Positive electrode for chlorine generation electrolysis

Abstract

An anode for chlorine evolution electrolysis having a low overvoltage for chlorine evolution and an excellent efficiency in chlorine evolution without using iridium (Ir) is disclosed. The anode is an anode 10 for chlorine evolution electrolysis, including: a substrate 2 formed of titanium or a titanium alloy; and a catalyst layer 5 having a first layer 5a disposed on the substrate 2 and a second layer 5b disposed on the first layer 5a, in which the first layer 5a contains respective oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr), and the second layer 5b contains respective oxides of ruthenium (Ru) and titanium (Ti).

Description

TECHNICAL FIELD

[0001] The present invention relates to an anode for chlorine evolution electrolysis.BACKGROUND ART

[0002] In the related art, chlorine gas, a chlorine compound, and the like are produced by electrolysis of salt water. In addition, in recent years, electrolysis of salt water is also used for production of hypochlorous acid, which has been increasingly used for purposes such as disinfection and deodorization. When chlorine gas or a chlorine compound is produced by electrolysis, a chlorine evolution reaction proceeds at an anode. For example, for producing hypochlorous acid water, water (H2O) is reduced on a cathode to evolve hydrogen (H2). On the other hand, on the anode, chloride ions (Cl−) are oxidized to evolve chlorine (Cl2), and the evolved chlorine reacts with water to evolve hypochlorous acid (HClO).

[0003] However, on the anode, not only chlorine but also oxygen is simultaneously evolved by oxidation of water. A ratio of the evolved chlorine to oxygen varies depending on the type and properties of the anode, and thus it is necessary to use an electrode (anode for chlorine evolution electrolysis) superior in a chlorine evolution efficiency when the main purpose is evolution of chlorine. As the anode for chlorine evolution electrolysis, an electrode employing a noble metal oxide such as iridium oxide (IrO2) as a catalyst is used. An electrode employing such a noble metal oxide as a catalyst has a low overvoltage for chlorine evolution and is superior in the chlorine evolution efficiency.

[0004] As an electrode for efficiently evolving chlorine by electrolysis, for example, an electrode having a catalyst coating containing respective oxides of tin (Sn), iridium (Ir), and ruthenium (Ru) at a predetermined proportion has been proposed (Patent Literature 1). In addition, an electrode having a catalyst coating containing respective oxides of tin (Sn), iridium (Ir), ruthenium (Ru), and titanium (Ti) at a predetermined proportion has been proposed (Patent Literature 2).CITATION LISTPatent LiteraturePatent Literature 1: JP2017-535680A

[0006] Patent Literature 2: JP2021-529251ASUMMARY OF INVENTIONTechnical Problem

[0007] However, a noble metal such as iridium (Ir) is an expensive rare metal. Furthermore, there is a problem that in recent years, the price of iridium (Ir) is rising, and iridium is not easily available. Therefore, it is desired to develop an electrode superior in a chlorine evolution efficiency using as little iridium (Ir) as possible.

[0008] The present invention has been made in view of such problems in the related art, and an object of the present invention is to provide an anode for chlorine evolution electrolysis having a low overvoltage for chlorine evolution and a superior efficiency in chlorine evolution without using iridium (Ir).Solution to Problem

[0009] That is, the present invention provides the following anode for chlorine evolution electrolysis.

[0010] [1] An anode for chlorine evolution electrolysis, including: a substrate formed of titanium or a titanium alloy; and a catalyst layer having a first layer disposed on the substrate and a second layer disposed on the first layer, in which the first layer contains respective oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr), and wherein the second layer contains respective oxides of ruthenium (Ru) and titanium (Ti).

[0011] [2] The anode for chlorine evolution electrolysis according to [1], in which contents of the ruthenium (Ru), the tin (Sn), and the zirconium (Zr) in the first layer are 7 to 40 mol % for the ruthenium (Ru), 50 to 90 mol % for the tin (Sn), and 3 to 10 mol % for the zirconium (Zr) (provided that a total of the Ru, the Sn, and the Zr is 100 mol %) on an element basis, and in which contents of the ruthenium (Ru) and the titanium (Ti) in the second layer are 5 to 40 mol % for the ruthenium (Ru) and 60 to 95 mol % for the titanium (Ti) (provided that a total of the Ru and the Ti is 100 mol %) on an element basis.

