Anode catalyst, anode electrode, and electrolytic reactor

Abstract

To provide an anode catalyst having excellent catalytic activity and durability.SOLUTION: An anode catalyst is characterized by comprising a composite oxide represented by a composition formula: Ru1-xTaxOy (wherein x and y satisfy 0.3≤x≤0.7, 1.8+0.45x≤y≤2.2+0.55x), and having a half-width of the diffraction peak of the (110) plane in an X-ray diffraction pattern exceeding 0.7°.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an anode catalyst, an anode electrode, and an electrolytic reactor. [Background technology]

[0002] The use of hydrogen energy and carbon dioxide fixation technology are attracting attention as solutions to global environmental problems and the depletion of fossil fuels. In particular, the water splitting reaction, which splits water into hydrogen and oxygen at room temperature and pressure, and the carbon dioxide reduction reaction, which uses water as an electron source, are expected to be clean energy generation methods. These reactions include the water oxidation reaction: 2H2O→O2+4H + +4e - , 1.23V (vs. RHE) is essential.

[0003] For example, Non-Patent Documents 1 to 3 disclose the use of IrOx nanoparticles as an anode catalyst to oxidize water in a neutral aqueous solution in an electrolytic reactor for carbon dioxide reduction. Also, Non-Patent Document 4 discloses the use of RuO2-Ta2O5 as an anode catalyst to oxidize water in an acidic aqueous solution with a pH of 1 to 2. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Naohiko Kato, Shintaro Mizuno, Masahito Shiozawa, Natsumi Nojiri, Yasuaki Kawai, Kazuhiro Fukumoto, Takeshi Morikawa and Yasuhiko Takeda, A large-sized cell for solar-driven CO2 conversion with a solar-to-formate conversion efficiency of 7.2%, Joule 5 (2121) 686-705 [Non-patent document 2] Kato Naohiko, Takeda Yasuhiko, Kawai Yasuaki, Nojiri Natsumi Shiozawa Masahito, Mizuno Shintaro, Yamanaka Ken-ichi, Morikawa Takeshi, Hamaguchi Tsuyoshi, Solar Fuel Production from CO2 Using a 1 m-Square-Sized Reactor with a Solar-to-Formate Conversion Efficiency of 10.5% ACS SUSTAINABLE CHEMISTRY & ENGINEERIG 9 (2021) 16031-16037 [Non-patent document 3] Masahito Shiozawa, Kousuke Kitazumi, Mina Iwai, Shintaro Mizuno, Naohiko Kato, Yasuhiko Takeda, Tsuyoshi Hamaguchi, Improved Durability of Highly Active IrOx Electrodes for Electrocatalytic Oxygen Evolution Reaction, Electrocatalysis 13 (2022) 830-837 [Non-patent document 4] Tian Zhang, Development of amorphous RuO2-Ta2O5 / Ti anode for oxygen evolution in electrowinning, Ph. D. Thesis, Doshisha Univ., 2015. https: / / doshisha.repo.nii.ac.jp / records / 1247 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional anode catalysts that promote water oxidation reactions are insufficient in terms of catalytic activity and durability (maintenance of catalytic activity), and improvements are needed. In particular, there is a need for anode catalysts that have excellent catalytic activity and durability when using a versatile neutral electrolyte (pH 6 to 8).

[0006] Therefore, an object of the present invention is to provide an anode catalyst having excellent catalytic activity and durability, and an anode electrode and an electrolytic reactor having the anode catalyst. [Means for solving the problem]

[0007] The anode catalyst according to an embodiment of the present invention has the composition formula: Ru 1-x Ta x O y (wherein x and y satisfy 0.3≦x≦0.7, 1.8+0.45x≦y≦2.2+0.55x), and is characterized by containing a composite oxide in which the half-width of the diffraction peak of the (110) plane in the X-ray diffraction pattern exceeds 0.7°.

[0008] Moreover, an anode electrode according to an embodiment of the present invention is characterized by having a substrate and the anode catalyst supported on the substrate.

