Catalyst for oxygen generation reaction, electrode, and electrochemical device

Abstract

To improve activity of a catalyst for an electrochemical reaction.SOLUTION: A catalyst for oxygen generation reaction is composed of an A-site ordered perovskite oxide, wherein the A-site ordered perovskite oxide is represented by composition formula: AA'3B4O12 (wherein, an element A is calcium (Ca), each of the element A' and an element B is one or more kinds of transition metal containing at least manganese (Mn)), in a powder X-ray diffraction pattern using CuKα rays, two diffraction peaks of a peak having highest intensity and a peak having second highest intensity at a diffraction angle 2θ of 34° to 35° exist, in the two diffraction peaks, peak intensity of a low angle side diffraction peak PL is represented by low angle side peak intensity IL, and peak intensity of a high angle side diffraction peak PH is represented by a high angle peak intensity IH, a peak intensity ratio (IL / IH) which is a ratio of the low angle side peak intensity IL to the high angle side peak intensity IH is less than 1.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to catalysts, electrodes, and electrochemical devices for the oxygen evolution reaction. [Background technology]

[0002] In recent years, various energy conversion systems, such as alkaline water electrolysis, fuel cells, and metal-air batteries, have been devised and studied as alternative energy sources that do not rely on fossil fuels such as coal and petroleum. These energy conversion systems generally involve the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and oxygen evolution reaction (OER). For practical application of these energy conversion systems, it is particularly important to improve the performance of catalysts for the oxygen evolution reaction (OER). Various catalysts have been investigated for the oxygen evolution reaction (OER), including noble metal catalysts such as RuO2 and IrO2, and perovskite-type oxide catalysts (see, for example, Non-Patent Document 1). Among these, catalysts composed of A-site ordered perovskite oxides are considered to have catalytic activity equivalent to or superior to that of conventional noble metal catalysts, as well as high stability and long service life under the operating environment (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5869169 [Non-patent literature]

[0004] [Non-Patent Document 1] Nian-Tzu Suen et al., Chem. Soc. Rev., 2017, 46, 337 Summary of the Invention [Problem to be solved by the invention]

[0005] Such oxygen generation reaction catalysts are generally provided on electrodes where the oxygen generation reaction proceeds in the energy conversion systems described above. In such devices, further improvements in the performance of oxygen generation reaction catalysts have been desired in order to suppress the overvoltage required to proceed with the oxygen generation reaction and thereby increase energy efficiency. [Means for solving the problem]

