JP2008050675A - Electrode for electrolysis - Google Patents

Abstract

Disclosed is an electrode for electrolysis that maintains high and stable chlorine generation efficiency and has high durability even when the polarity of an anode and a cathode is repeatedly used in dilute saline.
(A) an electrode substrate made of titanium or a titanium alloy; (b) a porous platinum coating layer provided on the electrode substrate and having an apparent density in the range of 8 to 19 g / cm ³ ; c) At least one metal oxide selected from tin oxide and ruthenium oxide provided on the porous platinum coating layer in an amount of 2 to 35 mol%, iridium oxide 2 to 25 mol%, tantalum oxide 6 An electrode for electrolysis characterized by comprising a complex of ˜35 mol% and platinum of 50 to 80 mol%.
[Selection figure] None

Description

  TECHNICAL FIELD The present invention relates to an electrode for electrolysis that is useful as an anode in dilute saline to generate electrolyzed water having a high sterilizing ability, and more particularly, stable and high chlorine generation efficiency characteristics even under conditions of switching polarity. And relates to an electrode for electrolysis having high durability.

Diluted salt water with salt added to tap water to generate chlorine at the anode, and using the bactericidal properties of hypochlorous acid produced by the reaction of this chlorine and water, cooking utensils, kitchen equipment, medical equipment It is known to perform sterilization at medical sites. In such electrolysis, tap water is used, so that calcium or magnesium in tap water may react with OH ⁻ generated on the cathode side during electrolysis and adhere to the cathode surface as hydroxide and become clogged. . In order to remove these deposits, it is common practice to periodically switch the polarity, that is, to use two or more similar electrodes and repeat the use as an anode and as a cathode. It is.

  As an electrode used in tap water, an electrode obtained by electroplating platinum on titanium and a titanium alloy substrate is widely used, and this electrode has high stability at the time of polarity switching and a small amount of platinum consumption. Because the chlorine generation efficiency is low, when using electrolyzed water for sterilization, it is necessary to increase the salt concentration, increase the current value, etc. in order to obtain a predetermined effective chlorine concentration. There is a problem of becoming higher.

  Patent Document 1 proposes an electrode in which a coating layer made of iridium oxide, tantalum oxide, and platinum is provided on a conductive substrate in order to increase chlorine generation efficiency. Although this electrode has the advantage that the chlorine generation efficiency is higher than that of the platinum plating electrode, the chlorine generation efficiency gradually decreases when the polarity of the anode and the cathode is switched repeatedly in dilute saline. There's a problem.

On the other hand, Patent Document 2 discloses an intermediate layer made of a metal oxide such as iridium oxide or tin oxide and a metal oxide such as tantalum oxide on an electrode base made of titanium or a titanium alloy, iridium oxide, and tantalum oxide. And an electrode provided with an outer layer made of platinum has been proposed as an electrode for oxygen generation. When electrolysis is performed in dilute saline using this electrode, initially high chlorine generation efficiency is obtained as compared with the platinum-plated electrode, but the anode and cathode are switched in polarity in dilute saline repeatedly. There is a problem that the chlorine generation efficiency decreases rapidly.
Japanese Patent Laid-Open No. 2-26389 Japanese Patent Laid-Open No. 2-200790

  An object of the present invention is to provide an electrode for electrolysis that maintains stable and high chlorine generation efficiency and has high durability even when repeated use is performed by switching the polarity of the anode and cathode in dilute saline. .

  As a result of intensive studies, the present inventors have provided a porous platinum coating layer having a specific apparent density on an electrode substrate made of titanium or a titanium alloy, and further, a specific component composition is further provided thereon. It was found that an electrode suitable for the above purpose can be obtained by supporting the metal oxide composite of the present invention, and the present invention has been completed.

Thus, according to the present invention,
(A) an electrode substrate made of titanium or a titanium alloy;
(B) a porous platinum coating layer having an apparent density in the range of 8 to 19 g / cm ³ provided on the electrode substrate;
(C) At least one metal oxide selected from tin oxide and ruthenium oxide provided on the porous platinum coating layer in an amount of 2 to 35 mol%, iridium oxide 2 to 25 mol%, tantalum oxide An electrode for electrolysis characterized by comprising a composite of 6 to 35 mol% and platinum of 50 to 80 mol% is provided.

