JPH0860390A - Electrolytic electrode and its production - Google Patents

Abstract

PURPOSE: To obtain an electrolytic electrode excellent in durability and having a long service life by forming a coating layer contg. iridium oxide, platinum and silicon oxide on a conductive substrate. CONSTITUTION: This electrolytic electrode has a coating layer contg. iridium oxide, platinum and silicon oxide on a conductive substrate, and the alloy of >=2 kinds of valve metals selected from among titanium tantalum, zirconium and niobium is exemplified as the conductive Since the coating layer is formed, the electrode is stably used for a long period when used as an electrolytic electrode in the various industrial and public-wellfare electrolytic processes. The iridium oxide content of the coating layer is controlled to 2-90 atomic %, expressed in terms of Ir, the platinum content to 2-92 atomic %, expressed in terms of Pt, and the silicon oxide content to 3-75 atomic %, expressed in terms of Si. An electrolytic electrode capable of being easily produced is obtained in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for electrolysis used in industrial and consumer electrolysis processes and a method for producing the same. More specifically, the present invention relates to an electrode for electrolysis, which is used as an anode in an electrolysis process and has excellent durability and low overvoltage, and a method for easily and efficiently producing the electrode.

[0002]

2. Description of the Related Art Conventionally, a metal electrode having a conductive titanium titanium substrate on which a coating layer of a platinum group metal or its oxide is provided has been used in various fields of the electrolysis industry.
For example, an electrode in which ruthenium and titanium oxides or ruthenium and tin oxides are coated on a titanium substrate by a thermal decomposition method is known as a chlorine generation anode by salt electrolysis (Japanese Patent Publication No. 46-21884). Publication, Japanese Patent Publication Sho 48
-3954, Japanese Examined Patent Publication No. 50-11330, and Japanese Unexamined Patent Publication No. 52-63176).

However, although these electrodes are suitable for electrolysis of a high-concentration salt aqueous solution such as salt electrolysis, they are not sufficiently durable in electrolysis of a dilute salt aqueous solution or seawater, and also have an efficiency of chlorine generation. I am not completely satisfied.

Further, in JP-A-55-152143 and JP-A-56-150148, an electrode using an amorphous alloy as an electrode material is an electrode for electrolysis of an aqueous solution of an alkali metal halide such as salt. Is disclosed as. However, an amorphous alloy requires a large-scale device for its production.

In the electrolysis industry, in addition to electrolysis involving chlorine generation as in the case of the above-mentioned salt electrolysis, recovery of acids, alkalis or salts, collection and purification of metals such as copper and zinc, plating, copper, etc. Metal foil manufacturing, metal surface treatment, cathodic protection,
Electrolysis processes involving oxygen generation such as waste liquid treatment are also used in many fields. The lead-based electrode is most commonly used in such electrolysis involving oxygen generation. Other known insoluble electrodes include electrodes coated with iridium oxide and platinum on a titanium substrate, iridium oxide-tin oxide-based electrodes, iridium oxide-based electrodes such as iridium oxide-tantalum oxide-based electrodes, and platinum-plated titanium electrodes. There is.

However, these known electrodes are not always suitable because they cause various troubles depending on the intended use. For example, when a soluble zinc anode is used as an anode for galvanizing, the anode is significantly dissolved, so that the distance between the electrodes must be adjusted frequently.
Further, when a lead-based insoluble anode is used, plating failure occurs due to the influence of lead mixed in the electrolytic solution. Further, an electrode coated with iridium oxide and platinum or a platinum-plated titanium electrode cannot be used severely when so-called high-speed zinc plating is performed at a high current density of 100 A / dm ² or more.

Therefore, it is one of the important subjects in the electrode manufacturing technique to develop an electrode which can be applied without any trouble for each application of the electrolytic process involving oxygen generation.
It is connected. As an example of such a special electrolytic process, in the electrolytic process of various metals such as zinc plating using a brightening agent, electrolytic refining of copper, and production of copper foil,
An electrolytic solution containing an organic substance such as glue or thiourea as an additive may be used.

In such a case, JP-A-63-23549
No. 3, gazette, Ir50-90 mol%, Ta50-10
An iridium oxide-tantalum oxide-based electrode provided with a mol% underlayer is disclosed. And this electrode can be used as an anode for plating in which the hydrophilic organic substance additive is not contained in the plating bath at all. However, it has been found that when a glue or the like is added to the plating bath, the durability may be lowered and the practicality may be lost.

