Electrolytic anode used for chlorine generation and method for manufacturing the same

Abstract

To provide an anode for electrolysis which has an extremely low anode potential in an anode for chlorine production such as chloro-alkali electrolysis and seawater electrolysis, suppresses oxygen in chlorine which is a side reaction of the anode to be extremely low, and enables stable electrolysis as a practical electrode for a long period.SOLUTION: An anode for electrolysis is obtained by alternately coating and laminating a metal alloy composed of platinum and palladium and an oxide composed of ruthenium and / or iridium and titanium and / or tin, on a surface of a base material composed of titanium or titanium alloy, and is used for chlorine production.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention mainly relates to an insoluble metal anode used for chlorine generation in ion-exchange membrane electrolysis of brine, seawater electrolysis, etc. It has a very low chlorine generation potential and a very low oxygen concentration in chlorine, and moreover, has a long service life and maintains its characteristics over a long period of time, being an anode for electrolysis.

Background Art

[0002] In the chlor-alkali electrolysis process of electrolyzing brine to obtain chlorine from the anode chamber and caustic soda from the cathode chamber, the so-called zero-gap ion-exchange membrane method electrolysis, which uses a cation-exchange membrane as a diaphragm and closely adheres both the anode and the cathode to this cation-exchange membrane to perform electrolysis under the condition of minimizing the electrical resistance, has become the mainstream. According to this, except for the electrode part, the electrical resistance of the ion-exchange membrane and the slight electrical resistance of the electrolytic solution before and after it are the electrical resistance components, and the quality of the electrolysis characteristics largely depends on the characteristics of the electrodes used. Therefore, in chlor-alkali electrolysis, the performance of the electrodes themselves is extremely important compared to other processes. In particular, for the anode, the anode overvoltage that determines the voltage, the selectivity between the chlorine generation reaction as the main reaction and the oxygen generation reaction as the side reaction in the anode reaction, and of course, minimizing the oxygen generation reaction there, are even more important. <>< / <>< /

[0003] <>< / In a metal electrode formed by thermally decomposing an electrode substance containing a platinum group metal oxide on the surface of a metal substrate, which is so-called DSA (Dimensionally Stable Anode), various uses are possible because the electrode substance can be relatively freely selected. As the main electrode substances for ion-exchange membrane electrolysis of brine mainly for chlorine generation and for dilute brine electrolysis such as seawater electrolysis, they are usually limited to platinum, iridium, and ruthenium, and one electrode is formed by adding titanium oxide, tin oxide, or zirconium oxide, etc. as these combinations and additive substances / auxiliary electrode substances. <>< / <>< /

[0004] <>< / In practice, for ion-exchange membrane electrolysis of sodium chloride, electrode materials are almost exclusively limited to ruthenium and iridium, and are often used as composite oxides with titanium (titanium oxide) or tin (tin oxide) added as stabilizers or for adjusting properties.

[0005] On the one hand, in these electrodes, the ruthenium component can reduce the overpotential for chlorine generation, but it slightly increases the selectivity of the electrolytic reaction, i.e., the side reaction of oxygen gas generation in chlorine. On the other hand, the iridium component has the characteristics of extremely long electrode life and reduced oxygen gas generation in chlorine, but it has the characteristic of increasing the anode potential. In actual industrial electrodes, these are subtly adjusted to achieve the desired electrolytic characteristics.

[0006] In their studies, the inventors of this invention have found that adding platinum to these materials allows for the initial maintenance of an extremely low chlorine generation potential and an extremely low oxygen concentration in the chlorine. However, this property is lost within several tens of hours after the start of electrolysis when the electrodes are fabricated under normal electrode fabrication conditions, and thereafter the electrodes exhibit the same properties as those without platinum. However, since the platinum is not being consumed, this is thought to be due to passivation occurring on the platinum surface, which is a characteristic of platinum during cation polarization.

[0007] It is known that adding palladium as an oxide or metal to a DSA-type electrode can lower the chlorine generation overpotential to the same extent as, or even less than, that of active platinum, and can also significantly reduce the amount of oxygen in the chlorine, which is a side reaction. However, it has been found that the palladium component is consumed very quickly during electrolysis, making it practically unusable. This is evident from the fact that in claim 1 of the basic patent for oxide-type coatings, Japanese Patent Publication No. 48-3954, palladium, which was published in the patent publication, is excluded.

