Catalyst for oxygen generating water electrolysis electrode and water electrolysis method

Abstract

To provide a catalyst for an oxygen generating water electrolysis electrode, which is capable of suppressing the rise of overvoltage during electrolysis and can stably be used for a long period of time.SOLUTION: The catalyst for an oxygen generating water electrolysis electrode provided with a catalyst on an electrode substrate, contains at least one species of metal element M selected from the group consisting of Fe, Co, Ni, Mn, Cr, Cu and Zn and a composite oxide including Mo and V. The catalyst for an oxygen generating water electrolysis electrode according to the present invention can suppress the rise of overvoltage and can stably be used for a long period of time.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a catalyst for an oxygen generating electrode in water electrolysis and a method for electrolyzing water. [Background technology]

[0002] Currently, there are two main types of water electrolysis (methods for electrolyzing water) in practical use: alkaline water electrolysis, which uses a strong alkaline solution such as potassium hydroxide, and proton exchange membrane (PEM) water electrolysis, which uses pure water for electrolysis. The water used in these water electrolysis processes must undergo pretreatment processes, such as desalination, purification, deionization, and alkalinization, which increases production costs. In addition, conventional water electrolysis requires the use of expensive precious metal catalysts such as platinum and iridium, which also increases production costs.

[0003] To prevent the cost of water electrolysis from increasing, a method has been proposed that uses seawater, which is infinitely available on Earth, instead of alkaline solutions and does not require a precious metal catalyst. However, in seawater electrolysis, the chlorine evolution reaction (CER) is kinetically far more favorable than the oxygen evolution reaction (OER), resulting in the production of toxic and highly corrosive chlorine gas. Furthermore, as the current density increases, the large number of gas bubbles released tends to promote the exfoliation of the catalyst from the support material (electrode substrate), which can easily cause physical structural damage to the catalyst, resulting in rapid electrode degradation. Therefore, there is a strong demand for electrocatalysts with porous nanostructures and hydrophilic surfaces that can be used for seawater electrolysis.

[0004] For example, Patent Document 1 proposes a technology for using a new material, such as a sulfide or oxide of a transition metal (e.g., Co, Ni, Mn, etc.) having a nanosized fine structure, as an electrode catalyst for water electrolysis. Recently, non-noble metal-based electrode catalysts, such as transition metal chalcogenides, transition metal carbides, phosphides, phosphorus sulfides, nitrides, borides, and selenides, have been researched as electrode catalysts for water electrolysis, taking advantage of their unique physical and chemical properties. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-000470 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in recent years, there has been a strong demand for further improvement in electrocatalytic performance in order to increase the decomposition efficiency in water electrolysis. From this perspective, there is an urgent need to develop a water electrolysis catalyst that can reduce overpotential and can be used stably for a long period of time.

[0007] The present invention has been made in view of the above, and an object of the present invention is to provide a catalyst for an oxygen generating electrode in water electrolysis that can suppress an increase in overvoltage during electrolysis and can be used stably for a long period of time. [Means for solving the problem]

[0008] As a result of extensive research to achieve the above-mentioned object, the inventors discovered that the above-mentioned object can be achieved by using a high-entropy complex oxide containing a specific metal as a catalyst, and thus completed the present invention.

[0009] That is, the present invention includes, for example, the subject matter described in the following sections. Item 1 A catalyst for an oxygen generating electrode in water electrolysis, comprising a catalyst on an electrode substrate, The catalyst is At least one metal element M selected from the group consisting of Fe, Co, Ni, Mn, Cr, Cu, and Zn; Mo and V and A catalyst for an oxygen generating electrode in water electrolysis, comprising a composite oxide containing: Section 2 Item 2. The catalyst for an oxygen generating electrode in water electrolysis according to Item 1, wherein the composite oxide is an oxide containing Fe, Co, Ni, Mo, and V. Section 3 Item 3. The catalyst for an oxygen generating electrode in water electrolysis according to Item 1 or 2, wherein the composite oxide is in the form of microsphere particles. Section 4 Item 3. A method for electrolyzing water, comprising a step of performing electrolysis using the oxygen generating electrode catalyst according to Item 1 or 2. [Effects of the Invention]