[0006] The present disclosure can be realized in the following forms. [1] According to one aspect of the present disclosure, there is provided a catalyst for an oxygen generation reaction. The catalyst for an oxygen generation reaction is composed of an A-site ordered perovskite oxide, and the A-site ordered perovskite oxide has the composition formula: AA'3B4O 12 (wherein element A is calcium (Ca), and element A' and element B are each one or more transition metals including at least manganese (Mn)), and in a powder X-ray diffraction pattern using CuKα radiation, it has at least two diffraction peaks, namely, the highest intensity peak and the second highest intensity peak within the diffraction angle 2θ range of 34° to 35°, and of the two diffraction peaks, the lower angle diffraction peak P L The peak intensity of the low-angle peak I L , high-angle diffraction peak P H The peak intensity of the high-angle peak I H When the peak intensity on the high-angle side is I H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) is less than 1. According to this form of catalyst for oxygen generation reaction, the composition formula: AA'3B4O 12In the powder X-ray diffraction pattern using CuKα radiation of an A-site ordered perovskite oxide represented by the formula (where element A is calcium (Ca), and element A' and element B are each one or more transition metals including at least manganese (Mn)), there are at least two diffraction peaks, the highest and second highest intensity peaks within the diffraction angle 2θ range of 34° to 35°. Furthermore, the high-angle peak intensity I H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) is less than 1. Therefore, high catalytic activity can be ensured due to the crystal structure of the oxygen generation reaction catalyst. [2] In the oxygen generation reaction catalyst of the above embodiment, the composition ratio of manganese (Mn) in the A-site ordered perovskite oxide may be 6.5 or more, when the total composition ratio of the element A' and the element B in the A-site ordered perovskite oxide is 7. With this configuration, the content of transition metals other than manganese (Mn) is reduced, thereby preventing the formation of subphases in the A-site ordered perovskite oxide. [3] In the oxygen generation reaction catalyst of the above embodiment, the A-site ordered perovskite oxide may further contain at least one of nickel (Ni), iron (Fe), and cobalt (Co) in addition to manganese (Mn) as the element A' and element B. In this configuration, in a powder X-ray diffraction pattern using CuKα radiation, two diffraction peaks are present within a diffraction angle range of 2θ = 34° to 35°, and a high-angle peak intensity I H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) is less than 1, it becomes easier to obtain an A-site ordered perovskite oxide. [4] According to another aspect of the present disclosure, there is provided an electrode comprising the catalyst for oxygen evolution reaction according to any one of [1] to [3]. According to this type of electrode, the activity of the oxygen generating reaction that proceeds at the electrode can be increased. [5] The electrode in the above form may be any one of an anode electrode for alkaline water electrolysis, an air electrode of a metal-air secondary battery, an anode electrode of a photoelectrode system, and an anode electrode of a solid oxide electrolysis cell. With such a configuration, the activity of the oxygen evolution reaction that proceeds at any one of the anode electrode for alkaline water electrolysis, the air electrode of a metal-air secondary battery, the anode electrode of a photoelectrode system, and the anode electrode of a solid oxide electrolysis cell can be increased. [6] According to yet another aspect of the present disclosure, there is provided an electrochemical device including the electrode of the above aspect. According to this embodiment of the electrochemical device, the activity of the oxygen evolution reaction that proceeds at the electrodes can be increased, thereby improving the performance of the electrochemical device. The present disclosure may be realized in various forms other than those described above, such as a method for producing a catalyst for oxygen evolution reaction, an alkaline water electrolysis device equipped with an electrode containing the catalyst, a metal-air secondary battery, a photoelectrode system, and a solid oxide electrolysis cell. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating the structure of an A-site ordered perovskite oxide. [Figure 2] FIG. 2 is an explanatory diagram showing an example of a method for producing a catalyst according to the present embodiment. [Figure 3] FIG. 1 is an explanatory diagram showing XRD charts of samples S1 to S3 side by side. [Figure 4] FIG. 4 is an explanatory diagram showing an enlarged portion of the XRD chart of FIG. 3. [Figure 5] FIG. 10 is an explanatory diagram showing the peak intensity ratios (IL / IH) of samples S1 to S3. [Figure 6] FIG. 1 is an explanatory diagram showing the results of electrochemical measurements as an OER evaluation. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. Catalyst for oxygen evolution reaction: The catalyst of this embodiment is an oxygen evolution reaction catalyst that promotes the oxygen evolution reaction (OER). The catalyst of this embodiment is a catalyst having a first composition formula of AA'3B4O 12 (where element A is calcium (Ca), and element A' and element B are each one or more transition metals containing at least manganese (Mn)).

[0009] FIG. 1 is an explanatory diagram showing a typical structure of an A-site ordered perovskite oxide. The A-site ordered perovskite oxide has the first composition formula AA'3B4O 12 where A is a rare earth element or alkaline earth metal, and A' and B are transition metals. The structure of such A-site ordered perovskite oxides, as shown in Figure 1, has an ordered A'O4 plane containing the element A' in addition to a BO6 octahedron containing the B-site element.

[0010] As described above, the A-site ordered perovskite oxide of this embodiment (hereinafter also simply referred to as the "oxide of this embodiment") has a first composition formula of AA'3B4O 12 (wherein element A is calcium (Ca), and element A' and element B are each one or more transition metals including at least manganese (Mn)), and the second composition formula is CaMnO 12 That is, the oxide of this embodiment has a basic structure represented by the first composition formula AA'3B4O 12 In the formula (I), the A site is occupied by calcium (Ca), and both the A' site and the B site, which are occupied by transition metal elements, may be composed of manganese (Mn) element only, or may be composed of manganese (Mn) element and one or more transition metal elements other than Mn.