[0009] Generally, when electrolysis involving oxygen generation is performed using a titanium substrate electrode having a coating layer as an anode, a titanium oxide layer is formed between the substrate and the coating layer, or the titanium substrate is corroded, so that the anode potential gradually increases. The phenomenon that the coating layer peels off and the anode is passivated is often observed. This phenomenon is particularly remarkable when an organic additive is added to the electrolytic solution or in an electrolytic process containing fluorine ions.

The formation of titanium oxide formed on such a titanium substrate is suppressed and the corrosion of the titanium substrate is suppressed,
In order to prevent passivation of the anode, various proposals have been made to select an appropriate coating layer or provide an appropriate underlayer.

For example, Japanese Examined Patent Publication No. 51-19429 discloses an electrode having a relatively thin intermediate barrier layer which is electrically conductive and relatively impermeable to oxygen. Further, JP-B-49-48072 discloses that an electrode substrate is immersed as an intermediate layer in an aqueous solution containing a film-forming metal ion, and an oxide of a film-forming metal is deposited from this solution by electrical or chemical oxidation. Disclosed is a method for manufacturing an electrode by which the intermediate layer is formed.
However, when glue such as glue, which is an organic substance additive, is added, the electrode catalyst layer is heavily consumed and its durability is insufficient, so that it cannot be used.

Further, in JP-A-6-146047, a thin film intermediate layer made of a mixture of silica and tantalum is provided on a valve metal substrate such as titanium by a physical vapor deposition method such as a sputtering method. An anode for oxygen generation is disclosed in which an electrode active layer made of a mixture of iridium oxide and tantalum oxide is provided thereon. However, in this electrode, since the thin film intermediate layer is formed by the sputtering method or the like, work efficiency is poor, and it is not suitable for manufacturing a large-scale electrode for electrolysis. In addition, the manufacturing cost becomes high.

On the other hand, as a consumer-use device utilizing an electrolysis process, an ionized water generator, a sterilized water generator, etc. are known. For example, JP-A-5-57283 and JP-A-6-33280 disclose these devices, and a platinum coating layer or platinum and Ti on a titanium substrate is used as an electrode for water electrolysis used in these devices. Ta, Z
An electrode provided with a coating layer containing at least one of r, Nb and Sn has been proposed. However, in such a device, since it is necessary to switch the positive and negative electrodes to electrolyze, the above-mentioned electrodes do not have sufficient durability, and particularly when the frequency of polarity reversal is high, the durability becomes extremely poor.

[0014]

The object of the present invention is, firstly, to be used in industrial and consumer electrolysis processes, to prevent abnormal wear, to enable long-term stable use, to have long life and durability. It is to provide an excellent electrode for electrolysis. Secondly, it is to provide a method for manufacturing an electrode for electrolysis that simply and efficiently manufactures such an electrode for electrolysis.

[0015]

Such an object is achieved by the following constitutions (1) to (5). (1) An electrode for electrolysis having a coating layer containing iridium oxide, platinum and silicon oxide on a conductive substrate. (2) The content of iridium oxide in the coating layer is I
2 to 90 atomic% in terms of r, platinum content 2 in terms of Pt
~ 92 atomic%, silicon oxide content is 3 to 75 in terms of Si
The electrode for electrolysis according to (1) above, which is in atomic%. (3) The electrode for electrolysis according to (1) or (2) above, wherein the coating layer further contains at least one kind of tantalum oxide, titanium oxide, niobium oxide, zirconium oxide, and tin oxide in an amount of 30 atomic% or less in terms of metal. (4) A method for producing an electrode for electrolysis, which comprises forming the coating layer by a thermal decomposition method to obtain the electrode for electrolysis according to any one of (1) to (3). (5) The method for producing an electrode for electrolysis according to (4) above, wherein the raw material of silicon oxide contained in the coating layer is silica sol.

[0016]

Specific Structure The specific structure of the present invention will be described in detail below.

The electrode for electrolysis of the present invention has a coating layer containing iridium oxide, platinum and silicon oxide on a conductive substrate.

As the conductive substrate used in the present invention,
Examples thereof include valve metals such as titanium, tantalum, zirconium, and niobium, and alloys of two or more kinds of metals selected from these valve metals.

By providing the above-mentioned coating layer, long-term stable use becomes possible when it is used as an electrode for electrolysis in various electrolytic processes for industrial use and consumer use.

