Anode for chlorine-producing electrolysis

Abstract

Provided is an anode for chlorine-producing electrolysis, which has a low chlorine-producing overvoltage and excellent chlorine-producing efficiency even without using iridium (Ir). An anode (10) for chlorine-generating electrolysis is provided with: a base material (2) comprising titanium or a titanium alloy; and a catalyst layer (5) having a first layer (5a) disposed on the base material (2) and a second layer (5b) disposed on the first layer (5a), the first layer (5a) containing oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr), and the second layer (5b) containing oxides of ruthenium (Ru) and titanium (Ti).

Description

Technical Field

[0001] The present invention relates to an anode for chlorine-producing electrolysis. Background Art

[0002] Conventionally, chlorine, chlorine compounds, etc. have been produced by electrolysis of brine. In addition, in recent years, hypochlorous acid has also been produced by electrolyzing brine, and the opportunities for using hypochlorous acid in sterilization, deodorization, etc. have been increasing. In the case of producing chlorine or chlorine compounds by electrolysis, a chlorine-producing reaction occurs at the anode. For example, in the case of producing hypochlorous acid water, at the cathode, water (H2O) is reduced to produce hydrogen (H2). On the other hand, at the anode, chloride ions (Cl - ) are oxidized to produce chlorine (Cl2), and the produced chlorine reacts with water to form hypochlorous acid (HClO).

[0003] However, not only chlorine but also oxygen is simultaneously produced by oxidation of water at the anode. The ratio of the produced chlorine to oxygen varies depending on the type and properties of the anode. Therefore, in the case of mainly producing chlorine, it is necessary to use an electrode with excellent chlorine-producing efficiency (anode for chlorine-producing electrolysis). As an anode for chlorine-producing electrolysis, an electrode using a noble metal oxide such as iridium oxide (IrO2) as a catalyst is used. An electrode using such a noble metal oxide as a catalyst has a low overvoltage for chlorine production and excellent chlorine-producing efficiency.

[0004] As an electrode for efficiently producing chlorine by electrolysis, for example, an electrode having a catalyst coating containing oxides of tin (Sn), iridium (Ir), and ruthenium (Ru) in a predetermined ratio has been proposed (Patent Document 1). In addition, an electrode having a catalyst coating containing oxides of tin (Sn), iridium (Ir), ruthenium (Ru), and titanium (Ti) in a predetermined ratio has been proposed (Patent Document 2). Prior Art Documents Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-535680 Patent Document 2: Japanese Patent Application Laid-Open No. 2021-529251 Summary of the Invention Problems to be Solved by the Invention

[0006] However, noble metals such as iridium (Ir) are expensive and rare metals. Moreover, in recent years, the price of iridium (Ir) has soared and it is not easily available. Therefore, it is desired to develop an electrode with excellent chlorine-producing efficiency that uses as little iridium (Ir) as possible.

[0007] The present invention has been made in view of the problems of such prior art, and an object thereof is to provide an anode for chlorine production electrolysis that has a low overvoltage for chlorine production and excellent chlorine production efficiency even without using iridium (Ir). Means for Solving the Problems

[0008] That is, according to the present invention, there is provided an anode for chlorine production electrolysis as shown below. [1] An anode for chlorine production electrolysis, comprising: 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 containing oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr) respectively, and the second layer containing oxides of ruthenium (Ru) and titanium (Ti) respectively. [2] The anode for chlorine production electrolysis according to [1] above, wherein the contents of ruthenium (Ru), tin (Sn), and zirconium (Zr) in the first layer are, on an elemental basis, ruthenium (Ru) 7 mol% to 40 mol%, tin (Sn) 50 mol% to 90 mol%, and zirconium (Zr) 3 mol% to 10 mol% (wherein Ru, Sn, and Zr total 100 mol%), and the contents of ruthenium (Ru) and titanium (Ti) in the second layer are, on an elemental basis, ruthenium (Ru) 5 mol% to 40 mol% and titanium (Ti) 60 mol% to 95 mol% (wherein Ru and Ti total 100 mol%). [3] The anode for chlorine production electrolysis according to [1] or [2] above, wherein the content of ruthenium (Ru) in the first layer in the total content of ruthenium (Ru) in the catalyst layer is 20 mol% to 80 mol% on an elemental basis. [4] The anode for chlorine production electrolysis according to any one of [1] to [3] above, wherein the catalyst layer substantially does not contain iridium (Ir). Advantages of the Invention

