Layered manganese oxide and method for producing the same

Abstract

To provide a catalyst with high catalytic activity for oxygen reduction reactions, hydrogen generation reactions, etc., and especially to provide a catalyst having a platinum group particle with a small particle size.SOLUTION: Provided is a layered manganese oxide having a platinum group metal particle between layers. Also provided is a method for producing the layered manganese oxide having a platinum-group metal particle between layers, or the platinum-group metal particle. In the method, a platinum-group complex is introduced between layers of the layered manganese oxide, the introduced platinum-group complex is reduced by electrolysis, and the potential applied to the platinum-group complex is changed in the positive and negative directions.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a layered manganese oxide containing platinum group particles between layers, an electrode having the layered manganese oxide on its surface, and a method for producing the layered manganese oxide and platinum group particles.

Background Art

[0002] In recent years, fuel cells, which are power generation devices with a low environmental impact, have attracted attention. The oxygen reduction reaction (ORR), which is the reaction on the cathode side, is a complex reaction involving 4 electrons, so the reaction rate is slow. Platinum exhibits the highest ORR activity, but it is a noble metal, and its high cost has become an obstacle to widespread use. In addition, hydrogen gas has attracted attention as a next-generation energy carrier such as a fuel for fuel cells. In particular, the hydrogen generation reaction (HER) capable of producing hydrogen from water holds the key to the large-scale spread of hydrogen gas. Platinum exhibits excellent HER activity, but it has not been put into large-scale practical use due to its high cost. Under such circumstances, in the development of materials based on the conventional bulk electronic state, performance improvement is reaching a plateau, and a new catalyst design is becoming necessary. Therefore, since changing the metal to sub-nano or single atom changes the surface energy state and improves the catalytic activity, the development of sub-nano or single atom metal catalysts has been studied aiming at improving the activity of fuel cell reactions and the utilization efficiency of catalysts (see Non-Patent Document 1 and Non-Patent Document 2). However, since the synthesis requires a plurality of steps including heat treatment, the synthesis procedure is complicated. In addition, in order to prevent aggregation during synthesis, it is necessary to support the metal catalyst by subjecting the carbon material to a special treatment. Therefore, there is a need to produce sub-nano or single atom metal catalysts, particularly platinum group catalysts such as platinum with high catalytic activity, by a simple method.

[0003] On the one hand, manganese dioxide (MnO₂) is inexpensive and abundant in resources. As can be seen from its long-term use as a battery material, it is safe and has a low environmental impact. Therefore, it has been developed as a cathode active material for secondary batteries, various catalysts, and catalyst supports. For example, those in which quaternary ammonium ions are introduced into the interlayer of layered manganese oxides (see Patent Document 1) and those in which cobalt ions are introduced as an aco complex into the interlayer have been proposed (see Non-Patent Document 3). However, what is introduced into the interlayer is an ion, not a metal such as platinum.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The object of the present invention is to provide a catalyst with high catalytic activity for reactions such as oxygen reduction and hydrogen evolution, and in particular to provide a catalyst using platinum group particles with a small particle size. [Means for solving the problem]

[0007] The inventors began investigating catalysts that exhibit excellent activity for oxygen reduction and hydrogen evolution reactions. In the course of this investigation, they focused on sub-nano or single-atom platinum group catalysts and proceeded to develop a method for producing them. They discovered that by utilizing the interlayers of layered manganese oxide, sub-nano or single-atom particles of platinum, palladium, etc., can be produced without complex steps and while suppressing aggregation. The platinum and palladium particles obtained from the interlayers of layered manganese oxide exist as metals, not cations, and exhibited excellent activity as catalysts for oxygen reduction and hydrogen evolution reactions. Furthermore, because layered manganese oxide has both a continuous oxide layer for electron transfer and a continuous space for ion transfer, the layered manganese oxide itself acts as an excellent support for platinum, etc., and layered manganese oxide containing platinum group particles in the interlayers can be used as a catalyst.

