JP2019119930A - Chlorine generating electrode - Google Patents

Abstract

To provide an electrode for electrolysis that: electrolyzes a saline solution with its saline concentration of 100-10000 ppm while repeatedly switching the polarity of an anode and a cathode at a prescribed current density; can suppress the electrochemical exhaustion and dropout of an electrode catalyst layer when generating chlorine; and has high chlorine generation efficiency characteristics.SOLUTION: An electrode for electrolysis is an electrode for generating chlorine in which an electrode catalyst layer is arranged on an electrode substrate composed of titanium or titanium alloy through an intermediate layer, and a saline solution with its saline concentration of 100-10000 ppm is electrolyzed while repeatedly switching the polarity of an anode and a cathode at a prescribed current density. The electrode catalyst layer comprises, in metal conversion, an iridium oxide of between 3 mol% and 10 mol%, a tantalum oxide of 20 mol% or more to less than 35 mol%, and a platinum of between 55 mol% and 77 mol%.SELECTED DRAWING: None

Description

  The present invention relates to an electrolytic electrode useful as an anode in a salt solution having a salt concentration of 100 to 10,000 ppm to generate a highly sterilizing electrolytic water, more specifically, stable and high chlorine under conditions of polarity switching. The present invention relates to an electrode for electrolysis having generation efficiency characteristics.

  In an apparatus that produces a bactericidal water by electrolyzing a saline solution having a salt concentration of several hundred to several thousand ppm, there is a strong demand for an electrode with higher chlorine generation efficiency in order to effectively utilize the added salt. For example, unlike in the case of direct electrolysis of tap water (e.g., every 3 minutes of switching time), the polarity switching is extended to 30 minutes or longer in order to obtain acidic sterile water continuously.

  A porous platinum coating layer and 30 to 65 mol% of iridium oxide, 10 to 40 mol% of tantalum oxide, and 25 to 60 platinum of platinum oxide supported on a titanium or titanium base alloy electrode substrate having a titanium oxide layer An electrode for seawater electrolysis comprising an electrode catalyst layer which is a composite of mol% has been proposed (see Patent Document 1). Although the proposed electrode has the advantage of high chlorine generation efficiency and stability even in the potential environment where acid pickling occurs, it has a sufficient life in an environment where the polarity switching of the anode and the cathode is repeated. There is a problem of not being.

  In addition, an electrode for electrolysis used as an anode in electrolysis such as electrolysis of seawater accompanied by oxygen generation at the anode, production of metal foil, and recovery has been proposed (see Patent Document 2). The intermediate layer of this proposed electrode is an intermediate layer composed of dispersion-coated platinum and a mixed metal oxide or a single metal oxide, and the outer layer of the electrode contains 5-94 mol% of iridium oxide and It is an outer layer composed of a mixed metal oxide consisting of 30 mol% and 5 to 94 mol% of at least one metal oxide selected from niobium oxide, tantalum oxide and zirconium oxide. Although the proposed electrode has the advantage of being stable even in a higher potential environment, there is a problem that the life is not sufficient in an environment in which the polarity switching of the anode and the cathode is repeated.

  In addition, alkaline ionized water as drinking water is obtained, and platinum containing 30 to 99 mol% of platinum and 1 to 70 mol% of tantalum in terms of metal on a conductive substrate as an electrode for drinking water electrolysis with little generation of chlorine An electrode for drinking water electrolysis has been proposed in which a coating layer of metal and tantalum oxide, or further, 40 mol% or less of iridium in terms of metal is added to the coating layer (see Patent Document 3).