[0009] According to the present invention, it is possible to provide an anode for chlorine production electrolysis that has a low overvoltage for chlorine production and excellent chlorine production efficiency even without using iridium (Ir). BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic view showing an embodiment of the anode for chlorine production electrolysis of the present invention. Figure 2 It is an electron micrograph of a cross section of the anode for chlorine production electrolysis of Example 2. Figure 3 It is a graph plotting the cell voltage (V) against the electrolysis time (h). Description of Reference Numerals

[0032] 2: Substrate 5a: First layer 5b: Second layer 5: Catalyst layer 10: Anode for chlorine - producing electrolysis Detailed implementation mode

[0011] <Anode for chlorine - producing electrolysis> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. The anode for chlorine - producing 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 oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr) respectively. The second layer contains oxides of ruthenium (Ru) and titanium (Ti) respectively. Hereinafter, the details of the anode for chlorine - producing electrolysis of the present invention will be described.

[0012] (Substrate) Figure 1 is a schematic diagram showing an embodiment of the anode for chlorine - producing electrolysis of the present invention. As Figure 1 shown, the anode 10 for chlorine - producing electrolysis in this 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. The overall shape of the substrate 2 is not particularly limited and can be appropriately designed according to the use. As the overall shape of the substrate, for example, a plate shape, a rod (column) shape, a net shape, etc. can be cited.

[0013] (Catalyst layer) The catalyst layer 5 disposed on the substrate 2 has a first layer 5a and a second layer 5b. The first layer 5a is the layer disposed on the substrate 2. The second layer 5b is the 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. It should be noted that the catalyst layer 5 is preferably a double - layer structure substantially composed only of the first layer 5a and the second layer 5b. The thickness of the catalyst layer 5 is not particularly limited and can be set arbitrarily. The thickness of the catalyst layer 5 is, for example, 1 μm to 10 μm.

[0014] The first layer 5a contains oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr) respectively. Specifically, the first layer 5a is formed of ruthenium oxide (RuO2), tin oxide (SnO2), and zirconium oxide (ZrO2). The second layer 5b contains oxides of ruthenium (Ru) and titanium (Ti) respectively. Specifically, the second layer 5b is formed of ruthenium oxide (RuO2) and titanium oxide (TiO2).

[0015] For an electrode having only a catalyst layer formed of RuO2 - SnO2 - ZrO2, the selectivity for chlorine production (Cl2) is low, and it is difficult to improve the chlorine production efficiency. In addition, for an electrode having only a catalyst layer formed of RuO2 - TiO2, the overvoltage for chlorine production (Cl2) is low. In contrast, the chlorine - producing electrolysis anode 10 of the present embodiment has a catalyst layer 5 provided on a substrate 2, and the catalyst layer 5 has a laminated structure in which a first layer 5a (i.e., the lower layer) formed of RuO2 - SnO2 - ZrO2 and a second layer 5b (i.e., the upper layer) formed of RuO2 - TiO2 are laminated. By providing the catalyst layer 5 having such a laminated structure on the substrate 2, an electrode with a lower overvoltage for chlorine production, a higher selectivity for chlorine production (Cl2), and excellent chlorine production efficiency can be produced.

[0016] The contents of ruthenium (Ru), tin (Sn), and zirconium (Zr) in the first layer are preferably 7 mol% to 40 mol% of ruthenium (Ru), 50 mol% to 90 mol% of tin (Sn), and 3 mol% to 10 mol% of zirconium (Zr) on an elemental basis. In addition, Ru, Sn, and Zr total 100 mol%. The content of ruthenium (Ru) in the first layer is more preferably 12 mol% to 25 mol% on an elemental basis. The content of tin (Sn) in the first layer is more preferably 65 mol% to 80 mol% on an elemental basis. In addition, the content of zirconium (Zr) in the first layer is more preferably 4 mol% to 8 mol% on an elemental basis. By setting the contents of the respective metals in the first layer within the above - mentioned ranges on an elemental basis, a chlorine - producing electrolysis anode with a lower overvoltage for chlorine production and excellent chlorine production efficiency can be obtained. It should be noted that the types and contents of the metal elements in each layer can be measured and calculated by analytical methods such as X - ray fluorescence (XRF) analysis.

