Chlorine generating electrode

Abstract

To provide an electrode for generating chlorine with characteristics of high chlorine generation efficiency in a stable phase.SOLUTION: An electrode for generating chlorine is an electrode which is provided with a catalyst layer through an intermediate layer on a substrate composed of titanium or a titanium alloy, and is attached to a device for electrolyzing diluted salt water (chlorine ion concentration: 100 to 20,000 ppm) by repeatedly switching the polarity between anode and cathode to produce sterilized water, wherein the catalyst layer is composed of 20 mol% to 85 mol% platinum, 5 mol% to 50 mol% ruthenium oxide, 10 mol% to 50 mol% tantalum oxide, and 0 mol% to 20 mol% at least one type of oxide selected from iron oxide, cobalt oxide, and nickel oxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a chlorine generating electrode useful for generating electrolyzed water with bactericidal properties, for example, by using it as an anode in dilute saline water of a predetermined concentration obtained by dissolving sodium chloride in tap water. More specifically, the present invention relates to a chlorine generating electrode having the characteristic of high chlorine generation efficiency during the stable phase under conditions of polarity switching. [Background technology]

[0002] In devices that electrolyze tap water to produce sterilized water, particularly those that use dilute saline water (tap water in which sodium chloride is dissolved) as the anode to produce electrolyzed water with sterilizing properties, there is a strong demand for chlorine generating electrodes that have high chlorine generation efficiency during the stable phase under conditions of polarity switching.

[0003] An electrolytic electrode has been proposed that, when electrolyzing a saline solution with a salt concentration of 100 to 10,000 ppm while repeatedly switching the polarity of the anode and cathode at a predetermined current density to generate chlorine, can suppress electrochemical wear and detachment of the electrode catalyst layer and has high chlorine generation efficiency characteristics (see Patent Document 1). Although this proposed electrode has the advantages of suppressing electrochemical wear and film detachment and having high chlorine generation efficiency, it has the problem that the chlorine generation efficiency during the stable phase is not sufficient under conditions of polarity switching. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-119930 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In a device that generates disinfectant water by directly electrolyzing dilute saline solution, which is prepared by dissolving sodium chloride in tap water to a predetermined concentration, it is preferable from a maintenance-free perspective to switch the polarity to remove scale components generated on the cathode side. Furthermore, there is a strong demand for chlorine generation electrodes that have higher chlorine generation efficiency during the stable phase. In other words, the challenge is to develop a chlorine generating electrode that has high chlorine generation efficiency during the stable phase when electrolyzing dilute saline solution under conditions of polarity switching. [Means for solving the problem]

[0006] As a result of diligent research to achieve the above objectives, the present inventors have discovered a chlorine generating electrode with high chlorine generation efficiency during the stable phase in an electrode used for electrolysis of dilute saline solution, obtained by dissolving sodium chloride in tap water to a predetermined concentration, under conditions of polarity switching. This electrode is constructed by supporting a mixture of platinum, ruthenium oxide, tantalum oxide, and at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide on an intermediate layer, with a predetermined mixing ratio {Pt:Ru:Ta:(Fe,Co,Ni)=20mol%~85mol%:5mol%~50mol%:10mol%~50mol%:0mol%~20mol%} in terms of metal equivalent. This leads to the completion of the present invention.

[0007] Thus, the present invention provides a chlorine generating electrode, which is mounted in an apparatus for electrolyzing dilute saline water to produce sterilized water by repeatedly switching the polarity of the anode and cathode, wherein the electrode catalyst layer is provided on an electrode substrate made of titanium or a titanium alloy via an intermediate layer, and the electrode is mounted in such an apparatus, the catalyst layer is made up of, in terms of metal equivalent, 20 mol% to 85 mol% platinum, 5 mol% to 50 mol% ruthenium oxide, 10 mol% to 50 mol% tantalum oxide, and 0 mol% to 20 mol% of at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a chlorine generating electrode that electrolyzes dilute saline under conditions of polarity switching, and which has the characteristic of high chlorine generation efficiency during the stable phase.