Japanese Patent Application Publication No. 08-170187 Japanese Patent Application Laid-Open No. 2-200790 Japanese Patent Application Publication No. 06-158378

As described above, there were electrodes for the area with high chlorine concentration (seawater) and the area with low chlorine concentration (tap water) in the PtIrTa-based electrode, but the electrode used for chlorine generation in the middle concentration area is disclosed It has not been.
An apparatus that produces a sterile water by electrolyzing a saline solution having a salt concentration of several hundred to several thousand ppm differs from the case where tap water is directly electrolyzed, for example, because acid sterile water is continuously obtained (for example, The switching time is increased every three minutes) and the polarity switching to 30 minutes or more. There is a strong demand for an electrode with a higher chlorine generation efficiency in order to make effective use of the added salt.
The object of the present invention is to electrolyze a saline solution having a salt concentration of 100 to 10000 ppm while repeating polarity switching of the anode and the cathode at a predetermined current density to produce chlorine, electrochemical consumption / dropping of the electrode catalyst layer It is providing an electrode for electrolysis which can be suppressed and has high chlorine generation efficiency characteristics.

  As a result of intensive studies to achieve the above object, the present inventors found that iridium oxide, tantalum oxide, and iridium oxide formed on the intermediate layer under electrolytic conditions that prolong the time for electrolysis of water added with sodium chloride with the same polarity. The present inventors have found that addition of a predetermined tantalum concentration (20 mol% or more and less than 35 mol%) in an electrode catalyst layer made of platinum can suppress electrochemical consumption and film detachment and has high chlorine generation efficiency characteristics. To complete.

  Thus, according to the present invention, the electrode catalyst layer is provided on the electrode substrate made of titanium or titanium alloy via the intermediate layer, and the salt concentration is 100 to 100 while repeating the polarity switching of the anode and the cathode at a predetermined current density. It is an electrode for electrolyzing 10000 ppm saline and generating chlorine, and the electrode catalyst layer is 3 mol% or more and 10 mol% or less of iridium oxide, 20 mol% or more and 35 mol% of tantalum oxide in metal conversion. An electrode for electrolysis is provided, characterized in that the electrode is composed of less than 10% and 55% by mole to 75% by mole of platinum.

The intermediate layer can be a porous platinum coating with an apparent density in the range of 8 to 19 g / cm ³ . In addition, the intermediate layer is platinum coated at a coverage of 10 to 80% to the extent that the substrate surface is partially exposed, and 3 to 30% by mole of iridium oxide and tantalum oxide covering at least the exposed portion of the substrate surface. The intermediate layer can be made of 70 to 97 mol% of the mixed metal oxide.

  The electrode according to the present invention is an electrode for electrolysis which has high chlorine generation efficiency characteristics when producing a chlorine by electrolyzing a saline solution having a salt concentration of 100 to 10000 ppm while repeating polarity switching of the anode and the cathode at a predetermined current density. Can be provided.

  Hereinafter, the electrode of the present invention and the method for producing the same will be described in more detail.

<Electrode substrate>
As a material of the electrode base used in the present invention, titanium or a titanium base alloy may be mentioned. As a titanium-based alloy, a corrosion-resistant conductive alloy mainly composed of titanium is used, and for example, a common electrode comprising a combination of Ti-Ta-Nb, Ti-Pd, Ti-Zr, Ti-Al, etc. Examples include Ti-based alloys used as materials. These electrode materials can be processed into desired shapes, such as plate shape, perforated plate shape, rod shape, mesh plate shape, etc., and can be used as an electrode base material.

Pretreatment of electrode substrate
It is desirable to pre-treat the electrode substrate as described above, as is commonly done. Preferred specific examples of such pretreatment include those described below. First, the surface of an electrode substrate (hereinafter sometimes referred to as "titanium substrate") made of titanium or a titanium-based alloy described above was cleaned in a usual manner, for example, with alcohol, acetone or the like and / or degreased by electrolysis in an alkaline solution. Then, the oxide film on the surface of the titanium substrate is removed by treatment with hydrofluoric acid having a hydrogen fluoride concentration of 1 to 20% by weight or a mixed acid of hydrofluoric acid and other acids such as nitric acid and sulfuric acid. Roughening of titanium grain boundary units is performed. The acid treatment can be carried out at a temperature of normal temperature to about 40 ° C. for several minutes to several tens minutes depending on the surface condition of the titanium substrate. In addition, in order to fully perform roughening, you may use a blast process together.

