Tungsten Oxide and Catalyst for Oxygen Evolution Reaction

Abstract

The object of the present invention is to provide a compound with high catalytic activity that can be used as a catalyst for the oxygen evolution reaction. A tungsten oxide is represented by Ni x Fe 1‑x WO4 (where 0 < x < 1). A catalyst for the oxygen evolution reaction for an anode or a positive electrode contains the aforementioned tungsten oxide. An electrolytic cell includes an anode chamber and a cathode chamber partitioned by an ion-permeable membrane. An anode is disposed in the anode chamber, and a cathode is disposed in the cathode chamber. Among them, a tungsten oxide represented by Ni x Fe 1‑x WO4 (where 0 < x < 1) is supported on the anode as a catalyst.

Description

Technical Field

[0001] The present invention relates to tungsten oxides represented by Ni x Fe 1-x WO4 (where 0 < x < 1), an oxygen evolution reaction catalyst containing the aforementioned tungsten oxide, and a method for producing the aforementioned tungsten oxide. Background Art

[0002] In recent years, in order to solve problems such as global warming caused by the greenhouse effect of carbon dioxide, methods for producing hydrogen using renewable energy have received attention. For hydrogen production using renewable energy, low-cost reduction competitive with conventional hydrogen production methods by fossil fuel reforming is required. As a hydrogen production method capable of meeting this requirement, water electrolysis (electrolysis) can be cited. As a representative water electrolysis method, there is alkaline water electrolysis. Power loss occurs during alkaline water electrolysis. As the main causes of power loss, anodic overvoltage, cathodic overvoltage, ohmic loss of an ion-permeable diaphragm, ohmic loss caused by the structural resistance of an electrolytic cell constituting an electrolytic cell unit, etc. can be cited. If these power losses can be reduced, the current density during electrolysis of an electrolytic cell can be increased and the entire system can be miniaturized, and as a result, equipment costs can be significantly reduced. Therefore, development of a catalyst capable of reducing power loss is desired.

[0003] Conventionally, as catalysts for oxygen evolution reactions, ruthenium oxide, iridium oxide, etc. have been used, but they are noble metals with high usage costs and limited resource amounts. Therefore, research has been conducted on using tungsten oxides as catalysts for oxygen evolution reactions, and tungsten oxides use tungsten, which has a lower cost and a larger resource amount than noble metals. Non-Patent Document 1 describes a composite of Co 1-x Fe x WO4 and carbon nanotubes (CNT), Co 1-x Fe x WO4-CNT, as a catalyst for oxygen evolution reaction (OER). However, although the overvoltage is reduced by composite with carbon nanotubes, the overvoltage of Co 0.5 Fe 0.5 WO4 without composite with carbon nanotubes is high, and its value is reported to be 420 mV. Non-Patent Document 2 reports the use of Ni-Fe-W hydroxide as a catalyst for oxygen evolution reaction, but it is also composite with carbon fiber. Therefore, development of a compound that exhibits high catalytic activity without using noble metals such as ruthenium and iridium is required.

[0004] Prior Art Documents

[0005] Non-Patent Documents

[0006] Non-Patent Document 1: Composite Metal Oxide-Carbon Nanotube Electrocatalysts for the Oxygen Evolution and Oxygen Reduction Reactions, ChemElectroChem, 5, 2850-2856 (2018).

[0007] Non-Patent Document 2: Jie Xu, Mingshuo Wang, Fei Yang, Xiaoqian Ju, Xilai Jia, “Self-Supported Porous Ni-Fe-W Hydroxide Nanosheets on Carbon Fiber: A Highly Efficient Electrode for Oxygen Evolution Reaction”, Inorg. Chem. 58, 13037-13048 (2019). Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] The problem of the present invention is to provide a compound with high catalytic activity that can be used as a catalyst for the oxygen evolution reaction.

[0010] Method for Solving the Problem

[0011] The present inventors have studied a new compound with high catalytic activity that can be used as a catalyst for the oxygen evolution reaction, and as a result, it has been found that tungsten oxide represented by Ni x Fe 1-x WO4 (where 0 < x < 1) has very high catalytic activity. Conventionally, although it has been described that M is set to various metal elements in the compound represented by MWO4, a compound in which M is a product of combining Ni and Fe and a very high catalytic activity can be obtained therefrom has not been known.

[0012] That is, the present invention is determined by the foregoing matters.

[0013] (1) A tungsten oxide represented by Ni x Fe 1-x WO4 (where 0 < x < 1).

[0014] (2) A catalyst for the oxygen evolution reaction to be used at an anode or a positive electrode, which contains the tungsten oxide described in the foregoing (1).

[0015] (3) A method for manufacturing a tungsten oxide, which is Ni x Fe1-x Method for manufacturing tungsten oxide represented by WO4 (where 0 < x < 1), wherein the tungsten oxide is synthesized by dissolving a tungstate, a nickel salt, and an iron salt in a polyol and heating the polyol solution in which the above salts are dissolved; or by putting the tungstate, the nickel salt, the iron salt, and water into a pressure-resistant container and heating to synthesize the above tungsten oxide.

[0016] (4) An electrolytic cell comprising an anode chamber and a cathode chamber partitioned by an ion-permeable diaphragm, an anode being disposed in the anode chamber and a cathode being disposed in the cathode chamber, wherein a tungsten oxide represented by Ni x Fe 1-x WO4 (where 0 < x < 1) is supported on the anode as a catalyst.

[0017] (5) The electrolytic cell according to (4) above, wherein a gas diffusion layer for supplying carbon dioxide to the cathode is provided, and reduction of carbon dioxide is carried out in the cathode chamber.

[0018] (6) The electrolytic cell according to (4) above, wherein a carbon dioxide introduction part for introducing carbon dioxide to contact the cathode is provided on the side of the cathode chamber opposite to the side facing the anode chamber, and reduction of carbon dioxide is carried out in the carbon dioxide introduction part.

[0019] (7) A method for electrolyzing brine, wherein brine containing an alkali is supplied to the anode chamber of the electrolytic cell according to (4) above, brine is supplied to the cathode chamber, and the brine is electrolyzed.

[0020] (8) A method for electrolyzing brine and reducing carbon dioxide, wherein brine containing an alkali is supplied to the anode chamber of the electrolytic cell according to (6) above, brine is supplied to the cathode chamber, carbon dioxide is introduced into the carbon dioxide introduction part, and the brine is electrolyzed and carbon dioxide is reduced.

[0021] Advantages of the Invention

[0022] When the tungsten oxide of the present invention is used as a catalyst for the oxygen evolution reaction, excellent catalytic activity is exhibited. The catalyst for the oxygen evolution reaction of the present invention exhibits excellent catalytic activity by containing the tungsten oxide of the present invention. The manufacturing method of the present invention can manufacture the tungsten oxide of the present invention. Description of the Drawings

[0023] Figure 1 Figure 1 is a diagram showing the XRD patterns of the specimens obtained in Example 1 and Comparative Example 2.

[0024] Figure 2 Figure 2 ​​​​It is a figure showing the XRD patterns of the specimens obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

[0025] Figure 3 Figure 3 It is a figure showing the linear sweep voltammograms of the specimens obtained in Examples 1 to 3 and Comparative Examples 1 to 4.

[0026] Figure 4 Figure 4 It is a figure showing the Tafel curves of the specimens obtained in Examples 1 to 3 and Comparative Examples 1 to 4.

[0027] Figure 5 Figure 5 It is a figure showing the XRD pattern of the specimen obtained in Example 4.

[0028] Figure 6 Figure 6 It is a figure showing the linear sweep voltammograms of the specimens obtained in Examples 1 and 4 and Comparative Examples 1, 2, and 4.