  The electrode of the present invention has excellent characteristics such as maintaining high chlorine generation efficiency and low consumption even when the polarity of the anode and the cathode is switched repeatedly in dilute saline.

  Hereinafter, the electrode of the present invention and the production method thereof will be described in more detail.

  Examples of the material of the electrode substrate used in the present invention include titanium or a titanium-based alloy. As the titanium-based alloy, a corrosion-resistant conductive alloy mainly composed of titanium is used. For example, a normal electrode material made of a combination of Ti—Ta—Nb, Ti—Pd, Ti—Zr, Ti—Al, etc. Ti-based alloys used as These electrode materials can be processed into a desired shape such as a plate shape, a perforated plate shape, a rod shape, or a net plate shape and used as an electrode substrate.

  It is desirable to pre-treat the electrode base as described above in advance, as is usually done. Specific examples of such pretreatment include the following.

  First, the surface of an electrode substrate (hereinafter referred to as titanium substrate) made of titanium or a titanium-based alloy described above is washed with alcohol, for example, and / or degreased by electrolysis in an alkaline solution, and then hydrogen fluoride. By treating with hydrofluoric acid having a concentration of 1 to 20% by weight or a mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid, the oxide film on the surface of the titanium substrate is removed, and titanium crystal grain boundaries Roughening the unit. The acid treatment can be performed for several minutes to tens of minutes at a temperature of room temperature to about 40 ° C. depending on the surface condition of the titanium substrate. In order to sufficiently roughen the surface, blasting may be used in combination.

  The surface of the titanium substrate thus treated with acid is brought into contact with hot concentrated sulfuric acid to roughen the inner surface of the titanium crystal grain boundary into fine projections and to form a thin layer of titanium hydride on the surface of the titanium substrate. Let me. Concentrated sulfuric acid to be used generally has a concentration within the range of 40 to 80% by weight, preferably 50 to 60% by weight. The concentrated sulfuric acid is used for the purpose of stabilizing the treatment, if necessary. A small amount of sodium sulfate and other sulfates may be added. The contact with the hot concentrated sulfuric acid can be usually carried out by immersing the titanium substrate in a bath of concentrated sulfuric acid, and the bath temperature is generally about 100 to about 150 ° C., preferably about 110 to about The temperature can be within the range of 130 ° C., and the immersion time is usually about 0.5 to about 10 minutes, preferably about 1 to about 3 minutes. By this hot concentrated sulfuric acid treatment, the inner surface of the titanium crystal grain boundary can be finely roughened in a protruding manner, and a very thin titanium hydride film can be formed on the surface of the titanium substrate. The titanium substrate treated with hot concentrated sulfuric acid is taken out of the sulfuric acid bath and preferably cooled rapidly in an inert gas atmosphere such as nitrogen or argon to lower the surface temperature of the titanium substrate to about 60 ° C. or lower. For this rapid cooling, it is appropriate to use a large amount of cold water also for washing.

  The titanium substrate on which a very thin titanium hydride coating layer is thus formed is immersed in a dilute hydrofluoric acid or dilute fluoride aqueous solution (for example, an aqueous solution of sodium fluoride, potassium fluoride, etc.). Then, the titanium hydride coating is grown to make the coating uniform and stable. The concentration of hydrogen fluoride in the dilute hydrofluoric acid or dilute fluoride aqueous solution that can be used here is generally 0.05 to 3% by weight, preferably 0.3 to 1% by weight. Moreover, the temperature at the time of the immersion process by these solutions can generally be in the range of 10-40 degreeC, Preferably it is 20-30 degreeC. This treatment can be carried out until a uniform coating of titanium hydride having a thickness of usually 0.5 to 10 microns, preferably 1 to 3 microns is formed on the surface of the titanium substrate. Since this titanium hydride (TiHy, where y is a number between 1.5 and 2) exhibits a grayish brown color to a blackish brown color depending on the degree of hydrogenation, a titanium hydride film having a thickness in the above range is formed. Can empirically control the change in color tone of the substrate surface by contrasting with a standard color source.

  The titanium substrate having the titanium substrate surface roughened and having a titanium hydride coating formed thereon is appropriately subjected to a treatment such as washing with water, and then a porous platinum coating layer is formed on the surface.