[0011] The composition ratio of manganese (Mn) in the A-site ordered perovskite oxide, which is the oxide of this embodiment, is the first composition formula AA'3B4O 12 When the total composition ratio of element A' and element B in the oxide of this embodiment is 7, the composition ratio of Mn is preferably 6.5 or more. This is because, in the oxide of this embodiment, the higher the content ratio of transition metal elements other than Mn contained in the A' site and the B site, the more likely a subphase is to be generated in the oxide. From the viewpoint of suppressing the generation of a subphase, it is desirable to set the composition ratio of Mn sufficiently high as described above.

[0012] First composition formula AA'3B4O 12 In the oxide of this embodiment represented by the formula: CaMnO, the element A' and the element B are transition metal elements further contained in addition to manganese (Mn), and the difference in ionic radius between them and Mn is not excessive. 12 Any element that can occupy the Mn site of the oxide of the present embodiment may be used. Such a transition metal element may be, for example, at least one of nickel (Ni), iron (Fe), and cobalt (Co). In the oxide of this embodiment, the total composition ratio of the other transition metals contained in addition to Mn is AA'3B4O 12 When the total composition ratio of element A' and element B in this compound is 7, the ratio is preferably less than 0.5, and more preferably less than 0.4. The type and content of the transition metal element used may be within a range that allows a characteristic pattern, as described below, to be obtained in the powder X-ray diffraction pattern of the A-site ordered perovskite oxide.

[0013] The crystal structure of the A-site ordered perovskite oxide catalyst of this embodiment can be confirmed by, for example, X-ray diffraction (XRD).

[0014] In the powder X-ray diffraction pattern using CuKα radiation, the oxide of this embodiment has two diffraction peaks, the highest and second highest peaks in the diffraction angle 2θ range of 34° to 35°. Of the two diffraction peaks, the lower angle diffraction peak P LThe peak intensity of the low-angle peak I L , high-angle diffraction peak P H The peak intensity of the high-angle peak I H When the peak intensity on the high-angle side is I H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) is less than 1. That is, in the powder X-ray diffraction pattern using CuKα radiation, there are the highest and second highest intensity peaks in the diffraction angle 2θ range of 34° to 35°, and when these peaks are compared, the peak with the highest intensity is on the higher angle side. In addition, in the quadruple perovskite belonging to the space group R-3, the low angle side diffraction peak P L is the diffraction peak from the (220) plane, and the high-angle diffraction peak P H is a diffraction peak from the (202) plane.

[0015] Conventionally known A-site ordered perovskite oxides generally have one diffraction peak within the diffraction angle range 2θ=34° to 35° in a powder X-ray diffraction pattern using CuKα radiation, or even if they have two diffraction peaks, the high-angle peak intensity I H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) was 1 or more. Conventionally, powder X-ray diffraction patterns of various A-site ordered perovskite oxides have been investigated and databases have been compiled. For example, the PDF (Powder Diffraction File) database compiled by the ICDD (International Centre for Diffraction Data) is known. Even in the data stored in this database, the high-angle peak intensity I H Low-angle peak intensity I L The peak intensity ratio (I L / I H) is less than 1, and this can be said to be a very unique structure.

[0016] B. Catalyst manufacturing method: FIG. 2 is a flowchart showing an example of a method for producing a catalyst according to this embodiment. The production method shown in FIG. 2 utilizes a complex polymerization method, which is known as a precision synthesis method for oxide powders. When producing a catalyst (the oxide according to this embodiment) by the method shown in FIG. 2, first, raw material powders are prepared, and a raw material solution is prepared by dissolving the raw material powders (step T100). The raw material powders are oxides of the metal elements that constitute the oxide according to this embodiment, or salts such as carbonates or nitrates. The raw material solution is then prepared by dissolving these raw material powders in pure water or the like. When calcium carbonate (CaCO3) is contained in the raw material powders, nitric acid or the like may be further added to dissolve the calcium carbonate. The composition of the final catalyst can be adjusted by changing the proportions of the raw material powders prepared in step T100.