[0008] Regarding the practical application of palladium, several patent applications have been filed in advance to stabilize its oxide crystals as palladium oxide (PdO) to prevent wear. However, even with these measures, it remains unstable, and there appear to be very few cases of its use as a practical electrode. Thus, while platinum and palladium exhibit extremely excellent properties in the short term, no electrode that is stable and practical for long-term use is known.

[0009] Japanese Patent Publications S. 45-11014 and S. 45-11015 describe the use of heat-treated platinum-palladium (Pt,Pd) alloy electrodes as anodes for salt electrolysis. These publications state that the alloy is superior to platinum and exhibits extremely low chlorine overpotential, as shown in graphs. However, there is no mention of coating the substrate; the only indication is "cladding." This suggests that an alloy block was somehow fabricated and then a plate of this cladding was applied to the substrate. While this may exhibit superior properties, it would require a large quantity of expensive platinum-palladium alloy, making it impractical. It can be considered completely unsuitable as a coating.

[0010] Japanese Patent Publication No. 62-7276 describes a patent in which palladium components exhibit excellent performance in dilute saline electrolysis, but their stabilization is problematic. It suggests mixing stable palladium oxide with other composition precursor solutions beforehand and then coating the material using this mixture as a coating solution via thermal decomposition. It also shows that when prepared by thermal decomposition, the palladium components are not stable and are quickly consumed. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Special Publication No. 48-3954 [Patent Document 2] Special Publication No. 45-11014 [Patent Document 3] Special Publication No. 45-11015 [Patent Document 4] Special Publication No. 62-7276 [Overview of the project] [Problems that the invention aims to solve]

[0012] The objective is to obtain an electrolytic anode that has an extremely low anode potential at the anode for chlorine generation in main reactions such as chlor-alkali electrolysis and seawater electrolysis, and that suppresses the amount of oxygen in the generated chlorine, which is a side reaction at the anode, to an extremely low level, while also providing a practical electrode that can perform electrolysis stably for a long period of time. [Means for solving the problem]

[0013] The present invention relates to an electrolytic anode primarily used for chlorine generation, in which titanium or a titanium alloy is used as a base material, and its surface is alternately coated and laminated with a metal alloy coating consisting of platinum and palladium and an oxide coating consisting of ruthenium and / or iridium and titanium and / or tin.

[0014] The inventors of this invention have discovered that by using a metal alloy of platinum and palladium, that is, a platinum-palladium alloy, the passivation seen in platinum is eliminated, and the significant wear seen in palladium and palladium oxide is eliminated. In other words, the alloy has a low rate of wear, maintains a low chlorine generation potential over a long period of time, and, in combination with ruthenium oxide and / or iridium oxide components, enables electrolysis with an extremely long lifespan, a low potential, and extremely low oxygen levels in the chlorine gas. This led to the present invention.

[0015] In other words, an alcohol solution containing platinum salt and palladium salt, or a mixture of alcohol and water, is applied to a titanium substrate and thermally decomposed by a flame to form a platinum-palladium alloy. Subsequently, a coating solution containing ruthenium and / or iridium and titanium and / or tin salts dissolved in a predetermined composition is applied and thermally decomposed in flowing air to form a composite oxide consisting of ruthenium and / or iridium and titanium and / or tin. These operations are repeated to form a coating layer consisting of a mixture of the platinum-palladium alloy and the composite oxide consisting of ruthenium and / or iridium and titanium and / or tin oxides. It should be noted that conventional experience has shown that platinum and palladium are stabilized only by creating an alloy of platinum and palladium, and are not stabilized at all as oxides, nor are they stabilized as a mixture of platinum and palladium.

[0016] To obtain a platinum-palladium alloy as a coating layer, a coating solution containing platinum and palladium salts is thermally decomposed in a reducing atmosphere, such as a gas flame. Furthermore, it is desirable to interpose organic substances such as lavender oil, clove oil, or turpentine oil as organic reducing agents in the coating solution to ensure more reliable flame decomposition, thereby producing a more complete metallic alloy. It is important to note that in conventional thermal decomposition methods in air, palladium becomes an oxide and does not form a metallic alloy with platinum. Therefore, the above method is necessary to ensure that the thermal decomposition is under reducing conditions.

[0017] On the other hand, composite oxides consisting of ruthenium and / or iridium and titanium and / or tin, which are oxide components, can be formed by applying a coating solution containing these salts and thermal decomposition in an oxidizing atmosphere, which is the condition for producing oxide coatings by conventional methods. The oxides produced under these conditions are not reduced even in a flame thermal decomposition atmosphere used to form alloys consisting of platinum and palladium, and are stably maintained as oxides. Furthermore, it has been found that under thermal decomposition conditions that form an oxide layer, the resulting platinum-palladium alloy does not oxidize and does not change as a metallic alloy.