[0009] An electrolytic reactor according to an embodiment of the present invention is characterized by comprising the anode electrode, a cathode electrode, and an electrolyte solution having a pH of 6-8.

[0010] Furthermore, an electrolytic reactor according to an embodiment of the present invention includes an anode electrode, a cathode electrode, and an electrolyte solution having a pH of 6 to 8. The anode electrode has a substrate and an anode catalyst supported on the substrate. The anode catalyst has a composition formula: Ru 1-x Ta x O y (wherein x and y satisfy 0.2≦x<0.3, 1.8+0.45x≦y≦2.2+0.55x), and is characterized by containing a composite oxide in which the half-width of the diffraction peak of the (110) plane in the X-ray diffraction pattern exceeds 0.7°.

[0011] In the electrolytic reactor, it is preferable that water is oxidized at the anode electrode and carbon dioxide is reduced at the cathode electrode. [Effects of the Invention]

[0012] According to an embodiment of the present invention, it is possible to provide an anode catalyst having excellent catalytic activity and durability, an anode electrode having the anode catalyst, and an electrolytic reactor. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an electrolytic reactor according to an embodiment of the present invention. [Figure 2] FIG. 1 shows Tafel plots in an electrochemical cell using anode electrodes (1) to (5). [Figure 3] FIG. 1 is a diagram showing the results of current-time characteristics in an electrochemical cell using anode electrodes (1) to (5). [Figure 4] FIG. 1 shows X-ray diffraction patterns of the catalysts of the anode electrodes (1) and (2). [Figure 5] FIG. 1 shows Tafel plots for electrochemical cells using anode electrodes (1), (3), (5), and (6) to (8). [Figure 6] FIG. 1 shows the voltage-time characteristics of electrochemical cells using anode electrodes (1), (3) and (6) to (8). [Figure 7] FIG. 1 shows X-ray diffraction patterns of the catalysts of the anode electrodes (1) and (6) to (8). DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below. The embodiment is an example of implementing the present invention, and the present invention is not limited to this embodiment.

[0015] FIG. 1 is a diagram showing an example of the configuration of an electrolytic reactor according to this embodiment. As shown in FIG. 1, the electrolytic reactor 100 includes a cathode electrode 102, an anode electrode 104, an electrolyte 106, and a container 108. The container 108 contains the electrolyte 106, and the cathode electrode 102 and the anode electrode 104 are immersed in the electrolyte 106 in the container 108. Reference numeral 110 shown in FIG. 1 denotes a device that applies an appropriate bias voltage between the cathode electrode 102 and the anode electrode 104. Examples of the device 110 that applies the bias voltage include a chemical battery (including a primary battery, a secondary battery, etc.), a constant voltage source, and a solar cell.

[0016] The cathode electrode 102 is an electrode used to reduce, for example, carbon compounds or protons through a reduction reaction. The cathode electrode 102 includes, for example, a substrate, a conductive layer disposed on the substrate, and a conductor layer disposed on the conductive layer.

[0017] The substrate is a member that structurally supports the cathode electrode 102. The material is not particularly limited, but may be, for example, a glass substrate. The substrate may also include, for example, a metal or a semiconductor. The metal used as the substrate is not particularly limited, but preferably includes titanium (Ti), silver (Ag), gold (Au), copper (Cu), zinc (Zn), indium (In), cadmium (Cd), tin (Sn), palladium (Pd), or lead (Pb). The semiconductor used as the substrate is not particularly limited, but preferably includes titanium oxide (TiO), silicon (Si), strontium titanate (SrTiO), zinc oxide (ZnO), or tantalum oxide (TaO).

[0018] The conductive layer is provided to improve the efficiency of current collection in the cathode electrode 102. The conductive layer is not particularly limited, but is preferably made of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide (ZnO), or the like. In particular, it is preferable to use fluorine-doped tin oxide (FTO) in consideration of its thermal and chemical stability.