[0017] After step T100, the prepared raw material solution is mixed with an oxycarboxylic acid such as citric acid and a glycol such as ethylene glycol to obtain a mixed solution (step T110). In step T110, the oxycarboxylic acid is added, and the metals constituting the raw material powder form a metal-oxycarboxylic acid complex. Then, the mixed solution obtained in step T110 is heated, whereby the oxycarboxylic acid and the glycol are polymerized to form a polyester polymer gel (step T120).

[0018] The polyester-containing solution obtained in step T120 is then heated and dried to remove moisture, followed by calcination to obtain a precursor oxide (step T130). In this embodiment, the "calcination" is performed as a heat treatment under conditions in which some of the organic matter contained in the polyester polymer gel described above remains without being decomposed and removed. For example, heating conditions can be set at approximately 350 to 450°C for approximately 30 minutes to 5 hours. The precursor oxide obtained in step T130 is then heat-treated (main calcination) to complete the catalyst of this embodiment (step T140). The heat treatment in step T140 can be performed, for example, at 1000°C for approximately 30 minutes to 15 hours. Note that by performing the calcination in step T130 under conditions in which some of the organic matter remains without being decomposed and removed, the atmosphere in the main calcination in step T140 is thought to be closer to a reducing atmosphere than when the calcination is performed under conditions in which the organic matter is completely decomposed and removed.

[0019] When the A-site ordered perovskite oxide is produced by the complex polymerization method, the oxide of this embodiment can be easily produced by carrying out a heat treatment under conditions in which a part of the organic substance remains without being decomposed and removed when obtaining the precursor oxide in step T130 as described above. H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) less than 1, it is possible to prepare A-site ordered perovskite oxides with any composition.

[0020] The catalyst of this embodiment may be produced by a method other than the citric acid complex polymerization method described above. For example, various methods known as methods for producing perovskite oxides, such as a solid-state reaction method, a coprecipitation method, or a sol-gel method, can be used. In this case, the high-angle peak intensity I can be increased by adjusting the composition of the A-site ordered perovskite oxide, specifically, by adjusting the type and content of transition metals contained in the A-site ordered perovskite oxide other than manganese (Mn). H Low-angle peak intensity I LThe peak intensity ratio (I L / I H ) is less than 1.

[0021] According to the A-site ordered perovskite oxide of this embodiment configured as described above, in a powder X-ray diffraction pattern using CuKα radiation, there are at least two diffraction peaks, namely, the peak with the highest intensity and the peak with the second highest intensity within the diffraction angle range 2θ=34° to 35°, and the above-mentioned high-angle peak intensity I H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) to be less than 1, the activity as an oxygen generating reaction catalyst can be enhanced. The reason why such an effect of improving catalytic activity can be obtained in the oxygen generating reaction catalyst of this embodiment is thought to be that adjusting the various conditions involved in the production of the oxygen generating reaction catalyst causes a change in the crystal structure, which changes the peak shape of the XRD diffraction pattern, as described above. Here, the various conditions involved in the production of the oxygen generating reaction catalyst refer to conditions including heating conditions, including calcination conditions, during catalyst production, conditions of the reactions that proceed during production (for example, when a complex polymerization method is used, the amounts of oxycarboxylic acid, glycol, etc. mixed in step T110), and the catalyst composition, which is determined by the types and mixing ratios of raw material powders (types of transition metals added other than Ca and Mn and the mixing ratios of these transition metals). It is thought that such a change in crystal structure changes the electronic state of the active site in the oxygen generating reaction catalyst, resulting in high activity as an oxygen generating reaction catalyst.

[0022] C. Application examples of catalysts: The oxygen generation reaction catalyst comprising the oxide of this embodiment can be suitably used in electrodes where the oxygen generation reaction proceeds. Examples of such electrodes include anodes for alkaline water electrolysis, air electrodes in metal-air secondary batteries, anodes in photoelectrode systems, and anodes in solid oxide electrolysis cells. However, the uses of the oxide of this embodiment are not limited to the above, and it may also be applied to electrodes where the oxygen generation reaction proceeds in other devices. Furthermore, it can be used as an oxygen generation reaction catalyst in various devices where the oxygen generation reaction proceeds, not limited to devices equipped with electrodes.

