JPH0238670B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an electrode for electrolysis, and more particularly to an electrode for electrolysis suitable as an anode for saline electrolysis using an ion exchange membrane method, and a method for manufacturing the same. [Conventional technology and problems] Conventionally, electrolysis has been performed using a valve metal such as titanium (Ti) as a base and an electrocatalytically active coating mainly composed of an oxide of a platinum group metal such as ruthenium (Ru). The electrode for
Since it was first known as a revolutionary insoluble metal electrode, it has been applied in various electrochemical fields, and in particular, it has been widely put into practical use as an anode in the salt electrolysis industry, replacing the conventional graphite electrode. Various applications and improvements have been made to these electrodes in accordance with the development of electrolytic technology and applications. The electrode disclosed in Japanese Patent Publication No. 46-21884 is coated with a solid solution of platinum group metal oxides and valve metal oxides such as Ti, Ta, and Nb, and is particularly durable as an anode for mercury salt electrolysis. , has been widely put into practical use, but
For chlorine generation, there is a disadvantage that a relatively large amount of oxygen is generated due to undesirable side reactions. The electrode of Japanese Patent Publication No. 50-11330 has a solid solution coating made of tin (Sn) oxide instead of the valve metal oxide of the above electrode, and has relatively good durability, but it With this combination, it is difficult to lower the chlorine overvoltage and reduce the amount of oxygen generated at the same time. JP-A No. 51-63374 describes an electrode having a coating layer composed of a platinum group metal oxide and an indium (In) oxide. This electrode was intended to be an inexpensive anode with low chlorine overvoltage and durability, but it uses rhodium (Rh) as the platinum group metal component and is substantially Rh ₂ O ₃ -In ₂ O ₃ or this. This paper presents a coated electrode to which a small amount of tin oxide is added. That is, the coating oxide is mainly of the R ₂ O ₃ type (R represents a metal), and therefore the Ti of the substrate
Rutile type (RO ₂
There are problems in that it is inferior to type 2) coatings, has insufficient durability as an electrode, and has a relatively high chlorine overvoltage. In recent years, due to the development of ion-exchange membrane electrolysis technology and the demand for energy conservation, electrodes with lower overvoltage and durability are desired, but these conventional electrodes cannot be said to fully meet these demands. [Object of the Invention] An object of the present invention is to provide an electrode that has a low chlorine overvoltage and excellent durability, and is particularly suitable for ion-exchange membrane electrolysis, and a method for manufacturing the same. [Means and effects for solving the problem] The objects of the present invention are achieved by the present invention described below. That is, the invention (1) provides an electrolytic electrode in which a coating having electrocatalytic activity is provided on a conductive substrate, wherein the coating contains 25 to 50 mol% of ruthenium oxide and a total of 75 to 30 mol% of ruthenium oxide. mole%
indium oxide and tin oxide (however, the atomic ratio of indium and tin is 90:10 to 10:90)
and 1 to 20 mol% of titanium oxide, and is substantially a rutile type composite oxide. The second invention is to apply a solution containing thermally decomposable salts of ruthenium, indium, tin, and titanium onto a conductive substrate, heat it in an oxidizing atmosphere, and apply 25 to
50 mol% ruthenium oxide and a total of 75-30
Mol% of indium oxide and tin oxide (however, the atomic ratio of indium and tin is 90:10 to 10:90)
) and 1 to 20 mol% of titanium oxide, forming a coating having electrocatalytic activity that is substantially a rutile type composite oxide. . In addition, in the present invention, a part of ruthenium oxide is substituted in the coating having electrocatalytic activity.
It can contain up to mol % of platinum (Pt). The present invention will be explained in more detail below. The conductive substrate in the present invention is a corrosion-resistant conductive metal such as Ti, Ta (tantalum), Nb (niobium), Zr (zirconium), or a base alloy thereof, and the conventionally used metal Ti, Or Ti
-Ti-based alloys such as Ta-Nb and Ti-Pd are preferred.
Its shape can be any desired, such as a plate, a perforated plate, a rod-like body, or a net-like body. The conductive substrate is suitably subjected to a surface cleaning treatment, etc., and is provided with a coating having electrocatalytic activity of the present invention. The coating comprises 25 to 50 mol% Ru oxide;