  The porous platinum coating layer can be usually formed by electroplating. Examples of the composition of the plating bath that can be used for this electroplating method include platinum compounds such as chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, and dinitrodiammine platinum, sulfuric acid solution (pH 1 to 3) or aqueous ammonia solution. In order to stabilize the bath, sodium sulfate (in the case of an acidic bath), sulfurous acid, and the like are dissolved in the solution so as to have a concentration of 2 to 20 g / l, especially 5 to 10 g / l in terms of platinum. Examples thereof include an acidic or alkaline plating bath to which a small amount of sodium, sodium sulfate (in the case of an alkaline bath) or the like is added.

Platinum electroplating using a plating bath having such a composition uses a high-speed plating method such as so-called strike plating in order to suppress decomposition of the titanium hydride film formed on the surface of the titanium substrate as much as possible. It is desirable to carry out at a relatively low temperature within the range. By this electroplating, a porous platinum coating layer having excellent physical adhesion strength can be formed on the titanium hydride coating on the titanium substrate. In this case, the apparent density of the platinum coating layer is suitably 8 to 19 g / cm ³ , preferably 12 to 18 g / cm ³ . If the apparent density of the porous coating layer is less than 8 g / cm ³ , the bond strength of platinum is lowered and peeling easily occurs. Conversely, if it exceeds 19 g / cm ³ , tin oxide obtained by thermal decomposition described later It becomes difficult to stably carry a coating layer made of a mixture of ruthenium oxide, iridium oxide, tantalum oxide and platinum.

  The apparent density of the platinum coating layer can be controlled, for example, by empirically adjusting the pretreatment conditions of titanium, the bath composition of the platinum plating bath and / or the plating conditions (current density, current waveform, etc.). . In order to obtain a more porous platinum coating layer, the porosity can be further increased by a chemical or electrochemical method after the porous platinum coating layer is formed.

The platinum electroplating is continued until the platinum coating amount on the substrate is usually at least 0.2 mg / cm ² or more. When the coating amount of platinum is less than 0.2 mg / cm ² , oxidation of the titanium hydride coating portion proceeds excessively during the baking treatment described later, and the conductivity tends to decrease. The upper limit of the coating amount of platinum is not particularly limited, but even if it is increased more than necessary, the effect associated therewith is not obtained, and it becomes uneconomical, so a coating amount of 5 mg / cm ² or less is usually sufficient It is. A suitable coating amount of platinum is in the range of 1 to 3 mg / cm ² .

Here, the coating amount of platinum in the porous platinum coating layer is an amount obtained as follows using a fluorescent X-ray analysis method. That is, as described above, platinum plating to various thicknesses is performed on the titanium substrate pretreated as described above, and after each sample is cut in half, each platinum is eluted with aqua regia and the amount of platinum is wet. Measure by analytical method, give a price, and make a standard plate. A calibration curve is created using the standard plate thus obtained. Next, the actual sample is subjected to fluorescent X-ray analysis, and the platinum coating amount is obtained from the calibration curve. The density of the platinum coating layer (δ g / cm ³ ) is determined by the platinum coating amount (w g / cm ² ) determined as described above and the thickness of the platinum coating layer determined by cross-sectional microscopic observation of the sample ( tcm) from δ = w / t.

The titanium substrate thus provided with the porous platinum coating layer is then calcined in the atmosphere, if necessary, to thermally decompose the titanium hydride coating layer under the platinum coating layer, The titanium hydride in the layer can be substantially returned to titanium metal, and the titanium in the vicinity of the boundary with the platinum coating layer can be changed to titanium oxide in a low oxidation state. This calcination can be generally performed by heating at a temperature of about 300 to about 600 ° C., preferably about 300 to about 400 ° C. for about 10 minutes to 4 hours. As a result, a very thin conductive titanium oxide layer is formed on the surface of the titanium substrate. The thickness of the titanium oxide layer is generally 100 to 1,000 angstroms, preferably is preferable to be within a range of 200 to 600 angstroms, and the composition of the titanium oxide, x as TiO _x is generally 1 < It is desirable that x <2, particularly 1.9 <x <2. As another method, the titanium substrate provided with the porous platinum coating layer may be directly subjected to the next step without performing the baking treatment as described above. In this case, the titanium hydride coating layer on the surface of the titanium substrate is converted into titanium metal and titanium oxide in a low oxidation state during firing in the next step. In this way, high adhesion strength between the porous platinum coating layer and the titanium interface is maintained, and furthermore, electrically conductive titanium oxide (passivated film) is formed, and chemical stability can be enhanced.