[0023] An alkaline water electrolysis device is a device that performs water electrolysis by disposing alkaline water as an electrolyte between a pair of electrodes, where the reaction of the following formula (1) proceeds at the anode, and the reaction of the following formula (2) proceeds at the cathode. In such an alkaline water electrolysis device, by using the oxide of this embodiment as the anode electrode, where the oxygen generation reaction proceeds, the oxygen generation reaction that proceeds at the anode electrode can be promoted, and the device performance can be improved.

[0024] 2OH - → H2O + 1 / 2O2 + 2e - … (1) 2H2O + 2e - → H2+ 2OH - … (2)

[0025] A metal-air secondary battery is a secondary battery that uses oxygen in the air as the positive electrode active material and a metal as the negative electrode active material. For example, in a zinc-air battery, the reaction of the following formula (3) proceeds at the air electrode (positive electrode) during discharge, and the reaction of the following formula (4) proceeds at the negative electrode. During charge, the reaction proceeds in the opposite direction to that during discharge. In such a metal-air secondary battery, by using the oxide of this embodiment as the air electrode, the oxygen evolution reaction that proceeds at the air electrode during charge can be promoted, thereby improving the device performance.

[0026] O2+ 2H2O + 4e - → 4OH -… (3) Zn + 2OH - → ZnO + H2O + 2e - … (4)

[0027] A photoelectrode system is a device that splits water using light such as sunlight, in which the reaction of formula (1) described above proceeds at the anode electrode, which is a photoelectrode, and the reaction of formula (2) described above proceeds at the cathode. By using the oxide of this embodiment as the anode electrode, where the oxygen evolution reaction proceeds in such a photoelectrode system, the oxygen evolution reaction that proceeds at the anode photoelectrode can be promoted, thereby improving the device performance.

[0028] A solid oxide electrolysis cell (SOEC) is a water electrolysis device that uses a high-temperature solid electrolyte, in which the reaction shown in formula (5) below proceeds at the anode, and the reaction shown in formula (6) below proceeds at the cathode. In such a solid oxide electrolysis cell, by using an electrode comprising the oxide of this embodiment as the anode electrode, the oxygen evolution reaction that proceeds at the anode electrode can be promoted, thereby improving the device performance.

[0029] 2O 2- → O2+ 4e - … (5) H2O + 2e - → H2+ O 2- … (6)

[0030] In addition, an electrode equipped with the catalyst for oxygen generation reaction of this embodiment may further comprise, in addition to the oxide of this embodiment, other catalysts (e.g., other types of catalyst for oxygen generation reaction) or other components other than the catalyst. [Example]

[0031] Three types of A-site ordered perovskite oxides, samples S1 to S3, were prepared and their XRD diffraction peak patterns and catalytic activity as catalysts for the oxygen evolution reaction were investigated. Sample S1 has the composition formula CaMnO 12The oxide represented by the formula CaMn was prepared by the citric acid complex polymerization method. 6.85 Ni 0.05 Fe 0.05 Co 0.05 O 12 The oxide represented by the formula CaMnO was prepared by a solid-state reaction method. 12 It is an oxide represented by the formula (I) and was produced by a solid-state reaction method.

[0032] <Preparation of each sample> [Sample S1] The catalyst of sample S1 (CaMnO 12 ) was prepared by the complex polymerization method as follows. Calcium carbonate (CaCO3) and manganese carbonate (MnCO3) were used as raw material powders. These raw material powders were weighed so that the metal element ratio was Ca:A':B = 1:3:4 (molar ratio), i.e., Ca:Mn = 1:7 (molar ratio). These raw material powders were then placed in a beaker, and pure water was added to cover the raw material powders. The beaker was then placed on a mantle heater, a stirring magnet was added, and heating and stirring were initiated. 10 mL of nitric acid was added to the beaker while stirring to dissolve the CaCO3. After the CaCO3 was dissolved, citric acid monohydrate was added and the solution was heated to 100°C. After confirming that the solution had reached 100°C, ethylene glycol was added and the solution was heated to 150°C. The solution temperature was monitored using an infrared thermometer. Heating was continued until NO2 was generated from the solution and all the water was gone. After drying, the resulting dried product was calcined in an electric furnace at 400°C for 3 hours. No further high-temperature treatment was performed after calcination, and a powder containing some of the organic matter present in the solution was obtained as the precursor oxide. This precursor oxide was mixed and ground in an agate mortar, placed in an alumina boat, and heat-treated at 1000°C for 12 hours to obtain catalyst sample S1.