[0008] In other words, the present invention is defined by the following: (1) Layered manganese oxide containing platinum group metal particles between layers. (2) The layered manganese oxide according to (1) above, characterized in that the particle size of the platinum group metal particles is ~0.7 nm, which is the atomic diameter of the platinum group. (3) The layered manganese oxide according to (2) above, characterized in that the particle size of the platinum group metal particles is the particle size obtained by subtracting the crystallographic thickness of the layer included in the interlayer distance, which is 0.45 nm, from the interlayer distance of the layered manganese oxide determined by X-ray diffraction measurement. (4) The layered manganese oxide described in (1) above, characterized in that the size of the gaps between layers in the layered manganese oxide is such that the atomic diameter of the platinum group is ~1 nm. (5) An electrode having a layered manganese oxide as described in any of (1) to (4) above on its surface. (6) A method for producing layered manganese oxide or platinum group metal particles containing platinum group metal particles between layers, comprising introducing a platinum group complex between layers of layered manganese oxide and reducing the introduced platinum group complex by electrolysis, wherein the potential applied to the platinum group complex is changed in the positive and negative directions. (7) The manufacturing method according to (6) above, characterized in that a layered manganese oxide with platinum group complexes introduced between the layers is formed on the surface of an electrode, and the potential of the electrode is changed in the positive and negative directions. The present invention can also be specified by the following: (i) Layered manganese oxide containing platinum group particles between layers. (ii) The layered manganese oxide according to (i), characterized in that the particle size of the platinum group particles is approximately 5 nm in atomic size of the platinum group. (iii) An electrode having the layered manganese oxide described in (i) or (ii) above on its surface. (iv) A method for producing layered manganese oxide or platinum group particles containing platinum group particles between layers, comprising introducing a platinum group complex between layers of layered manganese oxide, and reducing the introduced platinum group complex by electrolysis, wherein the potential applied to the platinum group complex is changed in the positive and negative directions. (v) The method for producing (iv) described above, characterized by forming a layered manganese oxide with a platinum group complex introduced between the layers on the surface of an electrode, and changing the potential of the electrode in the positive and negative directions. [Effects of the Invention]

[0009] The present invention can provide platinum group particles of nanoscale or smaller, particularly single atom size or sub-nanometer size, and can provide the platinum group particles supported between layers of a layered manganese oxide. The platinum group particles and the layered manganese oxide containing the platinum group particles between layers exhibit excellent catalytic activity in reactions such as oxygen reduction and hydrogen evolution. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows the X-ray diffraction peaks in Example 1. [Figure 2]Figure 2 shows the XPS spectrum in Example 1. [Figure 3] Figure 3 shows the XPS spectrum in Example 1. [Figure 4] Figure 4 shows the XPS spectrum in Example 1. [Figure 5] Figure 5 shows the X-ray diffraction peaks in Example 3. [Figure 6] Figure 6 shows the XPS spectrum in Example 3. [Figure 7] Figure 7 shows the XPS spectrum in Example 3. [Figure 8] Figure 8 shows the XPS spectrum in Example 3. [Figure 9] Figure 9 shows the XPS spectra in Examples 4-6. [Figure 10] Figure 10 shows the X-ray diffraction peaks in Examples 4-6. [Figure 11] Figure 11 shows the X-ray diffraction peaks in Examples 7-10. [Figure 12] Figure 12 shows the CV results of the precipitate obtained in Example 1. [Figure 13] Figure 13 shows the CV results for a platinum electrode. [Figure 14] Figure 14 shows the CV results for precipitate 3(2) obtained in Example 2. [Figure 15] Figure 15 shows the CV results of the precipitate obtained in Example 3. [Figure 16] Figure 16 shows the CV results for a platinum electrode. [Figure 17] Figure 17 shows the CV results of the precipitate obtained in Comparative Example 1. [Figure 18] Figure 18 shows the CV results of the precipitate obtained in Comparative Example 2. [Figure 19] Figure 19 shows the LSV results for the precipitate obtained in Example 1. [Figure 20]Figure 20 shows the LSV results for a platinum electrode. [Figure 21] Figure 21 shows the LSV results for the precipitate obtained in Example 1 and the LSV of the platinum electrode. [Figure 22] Figure 22 shows the LSV results for precipitate 3, the GC electrode, and the platinum electrode obtained in Example 1. [Figure 23] Figure 23 shows the LSV results (HER activity) of precipitate 3 obtained in Examples 4-6. [Figure 24] Figure 24 shows the LSV results (ORR activity) of precipitate 3 obtained in Examples 4-6. [Modes for carrying out the invention]