Hydrotitanation treatment
The surface of the acid-treated titanium substrate is brought into contact with concentrated sulfuric acid to finely roughen the inner surface of the titanium crystal grain boundary in a projecting manner and to form a thin layer of titanium hydride on the surface of the titanium substrate. The concentration of concentrated sulfuric acid to be used is generally 40 to 80% by weight, preferably 50 to 60% by weight. If necessary, a small amount of sodium sulfate or the like may be used to stabilize the treatment. And the like may be added. The contact with the concentrated sulfuric acid can generally be carried out by immersing the titanium substrate in a bath of concentrated sulfuric acid, wherein the bath temperature is generally in the range of about 100 to about 150 ° C, preferably about 110 to about 130 ° C. And the immersion time is usually about 0.5 to about 10 minutes, preferably about 1 to about 3 minutes. By this sulfuric acid treatment, the inner surface of the titanium crystal grain boundary can be finely roughened in the form of projections, and an extremely thin film of titanium hydride can be formed on the surface of the titanium base. The sulfuric acid treated titanium substrate is removed from the sulfuric acid bath and quenched preferably in an inert gas atmosphere such as nitrogen, argon or the like to reduce the surface temperature of the titanium substrate to about 60 ° C. or less. For this quenching, it is appropriate to use a large amount of cold water as well as washing.

  Thus, the titanium base on which the very thin coating layer of titanium hydride is formed on the surface is subjected to immersion treatment in a dilute hydrofluoric acid or dilute fluoride aqueous solution (for example, an aqueous solution such as sodium fluoride or potassium fluoride). The titanium hydride film is grown to make the film uniform and stable. The concentration of hydrogen fluoride in dilute hydrofluoric acid or dilute fluoride aqueous solution that can be used here can be generally in the range of 0.05 to 3 wt%, preferably 0.3 to 1 wt%. Moreover, the temperature at the time of immersion treatment with these solutions can be generally in the range of 10 to 40 ° C., preferably 20 to 30 ° C. The treatment can be carried out until a uniform coating of titanium hydride, typically 0.5 to 10 microns, preferably 1 to 3 microns thick, is formed on the titanium substrate surface. Since this titanium hydride (TiHy, where y is a number from 1.5 to 2) exhibits grayish brown to blackish brown depending on the degree of hydrogenation, the formation of a titanium hydride film having a thickness in the above range is Empirically, the change of the color tone of the substrate surface can be controlled by the brightness contrast with the standard color source.

<Formation of intermediate layer (porous platinum coating layer)>
The titanium substrate having the titanium substrate surface roughened and the titanium hydride film formed thereon as described above is subjected to appropriate processing such as washing with water, and then a porous platinum coating layer is formed on the surface. The formation of the porous platinum coating layer can usually be carried out by electroplating. The composition of the plating bath that can be used for this electroplating method is, for example, a platinum compound such as H ₂ PtCl ₆ , (NH 4) ₂ PtCl ₆ , K ₂ PtCl ₆ , Pt (NH ₃ ) ₂ (NO ₂ ) ₂ Dissolved in sulfuric acid solution (pH 1 to 3) or aqueous ammonia solution to a concentration of 2 to 20 g / l, especially 5 to 10 g / l in terms of platinum, and sodium sulfate for stabilization of the bath if necessary. An acid or alkaline plating bath to which a small amount of sodium sulfite, sodium sulfate (in the case of an alkaline bath), etc. is added (in the case of an acid bath) may be mentioned.