[0018] Thus, it was found that by forming the alloy layer and oxide tank as separate layers, that is, by alternating them as in the present invention and essentially mixing them, stabilization can be achieved without any problems, and the desired properties can be obtained.

[0019] Here, the composition of the platinum-palladium alloy should preferably be 50 to 90% platinum in molar ratio, with the remainder being palladium. Including 10% or more palladium in the alloy prevents the formation of a passive film on the platinum surface even with continuous electrolysis. Furthermore, if the platinum content is less than 50%, the rate of palladium consumption, which is inherently less corrosion-resistant, increases, potentially leading to electrode instability or a shortened lifespan.

[0020] The composition of the oxide layer is selected depending on the application in which the electrode will be used. For example, in ion-exchange membrane salt electrolysis, it is desirable to have an oxide composed of three components: ruthenium, iridium, and titanium. The composition range is preferably 0-30 mol% iridium, 20-40 mol% ruthenium, with the remainder being titanium (Ti). However, it is preferable that the titanium content be 30-70 mol%. The thermal decomposition temperature in this case is preferably 450°C to 520°C in flowing air. Furthermore, it is possible to create a four-component composite oxide by adding a tin component. In this case, it is possible to replace part of the titanium with the tin component, and also part of the ruthenium component with the tin component. This is because although the tin component itself is an additive component similar to titanium, when the tin component is adjacent to ruthenium, it is thought to have a so-called synergistic effect, acting as if it were ruthenium.

[0021] If the application is for dilute brine electrolysis, it is desirable that the oxide be composed of ruthenium, iridium, and tin or ruthenium, iridium, titanium, and tin. The composition preferably consists of 0 to 30 mol% of iridium and 20 to 40 mol% of ruthenium, with the balance being titanium or tin or a composite oxide composed of titanium and tin. The ratio of titanium to tin is preferably in a molar ratio of tin:titanium = 100:0 to 50:50). This is because the operating temperature in dilute brine electrolysis is usually 30°C or lower, which is lower than 80 to 100°C in ion-exchange membrane sodium chloride electrolysis.

[0022] As described above, the electrode coating is formed by alternately coating a plurality of times with a platinum and palladium alloy layer and a pyrolytic oxide layer to a predetermined thickness. The quantitative ratio between the alloy layer composed of platinum and palladium and the oxide layer is not particularly specified, but the platinum and palladium alloy layer is preferably about 5 to 20% in metal mol% because it exhibits substantially suitable characteristics from 5%.

[0023] The repetition of these two alternating layers of coating may start with the platinum and palladium alloy layer first or with the oxide layer first. Also, the formation of the coating layer may be performed by alternately applying the platinum and palladium alloy coating and the oxide coating once each, but the number of times of each can be changed, such as applying one coating a plurality of times and the other once. The ratio of these numbers can be arbitrarily changed depending on the mutual quantitative ratio and coating conditions. However, it is needless to say that it is desirable that the presence of the mutual metal alloy and oxide is not biased.

[0024] When the coating layer reaches the predetermined thickness in this way, it can be used as an anode as it is. After reaching the required thickness, in order to stabilize the coating, post-treatment heating can be performed in a flowing air atmosphere at a temperature equal to or slightly higher than the pyrolysis temperature during oxide formation for about 30 to 200 minutes.

Advantages of the Invention

[0025] Such electrodes are particularly useful in ion-exchange membrane electrolysis of sodium chloride, allowing for low electrolysis voltage and extremely low oxygen generation as a side reaction, thus achieving excellent electrolysis efficiency. Furthermore, they can be used in dilute saline electrolysis and seawater electrolysis to obtain high concentrations of hypochlorite. [Modes for carrying out the invention]

[0026] In the present invention, the electrode has a base material of titanium or a titanium alloy, and depending on the application, the base material may be in the form of a plate or a porous plate such as expanded metal or a punched plate, and the surface of the base material is subjected to an activation pretreatment such as etching along with blasting, and a platinum-palladium alloy layer is formed on the surface by flame thermal decomposition. (2) A coating layer of oxide is formed on the surface by thermal decomposition in normal flowing air. Furthermore, operations (1) and (2) are repeated to form an electrode coating of the desired thickness. Subsequently, the electrodes are completed by post-treatment heating in an oxidizing atmosphere as needed for stabilization. Note that the order in which steps (1) and (2) are performed may be either starting with (2) or starting with (1). Also, the total number of times steps (1) and (2) are performed does not necessarily have to be the same. The following examples illustrate the process, but it goes without saying that the method is not limited thereto. [Examples] [Examples]