[0011] The layered manganese oxide of the present invention is a layered manganese oxide containing platinum group particles between layers. The layered manganese oxide in the present invention is not particularly limited as long as layers of manganese oxide are formed and there are gaps between each layer, but examples include barnesite-type layered manganese oxide. Barnesite-type layered manganese oxide is a layered compound in which octahedral structures represented by MnO6, with manganese at the center and six oxygen atoms at the vertices, spread out to form layers that share vertices and edges with each other, and these layers are stacked on top of each other. 3+ / Mn 4+This is a manganese oxide (MnO2) with mixed valency. It is also called γ-MnO2 based on its crystal structure. In this invention, "interlayer" refers to the gap between layers. The size of the gap between layers in the layered manganese oxide of this invention depends on the size of the platinum group particles contained in the interlayer. If the platinum group particles are single atoms, the gap is approximately the atomic diameter of each platinum group particle. If several single-atom platinum group particles are stacked or the particle diameter of the platinum group particles is sub-nanometer (less than 1 nm), the gap is approximately the atomic diameter of ~1 nm. If there is a lot of overlap of single-atom platinum group particles or the particle diameter of the platinum group particles is nanometer-sized, the gap is 1 nm or more. The platinum group refers to ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt), and these atoms have approximately the same size (atomic diameter). For example, the atomic diameter of platinum is 0.278 nm, and the atomic diameter of palladium is 0.274 nm. However, from the viewpoint of maintaining a layered structure, the size of the gap is preferably 5 nm or less, and more preferably 3 nm or less. In this invention, a single-atom particle refers to a particle that is the size of one atom, that is, a particle that is approximately the same size as the atomic diameter. Furthermore, in this specification, the interlayer distance refers to the value obtained by adding the thickness of one layer to the size of the gap between it and the next layer, and the size of the gap can be determined by subtracting the thickness of one layer from the interlayer distance. The interlayer distance can be determined from the results of X-ray diffraction measurement. In addition, the crystallographic thickness calculated from the crystal structure can be used as the thickness of one layer. In the case of barnesite-type layered manganese oxide, the octahedral structure represented by MnO6, with manganese at the center and six oxygen atoms at its vertices, spreads out planarly, sharing vertices and edges with each other to form a single layer. When the octahedron is placed on a plane with one face facing downwards, the distance between the face touching the plane (bottom face) and the face parallel to this face (top face) is calculated assuming that the manganese and oxygen atoms are spheres with their respective atomic diameters. This value is the crystallographic thickness and can be used as the thickness of a single layer, and a value of 0.45 nm can be used for this purpose.In the present invention, platinum group particles smaller than the size of the voids are contained between the layers of the layered manganese oxide, either dispersed without aggregation, aggregated, or in a state where dispersed particles and aggregated particles coexist.

[0012] The particle size of the platinum group particles in the layered manganese oxide of the present invention is not particularly limited as long as it is small enough to exist between layers without causing delamination of the layers of the layered manganese oxide. For example, the atomic diameter of each platinum group atom can be in the range of ~5 nm. The layered manganese oxide of the present invention has both a continuous oxide layer for electron transfer and a continuous space (gaps between layers) for ion transfer, and contains small platinum group particles between layers, thus exhibiting excellent activity as a catalyst for hydrogen evolution reactions, oxygen reduction reactions, etc. From the viewpoint of further improving catalytic activity, the particle size of the platinum group particles is preferably in the range of ~5 nm of the atomic diameter of each platinum group, more preferably in the range of ~1 nm of the atomic diameter of each platinum group, and preferably in the range of ~0.7 nm of the atomic diameter of each platinum group. The particle size of the platinum group particles can be determined by observation with an electron microscope or by measuring the interlayer distance of the layered manganese oxide by X-ray diffraction. In the present invention, the platinum group particles exist between layers of the manganese oxide as platinum group metals, not as platinum group ions. Therefore, the platinum group particles in this invention refer to platinum group metal particles. However, platinum group ions may be included in a range that does not inhibit catalytic activity. The content of platinum group particles in the layered manganese oxide of this invention is not particularly limited as long as it is within a range that can be used as a catalyst, but examples include 0.05 to 80% by mass, 2 to 70% by mass, 5 to 60% by mass, etc., relative to the manganese oxide (which does not contain platinum group particles). In this invention, a catalyst layer of layered manganese oxide containing platinum group particles between layers can be formed on an electrode substrate or attached to it, and used as an electrode for various batteries such as fuel cells. The electrode substrate is not particularly limited as long as it can be used as an electrode, and examples include metal plates such as platinum, carbon paper, carbon cloth, and carbon materials such as graphite.

[0013] The layered manganese oxide of the present invention is not particularly limited in its manufacturing method, but it can be produced by introducing a platinum group complex between the layers of the layered manganese oxide and electrochemically reducing the platinum group complex by electrolysis. The manufacturing method and type of the layered manganese oxide into which the platinum group complex is introduced are not particularly limited, but for example, it can be obtained by electrochemically oxidizing a divalent manganese compound in the presence of a quaternary ammonium ion. The organic group of the quaternary ammonium can be selected according to the interlayer distance of the target manganese oxide. When the interlayer distance is wide, long-chain or branched alkyl groups, aromatic groups, or polymers such as cationic polymers can be selected, and when the interlayer distance is narrow, a quaternary ammonium with a small molecular weight such as tetramethylammonium can be selected. Examples of quaternary ammonium include tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, and polydiallyldimethylammonium. Compounds such as hydroxides, chlorides, nitrates, and sulfates of these compounds can be dissolved in an electrolyte and used. Examples of the aforementioned compounds include tetramethylammonium chloride, tetraethylammonium bromide, tetrabutylammonium chloride, trimethyldodecylammonium chloride, trimethylaniline chloride, and dimethyl ditert-butylammonium chloride. The divalent manganese compound is not particularly limited as long as it is a divalent manganese compound soluble in the electrolyte, and examples include salts of inorganic acids, such as manganese sulfate, manganese chloride, manganese nitrate, and manganese carbonate, as well as organic manganese compounds such as ammonium manganese oxalate and potassium manganese oxalate. Layered manganese oxide can be deposited on an electrode substrate by dissolving the divalent manganese compound and quaternary ammonium in the electrolyte and anodic oxidizing the divalent manganese ions in the presence of quaternary ammonium ions by electrochemical means.