[0019] The conductor layer is composed of a conductor containing a cathode catalyst (i.e., a reduction catalyst). The conductor layer can be constructed by supporting a cathode catalyst on a conductor. The conductor can be constructed, for example, from a material containing a carbon material (C). The carbon material preferably contains at least one of carbon nanotubes, graphene, and graphite. Graphene and graphite preferably have a size of 1 nm or more and 1 μm or less. Carbon nanotubes preferably have a diameter of 1 nm or more and 40 nm or less. The conductor can be formed by spraying a carbon material mixed with a liquid such as ethanol and heating it. Spin coating may be used instead of spraying. Alternatively, the solution may be directly dripped and dried to coat the conductor without using spin coating.

[0020] The cathode catalyst is not particularly limited as long as it is a material having a reduction catalytic function, but for example, a complex catalyst is preferable. For example, a ruthenium complex is preferable. For example, the complex catalyst is [Ru{4,4'-di(1-H-1-pyrrolypropyl carbonate)-2,2'-bipyridine}(CO)(MeCN)Cl2], [Ru{4,4'-di(1-H-1-pyrrolypropyl carbonate)-2,2'-bipyridine}(CO)2Cl2], [Ru{4,4'-di(1-H-1-pyrrolypropyl carbonate)-2,2'-bipyridine}(CO)2] n , [Ru{4,4'-di(1-H-1-pyrrolypropyl carbonate)-2,2'-bipyridine}(CO)(CHCN)Cl], etc.

[0021] The conductive layer can be produced, for example, by applying a solution in which a cathode catalyst is dispersed onto a conductive material.

[0022] The anode electrode 104 is an electrode used to oxidize water through an oxidation reaction. The anode electrode 104 has, for example, a substrate and a catalyst layer having an anode catalyst supported on the substrate. In the electrolytic reactor 100 of this embodiment, it is desirable that the catalyst layer of the anode electrode 104 is disposed opposite the conductive layer of the cathode electrode 102.

[0023] The substrate is preferably, for example, a conductive substrate, and specifically, a metal substrate, etc. The metal constituting the metal substrate preferably contains at least one selected from the group consisting of Ti, Au, Pt, Ru, Ir, Sn, and Rh, in terms of high conductivity, high corrosion resistance, etc., and particularly preferably contains Ti.

[0024] The catalyst layer is composed of an anode catalyst. The anode catalyst is a material having an oxidation catalyst function, and has the composition formula: (1) Ru 1-x Ta x O y (wherein x and y satisfy 0.3≦x≦0.7, 1.8+0.45x≦y≦2.2+0.55x), and the half-width of the diffraction peak of the (110) plane in the X-ray diffraction pattern is more than 0.7°; or (2) a composite oxide represented by the composition formula: Ru 1-x Ta x O y (wherein x and y satisfy 0.2≦x<0.3, 1.8+0.45x≦y≦2.2+0.55x), and the composite oxide has a half-width of the diffraction peak of the (110) plane in the X-ray diffraction pattern that exceeds 0.7°. The anode catalyst may also contain both of (1) and (2). Hereinafter, the composite oxide of (1) may be referred to as Ru-Ta composite oxide (1), and the composite oxide of (2) may be referred to as Ru-Ta composite oxide (2). When simply referred to as Ru-Ta composite oxide, it means at least one of the Ru-Ta composite oxides (1) and (2).

[0025] Although the structure of the Ru-Ta composite oxide according to this embodiment is not fully understood, it is presumed that the structure is such that amorphous Ta oxide serves as a matrix, with Ru oxide crystallites dispersed in the matrix, thereby suppressing the generation of cracks in the catalyst layer that are observed when Ta is not added.

[0026] The use of Ru-Ta composite oxide as an anode catalyst makes it possible to achieve both excellent catalytic activity and excellent durability. In the Ru-Ta composite oxide (1), x in the formula satisfies 0.3≦x≦0.7, but from the viewpoint of further enhancing catalytic activity or durability, it is more preferable that x satisfies 0.4≦x≦0.7, and even more preferable that x satisfies 0.4≦x≦0.6. Furthermore, in the Ru-Ta composite oxide (2), x in the formula preferably satisfies 0.2≦x≦0.25, from the viewpoint of further enhancing catalytic activity or durability. The composition ratio of the Ru-Ta composite oxide is measured by elemental analysis using ICP (inductively coupled plasma atomic emission spectroscopy).