[0029] Figure 7 Figure 7 It is a figure showing the Tafel curves of the specimens obtained in Examples 1 and 4 and Comparative Examples 1, 2, and 4.

[0030] Figure 8 Figure 8 It is a figure showing the overvoltage at a current density of 10 mA / cm 2 for Examples 1 to 3 and Comparative Examples 1 and 2.

[0031] Figure 9 Figure 9 It is a figure showing the linear sweep voltammograms of Examples 1 to 3 and Comparative Examples 1 and 2.

[0032] Figure 10 Figure 10 It is a figure showing the CV measurement results of the specimen obtained in Example 4.

[0033] Figure 11 Figure 11 It is a figure depicting the relationship between the difference Δj between the cathodic current and the anodic current and the scan rate at a specific potential (0.05 V vs Hg / HgO) for each specimen.

[0034] Figure 12 Figure 12 It is a figure showing the change in conversion frequency caused by overvoltage.

[0035] Figure 13 Figure 13 It is a figure showing the relationship between the elapsed time and the potential in the durability test. ​​​​​​​​​​​​​​​​​​​​​​

[0036] Figure 14 Figure 14 is a graph showing the results of the cyclic test.

[0037] Figure 15 Figure 15 is a graph showing the XRD patterns of the specimens obtained in Example 1 and Comparative Example 6 and the product obtained by heating the specimen obtained in Example 1 at 600 °C.

[0038] Figure 16 Figure 16 is a graph showing the linear sweep voltammograms of the specimens obtained in Example 1 and Comparative Example 6 and the product obtained by heating the specimen obtained in Example 1 at 600 °C.

[0039] Figure 17 Figure 17 is a graph showing the Tafel curves of the specimens obtained in Example 1 and Comparative Example 6 and the product obtained by heating the specimen obtained in Example 1 at 600 °C.

[0040] Figure 18 Figure 18 is a graph showing the XRD patterns of the products obtained by heating the specimen obtained in Example 1 at various temperatures.

[0041] Figure 19 Figure 19 is a graph showing the linear sweep voltammograms of the products obtained by heating the specimen obtained in Example 1 at various temperatures.

[0042] Figure 20 Figure 20 is a graph showing the Tafel curves of the products obtained by heating the specimen obtained in Example 1 at various temperatures.

[0043] Figure 21 Figure 21 is a graph showing the linear sweep voltammogram in Example 5.

[0044] Figure 22 Figure 22 is a graph showing the linear sweep voltammogram in Example 6.

[0045] Figure 23 Figure 23 is a graph showing the Tafel slope when the pH is changed and the overvoltage at 10 mA / cm 2 ².

[0046] Figure 24 Figure 24 is a graph showing the linear sweep voltammogram in Comparative Example 7.

[0047] Figure 25 ​​​​​​​​​​​​​​​​​​​​​​​Figure 25 It is a diagram showing the linear sweep voltammogram in Comparative Example 8.

[0048] Figure 26 Figure 26 It is a schematic diagram showing one embodiment of the electrolytic cell of the present invention.

[0049] Figure 27 Figure 27 It is a schematic diagram showing one embodiment of the electrolytic cell of the present invention.

[0050] Figure 28 Figure 28 It is a schematic diagram showing one embodiment of the electrolytic cell of the present invention. Detailed Embodiment

[0051] The tungsten oxide of the present invention is a compound represented by the chemical formula Ni x Fe 1-x WO4 (where 0 < x < 1). X is preferably 0.05 or more and 0.95 or less, preferably 0.10 or more and 0.90 or less, preferably 0.15 or more and 0.85 or less, preferably 0.2 or more and 0.8 or less, more preferably 0.4 or more and 0.6 or less. Conventionally, ruthenium oxide, iridium oxide, etc. have been used as catalysts for the oxygen evolution reaction, but the tungsten oxide of the present invention has a catalytic effect on the oxygen evolution reaction without using noble metals such as ruthenium and iridium, and is thus excellent in terms of cost. In addition, the toxicity of these metals has been a problem, but the tungsten oxide of the present invention also has no toxicity problem. Furthermore, the catalytic activity of the tungsten oxide of the present invention is more excellent than that in the case of using noble metals. Conventionally, as tungsten oxides having a catalytic activity for the oxygen evolution reaction, Co 1-x Fe x WO4 (where 0 < x < 1) as a wolframite-type tungsten oxide containing cobalt and iron has been known, but the tungsten oxide represented by Ni x Fe 1-x WO4 (where 0 < x < 1) has been unknown. As a catalyst for the oxygen evolution reaction formed of nickel, iron, and tungsten, hydroxides are known, which are different from the tungsten oxide of the present invention. The present invention has synthesized a tungsten oxide represented by Ni x Fe 1- x WO4 (where 0 < x < 1), and as one of the uses of this compound, it has been found to be excellent as a catalyst for the oxygen evolution reaction. The tungsten oxide of the present invention is preferably low-crystalline wolframite or a wolframite precursor that becomes wolframite upon heat treatment. As a preferred crystallite size of the tungsten oxide of the present invention, 2.0 nm to 15.0 nm, 2.0 nm to 14.0 nm, 3.0 nm to 14.0 nm, or 3.0 nm to 7.0 nm can be cited.

[0052] ​​​​​​​The catalyst for oxygen evolution reaction of the present invention contains Ni x Fe 1-x tungsten oxide represented by WO4 (where 0 < x < 1). The catalyst for oxygen evolution reaction of the present invention can be composed only of the tungsten oxide of the present invention, or can contain other compounds within the range of catalytic activity. In addition, it can be supported on carriers such as nickel foam, carbon materials, and metal plates. The catalyst for oxygen evolution reaction of the present invention can be used for anodes or positive electrodes. For example, it can be used as a catalyst for oxygen evolution reaction in electrolysis (electrolysis), batteries, etc. For example, it can be used for anodes in water electrolysis, air electrodes (positive electrodes) in metal-air batteries, and counter electrodes for reduction reactions in carbon dioxide electrolysis. If the tungsten oxide of the present invention is used as a catalyst for oxygen evolution reaction, it can become a catalyst for oxygen evolution reaction with an overvoltage of 250 - 400 mV, 250 - 350 mV, or 300 - 350 mV when the current density reaches 10 mA / cm 2 . In addition, it can become a catalyst for oxygen evolution reaction with a Tafel slope in the range of 30 - 50 mVdec -1 , 30 - 45 mVdec -1 or 30 - 40 mVdec -1 . In addition, it can become a catalyst for oxygen evolution reaction with an electrochemically active surface area in the range of 5 - 20 m 2 / g or 5 - 15 m 2 / g.