[0009] The electrode of the present invention and its manufacturing method will be described in more detail below. [Modes for carrying out the invention]

[0010] The present invention relates to an electrode for generating sterilized water by electrolyzing dilute saline while repeatedly switching the polarity of the anode and cathode, wherein the electrode is mounted on a substrate made of titanium or a titanium alloy with a catalyst layer provided via an intermediate layer, and the electrode is characterized in that the catalyst layer consists of, in terms of metal equivalent, 20 mol% to 85 mol% platinum, 5 mol% to 50 mol% ruthenium oxide, 10 mol% to 50 mol% tantalum oxide, and 0 mol% to 20 mol% of at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide. The total composition ratio is 100%.

[0011] Here, "0 mol% to 20 mol% of at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide" means either not adding at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide, or adding it in an amount of 20 mol% or less. In other words, at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide is an optional component. Furthermore, when adding at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide, any one of these oxides may be added, or two or more of these oxides may be added. When adding two or more oxides, the total amount added shall be 20 mol% or less.

[0012] Polarity switching refers to reversing the polarity of the voltage applied between the two electrodes each time the electrolysis time reaches a predetermined duration. When electrolysis is performed intermittently, the polarity of the voltage applied between the two electrodes is reversed each time the cumulative electrolysis time (cumulative electrolysis time) reaches a predetermined duration. The "predetermined duration" for polarity switching can be, for example, 1 to 60 minutes.

[0013] Current density is, for example, 0.01 to 0.25 A / cm². 2 It can be done this way.

[0014] <Electrode base> Examples of electrode substrate materials used in the present invention include titanium or titanium-based alloys. As titanium-based alloys, corrosion-resistant conductive alloys mainly composed of titanium are used. Examples include Ti-based alloys commonly used as electrode materials, consisting of combinations such as Ti-Ta-Nb, Ti-Pd, Ti-Zr, and Ti-Al. These electrode materials can be processed into desired shapes such as plates, perforated plates, rods, or mesh plates and used as electrode substrates.

[0015] <Pretreatment of electrode substrate> It is desirable to pre-treat the electrode substrate as described above, as is commonly done. Suitable examples of such pre-treatment are described below. First, the surface of the electrode substrate made of titanium or a titanium-based alloy (hereinafter sometimes referred to as "titanium substrate") is cleaned and / or degreased by electrolysis in an alkaline solution, according to conventional methods, for example, with alcohol, acetone, etc. Then, it is treated with hydrofluoric acid with a hydrogen fluoride concentration of 1 to 20% by weight, or a mixed acid of hydrofluoric acid and other acids such as nitric acid or sulfuric acid, to remove the oxide film on the surface of the titanium substrate and to roughen the titanium grain boundaries. This acid treatment can be carried out at room temperature or approximately 40°C for several minutes to more than ten minutes, depending on the surface condition of the titanium substrate. Blasting may also be used in combination to ensure sufficient roughening.

[0016] <Hydrogenated Titanium Treatment> The surface of the titanium substrate thus acid-treated is brought into contact with concentrated sulfuric acid to finely roughen the inner surface of the titanium crystal grain boundaries in a protruding shape and form a thin layer of titanium hydride on the surface of the titanium substrate. The concentrated sulfuric acid to be used is generally of a concentration of 40 to 80% by weight, preferably 50 to 60% by weight, and if necessary, a small amount of sodium sulfate, other sulfates, etc. may be added to this concentrated sulfuric acid for the purpose of stabilizing the treatment. The contact with the concentrated sulfuric acid can usually be carried out by immersing the titanium substrate in a bath of concentrated sulfuric acid. The bath temperature at that time can generally be within a 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, which is sufficient. By this sulfuric acid treatment, the inner surface of the titanium crystal grain boundaries can be finely roughened in a protruding shape, and a very thin coating of titanium hydride can be formed on the surface of the titanium substrate. The sulfuric acid-treated titanium substrate is taken out of the sulfuric acid bath and preferably quenched 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. It is appropriate to use a large amount of cold water for this quenching, which also serves as washing.