[0027] For Ru-Ta composite oxides, the half-width of the diffraction peak of the (110) plane in the X-ray diffraction pattern needs to be greater than 0.7°, but from the viewpoint of further enhancing catalytic activity or durability, it is preferably 0.8° or greater, and more preferably 0.9° or greater. The upper limit of the half-width of the diffraction peak of the (110) plane is not particularly limited, but may be, for example, 1.1° or less. The measurement conditions for the X-ray diffraction pattern in this disclosure are as described in the Examples below.

[0028] An example of a method for producing a Ru-Ta composite oxide is described below. A catalyst precursor solution is prepared by dissolving predetermined amounts of a ruthenium-containing compound and a tantalum-containing compound in a solvent, and the catalyst precursor solution is then calcined at a predetermined temperature. The ruthenium-containing compound and the tantalum-containing compound can be any substance that can produce the desired Ru-Ta composite oxide. Examples include chlorides such as ruthenium chloride and tantalum chloride, and hydroxides such as ruthenium hydroxide and tantalum hydroxide. The solvent can be any solvent that can dissolve the ruthenium-containing compound and the tantalum-containing compound, such as organic solvents such as alcohols, aldehydes, and ethers. The calcination temperature is, for example, 320°C or higher and 500°C or lower. The obtained Ru-Ta composite oxide can be dispersed in a solution containing a binder, applied to a substrate, and dried to obtain an anode electrode in which an anode catalyst containing the Ru-Ta composite oxide is supported on the substrate. Alternatively, the above-mentioned catalyst precursor solution can be applied to a substrate, dried, and then fired at a predetermined temperature to obtain an anode electrode in which an anode catalyst containing a Ru-Ta composite oxide is supported on the substrate.

[0029] The pH of the electrolyte 106 is preferably in the neutral range of 6 to 8. The anode catalyst containing the Ru—Ta composite oxide of this embodiment exhibits excellent catalytic activity and durability even in an electrolyte having a neutral pH range of 6 to 8. The electrolyte 106 is preferably, for example, a phosphate buffer solution or a borate buffer solution, in order to suppress pH fluctuations during the oxidation-reduction reaction. When carbon dioxide is reduced at the cathode electrode 102, it is preferable that carbon dioxide be dissolved in the electrolyte 106, for example.

[0030] In the electrolytic reactor 100 shown in FIG. 1, the cathode electrode 102 and the anode electrode 104 are immersed in the electrolytic solution 106, and a bias voltage is applied between the cathode electrode 102 and the anode electrode 104, for example, by a bias voltage application device 110. As a result, water in the electrolytic solution 106 is oxidized at the anode electrode 104 to produce oxygen (Equation (1)). At the cathode electrode 102, for example, CO2 in the electrolytic solution 106 is reduced to produce carbon monoxide, formic acid, etc. (Equations (2) and (3)), or protons are reduced to produce hydrogen (Equation (4)). The voltage applied to both electrodes may be any voltage that causes an oxidation-reduction reaction at both electrodes. For example, when carbon dioxide is reduced to produce formic acid, a voltage of 1.5 V to 3.0 V is preferred, and when protons are reduced to produce hydrogen, a voltage of 1.5 V to 2.2 V is preferred. Oxidation reaction: 2H2O → O2 + 4H + +4e - (1) Reduction reaction: CO2 + 2H + +2e - →CO+H2O (2) :CO2+2H + +2e - →HCOOH (3) :2H + +2e - →H2(4) [Example]