[0012] [3] The anode for chlorine evolution electrolysis according to [1] or [2], in which a content of the ruthenium (Ru) in the first layer in a total content of the ruthenium (Ru) in the catalyst layer is 20 to 80 mol % on an element basis.

[0013] [4] The anode for chlorine evolution electrolysis according to any one of [1] to [3], in which the catalyst layer substantially does not contain iridium (Ir).Advantageous Effects of Invention

[0014] The present invention allows for providing an anode for chlorine evolution electrolysis having a low overvoltage for chlorine evolution and a superior efficiency in chlorine evolution without using iridium (Ir).BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 is a schematic view showing an embodiment of an anode for chlorine evolution electrolysis of the present invention.

[0016] FIG. 2 is an electron micrograph of a cross section of an anode for chlorine evolution electrolysis of Example 2.

[0017] FIG. 3 is a graph in which a cell voltage (V) is plotted with respect to an electrolysis time (h).DESCRIPTION OF EMBODIMENTS<Anode for Chlorine Evolution Electrolysis>

[0018] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to the following embodiment. An anode for chlorine evolution electrolysis of the present invention (hereinafter, also simply referred to as “electrode” or “anode”) includes a substrate formed of titanium or a titanium alloy, and a catalyst layer having a first layer disposed on the substrate and a second layer disposed on the first layer. The first layer contains respective oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr). The second layer contains respective oxides of ruthenium (Ru) and titanium (Ti). Hereinafter, the anode for chlorine evolution electrolysis of the present invention will be described in detail.(Substrate)

[0019] FIG. 1 is a schematic view showing an embodiment of the anode for chlorine evolution electrolysis of the present invention. As shown in FIG. 1, an anode for chlorine evolution electrolysis 10 of the present embodiment includes a substrate 2 and a catalyst layer 5 disposed on the substrate 2. The substrate 2 is formed of titanium or a titanium alloy. An overall shape of the substrate 2 is not limited, and can be appropriately designed according to an application. Examples of the overall shape of the substrate include a plate shape, a rod (column) shape, and a mesh shape.(Catalyst Layer)

[0020] The catalyst layer 5 disposed on the substrate 2 includes a first layer 5a and a second layer 5b. The first layer 5a is a layer disposed on the substrate 2. The second layer 5b is a layer disposed on the first layer 5a. That is, the catalyst layer 5 has a laminated structure including the first layer 5a and the second layer 5b. The catalyst layer 5 preferably has a two-layer structure substantially composed of only the first layer 5a and the second layer 5b. A thickness of the catalyst layer 5 is not limited and can be freely set. The thickness of the catalyst layer 5 may be, for example, 1 μm to 10 μm.

[0021] The first layer 5a contains respective oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr). Specifically, the first layer 5a is formed of ruthenium oxide (RuO2), tin oxide (SnO2), and zirconium oxide (ZrO2). The second layer 5b contains respective oxides of ruthenium (Ru) and titanium (Ti). Specifically, the second layer 5b is formed of ruthenium oxide (RuO2) and titanium oxide (TiO2).

[0022] In the electrode having only a catalyst layer formed of RuO2—SnO2—ZrO2, selectivity of chlorine (Cl2) evolution is low, and it is difficult to improve a chlorine evolution efficiency. In the electrode having only a catalyst layer formed of RuO2—TiO2, an overvoltage of chlorine (Cl2) evolution is low. On the other hand, in the anode for chlorine evolution electrolysis 10 of the present embodiment, the catalyst layer 5 having the laminated structure in which the first layer 5a (that is, a lower layer) formed of RuO2—SnO2—ZrO2 and the second layer 5b (that is, an upper layer) formed of RuO2—TiO2 are laminated is provided on the substrate 2. Providing the catalyst layer 5 having such a laminated structure on the substrate 2 allows for providing an electrode having a low overvoltage for chlorine evolution, high selectivity of chlorine (Cl2) evolution, and a superior efficiency in chlorine evolution.