[0017] The titanium substrate having a very thin coating layer of titanium hydride formed on its surface in this way is subjected to an immersion treatment in dilute hydrofluoric acid or a dilute fluoride aqueous solution (for example, an aqueous solution of sodium fluoride, potassium fluoride, etc.) to grow the titanium hydride coating and achieve the homogenization and stabilization of the coating. The concentration of hydrogen fluoride in the dilute hydrofluoric acid or dilute fluoride aqueous solution that can be used here can generally be within a range of 0.05 to 3% by weight, preferably 0.3 to 1% by weight. Also, the temperature during the immersion treatment with these solutions can generally be within a range of 10 to 40 °C, preferably 20 to 30 °C. The treatment can be carried out until a uniform coating of titanium hydride with a thickness of usually 0.5 to 10 microns, preferably 1 to 3 microns, is formed on the surface of the titanium substrate. This titanium hydride (TiHy, where y is a number between 1.5 and 2) exhibits a grayish-brown to blackish-brown color depending on the degree of hydrogenation. Therefore, the formation of a titanium hydride coating with a thickness within the above range can be empirically controlled by comparing the lightness of the color tone of the substrate surface with a standard color source.

[0018] <Formation of Intermediate Layer> When the surface of the titanium substrate is roughened and a titanium hydride film is formed in this way, after performing treatments such as timely water washing, for example, a porous platinum coating layer is formed on its surface. The formation of this porous platinum coating layer can usually be carried out by an electroplating method. As the composition of the plating bath that can be used in this electroplating method, for example, platinum compounds such as H2PtCl6, (NH4)2PtCl6, K2PtCl6, Pt(NH3)2(NO2)2, etc. are dissolved in a sulfuric acid solution (pH 1 - 3) or an aqueous ammonia solution to a concentration of 2 - 20 g / L in terms of platinum, especially 5 - 10 g / L. Furthermore, if necessary, for the stabilization of the bath, a small amount of sodium sulfate (in the case of an acidic bath), sodium sulfite, sodium sulfate (in the case of an alkaline bath), etc. are added, and acidic or alkaline plating baths can be mentioned.

[0019] For platinum electroplating using a plating bath with such a composition, in order to suppress the decomposition of the titanium hydride film formed on the surface of the titanium substrate as much as possible, it is desirable to carry out the electroplating at a relatively low temperature within the range of about 30 to about 60 °C using a high-speed electroplating method such as so-called strike plating. By this electroplating, a porous platinum coating layer with excellent physical adhesion strength can be formed on the titanium hydride film of the titanium substrate. The apparent density of the platinum coating layer at that time is 8 - 19 g / cm 3 , preferably within the range of 12 - 18 g / cm 3 . It is appropriate that the apparent density of the porous platinum coating layer is within this range. If the apparent density of the porous platinum coating layer is less than 8 g / cm 3 , the bonding strength of platinum decreases and it becomes easy to peel off. On the contrary, if it exceeds 19 g / cm 3 , it becomes difficult to stably support the platinum and iridium oxide obtained by thermal decomposition described later. The control of the apparent density of the porous platinum coating layer can be carried out, 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 addition, when it is desired to obtain a platinum coating layer with higher porosity, after forming the porous platinum coating layer, the porosity can be further increased by chemical or electrochemical methods.

[0020] Also, the above platinum electroplating is continued until the coating amount of platinum on the above substrate usually becomes at least 0.2 mg / cm 2 or more. When the coating amount of platinum is less than 0.2 mg / cm 2 , during the firing process described later, oxidation of the titanium hydride coating portion tends to progress too much and the conductivity tends to decrease. The upper limit of the coating amount of platinum is not particularly limited, but even if it is made more than necessary, no corresponding effect can be obtained, and on the contrary, it becomes uneconomical, so usually 5 mg / cm 2 or less of the coating amount is sufficient. A suitable coating amount of platinum is within the range of 0.4 to 3 mg / cm 2 . Here, the coating amount of platinum in the porous platinum coating layer is the amount obtained as follows using the fluorescent X-ray analysis method. That is, as described above, the amount of platinum plating in various thicknesses was quantified by wet analysis method and fluorescent X-ray analysis method on the titanium substrate pretreated as described above, and the analysis values by both methods were plotted on a graph to create a standard calibration curve. Then, an actual sample is subjected to fluorescent X-ray analysis, and the coating amount of platinum is determined from the analysis value and the standard calibration curve. Also, the density (δ (g / cm 3 )) of the platinum coating amount is obtained by δ = w / t from the coating amount of platinum (w (g / cm 2 )) obtained as described above and the thickness (t (cm)) of the platinum coating layer determined by microscopic observation of the cross section of the sample.