[0033] [Sample S2] The catalyst of sample S2 (CaMn 6.85 Ni 0.05 Fe 0.05 Co 0.05 O12 ) was prepared by the solid-state reaction method as follows. The raw material powders used were calcium carbonate (CaCO3), manganese carbonate (MnCO3), nickel oxide (NiO), iron oxide (Fe2O3), and cobalt oxide (Co3O4). These raw material powders were weighed so that the ratio of metal elements was the target composition ratio. Ethanol was added to these raw material powders and wet-mixed in a ball mill for 15 hours to obtain a first slurry. The first slurry was then dried, and the resulting mixed powder was calcined in an air atmosphere at a temperature range of 600 to 850°C for 1 to 12 hours to obtain a calcined product. Ethanol was added to this calcined product, and the mixture was pulverized and mixed in a ball mill to obtain a second slurry. The resulting second slurry was dried and granulated, and then calcined in an air atmosphere at 850 to 950°C for approximately 10 to 30 hours to obtain the catalyst sample S2. It is not necessary to charge the raw material powder all at once, but it may be charged separately, for example, before calcination and after calcination.

[0034] [Sample S3] The catalyst of sample S3 (CaMnO 12 ) was prepared by a solid-state reaction method. Sample S3 was prepared under the same conditions as the catalyst for sample S2, except that calcium carbonate (CaCO3) and manganese carbonate (MnCO3) were used as raw material powders, weighed out so that the molar ratio of Ca:Mn was 1:7.

[0035] <Powder X-ray diffraction> Powder X-ray diffraction patterns were obtained for each of the catalyst samples S1 to S3 prepared as described above using the following method. First, each of the catalyst samples S1 to S3 was crushed and pulverized in a mortar to obtain catalyst powder, and the resulting catalyst powder was then fixed on an aluminum holder and measured using an X-ray diffractometer (Smart Lab, manufactured by Rigaku Corporation). XRD was measured using a CuKα radiation source. The tube voltage during measurement was 45 kV and the tube current was 200 mA.

[0036] FIG. 3 is an explanatory diagram showing XRD charts of samples S1 to S3 side by side. FIG. 4 is an explanatory diagram showing a part of the XRD charts of samples S1 to S3 of FIG. 3, enlarging the range including the diffraction angle 2θ=34° to 35°. As shown in FIGS. 3 and 4, each of samples S1 to S3 has two diffraction peaks in the powder X-ray diffraction pattern using CuKα radiation: the highest and second highest intensity peaks within the diffraction angle 2θ=34° to 35° range. In FIG. 4, the peaks on the lower angle side of the highest and second highest intensity peaks within the diffraction angle 2θ=34° to 35° range are referred to as low-angle diffraction peaks P L The peak on the high-angle side is shown as the high-angle diffraction peak P H is shown as

[0037] FIG. 5 shows the high-angle diffraction peak P H The high-angle peak intensity I H The low-angle diffraction peak P L The low-angle peak intensity I L The peak intensity ratio (I L / I H 5 is an explanatory diagram showing the results of calculating the peak intensity ratio (I L / I H ) is less than 1, whereas sample S3 has the above peak intensity ratio (I L / I H ) was equal to or greater than 1. That is, when comparing the highest intensity peak and the second highest intensity peak within the diffraction angle 2θ range of 34° to 35°, the highest peak was on the high-angle side in samples S1 and S2, whereas the highest peak was on the low-angle side in sample S3.