  Thereafter, the porous platinum-coated surface of the platinum-coated titanium substrate thus fired is infiltrated with a solution containing a tin compound, a ruthenium compound, an iridium compound, a tantalum compound and a platinum compound, dried and fired, A tin oxide-ruthenium oxide-iridium oxide-tantalum oxide-platinum composite is supported on the platinum coating layer.

  The tin compound, ruthenium compound, iridium compound, tantalum compound and platinum compound used here are compounds that decompose under the conditions described below and can be converted into tin oxide, ruthenium oxide, iridium oxide, tantalum oxide and platinum, respectively. is there. Thus, examples of the tin compound include tin chloride and tetraisopropoxide tin, and tin chloride is particularly preferable. Examples of the ruthenium compound include ruthenium chloride and ruthenium nitrate, and ruthenium chloride is particularly preferable. Examples of the iridium compound include iridium chloride, iridium chloride, iridium nitrate, and iridium chloride is particularly preferable. Examples of the tantalum compound include tantalum chloride and tantalum ethoxide, and tantalum ethoxide is particularly preferable. Examples of the platinum compound include chloroplatinic acid and platinum chloride, and chloroplatinic acid is particularly preferable.

  On the other hand, as a solvent for dissolving these tin compound, ruthenium compound, iridium compound, tantalum compound and platinum compound, a lower alcohol is suitable, for example, methanol, ethanol, propanol, butanol or a mixture thereof is used. .

  The total metal concentration of the tin compound, ruthenium compound, iridium compound, tantalum compound and platinum compound in the lower alcohol solution can be generally in the range of 20 to 200 g / l, preferably 40 to 150 g / l. When the metal concentration is lower than 20 g / l, the catalyst supporting efficiency is deteriorated. When the metal concentration exceeds 200 g / l, the catalyst tends to aggregate, and problems such as catalyst activity, supporting strength, and unevenness of the supporting amount occur.

  Moreover, the relative use ratio of the tin compound, ruthenium compound, iridium compound, tantalum compound and platinum compound is 2 to 35 mol%, preferably 10 to 25 mol% in total of the tin compound and ruthenium compound in terms of metal; iridium Compound is 2 to 25 mol%, preferably 10 to 15 mol%; Tantalum compound is 6 to 35 mol%, preferably 10 to 18 mol%; and Platinum compound is 50 to 80 mol%, preferably 60 to 75 mol% It can be.

  The substrate in which the porous platinum coating layer is impregnated with the solution is dried at a temperature in the range of about 20 to about 150 ° C., if necessary, and then fired in an oxygen-containing gas atmosphere, for example, air. Firing is carried out by heating to a temperature generally in the range of about 450 to about 650 ° C., preferably about 500 to about 600 ° C. in a suitable heating furnace such as an electric furnace, gas furnace, infrared furnace or the like. it can. The heating time can be about 5 to 30 minutes depending on the size of the substrate to be fired. By this firing, a tin oxide-ruthenium oxide-iridium oxide-tantalum oxide-platinum complex can be supported on the surface of the porous platinum coating layer (inside and / or outside of the pores).

  Here, "tin oxide-ruthenium oxide-iridium oxide-tantalum oxide-platinum composite" means that tin oxide, ruthenium oxide, iridium oxide, tantalum oxide, and platinum interact on the surface of the porous platinum coating layer. In this way, it is in a state of being mixed or in close contact.

  If a sufficient amount of tin oxide-ruthenium oxide-iridium oxide-tantalum oxide-platinum composite cannot be supported by a single loading operation, the above-described solution penetration- (drying) -calcination The process can be repeated as many times as desired.

  The ratio of each component in the tin oxide-ruthenium oxide-iridium oxide-tantalum oxide-platinum composite supported on the porous platinum coating layer is 2 to 35 mol% in total of tin oxide and ruthenium oxide in terms of metal. Preferably 10-25 mol%; iridium oxide 2-25 mol%, preferably 10-15 mol%; tantalum oxide 6-35 mol%, preferably 10-18 mol%; platinum 50-80 mol%, preferably 60 It can be -75 mol%.