[0017] The contents of ruthenium (Ru) and titanium (Ti) in the second layer are preferably 5 mol% to 40 mol% of ruthenium (Ru) and 60 mol% to 95 mol% of titanium (Ti) on an elemental basis. In addition, Ru and Ti total 100 mol%. The content of ruthenium (Ru) in the second layer is more preferably 8 mol% to 30 mol% on an elemental basis. In addition, the content of titanium (Ti) in the second layer is more preferably 70 mol% to 92 mol% on an elemental basis. By setting the contents of the respective metals in the second layer within the above - mentioned ranges on an elemental basis, a chlorine - producing electrolysis anode with a lower overvoltage for chlorine production and excellent chlorine production efficiency can be obtained.

[0018] The content of ruthenium (Ru) in the first layer in the total content of ruthenium (Ru) in the catalyst layer, on an elemental basis, is preferably 20 mol% to 80 mol%, more preferably 23 mol% to 77 mol%. By setting the content of ruthenium (Ru) in the first layer in the total content of ruthenium (Ru) in the catalyst layer within the above range, the overvoltage of chlorine production can be further reduced, and the chlorine production efficiency can be further improved.

[0019] The electrode of the present embodiment has a low overvoltage of chlorine production and excellent chlorine production efficiency even without using iridium (Ir) by providing a catalyst layer having the above-described laminated structure on a substrate, and can be substantially composed of materials that are relatively easily obtained. Therefore, from the viewpoints of ease of manufacture, price, etc., the catalyst layer constituting the electrode of the present embodiment preferably contains substantially no iridium (Ir). As long as it is within a range that does not substantially affect the ease of manufacture, price, etc., a trace amount of iridium (Ir) can also be contained in the catalyst layer in the state of a metal oxide.

[0020] (Method for manufacturing an anode for chlorine production electrolysis) The electrode of the present embodiment can be manufactured by forming a catalyst layer on a substrate. To form a catalyst layer on a substrate, for example, a coating liquid for the first layer and a coating liquid for the second layer containing various metals, salts of various metals, etc. in a desired ratio are respectively prepared. Then, if necessary, the prepared coating liquid for the first layer is coated on the surface of the substrate that has been subjected to surface treatment such as sandblasting treatment and etching treatment to form a coating layer. Next, by calcining under appropriate temperature conditions, the first layer can be formed on the substrate.

[0021] Then, the prepared coating liquid for the second layer is coated on the surface of the formed first layer to form a coating layer. Next, by calcining under appropriate temperature conditions, the second layer can be formed on the first layer, and an electrode having a catalyst layer with a laminated structure provided on the substrate can be obtained. In addition, by repeating the coating of the coating liquid and the calcination, the thickness of the formed catalyst layer and the content of the metal element can be controlled. The calcination temperature is usually 450°C to 550°C, and preferably 480°C to 520°C. Examples

[0022] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. It should be noted that "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[0023] <Pretreatment of the substrate> Prepare a titanium mesh substrate of 100 mm × 100 mm × 1 mm. Spray alumina powder with a particle size of 212 μm to 300 μm onto the prepared mesh substrate under a pressure of 0.3 MPa for sandblasting treatment. Then, immerse it in boiling 20% hydrochloric acid for 20 minutes for etching treatment, and wash it with ion-exchanged water. Then, place it in an oven at 60 °C and dry for 1 hour to obtain the pre-treated substrate.

[0024] <Manufacture of Anode for Chlorine-producing Electrolysis> (Example 1) [Formation of the First Layer] Prepare a coating solution for the first layer containing tin (Sn) hydroxyacetyl chloride complex (SnHAC), zirconium oxychloride complex (ZrOCl2), and ruthenium (Ru) hydroxyacetyl chloride complex (RuHAC). The contents of SnHAC, ZrOCl2, and RuHAC in the coating solution for the first layer are 200 g / L, 130 g / L, and 95 g / L, respectively. After coating the prepared coating solution for the first layer on the surface of the pre-treated substrate, dry it at room temperature (25 °C) for 10 minutes. Then, place it in an oven, hot air dry it at 60 °C for 10 minutes, then calcine it at 480 °C for 10 minutes, and air cool it to room temperature. Repeat the above coating to air cooling process a specified number of times to form the first layer on the substrate.