Platinum electroplating using a plating bath of this composition uses high-speed plating such as so-called strike plating to reduce decomposition of the titanium hydride film formed on the surface of the titanium substrate as much as possible. It is desirable to operate at a relatively low temperature within the range. This electroplating can form a porous platinum coating layer with excellent physical adhesion strength on the titanium hydride coating of the titanium substrate. The apparent density of the platinum coating layer at that time is suitably in the range of 8 to 19 g / cm ³ , preferably 12 to 18 g / cm ³ . When the apparent density of the porous platinum coating layer is less than 8 g / cm ³ , the bonding strength of platinum is reduced to facilitate peeling, while when it exceeds 19 g / cm ³ , platinum and iridium oxide obtained by thermal decomposition described later Stable loading of Control of the apparent density of the porous platinum coating layer is performed, 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.) Can. When it is desired to obtain a more porous platinum covering layer, after forming the porous platinum covering layer, the porosity can be further enhanced by a chemical or electrochemical method.

Further, the electroplating of platinum is continued until the amount of platinum coating on the substrate is usually at least 0.2 mg / cm ² or more. When the platinum coating amount is less than 0.2 mg / cm ² , the titanium hydride coating portion tends to be excessively oxidized at the time of the baking treatment described later, and the conductivity tends to be lowered. The upper limit of the coating amount of platinum is not particularly limited, but even if it is increased more than necessary, the effect accompanying it is not obtained and thus it becomes uneconomical, so a coating amount of 5 mg / cm ² or less is usually sufficient It is. The preferred coating amount of platinum is in the range of 1 to 3 mg / cm ² . Here, the amount of platinum coated on the porous platinum coating layer is an amount determined as follows using fluorescent X-ray analysis. That is, the amount of platinum plating is determined by wet analysis and fluorescent X-ray analysis to various thicknesses by the above method on the titanium substrate pretreated as described above, and the analysis values by both methods are plotted on a graph. A standard calibration curve is prepared, and then the actual sample is subjected to fluorescent X-ray analysis to determine the platinum coverage from the analysis value and the standard calibration curve. Also, the density of the platinum coverage (δ (g / cm ³ )) was determined by the platinum coverage (w (g / cm ² )) determined as described above and the platinum coverage obtained by cross-sectional microscopic observation of the sample. The thickness (t 2 (cm 2)) of the above is obtained by δ = w / t.

<Formation of titanium oxide>
The titanium substrate provided with the porous platinum coating layer is then calcined in the air, if necessary. This firing pyrolyzes the layer of titanium hydride coating under the platinum coating layer to substantially convert the titanium hydride in the layer back to titanium metal, and at least in the porous portion of the platinum coating layer. It is possible to convert the titanium which is not covered with platinum to titanium oxide in a low oxidation state. This calcination can be generally carried out 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 is formed on the surface of the titanium substrate. The thickness of the titanium oxide is generally in the range of 100 to 1,000 angstroms, preferably 200 to 600 angstroms, and the composition of titanium oxide is TiOx and x is generally 1 <x <2, In particular, it is desirable to be in the range of 1.9 <x <2. Alternatively, the titanium substrate on which the dispersion coating of platinum has been applied may be directly subjected to the next step without the above-mentioned baking treatment. In this case, the layer of titanium hydride coating on the surface of the titanium substrate is converted to titanium metal and titanium oxide in a low oxidation state during the thermal decomposition treatment in the next step. In this manner, high adhesion strength between the porous platinum coating layer and the titanium interface can be maintained, and further, titanium oxide (passivated film) having electrical conductivity can be formed to enhance chemical strength.

  The following intermediate layers may be provided instead of the above-mentioned intermediate layers (porous platinum coating layer). That is, the intermediate layer comprises platinum dispersedly coated at a coverage of 10 to 80% to the extent that the substrate surface is partially exposed, and 3 to 30 mol% of iridium oxide and tantalum oxide covering at least the exposed portion of the substrate surface. The intermediate layer can be made of 70 to 97 mol% of the mixed metal oxide. Specifically, first, dispersion-coated platinum is formed, and a mixed metal oxide of iridium oxide and tantalum oxide is provided thereon.