[0027] Expanded metal, made from a 1mm thick titanium plate with a 50% aperture ratio, was used as the base material. After blasting with alumina sand, it was etched with an aqueous hydrochloric acid solution. Specifically, a 20% by mass aqueous hydrochloric acid solution was used as the etching solution, and etching was performed at 95°C for 15 minutes to activate and prepare for coating. As the first coating solution, chloroplatinic acid and palladium chloride were dissolved in ethanol in a molar ratio of 70:30, and 15% by volume of lavender oil was added to the ethanol. The mixture was then heated to 40°C and stirred to create a homogeneous solution.

[0028] As a second coating solution, iridium chloride, ruthenium chloride, and titanium tetrachloride were prepared by dissolving them in a 10% by mass dilute hydrochloric acid solution in a molar ratio of iridium:ruthenium:titanium = 16:30:54. The solution concentration was adjusted so that the combined amount of iridium and ruthenium was 1 g per 30 ml of solution.

[0029] The first coating solution was applied to the titanium substrate surface with a brush, and the alcohol was evaporated using hot air at 40 to 60°C. Then, a portable gas burner was used to apply a gas flame to the coating surface and perform thermal decomposition. Initially, a black, sooty substance was formed, followed by a white substance. Further heating with the flame created a metallic, glossy film on the surface. The heating time was 3 minutes. After this, heating was stopped and the substrate was cooled. The second coating solution was applied to the coated substrate at room temperature, dried at 60°C, and then thermal decomposition was performed for 10 minutes in a muffle furnace maintained at 510°C after air was circulated.

[0030] Furthermore, the electrode coating was formed by repeating the combination of applying the first coating solution and then heating and decomposing it with a burner, followed by applying the second coating solution and decomposing it with a muffle furnace, five times.

[0031] For comparison, electrodes were prepared by repeatedly applying the second coating solution and performing muffle furnace treatment, without performing the first coating treatment at all. The application and thermal decomposition processes were repeated 10 times.

[0032] The electrode prepared in this manner was used as the anode, and its pH was adjusted to 1.8. The TIFF0007898724000001.tif8170 solution was performed. The main purpose of the preliminary electrolysis was to confirm the stability of the platinum and palladium components, specifically by measuring the passivation potential of platinum and the depletion of the palladium component. The depletion of the palladium component was measured by X-ray fluorescence. For electrodes that have undergone preliminary electrolysis, the anode potential (salt) is measured in a test ion exchange membrane electrolytic cell. The temperature was TIFF0007898724000002.tif917080℃. To avoid interference from the ion exchange membrane, the anode was positioned 20 mm away from it. The oxygen concentration in the chlorine was measured using a gas chromatograph; the oxygen and nitrogen concentrations were measured, and after correcting for entrained air, the oxygen concentration was measured. The potential was measured by electrolysis with the anode in close contact with the ion exchange membrane, and resistive losses were removed using the current interrupter method. As a result, the oxygen concentration in the chlorine was 0.3 A / cm³. 2 The concentration was 0.12% at pH=3. The chlorine generation potential at that time was 1.082V vs. Ag / AgCl. Excluding the platinum-palladium alloy process used as a comparison sample, the chlorine generation potential at the anode was 1.112V vs. Ag / AgCl, and the oxygen concentration in the chlorine was 0.45% at pH=3. [Examples]

[0033] Using the same electrode substrate as in Example 1, and performing the same pretreatment, a platinum-palladium alloy coating and a three-component oxide coating consisting of iridium, ruthenium, and titanium were applied to the substrate surface. The first coating solution, that is, the platinum-palladium alloy coating solution, was prepared using the same process as in Example 1, but with a different composition ratio of platinum and palladium. The second coating solution was prepared in the same manner as in Example 1, but its composition ratio was set to iridium:ruthenium:titanium = 25:25:50 in molar ratio. The coating process was essentially the same as in Example 1, but for the second oxide coating, the application and drying procedures were the same, while the thermal decomposition temperature was set to 460°C for 10 minutes. The first and second coatings were applied alternately five times each. After the coating was completed, a post-treatment was performed by heat treatment in a muffle furnace with air flowing through it at 520°C for three hours.