[0053] As the method for manufacturing the tungsten oxide of the present invention, there is no particular limitation, and for example, a polyol method, a hydrothermal synthesis method, etc. can be cited. The polyol method is a method of obtaining a target product by dissolving a raw material salt in a polyol and heating it; the hydrothermal synthesis method is a method of obtaining a target product by putting a raw material and water into a pressure-resistant closed container and heating it in a state where the container is closed. The polyol method includes a step of dissolving various raw materials in a polyol and a step of heating the polyol solution obtained in the above step; when manufacturing the tungsten oxide of the present invention by the polyol method, there is no particular limitation on the polyol used, and for example, ethylene glycol, 1,2-propanediol, tetraethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, dipropylene glycol, polyethylene glycol, etc. can be cited. The salt dissolved in the polyol is a salt containing at least one of nickel, iron, and tungsten which are components of the tungsten oxide of the present invention, and as long as it can be dissolved in the used polyol, there is no particular limitation. These salts are used in combination and dissolved so that the above three components are contained in the polyol. As the tungsten source, for example, tungstate can be cited. As the tungstate, sodium tungstate, ammonium tungstate, calcium tungstate, etc. can be cited. As the nickel source and iron source, their respective acetates, sulfates, nitrates, chlorides, etc. can be cited. There is no particular limitation on the heating temperature in the polyol method, but preferably it is near or below the boiling point of the polyol used as the solvent. In addition, there is no particular limitation on the heating method, but since the maximum amount of heat can be applied under normal pressure during the synthesis reaction, it is preferably refluxed at a temperature near the boiling point of the used polyol. The heating time can be appropriately selected as the time when the synthesis reaction proceeds sufficiently. For example, a salt containing nickel, a salt containing iron, and a salt containing tungsten are dissolved in a polyol. At this time, water can be appropriately added, and the pH can also be adjusted as needed. The solution is heated under reflux. The heating temperature at this time varies depending on the type of polyol used, the amount of water added to the polyol, etc., but as long as it is a temperature at which the above solution can reflux. The heating time is only required to be the time when the synthesis reaction proceeds sufficiently, and there is no particular limitation, and for example, 30 minutes to 3 hours, 30 minutes to 2 hours, etc. can be cited. After heating, the temperature of the above solution is lowered to room temperature, and the solid is recovered by a separation operation such as centrifugation, whereby the synthesized tungsten oxide of the present invention can be obtained. By using a polyol as the solvent, the polyol acts as a protective agent on the surface of the generated tungsten oxide particles and is considered to hinder the growth of catalyst particles due to aggregation. When used as a catalyst for the oxygen evolution reaction, tungsten oxide with a lower overvoltage, a larger electrochemically active surface, and higher catalytic activity can be obtained. In addition, since the polyol method can be synthesized in a polyol under normal pressure, it can be synthesized at a lower cost compared to the hydrothermal synthesis method that requires a pressure-resistant container.

[0054] When manufacturing the tungsten oxide of the present invention by the hydrothermal synthesis method, as the raw material, any substance that can be dissolved in water at a specified temperature and pressure in a pressure-resistant container may be used, and there is no particular limitation. For example, tungstate can be cited as the tungsten source. Examples of tungstate include sodium tungstate, ammonium tungstate, calcium tungstate, etc. In addition, as the nickel source and iron source, for example, their respective salts can be cited, and acetate, sulfate, nitrate, chloride, etc. can be cited. In the hydrothermal synthesis method, for example, by putting the raw material as the tungsten source, the raw material as the nickel source, and the raw material as the iron source together with water into a pressure-resistant container and heating them, and reacting them at a specified temperature and pressure for a specified time, the tungsten oxide of the present invention can be manufactured. The temperature and pressure in the hydrothermal synthesis method can be appropriately selected according to the raw materials used. For example, the temperature can be cited as 100 to 200 °C, and in this case, the pressure is about 1 to 15 atmospheres. As the synthesis time, any time as long as the synthesis reaction proceeds sufficiently may be used, and there is no particular limitation. For example, 12 to 48 hours can be cited. After the synthesis, by lowering the temperature and pressure in the pressure-resistant container and recovering the solid matter, the tungsten oxide of the present invention can be obtained.

[0055] The electrolytic cell of the present invention is an electrolytic cell having an anode chamber and a cathode chamber partitioned by an ion-permeable diaphragm, an anode is disposed in the anode chamber, and a cathode is disposed in the cathode chamber. Ni is supported on the anode. x Fe 1- xWO4 (where 0 < x < 1) represents the tungsten oxide of the present invention as a catalyst. As the ion-permeable membrane in the present invention, any ion-permeable membrane that can be used in an electrolytic cell for electrolysis of an aqueous solution or the like is acceptable, and there is no particular limitation. For example, porous membranes formed of asbestos or modified asbestos, porous diaphragms using polysulfone-based polymers, cloths using polyphenylene sulfide fibers, fluorine-based porous membranes, porous membranes using a mixed material containing both inorganic and organic materials, and ion-exchange membranes such as fluorine-based ion-exchange membranes can be cited. As the ion-permeable membrane of the present invention, a membrane with low air permeability, low conductivity, and high strength is preferred. The anode of the present invention has the tungsten oxide of the present invention supported on a conductive substrate as a catalyst. As the conductive substrate, any substrate that can be used in the electrodes of electrolysis is acceptable, and there is no particular limitation. For example, nickel, nickel alloy, nickel iron, vanadium, molybdenum, copper, silver, manganese, platinum group elements, graphite, or chromium, etc., or combinations thereof can be cited. The conductive substrate can be either a rigid substrate or a flexible substrate. As a rigid conductive substrate, for example, stretched metal mesh, punched metal mesh, etc. can be cited. As a flexible conductive substrate, for example, a metal mesh woven (or braided) from metal wires can be cited. As the method and amount of supporting the tungsten oxide of the present invention on the conductive substrate, as long as the tungsten oxide of the present invention can contact the electrolyte and function as a catalyst, there is no particular limitation. For example, as the supporting method, methods of covering all or part of the surface of the conductive substrate, attaching to all or part of the surface of the conductive substrate, etc. can be cited. As the cathode in the present invention, any substrate that can be used in the electrodes of electrolysis is acceptable, and there is no particular limitation. Generally, it has a conductive substrate and a catalyst layer supported on the surface of the substrate. As the conductive substrate, any substrate that can be used in the electrodes of electrolysis is acceptable, and there is no particular limitation. For example, nickel, nickel alloy, stainless steel, low-carbon steel, or a substrate obtained by nickel plating on the surface of stainless steel or low-carbon steel can be cited. The conductive substrate can be either a rigid substrate or a flexible substrate. As a rigid conductive substrate, for example, stretched metal mesh, punched metal mesh, etc. can be cited. As a flexible conductive substrate, for example, a metal mesh woven (or braided) from metal wires can be cited. As the catalyst layer of the cathode, a catalyst layer formed of a noble metal or noble metal oxide, nickel, cobalt, molybdenum, or manganese, or their oxides, etc. can be cited. In the anode chamber and cathode chamber of the present invention, the above-mentioned anode and cathode are respectively arranged.

[0056] In the electrolytic cell of the present invention, water containing an electrolyte is supplied to the anode chamber and the cathode chamber for electrolysis. Oxygen is generated in the anode chamber, and hydrogen is generated in the cathode chamber. Figure 26This is a diagram schematically showing the structure of the electrolytic cell of the present invention. Tungsten oxide of the present invention is supported on the anode. The left side of the diaphragm is the anode chamber, and the right side is the cathode chamber. The anode is disposed in the anode chamber, and the cathode is disposed in the cathode chamber. In Figure 26 , the anode and the cathode are respectively disposed at the ends of the anode chamber and the cathode chamber, but they may also be disposed at positions other than the ends, such as near the center. Water containing NaCl and KOH is supplied to the anode chamber, and water containing NaCl is supplied to the cathode chamber. The diaphragm is an anion-permeable membrane, and OH - moves from the cathode chamber to the anode chamber. Oxygen is generated near the anode, and hydrogen is generated near the cathode. The electrolytic cell of the present invention can be used to supply an alkaline brine to the anode chamber and a brine to the cathode chamber to electrolyze the brine. Here, the alkali is a compound that is dissolved in water to be alkaline, and examples thereof include hydroxides of alkali metals and hydroxides of alkaline earth metals. In Figure 26 , an example of using KOH as the alkali is shown, but in addition to KOH, for example, NaOH, LiOH, CsOH, etc. can also be used. In addition, brine refers to an aqueous solution containing NaCl. The electrolytic cell of the present invention can also perform alkaline water electrolysis or alkaline brine electrolysis. In the alkaline water electrolysis, water containing no NaCl but containing an alkali is supplied to the anode chamber and the cathode chamber to electrolyze the supplied water. In the alkaline brine electrolysis, water containing NaCl and an alkali is supplied as described above to electrolyze the supplied water.