[0021] The titanium substrate provided with the porous platinum coating layer is then fired in the atmosphere. By this firing, the film layer of titanium hydride under the platinum coating layer is thermally decomposed, and substantially almost all of the titanium hydride in the layer is returned to titanium metal, and furthermore, at least the titanium in the porous portion of the platinum coating layer that is not coated with platinum can be changed to titanium oxide in a low oxidation state. This firing can generally be 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. Thereby, a very thin conductive titanium oxide is formed on the surface of the titanium substrate. The thickness of this titanium oxide is generally preferably within the range of 10 to 100 nm, preferably 20 to 60 nm, and the composition of the titanium oxide is TiOx, where x is generally in the range of 1 < x < 2, particularly preferably in the range of 1.9 < x < 2. As another method, the titanium substrate with the dispersed platinum coating may be directly subjected to the next step without performing the firing treatment as described above. In this case, during the thermal decomposition treatment in the next step, the film layer of titanium hydride on the surface of the titanium substrate is converted into titanium metal and titanium oxide in a low oxidation state. In this way, a high adhesion strength between the porous platinum coating layer and the titanium interface is maintained, and furthermore, an intermediate layer in which an electrically conductive titanium oxide (passivation film) is formed and the chemical stability is also enhanced can be obtained.

[0022] 〈Formation of Catalyst Layer〉 Subsequently, a solution containing at least one compound selected from platinum compounds, ruthenium compounds, tantalum compounds, iron compounds, cobalt compounds, and nickel compounds is applied and infiltrated onto the porous platinum-coated surface thus coated, dried, and then fired to form a layer composed of at least one oxide selected from platinum-ruthenium oxide-tantalum oxide-iron oxide, cobalt oxide, and nickel oxide.

[0023] The at least one metallic compound used here, selected from platinum compounds, ruthenium compounds, tantalum compounds, iron compounds, cobalt compounds, and nickel compounds, is a compound that can decompose under the conditions described below to convert into platinum, ruthenium oxide, tantalum oxide, iron oxide, cobalt oxide, and nickel oxide, respectively. Examples of platinum compounds include dinitrodiammineplatinum, chloroplatinic acid, and platinum chloride, with chloroplatinic acid being particularly preferred. Examples of ruthenium compounds include ruthenium chloride and ruthenium nitrate. Examples of tantalum compounds include tantalum chloride and tantalum ethoxide. Examples of iron compounds include iron chloride and iron nitrate. Examples of cobalt compounds include cobalt chloride and cobalt nitrate. Examples of nickel compounds include nickel chloride and nickel nitrate.

[0024] On the other hand, lower alcohols are preferred as solvents for dissolving at least one metal compound selected from platinum compounds, ruthenium compounds, tantalum compounds, iron compounds, cobalt compounds, and nickel compounds. For example, methanol, ethanol, propanol, butanol, or mixtures thereof are advantageously used. Since dinitrodiammineplatinum does not dissolve directly in lower alcohols, it is preferable to first dissolve it in an aqueous nitric acid solution, adjust the concentration to 250-450 g / L in terms of platinum metal, and then dissolve it in a lower alcohol.

[0025] The total metal concentration of platinum, ruthenium, and tantalum compounds in a lower alcohol solution can generally be within the range of 20 to 200 g / L, preferably 40 to 150 g / L. If the metal concentration is lower than 20 g / L, the catalyst loading efficiency will be poor, and if it exceeds 200 g / L, the catalyst will tend to aggregate, leading to problems such as reduced catalytic activity, poor adhesion strength, and uneven loading.

[0026] Furthermore, the relative usage ratio of at least one metal compound selected from platinum compounds, ruthenium compounds, tantalum compounds, iron compounds, cobalt compounds, and nickel compounds shall be converted to at least one metal selected from metal Pt, metal Ru, metal Ta, metal Fe, metal Co, and metal Ni, respectively, and shall be 20 mol% to 85 mol for platinum, 5 mol% to 50 mol for ruthenium oxide, 10 mol% to 50 mol for tantalum oxide, and 0 mol% to 20 mol for at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide.