[0023] Contents of ruthenium (Ru), tin (Sn), and zirconium (Zr) in the first layer are preferably 7 to 40 mol % for ruthenium (Ru), 50 to 90 mol % for tin (Sn), and 3 to 10 mol % for zirconium (Zr) on an element basis. A total of Ru, Sn, and Zr is 100 mol %. The content of ruthenium (Ru) in the first layer is more preferably 12 to 25 mol % on an element basis. The content of tin (Sn) in the first layer is more preferably 65 to 80 mol % on an element basis. The content of zirconium (Zr) in the first layer is more preferably 4 to 8 mol % on an element basis. By adjusting the content of each of the metals in the first layer on an element basis within the above range, an anode for chlorine evolution electrolysis having a lower overvoltage for chlorine evolution and a superior efficiency in chlorine evolution can be provided. Types and contents of metal elements in each of the layers can be measured and calculated by an analysis method such as a fluorescent X-ray (XRF) analysis.

[0024] Contents of ruthenium (Ru) and titanium (Ti) in the second layer are preferably 5 to 40 mol % for ruthenium (Ru) and 60 to 95 mol % for titanium (Ti) on an element basis. A total of Ru and Ti is 100 mol %. The content of ruthenium (Ru) in the second layer is more preferably 8 to 30 mol % on an element basis. The content of titanium (Ti) in the second layer is more preferably 70 to 92 mol % on an element basis. By adjusting the content of each of the metals in the second layer on an element basis within the above range, an anode for chlorine evolution electrolysis having a lower overvoltage for chlorine evolution and a superior efficiency in chlorine evolution can be provided.

[0025] The content of ruthenium (Ru) in the first layer relative to the total content of ruthenium (Ru) in the catalyst layer is preferably 20 to 80 mol %, and more preferably 23 to 77 mol % on an element basis. Adjusting the content of ruthenium (Ru) in the first layer relative to the total content of ruthenium (Ru) in the catalyst layer within the above range allows for further reducing the overvoltage of chlorine evolution and further improving the chlorine evolution efficiency.

[0026] In the electrode of the present embodiment, the catalyst layer having the laminated structure as described above is provided on the substrate. Therefore, even without using iridium (Ir) the overvoltage for chlorine evolution can be low and the efficiency in chlorine evolution can be superior. Furthermore, the electrode can be substantially configured from a material that is relatively easily available. Thus, the catalyst layer constituting the electrode of the present embodiment preferably does not substantially contain iridium (Ir) in view of manufacturability, price, and the like. A small amount of iridium (Ir) may be contained in the catalyst layer in a state of a metal oxide as long as the amount of iridium does not substantially affect the manufacturability, price, and the like.(Method for Producing Anode for Chlorine Evolution Electrolysis)

[0027] The electrode of the present embodiment can be produced by forming a catalyst layer on a substrate. For forming the catalyst layer on the substrate, for example, a coating liquid for first layer and a coating liquid for second layer each containing various metals, salts of various metals, and the like at a desired ratio are prepared. Then, onto a surface of the substrate subjected to a surface treatment such as a blast treatment or an etching treatment as necessary, the prepared coating liquid for first layer is applied to form a coating layer. Next, the coating layer is calcined under appropriate temperature conditions to form the first layer on the substrate.

[0028] Thereafter, onto a surface of the formed first layer, the prepared coating liquid for second layer is applied to form a coating layer. Next, the coating layer is calcined under appropriate temperature conditions to form a second layer on the first layer. Accordingly, an electrode in which the catalyst layer having the laminated structure is provided on the substrate can be obtained. A thickness of the catalyst layer to be formed and a content of the metal element can be controlled by repeating the application of the coating liquids and the calcination. A calcination temperature is usually 450 to 550° C., preferably 480 to 520° C.EXAMPLES

[0029] Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited to these Examples. A “part” and “%” in Examples and Comparative Examples are based on mass unless otherwise specified.<Pretreatment of Substrate>