A feature of the present invention is that silicon oxide is used in addition to iridium oxide and platinum as a coating layer component having an electrocatalytic activity for various electrolytic reactions.

Iridium oxide has the effect of preventing an increase in oxygen overvoltage and chlorine overvoltage. On the other hand, platinum brings about an effect of preventing wear of the coating layer and improving durability in polarity reversal use in which the cathode and cathode are switched and used in applications such as an ion water generator and a sterilizing water generator. In addition, platinum has a function of lowering the resistance of the coating layer, which has the effect of extending the life of the electrode.

By containing silicon oxide in addition to these components, the above effect can be maintained for a long period of time. Silicon oxide in the coating layer,
According to the X-ray diffraction pattern, it is considered that they exist in an amorphous state. In such a silicon oxide phase, silicon oxide has a network structure due to a siloxane bond and is considered to be firmly bonded to each other. Therefore, elution of the catalyst component forming the coating layer is prevented, and long life and improvement of durability can be realized. In addition to this, the presence of silicon oxide improves the adhesion between the substrate and the coating layer, makes it difficult for the coating layer to peel, and prevents the substrate from corroding, so that the coating layer does not easily peel due to corrosion. Become. Further, it is possible to prevent an increase in electric resistance due to corrosion.

On the other hand, if any of the above three components is lacking, the above effect cannot be obtained. More specifically, if only iridium oxide and platinum are used and no silicon oxide is present, the durability is significantly deteriorated. Further, if only iridium oxide and silicon oxide are used and no platinum is present, the durability will deteriorate when the polarity is reversed. In addition, the increased resistance of the coating layer facilitates the passivation of the substrate and shortens the electrode life. Furthermore, when only platinum and silicon oxide are used and no iridium oxide is present, the oxygen overvoltage and chlorine overvoltage increase, and the coating layer is particularly consumed when oxygen is generated. In particular, the combined use of platinum and silicon oxide in the present invention further improves the effect of preventing the passivation of the substrate, and has the effect of further extending the electrode life.

In the present invention, in order to further improve the above effects, the content of silicon oxide in the coating layer is preferably 3 to 75 atom%, more preferably 5 to 70 atom% in terms of Si. When the content of silicon oxide is low, the effect of addition cannot be obtained, and when the content of silicon oxide is high, the adhesion between the substrate and the coating layer is reduced, and the electrical resistance of the coating layer is increased. It is necessary to increase the voltage.

On the other hand, the contents of iridium oxide and platinum are
Iridium oxide is preferably 2 to 90 atom% in terms of Ir, and platinum is preferably 2 to 92 atom% in terms of Pt. That is, the content of iridium oxide and platinum is 3 to 75 atomic% of silicon oxide, preferably 5 to 7
0 atom% and 2 to 2 depending on the use conditions of the electrolytic electrode, etc.
It is preferable to appropriately select from the range of 90 atomic% or 2 to 92 atomic%.

For example, for the purpose of polarity reversal in which the anode and cathode are switched and used in applications such as an ionized water generator and a sterilized water generator, the content of iridium oxide is 2 to 50 atom%, and the content of platinum is 50. It is preferable that the content be ˜92 atomic%. Further, for the purpose of using the electrolysis process involving oxygen generation, it is preferable that the iridium oxide content is 40 to 90 atom% and the platinum content is 2 to 50 atom%.

On the other hand, when the content of iridium oxide is low and the content of platinum is high, the oxygen overvoltage and the chlorine overvoltage are high and the durability is poor. On the other hand, when the content of iridium oxide increases and the content of platinum decreases,
Under the use condition of polarity reversal, the components of the coating layer are heavily consumed and the life is shortened. In addition, the increased resistance of the coating layer facilitates the passivation of the substrate.

In addition to the above, in the coating layer of the electrode for electrolysis of the present invention, in particular, when an organic additive is added to the electrolytic solution, an electrolytic process containing fluorine ions, and for the purpose of use in polarity reversal. Oxides of titanium, tantalum, niobium, zirconium or tin may be contained. These oxides may be used alone or in combination of two or more.
The content of these oxides in the coating layer may be 30 atom% or less, usually 2 to 25 atom% in total in terms of metal. By adding these oxides, the consumption of the coating layer components can be suppressed.