[0057] In addition, as another form of the electrolytic cell of the present invention, a gas diffusion layer for supplying carbon dioxide to the cathode may be provided in addition to the anode chamber, the diaphragm, and the cathode chamber to perform reduction of carbon dioxide. Figure 27 This is a diagram schematically showing the structure of such an electrolytic cell. Tungsten oxide of the present invention is supported on the anode. In Figure 27 , a composite cathode is composed of a cathode, a carbon dioxide reduction catalyst on the cathode surface, and an anion exchange membrane. A gas diffusion layer is provided on the side of the cathode opposite to the side facing the anode. Carbon dioxide reaches the cathode and the catalyst on the cathode through the gas diffusion layer, and carbon dioxide is reduced to carbon monoxide. An aqueous KOH solution is supplied to the anode chamber, and oxygen is generated near the anode. In this embodiment, the composite cathode also serves as the cathode chamber. Through the electrolytic cell of the present invention, it is possible to perform reduction of carbon dioxide by electrolysis while performing alkaline water electrolysis, that is, it is possible to perform alkaline water CO2 electrolysis. In addition, as another form of the electrolytic cell of the present invention, in addition to the anode chamber, the diaphragm, and the cathode chamber, a carbon dioxide introduction portion for introducing carbon dioxide into contact with the cathode may be provided on the side of the cathode chamber opposite to the side facing the anode chamber, and reduction of carbon dioxide is performed in the carbon dioxide introduction portion. Figure 28 This is a diagram schematically showing the structure of such an electrolytic cell. InFigure 28 In this case, an anodic chamber is provided on the left side of the diaphragm, a cathodic chamber is provided on the right side, and a carbon dioxide introduction part is provided on the right side of the cathodic chamber, that is, on the side opposite to the side facing the anodic chamber of the cathodic chamber. The carbon dioxide introduced here contacts the cathode and is reduced to carbon monoxide. As the carbon dioxide introduction part, any structure capable of introducing carbon dioxide so that the carbon dioxide contacts the cathode is acceptable, and there is no particular limitation. For example, a structure for providing a passage for carbon dioxide to flow, a structure for providing a gas diffusion layer, etc. can be cited. Water containing NaCl and NaOH is supplied to the anodic chamber, and water containing NaCl is supplied to the cathodic chamber. Oxygen is generated near the anode carrying the tungsten oxide of the present invention, and hydrogen is generated near the cathode. Through the electrolytic cell of the present invention, carbon dioxide can be reduced by electrolysis while electrolyzing alkaline brine, that is, alkaline brine CO2 electrolysis can be carried out. Figure 27 and Figure 28 The electrolytic cell and the electrolysis method using them utilize the excellent activity of the tungsten oxide catalyst of the present invention for the oxygen evolution reaction, and improve the activity of the entire reaction system by means of the driving force brought by the oxygen evolution reaction to activate the carbon dioxide reduction reaction. Above, an example of reducing carbon dioxide to carbon monoxide is given as an example, but the present invention is not limited thereto. For example, as other substances generated by reducing carbon dioxide, carbon compounds such as formic acid (HCOOH), methane (CH4), methanol (CH3OH), ethane (C2H6), ethylene (C2H4), ethanol (C2H5OH), formaldehyde (HCH), acetaldehyde (CH3CHO), acetic acid (CH3COOH), ethylene glycol (HOCH2CH2OH), and 1-propanol (CH3CH2CH2OH) can be cited.

[0058] Examples

[0059] The present invention will be described below through examples, but the present invention is not limited to these specific embodiments.

[0060] [Example 1]

[0061] Put 25 mL of diethylene glycol into a beaker, add hydrochloric acid diluted with distilled water, and adjust the pH to 5.5. Heat the solution with the adjusted pH to 70 °C, add 0.63 g of nickel(II) acetate tetrahydrate and 0.48 g of iron(II) acetate thereto, and stir strongly with a stir bar until homogeneous. Transfer the solution in the beaker to a four-necked flask, add a solution prepared by dissolving 1.67 g of sodium tungstate dihydrate in 2.5 mL of distilled water, and raise the temperature to 220 °C over 15 - 20 minutes. Reflux the solution at 220 °C for 1 hour while stirring strongly. After refluxing, allow it to cool naturally to room temperature. Add acetic acid and ethanol to the obtained mixed solution, perform centrifugation multiple times, and then add only distilled water and perform centrifugation multiple times. Dry the residue under vacuum at room temperature for 5 hours to obtain tungsten oxide (p-Ni 0.5 Fe 0.5 WO4) combined with nickel and iron in a ratio of 5:5.

[0062] [Example 2]

[0063] Except that the amount of nickel(II) acetate tetrahydrate added was set to 0.25 g and the amount of iron(II) acetate was set to 0.70 g, tungsten oxide (p-Ni 0.2 Fe 0.8 WO4) combined with nickel and iron in a ratio of 2:8 was obtained by the same method as in Example 1.

[0064] [Example 3]

[0065] Except that the amount of nickel(II) acetate tetrahydrate added was set to 1.0 g and the amount of iron(II) acetate was set to 0.18 g, tungsten oxide (p-Ni 0.8 Fe 0.2 WO4) combined with nickel and iron in a ratio of 8:2 was obtained by the same method as in Example 1.

[0066] [Example 4]

[0067] Place 25 mL of distilled water in a beaker, heat it to 70 °C, and add 0.11 g of nickel(II) hexahydrate and 0.09 g of iron(II) tetrahydrate thereto. Adjust the solution to pH 5.5 with an aqueous sodium hydroxide solution and stir it with a stir bar for 10 minutes. Then, add a solution prepared by dissolving 0.3 g of sodium tungstate dihydrate in 10 mL of distilled water to the stirred solution and stir for another 10 minutes. Transfer the solution in the beaker to a Teflon (registered trademark) container and heat it in an autoclave at 180 °C for 24 hours. After heating, allow it to cool naturally to room temperature. Add ethanol to the obtained mixed solution, perform centrifugation multiple times, and then add only distilled water and perform centrifugation multiple times. Dry the residue in vacuo at 60 °C for 12 hours to obtain tungsten oxide (h-Ni 0.5 Fe 0.5 WO4) in which nickel and iron are combined in a ratio of 5:5.

[0068] [Comparative Example 1]

[0069] Place 25 mL of diethylene glycol in a beaker, add hydrochloric acid diluted with distilled water, and adjust the pH to 5.5. Heat the solution with adjusted pH to 70 °C, add 0.97 g of iron(II) acetate thereto, and stir strongly with a stir bar until homogeneous. Transfer the solution in the beaker to a four-necked flask, add a solution prepared by dissolving 1.67 g of sodium tungstate dihydrate in 2.5 mL of distilled water, and heat it to 220 °C over 15 - 20 minutes. Reflux the solution at 220 °C for 1 hour while stirring strongly. After refluxing, allow it to cool naturally to room temperature. Add acetic acid and ethanol to the obtained mixed solution, perform centrifugation multiple times, and then add only distilled water and perform centrifugation multiple times. Dry the residue in vacuo at room temperature for 5 hours to obtain wolframite-type tungsten oxide (FeWO4) combined with iron.

[0070] [Comparative Example 2]

[0071] Place 25 mL of diethylene glycol in a beaker, add hydrochloric acid diluted with distilled water to adjust the pH to 5.5. Heat the solution with adjusted pH to 70 °C, add 1.26 g of nickel(II) acetate tetrahydrate thereto, and stir strongly with a stir bar until homogeneous. Transfer the solution in the beaker to a four-necked flask, add a solution prepared by dissolving 1.67 g of sodium tungstate dihydrate in 2.5 mL of distilled water, and heat it to 220 °C over 15 - 20 minutes. Reflux the solution at 220 °C for 1 hour while stirring strongly. After refluxing, allow it to cool naturally to room temperature. Add acetic acid and ethanol to the obtained mixed solution, perform centrifugation multiple times, and then add only distilled water and perform centrifugation multiple times. Dry the residue in vacuo at room temperature for 5 hours to obtain wolframite-type tungsten oxide (NiWO4) combined with nickel.