[0030] A titanium mesh substrate of 100 mm×100 mm×1 mm was prepared. Alumina powder having a particle diameter of 212 μm to 300 μm was blasted to the prepared mesh substrate at a pressure of 0.3 MPa. Then, the substrate was immersed in boiling 20% hydrochloric acid for 20 minutes, and then washed with ion-exchanged water. Further, the substrate was dried in an oven at 60° C. for 1 hour to obtain a pretreated substrate.Production of Anode for Chlorine Evolution ElectrolysisExample 1[Formation of First Layer]

[0031] A coating liquid for first layer containing a tin (Sn) hydroxyacetochloride complex (SnHAC), a zirconyl chloride complex (ZrOCl2), and a ruthenium (Ru) hydroxyacetochloride complex (RuHAC) was prepared. Contents of SnHAC, ZrOCl2, and RuHAC in the coating liquid for first layer were 200 g / L, 130 g / L, and 95 g / L, respectively. A surface of the pretreated substrate was applied with the prepared coating liquid for first layer, and then dried at room temperature (25° C.) for 10 minutes. Next, the resultant was placed in an oven, dried with hot air at 60° C. for 10 minutes, then calcined at 480° C. for 10 minutes, and air-cooled to reach room temperature. The steps from the application of coating to the air cooling were repeated a predetermined number of times to form a first layer on the substrate.[Formation of Second Layer]

[0032] A coating liquid for second layer containing a titanium chloride complex (TiCl4) and RuHAC was prepared. Contents of TiCl4 and RuHAC in the coating liquid for second layer were 260 g / L and 95 g / L, respectively. A surface of the formed first layer was applied with the prepared coating liquid for second layer, and then dried at room temperature for 10 minutes. Next, the resultant was placed in an oven, dried with hot air at 60° C. for 10 minutes, then calcined at 480° C. for 10 minutes, and air-cooled to reach room temperature. The steps from the application of coating to the air cooling were repeated a predetermined number of times to form a second layer on the first layer to obtain an anode for chlorine evolution electrolysis (electrode) in which a catalyst layer composed of the first layer and the second layer was disposed on the substrate. Contents (molar ratio and mol %) of the metal elements in the catalyst layer (first layer and second layer) of the obtained electrode and a ratio (mol %) of ruthenium (Ru) between the layers (first layer and second layer) are shown in Table 1.Examples 2 to 6 and Comparative Examples 1 to 5

[0033] Each of anodes for chlorine evolution electrolysis (electrode) was obtained in the same manner as in Example 1 described above except that compositions and the like of the coating liquids were appropriately adjusted to have a layer configuration, the contents (molar ratio and mol %) of the metal elements in the catalyst layer (first layer and second layer), and the ratio (mol %) of ruthenium (Ru) between the layers (first layer and second layer) as shown in Table 1. As an iridium (Ir) source, an iridium (Ir) hydroxyacetochloride complex (IrHAC) was used. FIG. 2 shows an electron micrograph of a cross section of the anode for chlorine evolution electrolysis of Example 2.TABLE 1Ratio SnZrRuTiIr(mol %) ofLayerMolarMolarMolarMolarMolarRu betweenconfigurationratiomol %ratiomol %ratiomol %ratiomol %ratiomol %layersExample 1Second layer0.1513.0 1.0087.0 75First layer0.5071.40.057.20.1521.4  25Example 2Second layer0.1513.0 1.0087.0 50First layer0.5071.40.057.20.1521.4  50Example 3Second layer0.1513.0 1.0087.0 25First layer0.5071.40.057.20.1521.4  75Example 4Second layer0.159.11.5090.9 75First layer0.5071.40.057.20.1521.4  25Example 5Second layer0.1513.0 1.0087.0 75First layer0.7578.90.055.30.1515.8  25Example 6Second layer0.159.11.5090.9 75First layer0.7578.90.055.30.1515.8  25ComparativeSingle layer0.5076.90.1523.1 100Example 1ComparativeSingle layer0.5071.40.057.20.1521.4 100Example 2ComparativeSingle layer0.1513.0 1.0087.0100Example 3ComparativeSingle layer0.5029.40.053.00.158.81.0058.8100Example 4ComparativeSingle layer0.2013.70.3020.5 0.9061.70.064.1100Example 5<Evaluation>(Overvoltage for Chlorine (Cl2) Evolution and Selectivity of Chlorine (Cl2) Evolution)An electrolysis cell for chlorine evolution using the produced electrode as an anode was assembled. The assembled electrolysis cell was operated, and an overvoltage for chlorine (Cl2) evolution and a ratio (O2 / Cl2 (vol %)) of evolved oxygen (O2) to evolved chlorine (Cl2) were measured under the following conditions. The results are shown in Table 2.Current density: 4 kA / m2