  The electrode for electrolysis of the present invention produced in this way exhibits stable and high chlorine generation efficiency characteristics when used as an anode and a cathode after switching the polarity, and is coated by an anchor effect with the porous platinum coating layer. It has the characteristics that the adhesiveness of the resin is good, the consumption is small, and the durability is excellent.

  EXAMPLES Next, although an Example demonstrates this invention further more concretely, this Example is only an illustration and does not limit the scope of the present invention.

Examples 1-5, Comparative Examples 1-2
A titanium plate material (1.0 mm x 100 mm x 100 mm) equivalent to JIS class 2 is washed with alcohol, then treated in an 8 wt% hydrofluoric acid aqueous solution at 20 ° C for 2 minutes, and further, a 60 wt% sulfuric acid aqueous solution at 120 ° C. Treated for 3 minutes. Next, the titanium substrate was taken out from the sulfuric acid aqueous solution and rapidly cooled by spraying cold water in a nitrogen atmosphere. Further, it was immersed in a 0.3 wt% hydrofluoric acid aqueous solution at 20 ° C. for 2 minutes and then washed with water.

After washing with water, dinitrodiammine platinum was dissolved in a sulfuric acid solution and plated at 30 mA / cm ² for about 6 minutes in a platinum plating bath adjusted to a platinum content of 5 g / l, pH of about 2 and 50 ° C. A porous platinum coating layer having an apparent density of 16 g / cm ³ and an electrodeposition amount of 1.7 mg / cm ² was formed on the titanium substrate.

  Thus, the titanium base | substrate which provided the porous platinum coating layer was heat-processed in 400 degreeC air | atmosphere for 1 hour. Subsequently, a butanol solution of tin chloride adjusted to a tin concentration of 100 g / l, a butanol solution of ruthenium chloride adjusted to a ruthenium concentration of 100 g / l, a butanol solution of chloroiridium acid adjusted to an iridium concentration of 100 g / l, and a tantalum concentration Table 1 shows the composition ratio of Sn-Ru-Ir-Ta-Pt for a butanol solution of tantalum ethoxide adjusted to 100 g / l and a butanol solution of chloroplatinic acid adjusted to a platinum concentration of 200 g / l. Each was weighed so as to be mol%, then diluted with butanol so that the total metal equivalent of Sn—Ru—Ir—Ta—Pt was 75 g / l, and Example 5 described in Table 1 below was used. The solutions of Example and Comparative Example 2 were prepared.

  After 0.2 ml of this solution was weighed with a pipette and permeated into the porous platinum coating layer, it was dried at room temperature for 30 minutes, and further baked in an atmosphere at 550 ° C. for 10 minutes. This infiltration-drying-firing process was repeated 5 times, and Example Electrode 1 shown in Table 1 below, in which the porous platinum coating layer was loaded with a tin oxide-ruthenium oxide-iridium oxide-tantalum oxide-platinum composite. To 5 and comparative electrodes 1 to 2 were prepared.

Comparative Examples 3-4
A titanium plate material (1.0 mm x 100 mm x 100 mm) equivalent to JIS type 2 is washed with alcohol, treated in an 8 wt% hydrofluoric acid aqueous solution at 20 ° C for 2 minutes, and further a 60 wt% sulfuric acid aqueous solution at 120 ° C. Treated for 3 minutes. Next, the titanium substrate was taken out of the sulfuric acid aqueous solution, and cooled rapidly by spraying cold water in a nitrogen atmosphere. Further, it was immersed in a 0.3 wt% hydrofluoric acid aqueous solution at 20 ° C. for 2 minutes and then washed with water.

After washing with water, the dinitrodiammine platinum was dissolved in a sulfuric acid solution and plated at 15 mA / cm ² for about 50 seconds in a platinum plating bath adjusted to a platinum content of 5 g / l, pH of about 2 and 50 ° C., Platinum having an electrodeposition amount of 0.1 mg / cm ² was dispersed and deposited on the titanium substrate.