[0072] [Comparative Example 3]

[0073] WO3 (purity 95.0%, Wako Pure Chemical Industries, Ltd.) was prepared as the sample for Comparative Example 3.

[0074] [Comparative Example 4]

[0075] RuO2 (purity 99.9%, Sigma-Aldrich) was prepared as the sample for Comparative Example 4.

[0076] [Comparative Example 5]

[0077] IrO2 (purity 99% (99.9+%-Ir), Strem Chemicals) was prepared as the sample for Comparative Example 5.

[0078] [Comparative Example 6]

[0079] 25 mL of diethylene glycol was placed in a beaker, and hydrochloric acid diluted with distilled water was added to adjust the pH to 5.5. The solution with the adjusted pH was heated to 70 °C, 0.63 g of nickel(II) acetate tetrahydrate and 0.48 g of iron(II) acetate were added thereto, and the mixture was strongly stirred with a stirring rod until homogeneous. The solution in the beaker was transferred to a four-necked flask and heated to 220 °C over 15 - 20 minutes. The solution was refluxed at 220 °C for 1 hour while being strongly stirred. After refluxing, it was naturally cooled to room temperature. Acetic acid and ethanol were added to the obtained mixed solution, and after centrifuging multiple times, only distilled water was added and centrifuged multiple times. The residue was vacuum dried at room temperature for 5 hours to obtain nickel-iron oxide (p-NiFe oxide).

[0080] The samples obtained in the Examples and Comparative Examples were evaluated by the following methods.

[0081] (X-ray diffraction (XRD))

[0082] The XRD pattern was measured with an X-ray diffractometer (Rigaku Ultima4) using CuKα radiation (40 kV, 40 mA).

[0083] (Linear sweep voltammetry (LSV))

[0084] 5 mg of each sample and 5 mg of acetylene black (conductive carbon) were added to a mixed solution containing 350 μL of ethanol, 350 μL of water, and 95 μL of perfluorosulfonic acid resin (Nafion), and ultrasonic dispersion treatment was performed for 60 minutes. 10 μL of the obtained dispersion was dropped onto a disk electrode polished with alumina (diameter 5 mm) (amount of active material: 0.32 mg). Then, the disk electrode was dried at room temperature in air and used as the working electrode. A three-electrode cell was used, a platinum mesh was used as the counter electrode, and Hg / HgO (1 M NaOH) was used as the reference electrode. 1 M KOH after purging with N2 for 30 minutes was used as the electrolyte. The scan rate was 1 mV / s, and the rotation speed was set to 1600 rpm in order to remove oxygen bubbles on the working electrode. The resistance of the solution generated between the working electrode and the reference electrode was compensated at a feedback rate of 60%. Since protons are generated in the oxygen evolution reaction, the pH of the electrolyte becomes smaller and the oxygen evolution potential changes. By converting to the reversible hydrogen electrode (RHE), the influence of pH can be eliminated. In the conversion, the formula E RHE = 0.059 × 14 + 0.123 + E Hg / HgO . The pH is 14.

[0085] (Cyclic Voltammetry)

[0086] 5 mg of each sample and 5 mg of acetylene black (conductive carbon) were added to a mixed solution containing 350 μL of ethanol, 350 μL of water, and 95 μL of perfluorosulfonic acid resin (Nafion), and ultrasonic dispersion treatment was performed for 60 minutes. 10 μL of the obtained dispersion was dropped onto a disk electrode polished with alumina (diameter 5 mm) (amount of active material: 0.32 mg). Then, the disk electrode was dried at room temperature in air and used as the working electrode. A three-electrode cell was used, a platinum mesh was used as the counter electrode, and Hg / HgO was used as the reference electrode. 1 M KOH after purging with N2 for 30 minutes was used as the electrolyte. The scan rate was set to 20 mV / s, and in the range where no Faraday reaction was observed, cycling was performed between 0 and +1 V (about 100 cycles).

[0087] (Durability Test (Chronopotentiometry; CP))

[0088] Add 5 mg of each sample and 5 mg of acetylene black (conductive carbon) to a mixed solution containing 350 μL of ethanol, 350 μL of water, and 95 μL of perfluorosulfonic acid resin (Nafion), and perform ultrasonic dispersion treatment for 60 minutes. Drop 10 μL of the obtained dispersion onto a disk electrode polished with alumina (diameter 5 mm) (amount of active material: 0.32 mg). Then, dry the disk electrode at room temperature in air and use it as the working electrode. Use a three-electrode cell, use a platinum mesh as the counter electrode, and use Hg / HgO as the reference electrode. Use 1 M KOH after purging with N2 for 30 minutes for the electrolyte. Maintain a constant current density of 10 mA / cm 2 for 24 hours. Similar to linear sweep voltammetry, rotate the working electrode at a speed of 1600 rpm.

[0089] Shown in Figure 1 are the XRD patterns of the samples obtained in Example 1 and Comparative Example 2. Figure 1 The Ni 0.5 Fe 0.5 WO4 in is the XRD pattern of the sample obtained in Example 1, and Ni 0.5 Fe 0.5 WO4cal is the XRD pattern of the sample obtained in Example 1 after heating in air at 600 °C for 3 hours. In addition, Figure 1 The NiWO4 in is the XRD pattern of the sample obtained in Comparative Example 2, and NiWO4cal is the XRD pattern of the sample obtained in Comparative Example 2 after heating at 600 °C for 3 hours. Both samples became a typical wolframite crystal structure after heating at 600 °C. Therefore, the obtained samples can be said to be wolframite precursors or wolframite with the same composition but lower crystallinity, and can be said to be substances with the same wolframite composition and insufficient crystallization progress. Figure 2 Shows the XRD patterns of the samples obtained in Examples 1 to 3 and Comparative Examples 1 and 2. From top to bottom are Comparative Example 1 (FeWO4), Example 2 (p-Ni 0.2 Fe 0.8 WO4), Example 1 (p-Ni 0.5 Fe 0.5 WO4), Example

[0090] 3 (p-Ni 0.8 Fe 0.2 WO4), and Comparative Example 2 (NiWO4) XRD patterns. The samples obtained in Examples 2 and 3 also showed the same XRD patterns as the sample obtained in Example 1.

[0091] Shown in Figure 3 are the linear sweep voltammograms of the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 4. FromFigure 3 It can be seen that a sharp increase in current can be observed in the specimens obtained in Examples 1 to 3, showing a catalytic activity far higher than that of RuO2 which has the highest catalytic performance for oxygen evolution.

[0092] In Figure 5 shows the XRD pattern of the specimen obtained in Example 4. Figure 5 The h-Ni 0.5 Fe 0.5 WO4 in 0.5 Fe 0.5 WO4cal in Figure 5 is the XRD pattern of the specimen obtained in Example 4 after heating the specimen obtained in Example 4 at 600 °C for 3 hours. "h-" is a symbol given to indicate that the specimen is obtained by hydrothermal synthesis. In addition, for the specimens obtained in Examples 1 to 3, the symbol "p-" is sometimes given to indicate that they are obtained by the polyol method. From Figure 6 shows the linear sweep voltammograms of the specimens obtained in Examples 1 and 4 and Comparative Examples 1, 2, and 4. From Figure 6 It can be seen that a sharp increase in current can be observed in the specimens obtained in Examples 1 and 4, reaching 10 mA / cm 2 or 100 mA / cm 2 with a lower overvoltage required, showing a catalytic activity far higher than that of RuO2 which has the highest catalytic performance for oxygen evolution. In addition, the specimen of Example 1 synthesized by the polyol method shows a more rapid increase than the specimen of Example 4 synthesized by hydrothermal synthesis.