[0010] The catalyst for an oxygen generating electrode in water electrolysis of the present invention can suppress an increase in overvoltage during water electrolysis and can be used stably for a long period of time. [Brief explanation of the drawings]

[0011] [Figure 1] 1 shows SEM images of catalyst portions in oxygen generating electrode catalysts obtained in Examples and Comparative Examples. [Figure 2] FIG. 1(a) is a measurement result of linear sweep voltammetry using the oxygen evolution electrode catalysts obtained in Examples 1 to 4 as electrodes, and FIG. 1(b) is a bar graph of the overvoltage measured in the measurement of FIG. 1(a). [Figure 3] (a) shows the results of linear sweep voltammetry measurements using the oxygen evolution electrode catalysts obtained in the examples and comparative examples as electrodes, (b) shows a bar graph of the overpotential measured in the measurement of (a), and (c) shows the Tafel slope calculated from the linear sweep voltammetry curve shown in (a). [Figure 4] FIG. 1 shows the measurement results of linear sweep voltammetry using the oxygen evolution electrode catalyst obtained in Example 1 as an electrode, and (b) is a bar graph of the overvoltage measured in the measurement of (a). [Figure 5] 1 shows the results of chronopotentiometry measurements using the oxygen evolution electrode catalyst obtained in Example 1 as an electrode. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0013] 1. Catalyst for oxygen evolution electrodes The present invention relates to a catalyst for an oxygen generating electrode for water electrolysis, which contains a high-entropy complex oxide. The catalyst for an oxygen generating electrode for water electrolysis of the present invention comprises a catalyst provided on an electrode substrate, and the catalyst contains a complex oxide containing Mo and V, as well as at least one metal element M selected from the group consisting of Fe, Co, Ni, Mn, Cr, Cu, and Zn. Hereinafter, in this specification, a complex oxide containing Mo and V, as well as at least one metal element M selected from the group consisting of Fe, Co, Ni, Mn, Cr, Cu, and Zn, will be referred to as a "high-entropy complex oxide" or simply as a "complex oxide."

[0014] The oxygen generating electrode catalyst for water electrolysis of the present invention (hereinafter simply referred to as "oxygen generating electrode catalyst") can be used for water electrolysis, can suppress an increase in overvoltage during water electrolysis, and can be used stably for a long period of time.

[0015] The oxygen generating electrode catalyst includes an electrode substrate. The type of the electrode substrate is not particularly limited, and examples thereof include various substrates that can be used as electrodes for water electrolysis. Specific examples of the electrode substrate include various substrates such as metal substrates, carbon substrates, and glass substrates.

[0016] Examples of metal substrates include substrates of simple metals such as nickel, titanium, iron, and copper, substrates of nickel-phosphorus alloys, nickel-tungsten alloys, and stainless steel alloys, and various metal foams (e.g., nickel foam, copper foam), etc. Among these, nickel foam is preferred as the metal substrate.

[0017] Examples of carbon substrates include carbon paper, carbon fiber paper, and carbon rods. Examples of glass substrates include conductive glass. The electrode substrate may be a porous material such as foam.

[0018] The electrode substrate is more preferably a metal substrate, more preferably a nickel substrate, and most preferably nickel foam.

[0019] The electrode substrate can be obtained, for example, by a known manufacturing method, or can be obtained from a commercial product. The shape and size of the electrode substrate are not particularly limited and can be appropriately selected depending on the intended use and required performance. For example, the shape of the electrode substrate can be foam, sheet, plate, rod, mesh, etc., and a foam shape is preferred.

[0020] The oxygen generating electrode catalyst comprises a catalyst formed on the electrode substrate. The catalyst contains the high-entropy complex oxide. As described above, the high-entropy complex oxide is a complex oxide containing Mo, V, and at least one metal element M selected from the group consisting of Fe, Co, Ni, Mn, Cr, Cu, and Zn as essential constituent elements.

[0021] The metal M may be one type, two or more types, or three or more types, preferably three types. That is, the high-entropy complex oxide is preferably an oxide composed of five or more types of metals, more preferably an oxide composed of five types of metals.