[0031] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0032] <Experimental Example 1> <Preparation of anode electrodes (1) and (2)> (I) The surface of a titanium plate (JIS Class 1) was polished with #400 emery paper, then ultrasonically cleaned in acetone for 20 minutes and degreased. (II) RuCl3·nH2O and TaCl5 were mixed so that the molar ratio of Ru to Ta was 0.8:0.2, and dissolved in a 1-butanol solution to prepare a coating solution. (III) The coating solution was coated onto the surface-treated titanium substrate, and then dried on a hot plate at 120°C for 10 minutes to evaporate the solvent in the coating solution. (IV) The substrate was baked in a baking oven at 260°C, 300°C, 360°C, or 470°C for 10 minutes to form a catalyst layer on the titanium substrate. (V) The catalyst layer had a coating weight of 1.5 mg / cm. 2 The operations (III) and (IV) were repeated so that the following was achieved:

[0033] Of the anodes obtained in this manner, the anodes fired at 260°C and 300°C had their catalyst layers easily peeled off from the titanium substrate, but the anodes fired at 360°C and 470°C did not have their catalyst layers peeled off from the titanium substrate. Therefore, the anode fired at 360°C was used as anode electrode (1), and the anode fired at 470°C was used as anode electrode (2). The composition of the catalyst supported on the titanium substrate in these anodes was analyzed by ICP, and it was found that Ru 0.8 Ta 0.2 O 2.1 It was.

[0034] <Preparation of anode electrodes (3) and (4)> (I) RuCl3·nH2O was dissolved in a 1-butanol solution to prepare a coating solution. (II) The coating solution was coated onto the surface-treated titanium substrate described above, and the substrate was dried on a hot plate at 120°C for 10 minutes to evaporate the solvent in the coating solution. (III) The substrate was baked at 360°C or 470°C for 10 minutes to obtain an anode electrode with a catalyst layer formed on the titanium substrate. (IV) The catalyst layer had a coating weight of 1.5 mg / cm 2The steps (II) and (III) were repeated until the temperature reached the desired value. Of the anodes obtained in this manner, the anode calcined at 360°C was used as anode (3), and the anode calcined at 470°C was used as anode (4). In these anodes, the catalyst composition supported on the titanium substrate was RuO2.

[0035] <Anode electrode (5)> The iridium oxide nanoparticle-containing solution prepared according to the description in Non-Patent Document 3 was applied to the surface-treated titanium substrate and dried to obtain an anode electrode (5) in which an iridium oxide catalyst layer was formed on the titanium substrate. The coating weight of the catalyst layer was 1.5 mg / cm. 2 is.

[0036] (Evaluation of catalytic activity and durability) The catalytic activity and durability of the above anode electrodes (1) to (5) were evaluated using a three-electrode system. In the three-electrode system, an electrolyte was placed in a container, and a three-electrode electrochemical cell was used in which the above anode electrode was immersed as a working electrode, a platinum wire as a counter electrode, and Ag / AgCl as a reference electrode in the electrolyte. The electrolyte used was 0.4 M phosphate buffer solution (K2HPO4 + KH2PO4).

[0037] Before the electrolysis test, CO2 was bubbled through the electrolyte at a flow rate of 20 mL / min for 1.5 hours. Then, while continuing to bubble CO2 through the electrolyte to maintain the electrolyte in a CO2 saturated state (pH 6.3), each electrode was connected to an electrochemical analyzer (Bio-Logic EC-LAB series VMP3) and the electrolysis test was performed. Specifically, the electrodes were run in constant current mode (current density: 0.5 mA / cm2). 2 , 1mA / cm 2 , 1.5mA / cm 2 , 2mA / cm 2 , 3mA / cm 2 , 4mA / cm 2 , 5mA / cm 2The voltage-time characteristics (Vt characteristics) were measured for 1 hour in the constant potential mode (1.2 V vs. Ag / AgCl) and a Tafel plot was obtained from the voltage and current density after 1 hour. The current-time characteristics (It characteristics) were then measured in the constant potential mode (1.2 V vs. Ag / AgCl).

[0038] FIG. 2 shows the Tafel plots for the electrochemical cells using the anode electrodes (1) to (5). As shown in FIG. 2, the anode electrode (1) (catalyst: Ru 0.8 Ta 0.2 O 2.1 The electrochemical cell and anode electrode (3) (catalyst: RuO2, calcination temperature: 360°C) using RuO2 (catalyst: RuO2, calcination temperature: 360°C) had higher Tafel plots than the other anode electrodes, demonstrating excellent catalytic activity in the water oxidation reaction.