[0093] To analyze Figure 3 and Figure 6 the rising parts, Tafel curves were made. In Figure 4 shows a curve with the common logarithm of the current density in Figure 3 as the horizontal axis and the difference (overvoltage) from the standard potential of 1.23 V for hydrogen oxidation as the vertical axis. In addition, in Figure 7 shows a curve plotted in the same manner as in Figure 6 . Table 1 shows the parameters calculated based on Figure 3 and Figure 4 and Figure 6 and Figure 7 (the initial overvoltage is defined as Figure 4 or Figure 7 the end point on the low potential side of the linear region). The Tafel slope is based onFigure 4 or Figure 7 The overlapping parts of the curves and straight lines Figure 7 are calculated, and approximated using the Tafel formula [η = a + b·log(j)]. Here, a is the Tafel constant, b is the Tafel slope, and j is the current density. The specimens obtained in Examples 1 to 4 showed an onset overvoltage comparable to that of RuO2 (Comparative Example 4), and the overvoltage at a current density of 10 mA / cm 2 was lower than that of the RuO2 (Comparative Example 4) specimen. Furthermore, the Tafel slope was also smaller than that of the RuO2 (Comparative Example 4) specimen. The Tafel slope is the potential difference required for the current value to become 10 times, and the smaller the value, the faster the reaction rate, indicating higher activity, which represents the rate of electron transfer during hydrogen oxidation. The results in Table 1 showed that the specimens obtained in Examples 1 to 4 had a significantly faster reaction rate compared to the RuO2 (Comparative Example 4) and the specimens obtained in other comparative examples. Figure 8 is a graph showing the overvoltage at a current density of 10 mA / cm 2 for Examples 1 to 3 and Comparative Examples 1 and 2, showing that the overvoltage decreased significantly after combining nickel and iron compared to the cases of combining nickel alone and combining iron alone. Figure 9 is from Figure 3 a linear sweep voltammogram that only extracts the results of Examples 1 to 3 and Comparative Examples 1 and 2.

[0094] [Table 1]

[0095]

[0096]

[0097] Next, the reaction surface area (electrochemical active surface area: ECSA) of the specimens obtained in Examples 1 to 4 and Comparative Examples 1, 2, and 6 was determined. For this purpose, the electrochemical double-layer capacitance (Cdl) proportional to the ECSA was calculated for each specimen by cyclic voltammetry (CV). Figure 10 is a graph showing the CV measurement results of the specimen obtained in Example 4. The potential range of the CV was set to 0 to 0.1 V in the range where no Faraday reaction was observed. Cdl was calculated from the relationship curve ( Figure 11 ) between the difference Δj between the cathodic current and the anodic current and the scan rate of each specimen at a specific potential (0.05 V vs Hg / HgO). The slope of the approximate straight line obtained from the graph corresponds to Cdl. ECSA was calculated according to the formula ECSA = Cdl / Cs. Here, Cs is the specific capacitance per unit area of the sample under the same electrolyte conditions or the capacitance of a smooth surface at the atomic level of the material. Cs was taken as the typical value of 0.040 mF / cm in 1.0 M KOH 2The calculated Cdl and ECSA are shown in Table 2. It can be seen that a catalyst with a very large ECSA was obtained in Example 4. The magnitude of the current obtained using the catalyst is considered to be determined by the product of (i) the intrinsic reaction rate of the active sites and (ii) the number of active sites (i.e., the size of the electrochemically available area). (i) is reflected by the Tafel slope and (ii) is reflected by the ECSA. Therefore, a large ECSA will improve the catalytic activity. In addition, although the ECSA of the catalysts obtained in Examples 1 to 3 is smaller than that of other catalysts, due to the small Tafel slope and fast intrinsic reaction rate, they have excellent catalytic activity.

[0098] [Table 2]

[0099] <![CDATA[Cdl(mF / cm 2 )]]> <![CDATA[ECSA(m 2 / g)]]> <![CDATA[Example 1 (p-Ni 0.5 Fe 0.5 WO4)]]> 0.87 6.77 <![CDATA[Example 2 (p-Ni 0.2 Fe 0.8 WO4)]]> 0.83 6.46 <![CDATA[Example 3 (p-Ni 0.8 Fe 0.2 WO4)]]> 1.11 8.67 <![CDATA[Example 4 (h-Ni 0.5 Fe 0.5 WO4)]]> 1.45 11.33 <![CDATA[Comparative Example 1 (FeWO4)]]> 0.942 7.36 <![CDATA[Comparative Example 2 (NiWO4)]]> 1.04 8.13 Comparative Example 6 (p-NiFe oxide) 1.39 10.86

[0100] For Examples 1 to 4 and Comparative Examples 1, 2, and 6, the turnover frequency (TOF) was calculated by the following formula. The results are shown in Table 3 and Figure 12 in.

[0101] TOF = [Current density (A cm -2 ) × Electrode surface area (cm 2 )] / [4 × F (96485 C mol -1 ) × Total number of moles of transition metal of the catalyst on the electrode (mol)]

[0102] [Table 3]

[0103] <![CDATA[TOF at 0.4V (s －1 )]]> <![CDATA[Example 1 (p-Ni 0.5 Fe 0.5 WO4)]]> 0.425 <![CDATA[Example 2 (p-Ni 0.2 Fe 0.8 WO4)]]> 0.238 <![CDATA[Example 3 (p-Ni 0.8 Fe 0.2 WO4)]]> 0.106 <![CDATA[Example 4 (h-Ni 0.5 Fe 0.5 WO4)]]> 0.072 <![CDATA[Comparative Example 1 (FeWO4)]]> 0.001 <![CDATA[Comparative Example 2 (NiWO4)]]> 0.020 Comparative Example 6 (p-NiFe oxide) 0.057

[0104] In Figure 13 shows the results of the durability test on p-Ni 0.5 Fe 0.5 WO4 obtained in Example 1, h-Ni 0.5 Fe 0.5 WO4 obtained in Example 4, FeWO4 obtained in Comparative Example 1, NiWO4 obtained in Comparative Example 2, and IrO2 (manufactured by Strem Chemicals, 99% (99.9+%-Ir)) of Comparative Example 5. For FeWO4, the potential increased sharply after about 3 hours from the start of the test. In addition, peeling of the catalyst film from the substrate was observed. This phenomenon is considered to be due to the formation of FeO4 at high potentials 2-It is caused by the oxidation and dissolution of []. For NiWO4, the potential increased after about 4.5 hours from the start of the test, and increased sharply after about 6 hours. In the observation of the catalyst film, after about 4.5 hours, oxygen bubbles were visually confirmed to adhere to the catalyst surface, and a part of the catalyst film peeled off from the substrate. Then, after about 6 hours, further peeling of the catalyst film was observed. This indicates that the catalyst film was physically damaged by the generation of oxygen bubbles on the catalyst surface. For IrO2, the overvoltage increased by nearly 1.0 V compared to the initial potential in 24 hours. Considering this is the result of the increased diffusion resistance of the reactant (H2O) and the product (O2). For p-Ni 0.5 Fe 0.5 WO4 and h-Ni 0.5 Fe 0.5 WO4, no increase in potential was observed in 24 hours, showing excellent long-term durability. Considering this is because it operates continuously at a potential about 170 mV lower than FeWO4, so oxidation to FeO4 did not occur 2- . Thus, the tungsten oxide of the present invention has excellent durability as a catalyst. In Figure 14 , the results of cyclic tests are shown in the same way as the above durability test using a three-electrode cell, using 1M KOH cleaned with N2 for 30 minutes in the electrolyte, and at 20 mV s -1 . The three-electrode cell uses a working electrode made of p-Ni 0.5 Fe 0.5 WO4 prepared in Example 1, uses a platinum mesh as the counter electrode, and uses Hg / HgO as the reference electrode. As Figure 14 shown, the current response hardly changed after the first cycle and 400 cycles. In addition, it was also shown that the physical damage of the catalyst film was suppressed by the rapid diffusion of the generated oxygen. Table 4 shows the values of the potential at 10 mA / cm 0.5 Fe 0.5 WO4, h-Ni 0.5 Fe 0.5 WO4 and IrO2 in LSV and the holding potential at 10 mA / cm 2 in CP. 2

