10
When a current of A / dm ² was applied, electrolysis was possible for 430 hours.

Comparative Example 1 Ir: Ta = 65: 3 on the same electrode substrate as in Example 1.
A 5 (weight ratio) Ir-Ta mixed solution was applied with a brush and baked in air at 520 ° C for 13 minutes. IrO _{2 is} obtained by repeating the operation from application of the mixed solution to firing 12 times.
A Ta ₂ O ₅ composite oxide-coated titanium electrode was prepared. When the electrode potential of this electrode was measured under the same conditions as in Example 1, it was 1.02V. The obtained electrode was treated in the same manner as in Example 1 in degassed 6M sulfuric acid under the condition of 40 ° C.
As a result of the immersion test for 5 hours, it was found that the coating was dropped off and the titanium substrate was exposed at various places on the surface.

Comparative Example 2 An iridium oxide powder prepared under the same conditions as in Example 1 was used to produce an electrode with an iridium oxide powder: fluororesin ratio of 1: 1.2, and an anode was provided with the same potential as in Example 2. When measured, it was 2.20V.

Example 2 Iridium oxide powder having an average particle size of 10 μm was used, and the ratio with the fluororesin was set to 1: 0.4, and 350
Bake at 90 ° C. for 90 minutes, and in the same manner as in Example 2, 10 A /
When the electrode potential at dm ² was measured, the potential was 1.1.
It was 9V.

Comparative Example 3 An electrode was prepared under the same conditions as in Example 2 except that iridium oxide powder having an average particle size of 100 μm was used, and the potential as an anode was measured in the same manner as in Example 3. However, it was 1.55V, which was extremely high.

Example 3 Example 1 except that the coating layer was fired for 90 minutes.
An electrode was prepared in the same manner as in 1., and a long-term electrolysis test was performed in 150 g / l sulfuric acid at 40 ° C. and 10 A / dm ² using the obtained electrode as an anode. As a result, electrolysis was possible for 150 days. .

Example 4 5 g of iridium chloride was dissolved in 60 ml of pure water to dissolve 480
After heat treatment for 30 minutes at ℃, pulverize for 2 hours, repeat this twice, and finally perform heat treatment for 90 minutes at 480 ℃,
The prepared iridium oxide powder was added to an aqueous polytetrafluoroethylene dispersion, and IrO ₂ : fluororesin solid content =
The mixture was mixed at a ratio of 1: 0.2 (weight ratio) to prepare a coating liquid. This was coated on the same electrode substrate as in Example 1 so that the solid content of the coating liquid would be 26 mg, dried at 60 ° C. for 30 minutes, and then baked at 370 ° C. for 90 minutes. The process was repeated again to produce an electrode. This electrode was used as an anode, and mercuric sulfate was used as a reference electrode at a temperature of 40 ° C. in 150 g / l of sulfuric acid, and a current density was 100 A / dm ^2.
The electrode potential when energized at 1.185 was 1.185.
It was V. Further, as a result of a long-term electrolysis test in which the electrode was used as an anode in 150 g / l sulfuric acid at 40 ° C. and a current density of 100 A / dm ² , it was possible to electrolyze for 140 days.

[0021]

The electrode of the present invention is impermeable to the electrolytic solution because it is coated with the water-repellent synthetic resin layer in which the electrode catalyst is dispersed. No damage occurs, the electrode damage is only the consumption of iridium oxide, no defective conductivity between the electrode catalyst coating and the electrode substrate, peeling of the coating, etc. occurs, and when regenerating the electrode coating, the hand is The stripping of the coating and the treatment of the substrate are simple and the regeneration of the electrodes is easy.

Claims (3)

[Claims] 1. An electrode for electrolysis, wherein a layer of a water-repellent synthetic resin in which powder of an electrode catalyst substance is dispersed is formed on an electrode substrate. 2. The electrocatalyst substance is a powder mainly composed of iridium oxide, and the water-repellent synthetic resin is a fluororesin,
The electrode for electrolysis according to claim 1, wherein the mixing ratio of the iridium oxide powder and the fluororesin is 1: 0.6 to 1: 0.2 by weight. 3. The electrode for electrolysis according to claim 1, wherein the average particle diameter of the electrode catalyst substance is 1 μm or more and 10 μm or less.