The thickness of the coating layer in the present invention is 1 cm for the substrate.
It is preferred ^{that 2} per platinum group metal (specifically, Pt, Ir) and the supported amount of the platinum group metal oxide is made to be 0.1~10mg about in terms of a metal. If the loading amount is small, the effect of the present invention cannot be obtained, and if the loading amount is large, the adhesion strength with the substrate tends to decrease. The supported amount can be determined by fluorescent X-ray analysis.

In the electrode for electrolysis of the present invention, a coating layer is formed by a thermal decomposition method in which a conductive base material is coated with a coating solution containing a predetermined amount of an iridium compound, a platinum compound and a silicon compound and then heat treated in an oxidizing atmosphere. Is manufactured.

In the above coating liquid, as the silicon compound which is a raw material of the silicon oxide component in the coating layer, any compound which becomes silicon oxide by thermal decomposition, such as silica sol or silicon alkoxide, may be used. It is preferable to use silica sol. By using silica sol, deterioration of the coating liquid can be prevented. Further, it is possible to form a dense coating layer having good adhesion to the substrate.

The silica sol may be a dispersion medium of alcohol such as isopropyl alcohol, water or the like, depending on the coating solvent used, and a commercially available product can be used as it is. Particle size of silica sol is 5-150nm
It is a degree.

Further, as the iridium compound as a raw material of iridium oxide and the platinum compound as a raw material of platinum, any compound can be used as long as it is a compound which becomes iridium oxide or platinum by thermal decomposition, and the iridium compound is iridium chloride. An acid (H ₂ IrCl ₆ · 6H ₂ O), iridium chloride or the like can be used, and a platinum compound such as chloroplatinic acid (H ₂ PtCl ₆ · 6H ₂ O) or platinum chloride can be used.

Furthermore, when an oxide of titanium, tantalum, niobium, zirconium or tin is further contained in the coating layer, a predetermined amount of these raw material compounds may be contained in the coating liquid. Examples of these raw material compounds include chlorides and alkoxides. Specifically, titanium butoxide, tantalum ethoxide, tantalum butoxide, tantalum chloride, zirconium chloride, niobium chloride, tin chloride and the like.

The solvent used for preparing the coating solution is not particularly limited, and usually alcohol or water may be used.

In the heat treatment in an oxidizing atmosphere in the present invention, the above-mentioned coating solution is applied onto a conductive substrate and dried, and then in the presence of oxygen, the oxygen partial pressure is generally 0.05 atm or more, preferably. It is performed by firing at a temperature in the range of 400 to 600 ° C. This operation is repeated multiple times until the required loading amount is reached.

The electrode for electrolysis of the present invention is an electrode for oxygen generation, an electrode for chlorine generation, in an electrolytic process of various electrolytic solutions,
It can be used as an electrode for water electrolysis.

More specifically, an oxygen generating electrode and salt used in the production of metal foil such as copper foil, plating such as zinc plating and tin plating, recovery of various metals, purification, drainage treatment and other electrolytic processes. It is used as an electrode for chlorine generation used in electrolytic processes such as decomposition, dilute salt water electrolysis, and seawater electrolysis. In particular, the chlorine generation electrode is preferably used in the electrolytic process of an electrolytic solution having a low salt concentration.

Further, it can be favorably used as a water electrolysis electrode for electrolyzing water while reversing the polarity in a consumer electrolysis process such as an ionized water generator or a sterilized water generator.

[0040]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1 Samples No. 1 to No. 8 of electrodes for electrolysis provided with a coating layer having the composition shown in Table 1 were prepared.

First, depending on the composition of the coating layer of each sample, chloroiridate (H ₂ IrCl ₆ .6H ₂ O), chloroplatinic acid (H ₂ PtCl ₆ .6H ₂ O), and silica sol dispersed in isopropyl alcohol (average) (A particle size of about 10 nm) was weighed and butanol was added to prepare a coating solution. The total content of chloroiridic acid (Ir conversion), chloroplatinic acid (Pt conversion), and silica sol (Si conversion) in this coating liquid was 50 g / liter.

Separately, the above coating solution was applied onto a titanium substrate etched with hot oxalic acid with a brush, dried, and then placed in an electric furnace and baked at 520 ° C. while blowing air. The operations of coating, drying and baking were repeated 20 times. In this way, a coating layer having a predetermined thickness [total supported amount of iridium oxide, platinum and silicon oxide per cm ^{2 of} substrate was about 5 mg in terms of metal (including Si)] was formed.