[0105] [Table 4]

[0106]

[0107] In Figure 15 , Figure 16 , Figure 17 , the p-Ni prepared in Example 1 is shown respectively 0.5 Fe 0.5WO4, the sample after heating it at 600 °C for 3 hours, and the XRD patterns, linear sweep voltammograms and Tafel curves of p-NiFe oxide prepared in Comparative Example 6. For p-Ni 0.5 Fe 0.5 WO4, the sample after heating it at 600 °C for 3 hours (p-Ni 0.5 Fe 0.5 WO4cal) exhibits a wolframite phase, while the unheated sample exhibits an underdeveloped wolframite phase. In addition, p-NiFe oxide exhibits a trevorite phase, which is assigned to Ni 1.43 Fe 1.7 O4 according to the Rigaku database. For the sample of p-Ni 0.5 Fe 0.5 WO4 prepared in Example 1 after heating it at 600 °C for 3 hours, the catalytic activity for oxygen evolution is not very high. In Figure 18 、 Figure 19 、 Figure 20 are shown the XRD patterns, linear sweep voltammograms and Tafel curves of p-Ni 0.5 Fe 0.5 WO4 prepared in Example 1, the sample after heating it at 300 °C for 3 hours, the sample after heating it at 450 °C for 3 hours, and the sample after heating it at 600 °C for 3 hours. Not only for the unheated sample (untreated), but also for the samples after heating at 300 °C and 450 °C, a sharp increase in current is observed, indicating excellent catalytic activity for oxygen evolution. The crystallite size of each sample was calculated using the following Scherrer formula.

[0108] Crystallite size = Kλ / (βcosθ)

[0109] (In the above formula, K is the Bragg constant (= 0.9), λ is the wavelength of the X-ray used (CuKα radiation: ), β is the full width at half maximum of the 30° peak, and θ is the Bragg angle (half of the diffraction angle 2θ)

[0110] As a result, for the crystallite size of p-Ni 0.5 Fe 0.5 WO4, the unheated sample is 5.0 nm, the sample after heat treatment at 300 °C is 6.4 nm, the sample after heat treatment at 450 °C is 13.0 nm, and the sample after heat treatment at 600 °C is 16.8 nm. The tungsten oxide of the present invention is preferably a low-crystalline wolframite or a wolframite precursor that becomes wolframite upon heat treatment.

[0111] [Example 5]

[0112] 5 mg of p-Ni prepared in Example 1 0.5 Fe 0.5 WO4 sample and 5 mg of acetylene black (conductive carbon) were added to a mixed solution containing 350 μL of ethanol, 350 μL of water, and 95 μL of perfluorosulfonic acid resin (Nafion), and ultrasonic dispersion treatment was carried out for 60 minutes. 10 μL of the obtained dispersion was dropped onto a polished alumina disk electrode (diameter 5 mm) (amount of active material: 0.32 mg). Then, the disk electrode was dried at room temperature in air and used as the working electrode. A three-electrode cell was used, with a platinum mesh as the counter electrode and Hg / HgO as the reference electrode. In the electrolyte, 0.5 M aqueous NaCl solution, aqueous solution containing 0.5 M NaCl and 0.1 M NaOH (+0.1 M NaOH), aqueous solution containing 0.5 M NaCl and 0.5 M NaOH (+0.5 M NaOH), aqueous solution containing 0.5 M NaCl and 1.0 M NaOH (+1.0 M NaOH), and aqueous solution containing 0.5 M NaCl and 0.1 M borate buffer were used respectively. 1 M KOH washed with N2 for 30 minutes was used. The scan rate was set at 1 mV / s, and the rotation speed was set at 1600 rpm to remove oxygen bubbles on the working electrode. The resistance of the solution generated between the working electrode and the reference electrode was compensated at a feedback rate of 60%. Since protons are generated in the oxygen evolution reaction, the pH of the electrolyte decreases and the oxygen evolution potential changes. By converting to a reversible hydrogen electrode (RHE), the influence of pH can be eliminated. In the conversion, the formula E RHE = 0.059×14 + 0.123 + E Hg / HgO was used. The obtained linear sweep voltammogram (LSV) is shown in Figure 21 In addition, the expressions in the brackets following the description of the above aqueous solution represent Figure 21 the expressions in

[0113] [Example 6]

[0114] In Example 5, 0.5 M aqueous NaClO4 solution, aqueous solution containing 0.5 M NaClO4 and 0.1 M NaOH (+0.1 M NaOH), aqueous solution containing 0.5 M NaClO4 and 0.5 M NaOH (+0.5 M NaOH), aqueous solution containing 0.5 M NaClO4 and 1.0 M NaOH (+1.0 M NaOH), and aqueous solution containing 0.5 M NaClO4 and 0.1 M borate buffer were used as the electrolytes respectively. Except for this, the same operations and treatments as in Example 5 were carried out. The obtained linear sweep voltammogram (LSV) is shown in Figure 22In addition, the notations in parentheses following the description of the above aqueous solution indicate Figure 22 the expressions in

[0115] The Tafel slope and the overpotential (η) at 10 mA / cm 2 were studied in Examples 5 and 6. The pH value of the 0.5 M NaCl aqueous solution in Example 5 was 5, the pH value of the aqueous solution containing 0.5 M NaCl and 0.1 M NaOH was 13, the pH value of the aqueous solution containing 0.5 M NaCl and 0.5 M NaOH was 13.5, the pH value of the aqueous solution containing 0.5 M NaCl and 1.0 M NaOH was 14, and the pH value of the aqueous solution containing 0.5 M NaCl and 0.1 M borate buffer was 9. The pH value of the 0.5 M NaClO4 aqueous solution in Example 6 was 5, the pH value of the aqueous solution containing 0.5 M NaClO4 and 0.1 M NaOH was 13, the pH value of the aqueous solution containing 0.5 M NaClO4 and 0.5 M NaOH was 13.5, the pH value of the aqueous solution containing 0.5 M NaClO4 and 1.0 M NaOH was 14, and the pH value of the aqueous solution containing 0.5 M NaClO4 and 0.1 M borate buffer was 9. In Figure 23 are shown the Tafel slope and the overpotential (η) at 10 mA / cm 2 for each pH.

[0116] [Comparative Example 7]

[0117] In Example 5, except that IrO2 of Comparative Example 5 was used instead of p-Ni 0.5 Fe 0.5 WO4, the same operations and treatments as in Example 5 were carried out. The obtained linear sweep voltammogram (LSV) is shown in Figure 24 below.

[0118] [Comparative Example 8]

[0119] In Example 6, except that IrO2 of Comparative Example 5 was used instead of p-Ni 0.5 Fe 0.5 WO4, the same operations and treatments as in Example 6 were carried out. The obtained linear sweep voltammogram (LSV) is shown in Figure 25 below.