It is a composite oxide that basically consists of a total of 75 to 30 mol% of In oxide and Sn oxide, and 1 to 20 mol% of Ti oxide, and the composite oxide is substantially of rutile type ( RO type ₂ ) mainly has a crystal structure. Further, the coating may be a mixture of metal oxides, a solid solution, or a mixture of both metal oxides. When Pt is contained in the coating, as will be described later, Pt is uniformly mixed or dissolved in a metallic state in the main rutile type composite oxide, and the basic rutile structure of the coating remains unchanged. In the present invention, the main structure of the electrode coating is rutile type (RO ₂ type).When In oxide is included in the coating, Rh oxide (Rh ₂ O ₃ ) and In ₂ O ₃ combined
It was found that the R ₂ O ₃ type had insufficient bonding properties with the substrate and the abrasion resistance of the coating, and these drawbacks were overcome by combining it with Ru oxide (RuO ₂ ) to form the RO ₂ type. This is due to the discovery that an excellent electrode can be obtained. By combining Ru-In-Sn-Ti, these composite oxides can be easily coated as a rutile structure as a whole. The method of coating the composite oxide on the substrate is as follows:
Various methods such as those described in the above-mentioned Japanese Patent Publication No. 48-3954 can be applied, but in particular, a solution containing a thermally decomposable inorganic or organic salt of each coating component metal is applied onto the substrate, and the solution is applied in an oxidizing atmosphere. A so-called pyrolytic oxidation method involving heating is preferred. The appropriate heating temperature is usually 300 to 600°C in air. The effects and composition ranges of the individual components constituting the electrode coating in the present invention will be explained below. (1) Ru oxide and Pt RuO ₂ have excellent functions mainly as electrocatalysts for chlorine generation, resulting in low chlorine overvoltage.
Therefore, in the present invention, it is preferable that the coating contains 25 to 50 mol% of RuO2 in the form of _RuO2 . twenty five
If it is less than mol %, the chlorine overvoltage tends to increase, and if it exceeds 50 mol %, durability deteriorates and the amount of oxygen generated increases. In addition, a portion of RuO ₂ can be replaced with Pt up to 15 mol%,
The addition of Pt has the effect of reducing the chlorine overvoltage and the amount of oxygen generated. But 15
If the mol% is exceeded, the chlorine overvoltage tends to increase over time during electrolytic use. The Pt component is
In ordinary thermal decomposition oxidation methods, it does not become an oxide, but is mixed in the coating in a metallic state. (2) Sn oxide and In oxide Both have a promoter function and have the effect of keeping the chlorine overvoltage low. This effect is more pronounced with In, but with In alone, it becomes In ₂ O ₃ and deteriorates durability. Sn oxide similarly has the function of lowering the chlorine overvoltage, and furthermore has the function of making In the rutile type of InO ₂ by coexisting with In oxide and improving corrosion resistance. Therefore, it is desirable that the total content of both is 75 to 30 mol% in the coating. Also, In and Sn
A sufficient effect can be achieved when the mutual composition ratio is in the range of 90:10 to 10:90 in atomic ratio. (3) Ti oxide TiO ₂ is a typical rutile-type oxide, and when it is included as an electrode coating component in the present invention in an amount of 1 to 20 mol%, it has the effect of increasing physical and chemical stability and improving the durability of the electrode. Improve your sexuality. However, if it exceeds 20 mol%, the chlorine overvoltage increases, which is not practical. [Examples] Examples of the present invention will be described below, but these Examples do not limit the present invention. Example 1 Alkoxytin was prepared in advance from butyl alcohol and stannic chloride, ruthenium chloride and indium chloride were dissolved in the butyl alcohol solution in various proportions, and the mixture was further heated under reflux for about 12 hours, and finally butyl titanate was dissolved. Coating liquids with various compositions were prepared by adding them in various proportions. This coating solution was degreased in advance and heated to 80°C at 25%
It was applied with a brush to an expanded mesh made of pure titanium that had been etched in an aqueous H ₂ SO ₄ solution for 4 hours, dried at 150°C for 15 minutes, and then heated at 480°C for 15 minutes in a Matsufuru furnace with air circulation. The above coating and heating steps were repeated eight times to produce sample electrodes having composite oxide coatings having the compositions shown in Table 1 (only metals are shown). For these samples,
The state of existence of the coating layer composition was measured by X-ray diffraction method, and the chlorine overvoltage in 200 g/NaCl solution at 90°C was measured, and the amount of loss of the coating layer was measured by saline electrolysis using ion exchange membrane method under normal conditions. I took measurements. For comparison, conventional coated electrode samples and coated electrode samples outside the scope of the present invention were prepared, and similar measurements were performed. The results are shown in Table 1.