[0034] The electrode samples prepared in this manner were subjected to preliminary electrolysis under the same conditions as in Example 1 to confirm initial coating wear and to verify their electrochemical properties. In other words, an initial accelerated electrolysis test was performed for 1200 hours under the same conditions as in Example 1. The sample after the preliminary electrolysis test was electrolyzed in the same ion exchange membrane electrolytic cell as in Example 1, and salt TIFF0007898724000003.tif10170 NaCl solution, 80°C, current density 0.3 A / cm² 2 That was the case.

[0035] The results are shown in Table 1. [Table 1] In Table 1, sample No. 1 shows a proportional relationship, and from the perspective of potential, it can be seen that the potential rises because the alloy layer is made of pure platinum rather than a palladium alloy, causing the surface to become passive. Samples No. 2 through No. 6 are examples, and even during preliminary electrolysis, almost no palladium consumption was observed, suggesting that long-term stable operation can be expected. Samples No. 7 and 8 showed a proportional relationship, suggesting that the high palladium content in the alloy composition may have resulted in insufficient stability, as at least some of the palladium was not stabilized, leading to early wear in that portion. Sample No. 9 had an alloy layer composed solely of palladium, and as expected, a significant amount of palladium was consumed in the early stages, making it unlikely to be practical for actual use. [Examples]

[0036] A 1mm thick JIS Class 1 pure titanium plate was used as the base material, and an electrode coating was prepared on its surface. As a pretreatment, the surface was roughened by blasting with steel grit, and then etched with 20% hydrochloric acid at 100°C. As an alloy coating solution, dinitrodiammineplatinum and dinitrodiamminepalladium were mixed in a metal molar ratio of 70% platinum and 30% palladium, dissolved in a mixture of isopropanolamine (20%) and pure water (80%) by volume, and then diluted with isopropyl alcohol. This was designated as coating solution 1. For the oxide coating solution and coating solution 2, ruthenium chloride, stannous chloride, and n-titanium butoxide were dissolved in n-butanol and a 10 mass percent aqueous hydrochloric acid solution in a volume ratio of 1:1. The composition of ruthenium, tin, and titanium was set to a molar ratio of ruthenium (Ru):tin (Sn):titanium (Ti) = 20:15:65.

[0037] Electrodes were fabricated on a titanium substrate using these coating solutions. First, oxide coating solution 2 was applied and dried at 120°C for 5 minutes, then thermal decomposition was performed in a muffle furnace with air circulation at 460°C for 10 minutes. This operation was repeated twice. After that, platinum-palladium alloy coating solution 1 was applied to the oxide coating surface and dried at 50°C for 5 minutes, then thermal decomposition was performed by heating with the flame of a portable gas burner. The gas burner treatment conditions were almost the same as in Example 1. After alloy coating in this manner, oxide coating was performed twice and alloy coating was performed once. The combination of two oxide coatings and one alloy coating was repeated to fabricate the desired electrodes. When the surface state was confirmed by X-ray diffraction, platinum-palladium alloy diffraction lines (diffraction lines that are the same as platinum diffraction lines but with a slightly shifted diffraction angle) and rutile-type oxide diffraction lines were observed, confirming that the coating consisted of oxide and metal alloy.

[0038] For comparison with the electrodes fabricated in this manner, electrodes coated only with oxide and without alloy coating were prepared. These electrodes were used as anodes, and the resulting sodium hypochlorite was analyzed after electrolysis in 3% saline solution. (Note: Preliminary analysis was also performed.) The procedure was performed for 1200 hours at a current density of TIFF0007898724000005.tif91702A / cm2. These electrodes were used as anodes, and a titanium plate of the same size was used as the cathode, with the inter-electrode distance fixed at 10 mm and maintained at 15°C with 30 g-NaCl / Electrolysis was carried out until the sodium hypochlorite was saturated and the concentration stopped changing. As a result, a sodium hypochlorite concentration of 12,500 to 13,000 ppm was obtained with the anode containing the platinum-palladium alloy of the present invention, while it was 9,500 ppm with only the oxide layer, clearly indicating that the platinum-palladium alloy was working effectively. [Industrial applicability] )

[0039] The electrolytic electrode of the present invention, particularly as an anode for ion-exchange membrane method salt electrolysis, has been widely used because it exhibits extremely low electrode wear during electrolysis and therefore has an extremely long electrode life. However, it solves the problems of high electrolytic potential and selectivity of the electrode reaction, i.e., the oxygen content in the generated reaction gas, which were problems with conventional iridium, ruthenium, and titanium oxide anodes. By maintaining an extremely low electrode wear rate, it is possible to achieve a very low electrolytic potential and extremely low oxygen characteristics in the generated chlorine.