The following characteristics of the sample produced above were examined. The results are shown in Table 1.

(1) Electrode life (1-1) In 1 mol / liter sulfuric acid-1 mol / liter acetonitrile aqueous solution An aqueous solution containing 1 mol / liter sulfuric acid-1 mol / liter acetonitrile at 60 ° C. with each sample as an anode. Inside, platinum was used for the cathode, electrolysis was performed at a current density of 200 A / dm ² , and the life was examined. In the table, ○, △, × are shown. ◯: Electrolyzable time is 200 hours or more Δ: Electrolyzable time is 100 hours or more and less than 200 hours X: Electrolyzable time is less than 100 hours

(1-2) Inversion of polarity For each of the above samples, 30 ppm of standard water [sodium hydrogen carbonate (NaHCO ₃ ) 21 ppm, calcium chloride (CaCl ₂ ) 28 ppm, magnesium sulfate (MgSO ₄ ).
₄ ) 30ppm, potassium hydrogen carbonate (KHCO ₃ ) 2.5
[ppm], a life test with polarity reversal was performed. Electrodes of the same kind were used for both the anode and the cathode, electrolysis was performed at a current density of 5 A / dm ² with polarity reversed every 15 minutes, and the time when electrolysis was possible was examined. In the table, ○, △, × are shown. ◯: Electrolyzable time is 500 hours or more Δ: Electrolyzable time is 100 hours or more and less than 500 hours X: Electrolyzable time is less than 100 hours

(2) Adhesion Strength A mechanical strength test of the electrode during electrolysis was conducted.

Each of the above samples was used as an anode, and electrolysis was carried out at 60 ° C. in a 1 mol / liter sulfuric acid aqueous solution using platinum as a cathode at a current density of 200 A / dm ² for up to 200 hours, and then ultrasonic vibration was applied for 5 hours. After applying for a minute, the thickness of the coating layer before and after applying vibration was measured by fluorescent X-ray analysis, and the amount of loss of the coating layer due to applying vibration was obtained and evaluated. In the table, ○, △,
It is shown by x. ◯: The weight loss of the coating layer is 5% by weight or less. Δ: The weight loss of the coating layer is more than 5% to 10% by weight. X: The weight loss of the coating layer is more than 10% by weight.

(3) Oxygen Overvoltage For each of the above samples, the voltage at a current density of 2 A / dm ² was measured in a 1 mol / liter sulfuric acid aqueous solution at 30 ° C. at a scanning rate of 10 mV / sec by the potential scanning method. In the table, ○, △, × are shown. ◯: Oxygen overvoltage is 0.5 V or less Δ: Oxygen overvoltage is over 0.5 V to 1 V ×: Oxygen overvoltage is over 1 V

[0050]

[Table 1]

Example 2 A coating liquid was prepared in the same manner as in the sample No. 1 of Example 1 except that tantalum chloride was further added as a component of the coating liquid for forming the coating layer.
No. 11 was produced.

Composition of coating layer Iridium oxide (80 atomic% as Ir) -Platinum (10 atomic% as Pt) -Silicon oxide (5 atomic% as Si) -Tantalum oxide (5 atomic% as Ta)

In this sample No. 11, it was found that the inclusion of tantalum oxide prolongs the electrode life at polarity reversal by about 20% as compared with sample No. 1 having a similar composition.

Further, in Sample No. 11, a coating solution was prepared by using titanium chloride, niobium chloride, zirconium chloride or tin chloride instead of tantalum chloride, and containing titanium oxide, niobium oxide, zirconium oxide or tin oxide. When a sample of the coating layer was prepared and the characteristics were examined in the same manner as above, the same result as that of Sample No. 11 was shown.

Example 3 Samples No. 21 to No. 29 of electrodes for electrolysis provided with a coating layer having the composition shown in Table 2 were prepared.

First, chloroplatinic acid, iridic acid chloride, hydrochloric acid, and a water-dispersible silica sol (average particle size of about 20 nm) were weighed according to the coating layer composition of each sample, and water was added to prepare a coating solution. Chloroplatinic acid (Pt conversion), chloroiridic acid (Ir conversion), silica sol (S
The total content (converted to i) was 50 g / liter.