[0036] Electrolyte solution: 200 g / L sodium chloride (NaCl) aqueous solution

[0037] pH of electrolyte solution: 3

[0038] Temperature of electrolyte solution: 90° C.TABLE 2Overvoltage(V) for Cl2O2 / Cl2evolution(vol %)Example 11.0850.32Example 21.0870.39Example 31.0870.80Example 41.1050.29Example 51.0890.27Example 61.1170.27Comparative1.0831.40Example 1Comparative1.0811.14Example 2Comparative1.0980.31Example 3Comparative1.0981.06Example 4Comparative1.0810.53Example 5(Stability of Catalyst Layer)

[0039] Electrolysis cells for chlorine evolution using the electrodes of Examples 1 and 4 as anodes were assembled. With the assembled electrolysis cells, electrolysis was performed under the following conditions to evaluate a stability of the catalyst layer. FIG. 3 shows a graph in which a cell voltage (V) is plotted with respect to an electrolysis time (h). As shown in FIG. 3, it has been confirmed that, in both the electrodes of Examples 1 and 4, the cell voltage remained stable even after long-term electrolysis, hence a stable catalyst layer was formed.

[0040] Current density: 8 kA / m2

[0041] Electrolyte solution: 200 g / L sodium chloride (NaCl) aqueous solution

[0042] pH of electrolyte solution: 3

[0043] Temperature of electrolyte solution: 90° C.INDUSTRIAL APPLICABILITY

[0044] The electrode of the present invention has a low overvoltage for chlorine evolution and is excellent in chlorine evolution efficiency without using iridium (Ir), and is useful as an anode for chlorine evolution electrolysis.REFERENCE SIGNS LIST2: substrate

[0046] 5a: first layer

[0047] 5b: second layer

[0048] 5: catalyst layer

[0049] 10: anode for chlorine evolution electrolysis

Claims

1. An anode for chlorine evolution electrolysis, comprising:a substrate formed of titanium or a titanium alloy; anda catalyst layer having a first layer disposed on the substrate and a second layer disposed on the first layer,wherein the first layer contains respective oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr), andwherein the second layer contains respective oxides of ruthenium (Ru) and titanium (Ti).

2. The anode for chlorine evolution electrolysis according to claim 1,wherein contents of the ruthenium (Ru), the tin (Sn), and the zirconium (Zr) in the first layer are 7 to 40 mol % for the ruthenium (Ru), 50 to 90 mol % for the tin (Sn), and 3 to 10 mol % for the zirconium (Zr) (provided that a total of the Ru, the Sn, and the Zr is 100 mol %) on an element basis, andwherein contents of the ruthenium (Ru) and the titanium (Ti) in the second layer are 5 to 40 mol % for the ruthenium (Ru) and 60 to 95 mol % for the titanium (Ti) (provided that a total of the Ru and the Ti is 100 mol %) on an element basis.

3. The anode for chlorine evolution electrolysis according to claim 1,wherein a content of the ruthenium (Ru) in the first layer in a total content of the ruthenium (Ru) in the catalyst layer is 20 to 80 mol % on an element basis.

4. The anode for chlorine evolution electrolysis according to claim 1,wherein the catalyst layer substantially does not contain iridium (Ir).

5. The anode for chlorine evolution electrolysis according to claim 2,wherein a content of the ruthenium (Ru) in the first layer in a total content of the ruthenium (Ru) in the catalyst layer is 20 to 80 mol % on an element basis.

6. The anode for chlorine evolution electrolysis according to claim 2,wherein the catalyst layer substantially does not contain iridium (Ir).

7. The anode for chlorine evolution electrolysis according to claim 3,wherein the catalyst layer substantially does not contain iridium (Ir).

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