【table】

[Table] In Table 1, Comparison 1 is a sample according to Example 1 of JP-A-51-63374, in which Rh was used instead of Ru. In addition, to measure the amount of coating loss, place the sample electrode in close contact with the ion exchange membrane and apply 200% of the anolyte
The electrolysis was carried out using the ion exchange membrane electrolysis conditions of g-NaCl aqueous solution pH 4.5 to 5.5, temperature approximately 90° C., and current density 30 A/dm ² . From the results shown in Table 1, it can be seen that the electrode according to the present invention has a low chlorine overvoltage and is extremely stable. On the other hand, the Rh-In type in Comparison 1 is
Shows Rh ₂ O ₃ phase, high chlorine overvoltage, and large loss of coating. Also, Ru− in Comparison 2 which does not contain Sn
The In-Ti type has a low initial overvoltage, but it increases over time and is unstable. Conventional Ru-Sn system and Ru-
Ti-based products have a slightly higher chlorine overvoltage and a slightly larger amount of depletion. Example 2 Ru-Pt-Sn-In-
Ti-based coating solutions with various compositions were prepared, sprayed onto titanium substrates, dried at 180°C for 10 minutes, and then heated and oxidized in a Matsufuru furnace at 480°C for 15 minutes. The coating and heating operations were repeated eight times to prepare sample electrodes having the coating compositions shown in Table 2, and were tested in the same manner as in Example 1. This test is based on Sn and
The effect was investigated by holding the In composition ratio constant and changing the Pt and Ti compositions. The results are summarized in Table 2.

[Table] From the results shown in Table 2, as the Ti composition amount in the coating increases, the chlorine overvoltage increases (Comparison 3).
It can be seen that if Ti is not included in the composition, the amount of coating loss is large (Comparison 1), and the durability is inferior. On the other hand, when Pt is used as a composition, the initial overvoltage becomes extremely low, but it tends to increase over time, and it increases by 15%.
If it exceeds, the rise in overvoltage will be too large (Comparison 3)
It turns out that it is not suitable for use. Example 3 Various coating liquid raw materials were prepared in the same manner as in Example 1, and various Ru-Sn-In-Ti coating liquids were prepared. This coating solution was applied onto a titanium substrate by a spray method in the same manner as in Example 1, and after drying at 180°C for 15 minutes,
The material was heated and oxidized for 15 minutes in a Matsufuru furnace at 450°C with air circulation. This coating and heating operation was repeated eight times to produce sample electrodes having the compositions shown in Table 3. These samples were further heated in a Matsufuru furnace for about 1 hour.
Final heating was performed at 480°C. Each sample electrode obtained was measured and measured in the same manner as in Example 1.
The results are summarized in Table 3.

[Table] From the results shown in Table 3, it is clear that within the coating composition range of the present invention, the chlorine overvoltage is extremely low and the amount of coating loss is also small. On the other hand, when Ti is not included in the composition (Comparison 1), the amount of depletion increases. In addition, when Ru is less than 25% (Comparison 2), the chlorine overvoltage is high and unstable, and when it exceeds 50% (Comparison 3), the chlorine overvoltage is low but the amount of depletion is excessive, and both are not suitable for practical use. I understand. [Effects of the Invention] The present invention provides Ru(Pt)-In-Sn on a conductive substrate.
- Since the Ti-based rutile type composite oxide coating with a specific composition is provided, it is possible to obtain an electrolytic device with excellent durability, in which the chlorine overvoltage is extremely low and the coating, which is highly alkali resistant and acid resistant, is firmly adhered. Therefore, the electrode of the present invention is particularly suitable for ion-exchange membrane method saline electrolysis, and can operate stably at low voltage for a long period of time.

Claims (1)

[Scope of Claims] 1. An electrolytic electrode comprising a coating having electrocatalytic activity on a conductive substrate, wherein the coating contains 25 to 50 mol% of ruthenium oxide and a total of 75 to 30 mol% of ruthenium oxide. Consisting of indium oxide and tin oxide (however, the atomic ratio of indium and tin is 90:10 to 10:90) and 1 to 20 mol% of titanium oxide, it is essentially a rutile type composite oxide. An electrode for electrolysis characterized by: 2. The electrolysis electrode according to claim 1, wherein up to 15 mol% of the ruthenium oxide is replaced with platinum. 3 Ruthenium, indium,
A solution containing thermally decomposable salts of tin and titanium is applied and heated in an oxidizing atmosphere onto the substrate for 25 to 30 minutes.
50 mol% ruthenium oxide and a total of 75-30
Mol% of indium oxide and tin oxide (however, the atomic ratio of indium and tin is 90:10 to 10:90)
1) and 1 to 20 mol% of titanium oxide, and forms a coating having electrocatalytic activity that is substantially a rutile type composite oxide. 4 A thermally decomposable salt of platinum is further added to a solution containing thermally decomposable salts of ruthenium, indium, tin, and titanium to form a coating with electrocatalytic activity in which up to 15 mol% of the ruthenium oxide is replaced with platinum. A method of manufacturing an electrode for electrolysis according to claim 3.