Formation of dispersion coated platinum
In the formation of the dispersion-coated platinum, a plating bath having the same bath composition as that described above in "Formation of Porous Platinum Coating Layer" is used. 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 of about 30 to about 60 ° C. using high speed plating method such as so-called strike plating.

The control of the dispersion state of platinum at that time can be performed, for example, by empirically adjusting the plating conditions (current density, current waveform, etc.). This electroplating can form platinum dispersedly coated on a titanium hydride coating of a titanium substrate. Thus, the dispersion-coated platinum is deposited on the titanium substrate to such an extent that the substrate surface is partially exposed. The observation of the state of the dispersion coating with a 5000 × electron microscope shows that platinum is dispersed in the form of dots, lines and networks on the surface of the titanium substrate. The deposition amount of platinum can be generally 0.01 to ² mg / cm ² , preferably 0.02 to 0.5 mg / cm ² . If the amount of platinum deposited is too small, the resulting electrode will be inferior in durability to the electrode obtained, and if too large, on the other hand, the electrode obtained will be unstable under a low potential environment.

The degree of dispersion coating of platinum, expressed in coverage, is suitably in the range of 10 to 80%. In the present specification, the "coverage" of platinum is obtained by taking titanium dispersedly coated with platinum on the surface of a substrate, for example, at 40,000 times, and measuring the coverage of platinum per 1 μm ^{2 of} titanium substrate surface from the photograph. It means the value calculated by the following formula.
Coverage (%) = (platinum coverage area at the photo plane) / (titanium substrate surface area at the photo plane) × 100

<Formation of titanium oxide layer>
The titanium substrate coated with platinum in this manner is then calcined in the air to thermally decompose the layer of the titanium hydride film to make substantially all titanium hydride in the layer titanium metal. Further, at least a portion of titanium not dispersedly coated with platinum is converted to titanium oxide in a low oxidation state. This calcination can be generally carried out 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 is formed on the surface of the titanium substrate. The thickness of the titanium oxide is generally in the range of 100 to 1,000 Å, preferably 200 to 600 Å, and the composition of the titanium oxide as TiO x is generally 1 ≦ x <2, especially 1.9 <x It is desirable to be in the range of <2.
Alternatively, the titanium base on which the dispersion coating of platinum is applied may be directly subjected to the next step without the above-mentioned baking treatment. In this case, the layer of titanium hydride film on the surface of the titanium substrate is converted to titanium metal and titanium oxide in a low oxidation state during the thermal decomposition treatment in the next step.

<Formation of intermediate oxide>
Thereafter, the surface of the titanium substrate on which the platinum is dispersed is coated on at least the uncoated portion (exposed portion) of the substrate surface, 3 to 30% by mole of iridium oxide and 70 to 97% by mole of tantalum oxide, preferably 5 to 15 A mixed oxide (hereinafter sometimes referred to as an intermediate oxide) consisting of mol% of iridium oxide and 85 to 95 mol% of tantalum oxide is coated.

This intermediate oxide is useful for improving the corrosion resistance of the obtained electrode, and the coating amount (in terms of metal) is generally 0.5 to 10.0 g · m ⁻² , preferably 1.0 to 5 It can be in the range of .0 gm ^-2 .

  Specifically, the coating with the intermediate oxide of the above composition can be performed, for example, as described below.

  As described above, the iridium compound and the tantalum compound are attached by applying and drying a solvent solution containing an iridium compound and a tantalum compound, preferably a lower alcohol solution, on a titanium substrate on which platinum is dispersed and coated. Examples of iridium compounds and tantalum compounds that can be used herein include compounds soluble in lower alcohol solvents that can be thermally decomposed under conditions of calcination described later and converted to iridium oxide and tantalum oxide, respectively. Examples of the compound include, for example, iridium chloride, iridium chloride, potassium iridium chloride and the like, and examples of the tantalum compound include, for example, tantalum chloride and tantalum ethoxide.