[0022] The metal element M contained in the high-entropy complex oxide is preferably at least one selected from the group consisting of Fe, Co, and Ni, and more preferably at least two selected from the group consisting of Fe, Co, and Ni. Particularly preferably, the metal element M contained in the high-entropy complex oxide is Fe, Co, and Ni. That is, in a particularly preferred embodiment, the complex oxide contained in the catalyst contains all of Fe, Co, and Ni. In this case, the oxygen generating electrode catalyst of the present invention can particularly suppress an increase in overvoltage during water electrolysis and can be used stably for a longer period of time.

[0023] From the above, a particularly preferred catalyst for an oxygen generating electrode of the present invention is one that contains a composite oxide (high-entropy composite oxide) containing Fe, Co, Ni, Mo, and V. However, regardless of the metal element that the metal M is, the effects of the present invention are not impaired.

[0024] The composite oxide may contain other metals in addition to the metal M (such as Fe, Co, and Ni), Mo, and V, or the metals contained in the composite oxide may consist solely of the metals M, Mo, and V. The total mass of the metals M, Mo, and V relative to the total amount of metals contained in the composite oxide is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The metals contained in the composite oxide may be only Fe, Co, Ni, Mo, and V. However, in these cases, the inclusion of other metal elements that may be unavoidably contained in the composite oxide is not excluded; for example, the inclusion of other metal elements that are unavoidably contained in the catalyst production process is permitted.

[0025] The content ratio of each metal element contained in the complex oxide is not particularly limited. For example, based on one metal M in the high-entropy complex oxide, that is, assuming the number of moles of one metal M to be 1, the content ratio of V (M:V) can be as follows: Preferably, M:V = 1:0.1 to 1:4, more preferably M:V = 1:0.3 to 1:3, further preferably M:V = 1:0.5 to 1:2.5, and particularly preferably M:V = 1:0.8 to 1:2. In these cases, the metal M is preferably Fe, Co, or Ni.

[0026] Furthermore, with one type of metal M in the composite oxide as the standard, that is, with the number of moles of one type of metal M being 1, the content ratio of Mo (M:Mo) can be as follows: Preferably, M:Mo=1:0.1 to 1:4, more preferably M:Mo=1:0.3 to 1:3, further preferably M:Mo=1:0.5 to 1:2, and particularly preferably M:Mo=1:1 to 1:1.5. In these cases, the metal M is preferably Fe, Co, or Ni.

[0027] When the metal M contains two or more kinds of metals M, the ratio of one kind of metal M to another kind of metal is preferably 1:0.5 to 1:1.5, more preferably 1:0.8 to 1:1.2.

[0028] The content of oxygen (O) in the composite oxide is not particularly limited. For example, the content of O is preferably 20 to 40 mol % relative to the total amount of the composite oxide.

[0029] In the composite oxide, the valence of the metals M, Mo, and V is not particularly limited, and each can be divalent or trivalent.

[0030] The catalyst contained in the oxygen generating electrode catalyst of the present invention may consist solely of the composite oxide, or may contain other components to the extent that the effects of the present invention are not impaired. Examples of other components include known electrode catalysts and additives that can be contained in known catalysts. The catalyst preferably contains 90 mass % or more of the composite oxide (the high-entropy catalyst), more preferably 95 mass % or more, and particularly preferably 99 mass % or more.

[0031] The shape of the composite oxide is not particularly limited, and examples thereof include various shapes such as film, particle, wire, fiber, needle, rod, and scale. Among these, the composite oxide is preferably in the form of microsphere particles. In this case, the oxygen generating electrode catalyst can further suppress an increase in overvoltage during water electrolysis and can be used stably for a longer period of time.

[0032] The composite oxide microsphere particles are micron-order particles, and their average particle diameter is preferably 1 to 10 μm, more preferably 2 to 8 μm, in order to better suppress an increase in overvoltage and enable stable use for a longer period of time. The average particle diameter here refers to the arithmetic mean of the circle-equivalent diameters measured for 50 particles randomly selected by direct observation with a scanning electron microscope.

[0033] The composite oxide microspheres may be spherical or irregularly shaped. They may also be porous, which facilitates mass transfer and gas release, and increases catalytic activity.

[0034] The porous particles may be, for example, particles with a pleated (or petal-like) surface. In this case, the surface area of ​​the complex oxide is increased, thereby enhancing catalytic activity and increasing the efficiency of water electrolysis. When the surface of the high-entropy complex oxide microsphere particles is pleated, for example, the thickness of the pleated portion is preferably 100 nm or less. Therefore, the microsphere particles may be in the form of a so-called nanoflower, which allows the inner surface to be used as a reaction field, thereby further enhancing catalytic activity and further increasing the efficiency of water electrolysis.