  The titanium substrate on which platinum was dispersed and precipitated in this manner was heat-treated in the atmosphere at 400 ° C. for 1 hour. Then, a butanol solution of iridium chloride adjusted to an iridium concentration of 100 g / l and a butanol solution of tantalum ethoxide adjusted to a tantalum concentration of 100 g / l were mixed to contain iridium 5.9 g / l and tantalum 50 g / l. A solution was prepared, 0.27 ml of this solution was weighed with a pipette, applied onto a titanium substrate on which platinum was dispersed and deposited, dried at room temperature for 30 minutes, and further baked in an atmosphere at 500 ° C. for 10 minutes. . This coating-drying-firing process was repeated once to form an intermediate layer.

  Next, a butanol solution of chloroiridium acid adjusted to an iridium concentration of 100 g / l, a butanol solution of tantalum ethoxide adjusted to a tantalum concentration of 100 g / l, and a butanol solution of chloroplatinic acid adjusted to a platinum concentration of 200 g / l, Each is weighed so that the composition ratio of Ir-Ta-Pt becomes the mol% described in Table 1 below, and then in butanol so that the total metal equivalent of Ir-Ta-Pt is 70.5 g / l. The solutions of 2 Comparative Examples described in Table 1 below were prepared.

  0.27 ml of this solution was weighed with a pipette, coated on the intermediate layer, dried at room temperature for 30 minutes, and further baked in air at 500 ° C. for 10 minutes. This coating-drying-firing process was repeated 11 times, and Comparative Examples 3 to 4 shown in Table 1 in which the iridium oxide-tantalum oxide-platinum composite was supported on the intermediate layer were produced.

Comparative Examples 5-7
A titanium plate material (1.0 mm × 100 mm × 100 mm) corresponding to JIS type 2 was washed with alcohol, pretreated with a hot oxalic acid aqueous solution, and washed with water. Next, a butanol solution of chloroiridium acid adjusted to an iridium concentration of 100 g / l, a butanol solution of tantalum ethoxide adjusted to a tantalum concentration of 100 g / l, and a butanol solution of chloroplatinic acid adjusted to a platinum concentration of 200 g / l, Each of them was weighed so that the composition ratio of Ir-Ta-Pt would be the mol% described in Table 1 below, and then diluted with butanol so that the total metal equivalent of Ir-Ta-Pt would be 75 g / l. The solutions of Comparative Examples 5 to 7 described in Table 1 below were prepared.

  After 0.2 ml of this solution was weighed with a pipette and applied onto the above pretreated titanium substrate, it was dried at room temperature for 30 minutes and further baked in an atmosphere at 550 ° C. for 10 minutes. This coating-drying-firing process was repeated 5 times to produce comparative electrodes 5-7.

Using the electrode obtained in Examples and Comparative Examples described above, in a 0.1 wt% of 25 ° C. aqueous sodium chloride solution, at 2A / dm ² in -2A / dm ² after electrolysis for 30 seconds 30 seconds Electrolysis which is repeated alternately was performed for 200 hours. The chlorine generation efficiency before and after electrolysis is shown in Table 1 below.

  The chlorine generation efficiency is a measured value in a 0.1 wt% sodium chloride aqueous solution.

  Comparative example electrodes 1 to 7 have a high chlorine generation efficiency before the electrolytic test of 24 to 32%, whereas the chlorine generation efficiency after the electrolytic test is remarkably reduced to 11 to 15%. No. 5 has a chlorine generation efficiency of 30 to 33% before the electrolytic test and maintains a high chlorine generation efficiency of 22 to 25% even after the electrolytic test. Moreover, the result of having measured the consumption of the coating | cover by the electrolysis test with the fluorescent X-ray film thickness meter is as showing in Table-1, and the consumption of the coating | cover of the comparative example electrodes 1-6 is 7-20%. On the other hand, the consumption of the coating of Example electrodes 1 to 5 is extremely small at 5%.

  As described above, it can be seen that the electrode of the present invention has excellent characteristics of maintaining high chlorine generation efficiency and low consumption even when the polarity is switched and used as an anode and a cathode for a long time. .

Claims (1)

(A) an electrode substrate made of titanium or a titanium alloy;
(B) a porous platinum coating layer having an apparent density in the range of 8 to 19 g / cm ³ provided on the electrode substrate;
(C) At least one metal oxide selected from tin oxide and ruthenium oxide provided on the porous platinum coating layer in an amount of 2 to 35 mol%, iridium oxide 2 to 25 mol%, tantalum oxide An electrode for electrolysis comprising a complex of 6 to 35 mol% and platinum of 50 to 80 mol%.