  On the other hand, as lower alcohols which can dissolve these iridium compounds and tantalum compounds, there may be mentioned, for example, methanol, ethanol, propanol, isopropanol, butanol and the like, or mixtures thereof.

  The ratio of the iridium compound to the tantalum compound in the solution can be in the range of 3/97 to 30/70, preferably 5/95 to 15/85, in terms of the metal conversion molar ratio of Ir / Ta.

  The coating of the pretreated surface on the titanium substrate or the titanium oxide surface on the titanium substrate with the solution can be carried out by, for example, a spraying method, a brush coating method, an immersion method, etc., and in this way iridium compounds and tantalum The titanium substrate to which the lower alcohol solution of the compound is applied is generally dried at a relatively low temperature in the range of about 20 to about 100 ° C. and then fired in an oxidizing atmosphere, usually in the air. The treatment described above can be repeated until the amount of coating reaches the above range.

  The firing is performed, for example, by heating to a temperature usually in the range of about 450 to about 600 ° C., preferably about 450 to about 550 ° C., in a suitable heating furnace such as an electric furnace, a gas furnace or an infrared furnace. be able to. The heating time at that time can be approximately 5 minutes to 2 hours depending on the size of the substrate to be fired and the like. By this firing, the iridium compound and the tantalum compound are respectively changed to iridium oxide and tantalum oxide to form an intermediate oxide.

  As described above, the intermediate oxide layer having corrosion resistance and electrical conductivity can be formed on the titanium base on which platinum is dispersed and coated, and the durability of the electrode can be enhanced.

<Formation of electrode catalyst layer>
Thereafter, a solution containing a platinum compound, an iridium compound and a tantalum compound is infiltrated onto the porous platinum-coated surface of the platinum-coated titanium substrate thus fired or onto the intermediate oxide layer, dried and fired. A layer of iridium oxide-tantalum oxide-platinum is formed.

  The platinum compound, iridium compound and tantalum compound used herein are compounds which can be decomposed into platinum and iridium oxide and tantalum oxide respectively under the conditions described below, and as the platinum compound, dinitrodiammine platinum and platinum chloride Examples thereof include acids, platinum chloride and the like, and dinitrodiammine platinum is particularly preferable. Further, as the iridium compound, for example, iridium chloride chloride, iridium chloride, potassium iridium chloride and the like can be mentioned, and in particular, chloride chloride iridium acid is preferable. Furthermore, as a tantalum compound, a tantalum chloride, a tantalum ethoxide etc. are mentioned, for example.

  On the other hand, lower alcohols are suitable as solvents for dissolving these platinum compounds, iridium compounds and tantalum compounds, and for example, methanol, ethanol, propanol, butanol or a mixture thereof is advantageously used. In addition, since dinitro diammine platinum is not directly dissolved in lower alcohol, it is preferable to dissolve first in nitric acid aqueous solution, adjust to a concentration of 250 to 450 g / l in terms of platinum metal, and then dissolve in lower alcohol.

  The total metal concentration of the platinum compound, the iridium compound and the tantalum 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 less than 20 g / l, the catalyst loading efficiency is deteriorated, and when it exceeds 200 g / l, the catalyst is easily aggregated, and problems such as catalyst activity, loading strength, non-uniform loading amount, etc. occur.

  The relative proportions of the platinum compound, the iridium compound and the tantalum compound are 55 mol% or more and 77 mol% or less of the platinum compound and 3 mol% of the iridium compound, respectively, in terms of metal Pt, metal Ir and metal Ta The above amount is 10 mol% or less, and the tantalum compound is 20 mol% or more and less than 35 mol%.