[0035] In the oxygen generating electrode catalyst, the catalyst formed on the electrode substrate can cover part or all of the electrode substrate. Alternatively, the catalyst can be formed directly on the electrode substrate (without any other layer interposed therebetween). The catalyst is preferably disposed on the outermost layer of the electrode substrate.

[0036] The oxygen generating electrode catalyst of the present invention can provide excellent oxygen generating efficiency when used as an electrode for water electrolysis, and specifically can be used as an anode.

[0037] By using the oxygen generating electrode catalyst of the present invention as an anode to electrolyze water, it is possible to further suppress the increase in overvoltage, lower the Tafel slope, and enable stable electrolysis for a longer period of time.

[0038] The oxygen generating electrode catalyst of the present invention can also be used as an electrode for the electrolysis of seawater. The seawater may be natural seawater or imitation seawater (e.g., an aqueous solution containing 1 M KOH and 0.5 M NaCl).

[0039] 2. Manufacturing method of catalyst for oxygen evolution electrode The method for producing the oxygen generating electrode catalyst of the present invention is not particularly limited, and for example, a wide variety of known production methods can be used. For example, the oxygen generating electrode catalyst of the present invention can be produced by immersing an electrode substrate in a raw material solution and heat treating it. More specifically, the method for producing the oxygen generating electrode catalyst of the present invention can include step 1 of forming a composite oxide on the electrode substrate by immersing the electrode substrate in the raw material solution and performing hydrothermal synthesis.

[0040] The electrode substrate used in step 1 is the same as the electrode substrate used in the above-mentioned electrode catalyst, and therefore examples thereof include a metal substrate, a carbon substrate, a glass substrate, etc., and is preferably a metal substrate, more preferably a nickel substrate, and particularly preferably nickel foam.

[0041] The raw material solution used in step 1 contains at least a metal M source, a Mo source, and a V source. The metal M source, the Mo source, and the V source may each be a metal compound containing the corresponding metal. Examples of the metal compound include inorganic acid salts, organic acid salts, hydroxides, halides, and metal acid salts of metals.

[0042] For example, preferred examples of the metal M source include chlorides and nitrates of metal M, more specifically, iron(III) chloride, cobalt nitrate, nickel nitrate, etc. Preferred examples of the V source include chlorides and nitrates of V, more specifically, vanadium(III) chloride, etc. Preferred examples of the Mo source include sodium molybdate.

[0043] The raw material liquid may contain, for example, an aqueous solvent as a solvent, preferably water, a lower alcohol having about 1 to 4 carbon atoms, or a mixed solvent thereof, more preferably water.

[0044] The concentration of the raw material solution is not particularly limited, and for example, concentrations used in conventional hydrothermal synthesis can be widely used in the present invention. For example, the concentration of each metal per liter of solvent can be 1 to 100 mM, more preferably 2 to 80 mM, even more preferably 3 to 70 mM, and particularly preferably 5 to 65 mM. In the raw material solution, the concentrations of the metal M source, V source, and Mo source may be equal or different. The molar ratio of each metal in the raw material solution can be considered to match the molar ratio of each metal in the composite oxide to be produced. Therefore, the molar ratio of each metal in the raw material solution can be adjusted within an appropriate range depending on the molar ratio of each metal in the target composite oxide.

[0045] The raw material solution may contain other additives. Examples of other additives include organic acids and pH adjusters. An example of an organic acid is citric acid. Examples of pH adjusters include urea (CO(NH2)2), NH4F, and ammonium hydroxide. The pH adjusters may be used alone or in combination of two or more. When citric acid or a pH adjuster is contained, the respective concentrations may be, for example, 100 to 500 mM.

[0046] In step 1, the method for immersing the electrode substrate in the raw material solution is not particularly limited, and the electrode substrate can usually be immersed entirely in the raw material solution. Hydrothermal synthesis can be carried out, for example, in a pressure-resistant autoclave. The inner surface of the autoclave can be coated with a fluororesin such as Teflon (registered trademark).