[0038] Here, samples S1 and S3 both have the composition formula CaMnO 12 The sample S1 is an A-site ordered perovskite oxide represented by the formula: Sample S1 was produced under different conditions from those of sample S3, and as a result, the crystal structure was changed, resulting in the peak intensity ratio (IL / I H ) is considered to have changed. In the complex polymerization method used to prepare sample S1, heating is generally performed under conditions that are considered to completely remove organic matter from the precursor oxide before the main calcination corresponding to step T140 in FIG. 2. Sample S1 is heat-treated under conditions that leave some organic matter in the precursor oxide, and therefore the atmosphere in the main calcination in step T140 is closer to a reducing atmosphere than when heat-treatment is performed under conditions that completely decompose and remove organic matter, and it is considered that this difference in calcination conditions caused the change in the crystal structure. In other words, in the past, in the complex polymerization method, heating was generally performed under conditions that are considered to completely remove organic matter from the precursor oxide before the main calcination, and therefore the above-mentioned peak intensity ratio (I L / I H ) less than 1.

[0039] Sample S2 has the composition formula CaMn 6.85 Ni 0.05 Fe 0.05 Co 0.05 O 12 Sample S2 was produced under the same conditions as sample S3, but by containing trace amounts of transition metal elements other than Mn at specific content ratios, the crystal structure changed and the peak intensity ratio (I L / I H ) is thought to have changed.

[0040] <Catalyst characteristic evaluation> [Electrode preparation] For each sample oxide (catalyst), a catalytic electrode was fabricated and evaluated based on the method described in I. Yamada et al., Adv. Mater., 29, 1603004 (2017). Specifically, to fabricate the catalytic electrode, a catalytic ink was first prepared using the catalyst powder of each sample. The catalytic ink was prepared by mixing 50 mg of the catalyst powder of each sample with 10 mg of acetylene black (AB) and K. +The catalyst ink was thoroughly dispersed by ultrasonic treatment, and then applied to the working electrode of a rotating disk electrode in a catalyst amount of 0.25 mg / cm. 2 The rotating disk electrode working electrode was composed of glassy carbon (GC) with a diameter of 4 mm and a platinum (Pt) ring with an outer diameter of 7 mm and an inner diameter of 5 mm. After applying the catalyst ink, the catalyst electrode was obtained by vacuum drying.

[0041] [Evaluation of catalytic activity for the oxygen evolution reaction (OER)] The catalytic activity of each of the prepared catalytic electrodes was evaluated using the RDE (rotating disk electrode) method with a rotating ring-disk apparatus equipped with a bipotentiostat. Specifically, the potential was swept to a specific potential at a specific potential sweep rate (described below), and then swept back to the initial potential at the same potential sweep rate, and the current density was measured during this period. Specifically, the electrochemical properties of the prepared catalytic electrodes were measured using a Pt coil electrode as the counter electrode and a Hg / HgO electrode filled with 0.1 M potassium hydroxide (KOH) aqueous solution as the reference electrode. All measurements were performed at room temperature under oxygen saturation.

[0042] For the evaluation of the catalytic oxide properties for OER, the potential of the catalytic electrode was controlled at 0.3–0.9 V vs. Hg / HgO (1.23–1.83 V vs. RHE) with respect to the reference electrode Hg / HgO at a potential sweep rate of 10 mV / s. The potential was corrected for the iR drop (the voltage drop caused by the current flowing between the working and counter electrodes due to the solution resistance between the working and reference electrodes) caused by the resistance component of the electrolyte, and the potential was expressed as a potential relative to RHE.

[0043] FIG. 6 is an explanatory diagram showing the results of electrochemical measurements for evaluating catalytic activity related to OER. As a result of evaluating catalytic activity related to OER, FIG. 6 shows the current density (specific activity when the RHE-based potential is 1.7 V) when the electrode potential of the catalytic electrode is 1.7 V vs. RHE based on the electrochemical measurement results for each sample. Note that the RHE-based potential of 1.7 V corresponds to the generally assumed conditions for use in water electrolysis. As shown in FIG. 6, the peak intensity ratio (I L / I H Samples S1 and S2, which satisfy the condition that the peak intensity ratio (I L / I H ) is 1 or more, it was confirmed that the specific catalytic activity at the same potential was higher and the OER catalytic performance was higher.