  The porous platinum coating layer or the substrate impregnated with the solution on the intermediate oxide layer is optionally dried at a temperature in the range of about 20 to about 150 ° C., and then in an oxygen-containing gas atmosphere, for example, in air. Baking at. Firing is generally carried out by heating to a temperature generally within the range of about 450 ° C. to about 650 ° C., preferably about 500 ° C. to about 600 ° C., in a suitable furnace such as an electric furnace, gas furnace, infrared furnace and the like. it can. The heating time can be about 3 minutes to 30 minutes depending on the size of the substrate to be fired. By this baking, a layer of iridium oxide-tantalum oxide-platinum can be formed and supported on the surface (inside and / or outside of the pores) of the porous platinum coating layer.

  Then, if a layer consisting of a sufficient amount of iridium oxide-tantalum oxide-platinum can not be formed and supported by one carrying operation, the above-mentioned process of permeation- (drying) -baking of the solution is desired. It can be repeated many times.

  The proportions of the respective components in the porous platinum coating layer or the layer consisting of iridium oxide-tantalum oxide-platinum supported on the intermediate oxide layer (electrode catalyst layer / composite) are respectively metal Pt, metal Ir and metal Ta In terms of platinum, 55 mol% or more and 77 mol% or less of platinum, 3 mol% or more and 10 mol% or less of iridium oxide, and 20 mol% or more and less than 35 mol% of tantalum oxide.

  The proportions of the respective components in the porous platinum coating layer or the layer consisting of iridium oxide-tantalum oxide-platinum supported on the intermediate oxide layer (electrode catalyst layer / composite) are respectively metal Pt, metal Ir and metal Ta In terms of platinum, platinum is preferably 55 to 66 mol%, iridium oxide is preferably 3 to 10 mol%, and tantalum oxide is preferably 31 to 35 mol%.

Under the conditions of the present application, when the proportion of tantalum oxide in the composite in terms of metal is less than 20 mol% or more than 35 mol%, the chlorine generation efficiency of the electrode becomes low. It is considered that if the content of tantalum is less than 20 mol%, the combined action of platinum, iridium oxide and tantalum oxide is weakened, and if the content of tantalum exceeds 35 mol%, tantalum suppresses the function of platinum and iridium. When the proportion of platinum in the complex in terms of metal is less than 55 mol%, or more than 77 mol%, the chlorine generation efficiency of the electrode becomes low. It is considered that the combined action of platinum, iridium oxide and tantalum oxide is weakened.

  In this way, an electrode composed of “electrode catalyst layer (outer layer) / intermediate layer / substrate” can be manufactured.

  Next, the production method and characteristics of the electrode of the present invention will be more specifically described by way of examples.

Examples 1, 2, 3 and Comparative Examples 2, 3, 4
As a titanium substrate, JIS Class 1 titanium plate material (t 0.5 mm x 100 mm x 100 mm) is immersed in acetone, ultrasonically cleaned for 10 minutes, degreased, and then treated for 2 minutes in an aqueous solution of 20 wt. And then treated for 3 minutes in a 60% by weight aqueous sulfuric acid solution at 120.degree.
The titanium substrate was then removed from the aqueous sulfuric acid solution and quenched by spraying cold water in a nitrogen atmosphere. Further, it was immersed in an aqueous solution of 0.3% by weight hydrofluoric acid at 20 ° C. for 2 minutes and then washed with water.

After washing with water, plating is carried out for about 6 minutes at 30 mA / cm ² in a platinum plating bath in which dinitrodiammine platinum is dissolved in a sulfuric acid solution to adjust the platinum content to 5 g / l, pH ≒ 2, 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.

  Next, a butanol chloride solution of iridium chloride adjusted to an iridium concentration of 100 g / L, a butanol solution of tantalum ethoxide adjusted to a tantalum concentration of 200 g / L, and a butanol solution of chloroplatinic acid adjusted to a platinum concentration of 70 g / L And Ir-Ta-Pt were weighed so that the composition ratio in metal conversion shown in Table 1 would be as shown in Table 1, and the total concentration obtained by adding the metal conversion value of each metal component was 75 g / L with butanol It diluted and the electrode catalyst layer coating solution was produced by the composition ratio of metal conversion shown in Table 1. Pipette 250 μl of the application solution, weigh it on a titanium substrate, tilt the titanium substrate using tweezers, spread the solution on the entire surface of the titanium substrate, dry at room temperature, and then in the air at 530 ° C. Baking for 10 minutes. The application, drying, and firing were repeated four times to fabricate electrodes of Examples 1, 2, 3 and Comparative Examples 2, 3, 4.