[0027] The substrate, which has been coated and impregnated with the solution onto a porous platinum coating layer, is dried at a temperature in the range of approximately 20 to 150°C as necessary, and then fired in an oxygen-containing gas atmosphere, for example, in air. The firing can be carried out by heating in a suitable heating furnace, such as an electric furnace, gas furnace, or infrared furnace, to a temperature generally in the range of approximately 450 to 650°C, preferably approximately 500 to 600°C. The heating time can be approximately 3 to 30 minutes, depending on the size of the substrate to be fired. This firing process allows a layer to be formed and supported on the surface (inside and / or outside of the pores) of the porous platinum coating layer, consisting of at least one oxide selected from platinum-ruthenium oxide-tantalum oxide-iron oxide, cobalt oxide, and nickel oxide.

[0028] Furthermore, if a sufficient amount of platinum-ruthenium oxide-tantalum oxide layer cannot be formed and supported in a single loading operation, the above-described steps of coating, impregnation, drying, and firing of the solution can be repeated the desired number of times.

[0029] In the layer supported on the intermediate layer, which consists of at least one oxide selected from platinum, ruthenium oxide, tantalum oxide, iron oxide, cobalt oxide, and nickel oxide, the proportion of each component shall be converted to at least one metal selected from metal Pt, metal Ru, metal Ta, and metal Fe, metal Co, and metal Ni, respectively, and shall be 20 mol% to 85 mol for platinum, 5 mol% to 50 mol for ruthenium oxide, 10 mol% to 50 mol for tantalum oxide, and 0 mol% to 20 mol for at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide.

[0030] If the amount of platinum in the electrode catalyst layer is less than 20 mol% or more than 85 mol% in terms of metal, the chlorine generation efficiency during the stable phase will decrease. Preferably, it is 25 mol% to 80 mol%, more preferably 35 mol% to 70 mol%. If the amount of ruthenium oxide is less than 5 mol% or more than 50 mol% in terms of metal equivalent, the chlorine generation efficiency during the stable phase will decrease. Preferably, it is between 10 mol% and 40 mol%. If the amount of tantalum oxide is less than 10 mol% in terms of metal equivalent, consumption will be high. On the other hand, if it exceeds 50 mol%, the chlorine generation efficiency during the stable phase will be low. Preferably, it is 20 mol% to 45 mol%, more preferably 20 mol% to 35 mol%. At least one oxide selected from iron oxide, cobalt oxide, and nickel oxide will be consumed in large quantities if its metal equivalent exceeds 20 mol%. Preferably, it is 5 mol% to 15 mol%, more preferably 7 mol% to 12 mol%.

[0031] In this way, an electrode composed of a catalyst layer (outer layer), an intermediate layer (porous platinum-coated layer - titanium oxide), and a substrate can be manufactured. Specifically, titanium oxide is formed on the surface of the titanium substrate in the porous portion of the platinum-coated layer that is not coated with platinum.

[0032] Next, the manufacturing method and characteristics of the electrode of the present invention will be described in more detail with reference to examples. [Examples]

[0033] Examples 1-16, Comparative Examples 1-2 As the titanium substrate, JIS Class 1 titanium plate material (t0.5mm x 100mm x 100mm) was immersed in acetone and ultrasonically cleaned for 10 minutes to degrease it, then treated in an 8 wt% hydrofluoric acid aqueous solution at 20°C for 2 minutes, and then treated in a 60 wt% sulfuric acid aqueous solution at 120°C for 3 minutes. Next, the titanium substrate was removed from the sulfuric acid solution and rapidly cooled by spraying it with cold water in a nitrogen atmosphere. It was then immersed in a 0.3 wt% hydrofluoric acid solution at 20°C for 2 minutes and then washed with water.

[0034] After rinsing with water, dinitrodiammineplatinum was dissolved in sulfuric acid solution to adjust the platinum content to 5 g / L, pH ≈ 2, and temperature to 50°C. In this platinum plating bath, the device was subjected to a 30 mA / cm² load. 2 Plating was performed for approximately 2 minutes, resulting in an apparent density of 16 g / cm³. 3 The electrodeposition amount was 0.43 mg / cm². 2 A porous platinum coating layer was formed on a titanium substrate.

[0035] After drying, it was baked in air at 400°C for 1 hour.