[0044] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0045] The present disclosure can also be realized in the following forms. [Application example 1] A catalyst for an oxygen generation reaction, comprising: It is composed of A-site ordered perovskite oxides, The A-site ordered perovskite oxide is Composition formula: AA'3B4O 12 (wherein element A is calcium (Ca), and element A' and element B are each one or more transition metals containing at least manganese (Mn)), In a powder X-ray diffraction pattern using CuKα radiation, the powder has at least two diffraction peaks, namely, the peak with the highest intensity and the peak with the second highest intensity within the diffraction angle 2θ range of 34° to 35°; The lower-angle diffraction peak P L The peak intensity of the low-angle peak I L , high-angle diffraction peak P H The peak intensity of the high-angle peak I H When the peak intensity on the high-angle side is I H Low-angle peak intensity I L The peak intensity ratio (I L / I H ) is less than 1 Catalyst for oxygen evolution reaction. [Application example 2] The catalyst for oxygen generation reaction according to Application Example 1, The composition ratio of manganese (Mn) in the A-site ordered perovskite oxide is 6.5 or more when the total composition ratio of the element A' and the element B in the A-site ordered perovskite oxide is 7. Catalyst for oxygen evolution reaction. [Application example 3] The catalyst for oxygen generation reaction according to Application Example 1 or 2, The A-site ordered perovskite oxide is characterized in that the element A' and the element B further contain, in addition to manganese (Mn), at least one of nickel (Ni), iron (Fe), and cobalt (Co). Catalyst for oxygen evolution reaction. [Application example 4] An electrode comprising the catalyst for oxygen evolution reaction according to any one of Application Examples 1 to 3. [Application example 5] The electrode according to Application Example 4, The electrode is any one of an anode electrode for alkaline water electrolysis, an air electrode of a metal-air secondary battery, an anode electrode of a photoelectrode system, and an anode electrode of a solid oxide electrolysis cell. electrode. [Application Example 6] An electrochemical device comprising the electrode according to Application Example 4 or 5.

Claims

1. A catalyst for an oxygen generation reaction, comprising: It is composed of A-site ordered perovskite oxide, The A-site ordered perovskite oxide is Composition formula: AA' ３ B ４ O １２ (wherein element A is calcium (Ca), and element A′ and element B are each one or more transition metals containing at least manganese (Mn)), In a powder X-ray diffraction pattern using CuKα radiation, the powder has at least two diffraction peaks, namely, the peak with the highest intensity and the peak with the second highest intensity within the range of a diffraction angle 2θ=34° to 35°, The lower-angle diffraction peak P Ｌ The peak intensity of the low-angle peak I Ｌ , high-angle diffraction peak P Ｈ The peak intensity of the high-angle peak I Ｈ When the peak intensity on the high angle side is I Ｈ Low-angle peak intensity I Ｌ The peak intensity ratio (I Ｌ / I Ｈ ) is less than 1 Catalyst for oxygen evolution reaction.

2. The catalyst for oxygen generation reaction according to claim 1, The composition ratio of manganese (Mn) in the A-site ordered perovskite oxide is 6.5 or more when the total composition ratio of the element A' and the element B in the A-site ordered perovskite oxide is 7. Catalyst for oxygen evolution reaction.

3. The catalyst for oxygen generation reaction according to claim 1, The A-site ordered perovskite oxide is characterized in that the element A' and the element B further contain, in addition to manganese (Mn), at least one of nickel (Ni), iron (Fe), and cobalt (Co). Catalyst for oxygen evolution reaction.

4. An electrode comprising the catalyst for the oxygen evolution reaction according to any one of claims 1 to 3.

5. 5. The electrode of claim 4, The electrode is any one of an anode electrode for alkaline water electrolysis, an air electrode of a metal-air secondary battery, an anode electrode of a photoelectrode system, and an anode electrode of a solid oxide electrolysis cell. electrode.

6. An electrochemical device comprising the electrode according to claim 4.

Images