Separately, the above coating solution was applied onto a titanium substrate etched with hot oxalic acid with a brush, dried, and then placed in an electric furnace and baked at 520 ° C. while blowing air. The operations of coating, drying and baking were repeated an appropriate number of times until a predetermined coating layer thickness [total supported amount of iridium oxide, platinum and silicon oxide per 1 cm ^{2 of the} substrate was 2 mg in terms of metal (including Si)].

The following characteristics of the sample produced above were examined. Table 2 shows the results.

(1) Electrode Life (1-1) In NaCl Aqueous Solution Each sample was used as an anode, and platinum was used as a cathode in a 0.5 mol / liter NaCl aqueous solution at 20 ° C. at a current density of 50 A / dm ² . Electrolysis was performed to check the life. ○ in the table
Δ and × are shown. ◯: Electrolyzable time is 1000 hours or more Δ: Electrolyzable time is 500 hours or more and less than 1000 hours X: Electrolyzable time is less than 500 hours

(1-2) Inversion of polarity The same as in Example 1, the investigation was carried out. In the table, ○, △, × are shown. ◯: Electrolyzable time is 500 hours or more Δ: Electrolyzable time is 100 hours or more and less than 500 hours X: Electrolyzable time is less than 100 hours

(2) Adhesion Strength In Example 1, the electrolysis condition in the mechanical strength test was set to 20.
℃, 1.5 wt% NaCl aqueous solution, electrolysis time 1
It investigated similarly except having set it as 00 hours. In the table, ◯, Δ, and X, which are the same criteria as in Example 1, are shown.

(3) Chlorine generation efficiency 150 ml of 0.5 mM NaCl aqueous solution was placed in a glass beaker and a platinum electrode was used as the cathode at 20 ° C., and the electrode area was 20.
12 Coulomb energization condition 2A / dm ² as cm ^2, 12
The chlorine generation amount after time electrolysis was obtained, and the current efficiency (%) was calculated from the electricity amount and the chlorine generation amount to obtain the chlorine generation efficiency. The amount of chlorine generated was determined by measuring residual chlorine by the orthotolidine method. In the table, ○, △, × are shown. ○: 8% or more △: 5% or more and less than 8% ×: less than 5%

(4) Chlorine overvoltage With respect to each of the above samples, a scanning rate of 10 mV / sec, 30 ° C., 30 wt% NaCl aqueous solution (pH
(Adjusted to = 1) to measure the voltage at a current density of 20 A / dm ² . In the table, ○, △, × are shown. ◯: Oxygen overvoltage is 0.1 V or less Δ: Oxygen overvoltage is over 0.1 V and 0.2 V or less ×: Oxygen overvoltage is over 0.2 V

[0064]

[Table 2]

Example 4 A coating liquid was prepared in the same manner as in the sample No. 22 of Example 3 except that tantalum chloride was further added as a component of the coating liquid for forming the coating layer. .31 was produced.

Multilayer composition Iridium oxide (10 atom% as Ir) -Platinum (40 atom% as Pt) -Silicon oxide (40 atom% as Si)-
Tantalum oxide (Ta equivalent 10 atom%)

In this sample No. 31, it was found that the inclusion of tantalum oxide prolongs the electrode life at polarity reversal by about 20% as compared with sample No. 22 having a similar composition.

According to JP-A-6-33280, P
When a comparative sample having a coating layer of t (60 mol%)-Ta ₂ O ₅ (40 mol%) was prepared and the electrode life was examined in the same manner as above, not only the sample No. 31 but also
It was found that the sample Nos. 21 to 26 of Example 3 were obviously inferior.

Further, in sample No. 31, a coating solution was prepared using titanium chloride, niobium chloride, zirconium chloride or tin chloride instead of tantalum chloride, and titanium oxide, niobium oxide, zirconium oxide or tin oxide was added to the coating solution. When the samples of the coating layers contained therein were prepared and the characteristics were examined in the same manner as above, the same result as that of Sample No. 31 was shown.

Example 5 Samples No. 41 to No. 45 of electrodes for electrolysis provided with a coating layer having the composition shown in Table 3 were prepared.

First, according to the composition of the coating layer of each sample, iridium chlorochloride, chloroplatinic acid, water-dispersed silica sol and tantalum chloride were weighed and an aqueous hydrochloric acid solution was added to prepare a coating solution. The total content of chloroiridic acid (Ir conversion), chloroplatinic acid (Pt conversion), silica sol (Si conversion), and tantalum chloride (Ta conversion) in this coating liquid was 100.
It was g / liter.