Comparative Example 1
As a titanium substrate, JIS Class 1 titanium plate material (t 0.5 mm x 100 mm x 100 mm) is immersed in acetone, ultrasonically cleaned for 10 minutes, degreased, and then treated for 2 minutes in an aqueous solution of 20 wt. And then treated for 3 minutes in a 60% by weight aqueous sulfuric acid solution at 120.degree.
The titanium substrate was then removed from the aqueous sulfuric acid solution and quenched by spraying cold water in a nitrogen atmosphere. Further, it was immersed in an aqueous solution of 0.3% by weight hydrofluoric acid at 20 ° C. for 2 minutes and then washed with water.

After washing with water, the dinitrodiammine platinum is 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, pHpH2, 50 ° C. A porous platinum coating layer (intermediate layer) with an electrodeposition amount of 1.7 mg / cm ^{2 and} an applied density of 16 g / cm ³ was formed on a titanium substrate, and an electrodeposition amount of 9.0 mg / cm ^{2 was obtained} at 15 mA / cm ^2. A platinum catalyst layer of cm ² was formed.

The chlorine generation efficiency was evaluated as follows using the electrode of the produced Example and comparative example. As an electrolyte, 500 ml of an aqueous solution of NaCl with 1000 ppm of chloride ion was used. Electrolysis was carried out for 30 minutes under constant current control with an electrode distance of 5 mm and a current density of 2.0 A / dm ² , 5 ml was collected from the electrolyzed solution, and the chlorine generation amount was determined by the iodine method. The chlorine generation efficiency was calculated from the determined chlorine generation amount and the theoretical chlorine generation amount.

The lifetime was evaluated as follows using the electrode of the produced Example and comparative example. An electrolysis test is performed in which an electrode is made into a sample area of 0.01 dm ² (10 mm × 10 mm), and chloride ions in 25 ° C. in 1000 ppm NaCl aqueous solution are electrolyzed while switching polarity every 30 minutes at 2.0 A / dm ² went. Determine the number of polarity switching when the chlorine generation efficiency reaches 50% of the initial value by electrolysis test, and ○ for which the number of polarity switching is 6,000 times or more, 、 for 2000 to 6000 times The following is indicated as x. In the case of a durable life of 3000 hours, the number of polarity switchings to reach the life is 6,000 times.

  Data of the obtained Examples and Comparative Examples are shown in Table 1.

  In Examples 1, 2 and 3, the chlorine generation efficiency was as high as 61%, 59% and 56%, and the durability judgment was ○. On the other hand, in Comparative Examples 1, 2, 3 and 4, the chlorine generation efficiency showed values of 3%, 47%, 43% and 43%.

  From the above results, it is provided with an electrode catalyst layer comprising 3 mol% or more and 10 mol% or less of iridium oxide, 20 mol% or more and less than 35 mol% tantalum oxide and 55 mol% or more and 77 mol% or less of platinum. It can be seen that the electrode exhibits good characteristics.

Claims (1)

An electrode catalyst layer is provided on an electrode substrate made of titanium or a titanium alloy via an intermediate layer, and a saline solution having a salt concentration of 100 to 10000 ppm is electrolyzed while repeatedly switching the polarity of the anode and the cathode at a predetermined current density. An electrode for producing
The electrode catalyst layer is composed of 3 mol% or more and 10 mol% or less of iridium oxide, 20 mol% or more and less than 35 mol% of tantalum oxide, and 55 mol% or more and 77 mol% or less of platinum in metal conversion.
An electrode for electrolysis characterized by