[0025] [Formation of the Second Layer] Prepare a coating solution for the second layer containing titanium chloride complex (TiCl4) and RuHAC. The contents of TiCl4 and RuHAC in the coating solution for the second layer are 260 g / L and 95 g / L, respectively. After coating the prepared coating solution for the second layer on the surface of the formed first layer, dry it at room temperature for 10 minutes. Then, place it in an oven, hot air dry it at 60 °C for 10 minutes, then calcine it at 480 °C for 10 minutes, and air cool it to room temperature. Repeat the above coating to air cooling process a specified number of times to form the second layer on the first layer, and obtain an anode (electrode) for chlorine-producing electrolysis with a catalyst layer composed of the first layer and the second layer configured on the substrate. The contents (molar ratio and mol%) of metal elements in the catalyst layer (the first layer and the second layer) of the obtained electrode and the ratio (mol%) of ruthenium (Ru) between the layers (the first layer and the second layer) are shown in Table 1.

[0026] (Examples 2 - 6, Comparative Examples 1 - 5) An anode (electrode) for chlorine production electrolysis was obtained in the same manner as in Example 1 above, except that the composition of the coating solution was appropriately adjusted to obtain the layer constitution shown in Table 1, the content (molar ratio and mol%) of metal elements in the catalyst layer (the first layer and the second layer), and the ratio (mol%) of ruthenium (Ru) between the layers (the first layer and the second layer). As the iridium (Ir) source, iridium (Ir) hydroxyacetyl chloride complex (IrHAC) was used. Figure 2 An electron micrograph showing a cross-section of the anode for chlorine production electrolysis of Example 2 is shown.

[0027]

[0028] <Evaluation> (Overvoltage of chlorine production (Cl2) and selectivity of chlorine production (Cl2)) An electrolytic cell for chlorine production in which the fabricated electrode was used as the anode was assembled. Using the assembled electrolytic cell, the overvoltage of chlorine production (Cl2) and the ratio of oxygen (O2) to the produced chlorine (Cl2) (O2 / Cl2 (volume%)) were measured respectively under the conditions shown below. The results are shown in Table 2. · Current density: 4 kA / m 2 · Electrolyte: 200 g / L aqueous sodium chloride (NaCl) solution · pH of the electrolyte: 3 · Temperature of the electrolyte: 90 °C

[0029]

[0030] (Stability of the catalyst layer) An electrolytic cell for chlorine production in which the electrodes of Example 1 and 4 were used as the anodes respectively was assembled. Using the assembled electrolytic cell, electrolysis was carried out under the conditions shown below to evaluate the stability of the catalyst layer. Figure 3 A graph showing the cell voltage (V) plotted against the electrolysis time (h) is shown. As Figure 3 shown, for either electrode of Example 1 and 4, even during long-term electrolysis, the cell voltage did not change stably, indicating that a stable catalyst layer was formed. · Current density: 8 kA / m 2 · Electrolyte: 200 g / L aqueous sodium chloride (NaCl) solution · pH of the electrolyte: 3 · Temperature of the electrolyte: 90 °C Industrial applicability

[0031] Even without using iridium (Ir), the electrode of the present invention has a low overvoltage for chlorine production and excellent chlorine production efficiency, and can be used as an anode for chlorine production electrolysis.

Claims

1. An anode for chlorine - producing electrolysis, comprising: 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, wherein the first layer contains oxides of ruthenium (Ru), tin (Sn), and zirconium (Zr) respectively, and the second layer contains oxides of ruthenium (Ru) and titanium (Ti) respectively.

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

3. The anode for chlorine - producing electrolysis according to claim 1 or 2, wherein the content of ruthenium (Ru) in the first layer in the total content of ruthenium (Ru) in the catalyst layer is 20 mol% - 80 mol% on an elemental basis.

4. The anode for chlorine - producing electrolysis according to any one of claims 1 to 3, wherein the catalyst layer is substantially free of iridium (Ir).

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