Separately, the above coating solution was applied onto a titanium substrate etched with hot oxalic acid with a brush, dried, and then placed in an electric furnace and baked at 550 ° C. while blowing air. The operations of coating, drying and baking were repeated an appropriate number of times until a predetermined loading amount [the total loading amount of iridium oxide, platinum and silicon oxide per 1 cm ^{2 of the} substrate was 3 mg in terms of metal (including Si)].

The following characteristics of the sample produced above were examined. The results are shown in Table 3.

(1) Electrode Life (1-1) 1 mol / liter sulfuric acid-1 mol / liter in acetonitrile aqueous solution The same procedure as in Example 1 was carried out. In the table, ○, △, × are shown. ◯: Electrolyzable time is 200 hours or more Δ: Electrolyzable time is 100 hours or more and less than 200 hours X: Electrolyzable time is less than 100 hours

(1-2) 100 pp of glue to an aqueous solution of 2 mol / liter sulfuric acid in an electrolyte containing organic matter
Using an organic-material-containing electrolytic solution added with m 2, thiourea 50 ppm, and hydrochloric acid 100 ppm, the electrolytic solution temperature was 70 ° C., the current density was 200 A / dm ^2, and electrolysis was performed by using a copper plate as the cathode and the life was examined. In the table, ○, △, × are shown. ◯: Electrolyzable time is over 500 hours Δ: Electrolyzable time is over 100 hours to 500 hours ×: Electrolyzable time is 100 hours or less

(1-3) Inversion of polarity The same as in Example 1 was examined. In the table, ○, △, × are shown. ◯: Electrolyzable time is 500 hours or more Δ: Electrolyzable time is 100 hours or more and less than 500 hours X: Electrolyzable time is less than 100 hours

(2) Adhesion strength The same examination as in Example 1 was carried out. In the table, ○, △, × are shown. ◯: The weight loss of the coating layer is 5% by weight or less. Δ: The weight loss of the coating layer is more than 5% to 10% by weight. X: The weight loss of the coating layer is more than 10% by weight.

(3) Oxygen overvoltage It was examined in the same manner as in Example 1. In the table, ○, △, × are shown. ◯: Oxygen overvoltage is 0.5 V or less Δ: Oxygen overvoltage is over 0.5 V to 1 V ×: Oxygen overvoltage is over 1 V

[0079]

[Table 3]

Sample No. 41 and No. 4 in Table 3
The electrode life in electrolysis in an electrolyte containing an organic substance and the use of polarity reversal is the same indication of ○ and △, respectively, but in reality, sample No. 41 of the coating layer containing tantalum oxide is more It had a longer life than No. 42.

Example 6 Samples prepared by adding titanium oxide, niobium oxide, zirconium oxide or tin oxide in place of tantalum oxide in the coating layer in samples No. 41 to No. 45 of Example 5 were prepared. When the characteristics were evaluated, the same tendency was shown depending on the composition of the coating layer.

The coating liquid for forming the coating layer contained titanium chloride, niobium chloride or tin chloride instead of tantalum chloride.

Among these, Table 4 shows changes in electrode life in the electrolysis using an organic-containing electrolytic solution as a function of the presence or absence of silicon oxide.

[0084]

[Table 4]

[0085]

According to the present invention, it is possible to obtain an electrode for electrolysis which has excellent durability in various electrolytic reactions and has a long life. Also,
The manufacturing method is simple.

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Claims (5)

[Claims] 1. An electrode for electrolysis having a coating layer containing iridium oxide, platinum and silicon oxide on a conductive substrate. 2. The iridium oxide content in the coating layer is 2 to 90 atomic% in terms of Ir, and the platinum content is Pt.
The electrode for electrolysis according to claim 1, which has a conversion of 2 to 92 atomic% and a silicon oxide content of 3 to 75 atomic% in terms of Si. 3. The electrode for electrolysis according to claim 1, wherein the coating layer further contains at least one kind of tantalum oxide, titanium oxide, niobium oxide, zirconium oxide and tin oxide in an amount of 30 atomic% or less in terms of metal. 4. A method for producing an electrode for electrolysis, which comprises forming the coating layer by a thermal decomposition method when obtaining the electrode for electrolysis according to claim 1. 5. The method for producing an electrode for electrolysis according to claim 4, wherein the raw material of silicon oxide contained in the coating layer is silica sol.