[0040] Furthermore, the electrolytic electrode according to the present invention has been confirmed to have extremely excellent electrolytic characteristics and a sufficiently long lifespan, even when used as an anode for seawater electrolysis and dilute saltwater electrolysis, which differ in electrolysis methods and conditions, although they both primarily generate chlorine. Thus, an extremely superior electrode has been obtained.

Claims

1. A titanium or titanium alloy is used as the base material, and a coating is laminated on the surface of the base material. The lamination of the aforementioned coating is It includes, at least, a coating of a metal alloy consisting of platinum and palladium, and a coating of an oxide consisting of ruthenium and / or iridium and titanium and / or tin formed on the surface of said coating, and a coating of an oxide consisting of ruthenium and / or iridium and titanium and / or tin, and a coating of a metal alloy consisting of platinum and palladium formed on the surface of said coating, An electrolytic anode for chlorine generation, characterized by a coating layer consisting of a mixture of the aforementioned metal alloy and the aforementioned oxide.

2. The metal alloy comprising platinum and palladium is characterized in that its composition is 50 to 90% platinum and the remainder being palladium, as described in claim 1, for use as an electrolytic anode for chlorine generation.

3. The electrolytic anode for chlorine generation according to claim 1 or 2, characterized in that the oxide is a composite oxide consisting of iridium, ruthenium, and titanium, wherein iridium accounts for 0 to 30 mol%, ruthenium for 20 to 40 mol%, and the remainder is titanium.

4. The electrolytic anode for chlorine generation according to claim 1 or 2, characterized in that the oxide is a composite oxide consisting of iridium, ruthenium, and tin, wherein the composite oxide consists of 5 to 30 mol% iridium, 20 to 50 mol% ruthenium, and the remainder being tin (Sn).

5. The process involves preparing a titanium or titanium alloy substrate by pre-treating the surface and then activating it through etching, A step of forming a laminate of a coating of a predetermined thickness on the surface of the substrate, The lamination of the aforementioned coating is (1) A first layer is formed by applying an alcohol solution containing a platinum salt, a palladium salt, and an organic reducing agent, and then thermally decomposing it with a flame to form a coating of a metal alloy made of platinum and palladium at least once, and then (2) applying a coating solution in which a ruthenium metal salt and / or iridium metal salt and a titanium salt and / or tin salt are dissolved in a solvent, and then thermally decomposing it by heating in flowing air to form an oxide coating at least once. And, (2) A coating solution in which a ruthenium metal salt and / or iridium metal salt and a titanium salt and / or tin salt are dissolved in a solvent is applied, and a coating of oxide is formed at least once by thermal decomposition by heating in flowing air, and then a second layer is formed at least once by applying (1) an alcohol solution containing a platinum salt, a palladium salt and an organic reducing agent to the surface of the oxide coating and thermal decomposition by a flame, thereby forming a coating of a metal alloy consisting of platinum and palladium. A method for manufacturing an electrolytic anode used for chlorine generation, characterized in that the lamination of the coating is a coating layer made of a mixture of the metal alloy and the oxide.

6. The method for manufacturing an electrolytic anode used for chlorine generation according to Claim 5, characterized in that (1) and (2) are repeated, or (2) and (1) are repeated to form a laminate of coatings of a predetermined thickness.

7. The method for manufacturing an electrolytic anode used for chlorine generation according to claim 5 or 6, characterized in that the metal alloy consisting of platinum and palladium is a metal alloy formed by applying an alcohol solution containing a platinum salt, a palladium salt, and an organic reducing agent, and then thermally decomposing it with a flame.

8. The method for manufacturing an electrolytic anode used for chlorine generation according to claim 5 or 6, characterized in that the coating of the metal alloy consisting of platinum and palladium has a composition in which platinum is 50 to 90% in molar ratio and the remainder is palladium.

9. The method for producing an electrolytic anode for chlorine generation according to claim 5 or 6, characterized in that the oxide is a composite oxide formed by applying a coating solution in which a ruthenium metal salt and / or iridium metal salt and a titanium salt and / or tin salt are dissolved in a solvent, and then thermally decomposing it in flowing air.

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