[0047] In step 1, the electrode substrate is immersed in the raw material solution and subjected to a heat treatment, i.e., hydrothermal synthesis. The temperature of the heat treatment is not particularly limited as long as the temperature satisfies the conditions for forming the composite oxide. For example, the temperature can be 80 to 200°C, preferably 100 to 180°C, and more preferably 120 to 160°C. The time for the heat treatment is not particularly limited, and can be, for example, 2 to 24 hours. The pressure inside the vessel during hydrothermal synthesis can also be set appropriately.

[0048] A composite oxide is formed on the electrode substrate by the hydrothermal synthesis in step 1. That is, a catalyst containing a composite oxide is formed on the electrode substrate by the hydrothermal synthesis in step 1. Such a composite oxide is an oxide composed of various metal elements contained in the raw material solution. Therefore, the composite oxide formed by hydrothermal synthesis is a composite oxide containing the metal elements M, Mo, and V, for example, a composite oxide containing Fe, Co, Ni, Mo, and V (high-entropy composite oxide).

[0049] 3.Water electrolysis method The method for electrolyzing water of the present invention includes a step of performing electrolysis using an oxygen generating electrode catalyst as an electrode.

[0050] In the method for electrolyzing water of the present invention, the oxygen generating electrode catalyst can be used as an anode, that is, it can generate oxygen.

[0051] In the water electrolysis method of the present invention, the cathode may be any electrode generally used in water electrolysis, such as a carbon rod or platinum wire.

[0052] The aqueous solution used in the electrolysis of water of the present invention can be alkaline water or seawater. The seawater can be natural seawater, or imitation seawater (e.g., an aqueous solution containing 1 M KOH and 0.5 M NaCl).

[0053] To cite a specific example of water electrolysis according to the present invention, a voltage is applied to an oxygen generating electrode catalyst as the anode, a platinum plate as the cathode, and simulated seawater as the electrolyte. This produces oxygen at the anode and hydrogen at the cathode. Furthermore, increasing the applied voltage can increase the rate of hydrogen production. The produced hydrogen can be used as fuel for fuel cells, hydrogen engines, and other applications.

[0054] In the water electrolysis of the present invention, an oxygen generating electrode catalyst is used as the electrode (anode), so that an increase in overvoltage is unlikely to occur, the Tafel slope can be reduced, and the durability of the electrode catalyst is excellent, so that performance is unlikely to deteriorate even when used for a long period of time. [Example]

[0055] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0056] Example 1 First, a 2 x 2 cm piece of foamed nickel (nickel foam) was treated with 3M hydrochloric acid for 30 minutes, then washed several times with ethanol and deionized water, and then dried in a vacuum oven for 6 hours to pretreat the nickel foam. This nickel foam was used as the substrate.

[0057] Separately, a homogeneous solution A was prepared by dissolving FeCl3·6H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, VCl3, and citric acid in 20 mL of deionized water and mixing them under magnetic stirring. In this solution A, the amounts of FeCl3·6H2O, Co(NO3)2·6H2O, and Ni(NO3)2·6H2O were 1 mmol, and the amount of VCl3 was 1.5 mmol. Separately from solution A, 1.25 mmol of Na2MoO4·2H2O was dissolved in 15 mL of deionized water and mixed under magnetic stirring to prepare a homogeneous solution B.

[0058] Next, solutions A and B were mixed to obtain a raw material solution. This raw material solution and the pretreated nickel foam were transferred to a 50 mL autoclave lined with Teflon (registered trademark). The nickel foam was immersed in the raw material solution, and the container was sealed. The container was then heated at 140°C for 14 hours (hydrothermal synthesis). After natural cooling, the nickel foam was removed, washed with ethanol and deionized water, and dried in a vacuum oven at 60°C for 12 hours. This resulted in an oxygen generating electrode catalyst in which a catalyst composed of a composite oxide was formed on the electrode substrate. This oxygen generating electrode catalyst was named "FeCoNiMoVO-1.5."

[0059] Example 2 An oxygen generating electrode catalyst in which a catalyst made of a composite oxide was formed on an electrode substrate was obtained in the same manner as in Example 1, except that the amount of VCl used was changed to 2 mmol. This oxygen generating electrode catalyst was named "FeCoNiMoVO-2."