[0039] Figure 3 shows the current-time characteristics of the electrochemical cells using anode electrodes (1) to (5). As shown in Figure 3, of the anode electrodes (1) and (3) that exhibited excellent catalytic activity, anode electrode (3) began to show a decrease in current density after 370 hours. On the other hand, anode electrode (1) showed no decrease in current density even after 751 hours, demonstrating excellent durability.

[0040] Figure 4 shows the X-ray diffraction patterns of the anode electrodes (1) and (2). The conditions for measuring the X-ray diffraction patterns are as follows: An Ultima IV X-ray diffraction measurement device (Rigaku Corporation) was used. The voltage applied to the X-ray tube was set to 40 kV, the current to 40 mA, CuKα radiation was used, the divergence vertical limiting slit was set to 10 mm, the scattering slit was set to 8 mm, the receiving slit was set to open, a CuKβ filter was used, the scan speed was set to 20° / mm, and the data sample interval was set to 0.02°.

[0041] The half-width of the diffraction peak of the (110) plane of RuO2 with a rutile structure was calculated from the X-ray diffraction pattern shown in Figure 4. As a result, the half-width of the diffraction peak of the (110) plane in the X-ray diffraction pattern of anode electrode (1), which showed excellent catalytic activity and excellent durability, was 0.90°. On the other hand, the half-width of the diffraction peak of the (110) plane in the X-ray diffraction pattern of anode electrode (2), which had inferior catalytic activity to anode electrodes (1) and (3), was 0.70°.

[0042] <Experimental Example 2> <Anode electrode (6)> Anode electrode (6) was prepared in the same manner as anode electrode (1), except that RuCl3·nH2O and TaCl5 were mixed so that the molar ratio of Ru to Ta was 0.7:0.3. In anode electrode (6), the composition of the catalyst supported on the titanium substrate was analyzed by ICP, and the results showed that Ru 0.7 Ta 0.3 O 2.15 It was.

[0043] <Anode electrode (7)> Anode electrode (7) was prepared in the same manner as anode electrode (1), except that RuCl3·nH2O and TaCl5 were mixed so that the molar ratio of Ru to Ta was 0.5:0.5. The composition of the catalyst supported on the titanium substrate in anode electrode (7) was analyzed by ICP, and the results showed that Ru 0.5 Ta 0.5 O 2.25 It was.

[0044] <Anode electrode (8)> Anode electrode (8) was prepared in the same manner as anode electrode (1), except that RuCl3·nH2O and TaCl5 were mixed so that the molar ratio of Ru to Ta was 0.3:0.7. The composition of the catalyst supported on the titanium substrate in anode electrode (8) was analyzed by ICP, and the results showed that Ru 0.3 Ta 0.7 O 2.35 It was.

[0045] (Evaluation of catalytic activity and durability) The catalytic activity and durability of the above anode electrodes (1), (3), (5), and (6) to (8) were evaluated using a three-electrode system.

[0046] In the three-electrode system, an electrolyte was placed in a container, and a three-electrode electrochemical cell was used, with the above-mentioned anode electrode as the working electrode, a platinum wire as the counter electrode, and Hg / Hg2SO4 as the reference electrode immersed in the electrolyte. The electrolyte used was 0.4 M phosphate buffer (K2HPO4 + KH2PO4).

[0047] Before the electrolysis test, CO2 was bubbled through the electrolyte at a flow rate of 20 mL / min for 1.5 hours. Then, while continuing to bubble CO2 through the electrolyte to maintain the electrolyte in a CO2 saturated state (pH 6.3), each electrode was connected to an electrochemical analyzer (Bio-Logic EC-LAB series VMP3) and the electrolysis test was performed. Specifically, the electrodes were run in constant current mode (current density: 0.5 mA / cm2). 2 , 1mA / cm 2 , 1.5mA / cm 2 , 2mA / cm 2 , 3mA / cm 2 , 4mA / cm 2 , 5mA / cm 2 The voltage-time characteristics (Vt characteristics) were measured for 1 hour in constant current mode (10 mA / cm). Tafel plots were obtained from the voltage and current density after 1 hour. 2 ) and measured the voltage-time characteristics (Vt characteristics).