[0036] Next, butanol solutions of chloroplatinic acid adjusted to a platinum concentration of 100 g / L, butanol solutions of ruthenium chloride adjusted to a ruthenium concentration of 100 g / L, butanol solutions of tantalum ethoxide adjusted to a tantalum concentration of 100 g / L, ethanol solutions of iron chloride adjusted to an iron concentration of 100 g / L, ethanol solutions of cobalt chloride adjusted to a cobalt concentration of 100 g / L, and ethanol solutions of nickel chloride adjusted to a nickel concentration of 100 g / L were each weighed out so that the metal-based composition ratio of Pt-Ru-Ta-(Fe-Co-Ni) was as shown in Table 1. These were then diluted with butanol so that the total concentration obtained by adding the metal-based values ​​of each metal component was 70 g / L, and electrode catalyst layer coating solutions were prepared with the metal-based composition ratios shown in Table 1. 0.25 mL of the coating solution was weighed using a pipette, and it was applied and permeated onto the platinum coating layer on the titanium substrate. After spreading the solution over the entire surface of the titanium substrate, it was dried at room temperature and then fired in air at 550°C for 10 minutes. This application, permeation, drying, and firing process was repeated four times to produce the electrodes for Examples 1-16 and Comparative Example 1.

[0037] The electrode for Comparative Example 2 was prepared in the same manner as above, except that ruthenium chloride was replaced with iridium chloride, and the metal-based composition ratio of Pt-Ir-Ta was adjusted to the mol% shown in Table 1.

[0038] Using the electrodes prepared in Examples 1-16 and Comparative Examples 1-2, a current density of 0.015 A / cm² was measured in a 0.2 wt% NaCl aqueous solution. 2 An electrolysis test was conducted by switching the polarity every 20 minutes, and the chlorine generation efficiency was evaluated before the electrolysis test (initial value) and during the stable period. Here, the stable period is defined as the period when the cumulative electrolysis time is approximately 50 hours or more and the chlorine generation efficiency of the electrode stabilizes. Here, the chlorine generation efficiency after 100 hours of electrolysis was evaluated as the stable period. The chlorine generation efficiency was evaluated as follows. A 0.2 wt% NaCl aqueous solution was used as the electrolyte, with an electrode distance of 5 mm and a current density of 0.015 A / cm². 2 The solution was electrolyzed for 20 minutes, and the amount of chlorine generated from the electrolyzed solution was determined by the iodine method. The chlorine generation efficiency was then calculated from the determined amount of chlorine generated and the theoretical amount of chlorine generated. The table shows the values ​​of chlorine generation efficiency for Examples 1-16 and Comparative Examples 1-2 before the electrolysis test (initial stage of chlorine generation efficiency) and 100 hours after the electrolysis test (stabilized stage of chlorine generation efficiency).

[0039] [Table 1]

[0040] Although each electrode showed high chlorine generation efficiency before the electrolysis test, after 100 hours of the electrolysis test (the period when chlorine generation efficiency stabilized), the electrodes of Examples 1 to 16 achieved high chlorine generation efficiencies of 48% or more, while the electrode of Comparative Example 1 achieved 18% and the electrode of Comparative Example 2 achieved 36%.

[0041] From the above results, it can be seen that an electrode equipped with an electrode catalyst layer on an intermediate layer provided on a titanium substrate, comprising, in terms of metal equivalent, 20 mol% to 85 mol% platinum, 5 mol% to 50 mol% ruthenium oxide, 10 mol% to 50 mol% tantalum oxide, and 0 mol% to 20 mol% of at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide, exhibits high chlorine generation efficiency during the stable phase.

Claims

[Claim 1] An electrode, which is attached to a device for generating sterilized water by electrolyzing dilute saline solution (chloride ion concentration: 100 to 20,000 ppm) while repeatedly switching the polarity of the anode and cathode, having a catalyst layer provided on a substrate made of titanium or a titanium alloy via an intermediate layer, The catalyst layer consists of, in terms of metal equivalent, 20 mol% to 85 mol% platinum, 5 mol% to 50 mol% ruthenium oxide, 10 mol% to 50 mol% tantalum oxide, and 0 mol% to 20 mol% of at least one oxide selected from iron oxide, cobalt oxide, and nickel oxide, with a total composition ratio of 100%. A chlorine-generating electrode characterized by the following features.

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