[0060] Example 3 An oxygen generating electrode catalyst in which a catalyst made of a composite oxide was formed on an electrode substrate was obtained in the same manner as in Example 1, except that the amount of VCl used was changed to 1 mmol. This oxygen generating electrode catalyst was named "FeCoNiMoVO-1."

[0061] Example 4 An oxygen generating electrode catalyst in which a catalyst made of a composite oxide was formed on an electrode substrate was obtained in the same manner as in Example 1, except that the amount of VCl used was changed to 0.5 mmol. This oxygen generating electrode catalyst was named "FeCoNiMoVO-0.5."

[0062] (Comparative Example 1) An oxygen generating electrode catalyst in which a catalyst made of a composite oxide was formed on an electrode substrate was obtained in the same manner as in Example 1, except that solution A was prepared without using FeCl3·6H2O, Co(NO3)2·6H2O, or VCl3. This oxygen generating electrode catalyst was named "NiMoO."

[0063] (Comparative Example 2) An oxygen generating electrode catalyst in which a catalyst made of a composite oxide was formed on an electrode substrate was obtained in the same manner as in Example 1, except that solution A was prepared without using Co(NO3)2·6H2O and VCl3. This oxygen generating electrode catalyst was named "FeNiMoO."

[0064] (Comparative Example 3) An oxygen generating electrode catalyst in which a catalyst made of a composite oxide was formed on an electrode substrate was obtained in the same manner as in Example 1, except that solution A was prepared without using VCl. This oxygen generating electrode catalyst was named "FeCoNiMoO."

[0065] (Evaluation results) FIG. 1 shows SEM images of the catalytic portion in the oxygen generating electrode catalyst obtained in each example and comparative example, where (a) is Comparative Example 3, (b) is Example 4, (c) is Example 3, (d) is Example 1, (e) is an enlarged photograph of the SEM image of (d), and (f) is an SEM image of the catalytic portion in the oxygen generating electrode catalyst obtained in Example 2.

[0066] The SEM images in Figure 1 confirm that the catalysts for oxygen evolution electrodes obtained in Examples 1 to 4 were formed as microsphere particles on the electrode substrate. Specifically, they were porous particles, more specifically, they had a nanoflower-like morphology (Figures 1(b) to 1(f)). In Example 4 (FeCoNiMoVO-0.5), the microsphere surface became rough, and several nanosheets appeared on the surface (Figure 2(b)). In Examples 1 to 3, a microflower morphology composed of petal-like nanosheets was observed (Figures 1(c) to 1(f)). The oxygen evolution electrode catalysts obtained in the examples had a large surface area, potentially providing more active sites. Furthermore, the spaces between the nanosheets are thought to promote material transport and improve catalytic performance.

[0067] Fig. 2(a) shows the results of linear sweep voltammetry measurements using the oxygen evolving electrode catalysts obtained in Examples 1 to 4 as electrodes. In these measurements, the oxygen evolving electrode catalysts obtained in Examples 1 to 4 were used as the anodes, and an Ag / AgCl electrode was used as the reference electrode. The electrolyte used in the measurements was a 1 M KOH aqueous solution. The scan rate was 2 mV / s, and the current density was 10, 50, or 100 mAcm. -2 The evaluation of electrical properties such as linear sweep voltammetry curves was performed using a standard three-electrode cell and a VersaSTAT4 potentiostat galvanostat electrochemical workstation (USA).

[0068] Figure 2(b) shows the overpotential calculated from the linear sweep voltammetry curve shown in (a). The numbers on the X-axis represent the number of moles (mmol) of VCl used, and the corresponding example number is shown in parentheses. In each example, the left bar, center bar, and right bar represent the overpotential calculated from the linear sweep voltammetry curve shown in (a). -2 , 50mAcm -2 and 100mAcm -2 The overvoltage at

[0069] 2, it was found that the oxygen evolution electrode catalysts obtained in the examples suppressed the increase in overvoltage during water electrolysis. In particular, it was found that FeCoNiMoVO-1.5 obtained in Example 1 exhibited the most excellent activity.