[0048] Figure 5 shows the Tafel plots for the electrochemical cells using anode electrodes (1), (3), (5), and (6) to (8). As shown in Figure 5, when anode electrodes (1), (6) to (8) using a composite oxide of Ru and Ta as a catalyst were used, the Tafel plots were higher than those for anode electrode (5) using iridium oxide as a catalyst, demonstrating superior catalytic activity in the water oxidation reaction.

[0049] Figure 6 shows the voltage-time characteristics of the electrochemical cells using anode electrodes (1), (3), and (6) to (8). As shown in Figure 6, anode electrode (3), which used Ru oxide as a catalyst, showed a sudden increase in potential after about 600 hours, after which it reached the end of its electrode life. On the other hand, anode electrodes (1), (6) to (8), which used Ru and Ta composite oxide as a catalyst, showed only a slight increase in potential and continued to function for 1,000 hours, demonstrating excellent durability.

[0050] Figure 7 shows the X-ray diffraction patterns of anode electrodes (1) and (6) to (8). The measurement conditions for the X-ray diffraction patterns were the same as those described above. The half-widths of the diffraction peaks of the (110) plane were calculated from the X-ray diffraction patterns shown in Figure 7. As a result, the half-widths of the diffraction peaks of the (110) plane in the X-ray diffraction patterns of anode electrodes (1) and (6) to (8), which exhibited excellent catalytic activity and excellent durability, were 0.90°, 0.74°, 0.94°, and 0.72°, as shown in Table 1, all of which were greater than 0.7°.

[0051] [Table 1]

[0052] From the results of Experimental Examples 1 and 2, the composition formula: Ru 1-x Ta x O y (wherein x and y satisfy 0.3≦x≦0.7, 1.8+0.45x≦y≦2.2+0.55x), and the half width of the diffraction peak of the (110) plane in the X-ray diffraction pattern exceeds 0.7°; or 1-x Ta x O y (where x and y satisfy the conditions 0.2≦x<0.3 and 1.8+0.45x≦y≦2.2+0.55x), and the full width at half maximum of the (110) diffraction peak in the X-ray diffraction pattern exceeds 0.7°. It has been found that this composite oxide exhibits excellent catalytic activity and durability as an anode catalyst. In particular, it exhibits excellent catalytic activity and durability as an anode catalyst even in an electrolyte in the neutral region. [Explanation of symbols]

[0053] 100 electrolytic reactor, 102 cathode electrode, 104 anode electrode, 106 electrolyte, 108 container, 110 bias voltage application device.

Claims

1. Composition formula: Ru １－ｘ Ta ｘ O ｙ (wherein x and y satisfy 0.3≦x≦0.7, 1.8+0.45x≦y≦2.2+0.55x), and the full width at half maximum of the diffraction peak for the (110) plane in an X-ray diffraction pattern exceeds 0.7°.

2. An anode electrode comprising: a substrate; and the anode catalyst according to claim 1 supported on the substrate.

3. An electrolytic reactor comprising the anode electrode according to claim 2, a cathode electrode, and an electrolyte solution having a pH of 6 to 8.

4. The device comprises an anode electrode, a cathode electrode, and an electrolyte solution having a pH of 6 to 8; the anode electrode has a substrate and an anode catalyst supported on the substrate; The anode catalyst has the composition formula: Ru １－ｘ Ta ｘ O ｙ (wherein x and y satisfy 0.2≦x<0.3, 1.8+0.45x≦y≦2.2+0.55x), and the full width at half maximum of the diffraction peak for the (110) plane in an X-ray diffraction pattern exceeds 0.7°.

5. 5. The electrolytic reactor according to claim 3, wherein water is oxidized at the anode electrode and carbon dioxide is reduced at the cathode electrode.

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