[0120] The 0.5 M NaCl aqueous solution in Example 5 is an aqueous solution simulating seawater. According to Figure 21It can be seen that by adding an alkali to an aqueous solution of 0.5 M NaCl, a sharp increase in current can be observed for the tungsten oxide of the present invention, indicating high catalytic activity for oxygen evolution. Therefore, the tungsten oxide of the present invention is excellent as a catalyst for the oxygen evolution reaction in alkaline seawater electrolysis. In addition, in an electrolytic cell in which the tungsten oxide of the present invention is supported on the anode as a catalyst, since the oxygen evolution reaction at the anode is vigorous, the hydrogen evolution reaction at the cathode is also vigorous. Therefore, it is excellent as an electrolytic cell for hydrogen evolution by alkaline seawater electrolysis. In Example 6 Figure 22 it can also be seen that by adding an alkali to an aqueous solution of 0.5 M NaClO4, a sharp increase in current can be observed, indicating high catalytic activity for oxygen evolution. In Example 6, since an aqueous solution of NaClO4 is used, there are no chloride ions in the aqueous solution and no chlorine gas (Cl2) is generated. The LSV in Example 5 is almost the same as that in Example 6, indicating that almost no chlorine gas is generated in Example 5 where chloride ions are present in the aqueous solution.

[0121] Furthermore, using the p-Ni 0.5 Fe 0.5 WO4 electrode used in Example 5, a constant current electrolysis was carried out at 10 mA / cm 2 until the charge passed reached 40 C / cm 2 (= 10 mA / cm 2 × 4000 s). The residual chlorine concentration of the test solution after electrolysis was measured by a general iodine titration method. Potassium iodide was added to the test solution after electrolysis, and the free iodine was titrated with a sodium thiosulfate solution for measurement. The Faraday efficiency of chlorine evolution (chlorine evolution efficiency) was determined by the following formula.

[0122] Faraday efficiency of chlorine evolution (%) = ([Cl2] × V) / {Q / (nF)} × 100

[0123] (In the above formula, n is the number of electrons involved (= 2) (2Cl - → Cl2 + 2e - ), V is the volume of the test solution, Q is the charge passed, and F is the Faraday constant (= 96,485 C / mol)).

[0124] As a result, the Faraday efficiency of chlorine evolution is 16% in the case of 0.5 M aqueous NaCl solution, 0.3% in the case of an aqueous solution containing 0.5 M NaCl and 0.1 M NaOH, 0.2% in the case of an aqueous solution containing 0.5 M NaCl and 0.5 M NaOH, 0.1% in the case of an aqueous solution containing 0.5 M NaCl and 1.0 M NaOH, and 0.3% in the case of an aqueous solution containing 0.5 M NaClO4 and 0.1 M borate buffer; the results also show that if the tungsten oxide of the present invention is used as a catalyst, oxygen can be generated while suppressing the generation of chlorine, which is a toxic gas, in the electrolysis of brine such as seawater. In addition, using the IrO2 electrode used in Comparative Example 7, by the same test method and measurement method as in the case of the p-Ni 0.5 Fe 0.5 WO4 electrode, the residual chlorine concentration of the test solution after electrolysis was measured. As a result, the chlorine evolution efficiency was 47% in the case of 0.5 M aqueous NaCl solution, 0.6% in the case of an aqueous solution containing 0.5 M NaCl and 0.1 M NaOH, 0.5% in the case of an aqueous solution containing 0.5 M NaCl and 0.5 M NaOH, 0.1% in the case of an aqueous solution containing 0.5 M NaCl and 1.0 M NaOH, and 0.6% in the case of an aqueous solution containing 0.5 M NaCl and 0.1 M borate buffer. From these results, it can be seen that if the tungsten oxide of the present invention is used as a catalyst, the generation of chlorine during oxygen evolution can be suppressed compared to the case of using IrO2, which has been used as a catalyst showing high activity for the oxygen evolution reaction in the past.

[0125] In addition, Figure 23 shows that when the tungsten oxide of the present invention is used as a catalyst, it has a high oxygen evolution reaction activity at pH 9 or higher, 10 or higher, 11 or higher, 12 or higher, or 13 or higher. Comparative Examples 7 and 8 are examples of using IrO2, which has been used as a catalyst showing high activity for the oxygen evolution reaction in the past, and their results are shown in Figure 24 and Figure 25 . Comparing Figure 21 and Figure 22 , which are the results of using the tungsten oxide of the present invention, with Figure 24 and Figure 25 , which are the results of using IrO2, it can be seen that compared with IrO2, the tungsten oxide of the present invention has a smaller overvoltage to reach 60 mA / cm 2 at pH 13 or higher and has excellent activity compared to the IrO2 catalyst in alkaline seawater (brine) electrolysis.

[0126] Industrial Applicability

[0127] The tungsten oxide of the present invention can be suitably used as a catalyst for the oxygen evolution reaction in electrolysis (electrolytic decomposition), batteries, etc. For example, it can be used for the anode in water electrolysis, the air electrode (positive electrode) in metal-air batteries, the counter electrode for the reduction reaction in carbon dioxide electrolysis, etc. In the case of water electrolysis, it can also be suitably used as a catalyst for electrolysis such as alkaline water electrolysis, alkaline seawater (brine) electrolysis, alkaline CO2 electrolysis, alkaline CO2 seawater (brine) electrolysis, etc. In addition, since the electrolytic cell of the present invention includes the tungsten oxide of the present invention as a catalyst, it can be suitably used as an electrolytic cell in various electrolyses such as water electrolysis. For example, it can be preferably used as an electrolytic cell for electrolysis such as alkaline water electrolysis, alkaline seawater (brine) electrolysis, alkaline CO2 electrolysis, alkaline CO2 seawater (brine) electrolysis, etc. The manufacturing method of the present invention is suitable as a method for manufacturing such tungsten oxide.

Claims

1. Use of tungsten oxide represented by Ni x Fe 1-x WO4 as a catalyst for oxygen evolution reaction used in an anode or a positive electrode, wherein, 0＜x＜1。 2. An anode or positive electrode of an oxygen evolution reaction catalyst carrying tungsten oxide represented by Ni x Fe 1-x WO4, wherein 0＜x＜1。 3. A method for manufacturing tungsten oxide uses Ni x Fe 1-x to manufacture tungsten oxide represented by WO4, where 0 < x < 1, wherein the tungsten oxide is synthesized under atmospheric pressure by dissolving a tungstate, a nickel salt, and an iron salt in a polyol and heating the polyol solution in which the above salts are dissolved.

4. An electrolytic cell includes an anode chamber and a cathode chamber partitioned by an ion-permeable membrane, an anode is disposed in the anode chamber, and a cathode is disposed in the cathode chamber, wherein, The anode is the anode described in claim 2.

5. The electrolytic cell according to claim 4, wherein, A gas diffusion layer for supplying carbon dioxide to the cathode is provided, and carbon dioxide reduction is carried out in the cathode chamber.

6. The electrolytic cell according to claim 4, wherein, A carbon dioxide introduction part for introducing carbon dioxide to contact the cathode is provided on the side of the cathode chamber opposite to the side facing the anode chamber, and carbon dioxide reduction is carried out in the carbon dioxide introduction part.

7. A method for electrolyzing brine, wherein, Brine containing an alkali is supplied to the anode chamber of the electrolytic cell described in claim 4, brine is supplied to the cathode chamber, and the brine is electrolyzed.

8. A method for electrolysis of brine and reduction of carbon dioxide, wherein, Brine containing an alkali is supplied to the anode chamber of the electrolytic cell described in claim 6, brine is supplied to the cathode chamber, carbon dioxide is introduced into the carbon dioxide introduction part, and the brine is electrolyzed and carbon dioxide reduction is carried out.

Images