[0070] Figure 3(a) shows the results of linear sweep voltammetry measurements using the oxygen evolution electrode catalysts obtained in Example 1 and Comparative Examples 1 to 3 as electrodes. The measurement conditions were the same as those in Figure 2(a). Figure 3(b) shows the overpotential calculated from the linear sweep voltammetry curve shown in Figure 3(a). In each example in Figure 3(b), the left bar, center bar, and right bar represent the overpotentials calculated at 10 mAcm. -2 , 50mAcm -2 and 100mAcm -2 Figure 3(c) shows the measurement results of the Tafel slope calculated from Figure 3(a).

[0071] The results in Figure 3 show that the catalyst for oxygen generating electrodes obtained in Example 1 suppressed the increase in overvoltage during water electrolysis and had a lower Tafel slope than the catalysts for oxygen generating electrodes obtained in Comparative Examples 1 to 3.

[0072] Table 1 summarizes the results of Figure 3 and shows the results of the oxygen evolution electrode catalysts at 10 mAcm -2 , 50mAcm -2 and 100mAcm -2 The values ​​of the overpotential at 1000 kJ / s, as well as the Tafel slope are shown.

[0073] [Table 1]

[0074] Table 1 shows that the overpotential and Tafel slope of the high-entropy catalyst Example 1 (FeCoNiMoVO-1.5) are significantly lower than those of the binary, ternary, and quaternary metal oxide catalysts of Comparative Examples 1 to 3, indicating excellent OER kinetics.

[0075] Figure 4(a) shows the results of linear sweep voltammetry measurements using the oxygen evolution electrode catalyst obtained in Example 1 as an electrode. Three types of electrolytes were used in the measurements: a 1 M KOH aqueous solution, alkaline simulated seawater (a mixture of 1 M KOH and 0.5 M NaCl aqueous solutions), and alkaline natural seawater (a mixture of 1 M KOH and seawater). The other measurement conditions were the same as those in Figure 2(a).

[0076] Figure 4(b) shows the bar graphs of the overpotentials in each electrolyte measured in Figure 4(a). For each electrolyte, the left bar, center bar, and right bar represent the overpotentials at 10 mAcm², respectively. -2 , 50mAcm -2 and 100mAcm -2 The overvoltage at

[0077] 4(a) and (b) show that the increase in overvoltage is suppressed regardless of whether a 1 M KOH aqueous solution, alkaline simulated seawater, or alkaline natural seawater is used as the electrolyte. Therefore, it can be said that the oxygen evolving electrode catalyst obtained in Example 1 has excellent catalytic performance for various electrolytes.

[0078] Figure 5 shows the results of chronopotentiometry measurements using the oxygen evolution electrode catalyst obtained in Example 1 as an electrode. In this measurement, the current density was set to 1 A / cm 2 The electrolytes used were the aforementioned 1M KOH aqueous solution, alkaline simulated seawater, and alkaline natural seawater (top, middle, and bottom rows in Figure 5, respectively). Measurements were performed using a VersaSTAT4 potentiostat galvanostat electrochemical workstation from the United States together with a two-electrode cell.

[0079] 5, the oxygen generating electrode catalyst obtained in Example 1 exhibited excellent stability for more than 100 hours, demonstrating that the oxygen generating electrode catalyst obtained in Example 1 can be operated stably for a long period of time even at a high current density.

[0080] The above results demonstrate that the oxygen generating electrode catalyst of the present invention can suppress an increase in overpotential during electrolysis, can reduce the Tafel slope, and can be used stably for a long period of time. Furthermore, it can efficiently split water not only in alkaline solutions but also in alkaline simulated seawater and alkaline natural seawater, making it promising for application to industrial seawater electrolysis.

Claims

1. A catalyst for an oxygen generating electrode in water electrolysis, comprising a catalyst on an electrode substrate, The catalyst is At least one metal element M selected from the group consisting of Fe, Co, Ni, Mn, Cr, Cu, and Zn; Mo and V and A catalyst for an oxygen generating electrode in water electrolysis, comprising a composite oxide containing:

2. 2. The catalyst for an oxygen generating electrode for water electrolysis according to claim 1, wherein the composite oxide is an oxide containing Fe, Co, Ni, Mo, and V.

3. 3. The catalyst for an oxygen generating electrode in water electrolysis according to claim 1, wherein the composite oxide is in the form of microsphere particles.

4. A method for electrolyzing water, comprising a step of performing electrolysis using the oxygen generating electrode catalyst according to claim 1 or 2.

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