[0014] In the present invention, the platinum group complex introduced into the interlayer of the layered manganese oxide is not particularly limited as long as it is a complex having a size that can be introduced into the interlayer of the layered manganese oxide and is cationic. The ligands constituting the platinum group complex may be monodentate ligands, bidentate ligands, or ligands having three or more coordination sites. For example, aqua (H2O), ammine (NH3), chloride (Cl - ), cyanide (CN - ), hydroxide (OH - ), thiocyanato (SCN - ), carbonate (CO3 2- ), nitrito (NO2 - ), oxalato (C2O4 2-Examples of ligands include carbonyl(CO), nitrosyl(NO), ethylenediamine, acetylacetonate, 2,2'-dipyridyl, and 1,10-phenanthroline. Examples of complexes of these ligands with platinum group metals include, for example, in the case of platinum, tetraammineplatinum complex, dinitrodiammineplatinum complex, chlorplatinum(IV) hexahydrate, bis(acetylacetonate)platinum complex, and dichloro(η4-1,5-cyclooctadiene)platinum complex. Similarly, in the case of other platinum group metals such as ruthenium, rhodium, palladium, and iridium, examples of complexes with the above ligands include hexaammineruthenium complex, hexaamminerhodium complex, chloropentaamminerhodium complex, tetraamminepalladium complex, and hexaammineiridium complex. There are no particular limitations on the method for introducing platinum group complexes into the interlayers of layered manganese oxide, but for example, they can be introduced by ion exchange with cations present in the interlayers of the manganese oxide before introduction. If quaternary ammonium ions are present in the interlayers of the manganese oxide, the platinum group complex can be introduced by ion exchange with the quaternary ammonium ions. As an example of an ion exchange method, the layered manganese oxide can be immersed in an aqueous solution containing a compound that dissolves in water to produce cations of the platinum group complex. Examples of the aforementioned compounds include, in the case of platinum, tetraammineplatinum(II) chloride, dinitrodiammineplatinum complex, bis(acetylacetonato)platinum complex, dichloro(η4-1,5-cyclooctadiene)platinum complex, etc. Similarly, in the case of other platinum group metals, compounds can be selected in the same way as in the case of platinum, such as hexaammineruthenium(III) chloride, hexaamminerhodium(III) chloride, chloropentaamminerhodium(III) chloride, tetraamminepalladium(II) chloride, hexaammineiridium(III) hydroxide, hexaammineiridium(III) chloride, etc.

[0015] One method for reducing a platinum group complex introduced between layers of manganese oxide to a platinum group complex by electrolysis is to vary the potential applied to the platinum group complex in the positive and negative directions. This method involves immersing an electrode (working electrode) with manganese oxide containing the introduced platinum group complex on its surface in an electrolyte, and a counter electrode, with the working electrode set to a potential at which the reduction of the platinum group complex occurs. Preferably, the potential of the working electrode is varied in the positive and negative directions, so that it is varied between the potential at which reduction occurs and the potential at which oxidation occurs. Specifically, the potential of the working electrode can be swept in the negative direction and then in the positive direction. Alternatively, it can be swept in the positive direction and then in the negative direction. The range of potential to be swept is not particularly limited, but for example, ranges such as -1.5 to 1.5V, -1.5 to 1.0V, -1.3 to 1.0V, -1.3 to 0.7V, and -1.0 to 0.6V can be used for a silver-silver chloride electrode. To efficiently complete metallization, it is preferable to set the lower limit of the potential swept with respect to the silver-silver chloride electrode to approximately -1.0V or less. To perform metallization stably, it is preferable to set the potential range of the sweep to approximately -1.3V to 0.6V. Examples of sweep speeds include 1 to 200 mV / second. If one cycle is defined as one round trip between the lower and upper limits of the potential, the number of cycles can be determined according to the desired particle size of the platinum group metal. However, from the viewpoint of obtaining sub-nanometer or single-atom-size platinum group metal particles, a larger number of cycles is preferable. For example, the number of cycles can be 10 to 150, or 100 to 8000. Furthermore, by changing the potential between the reduction side and the oxidation side, where the sweep speed is faster, the reduction of the platinum group complex occurs gradually, which is thought to generate small-particle-sized platinum group metal particles such as sub-nanometer or single-atom-size. The range of the sweep potential may be changed during the process. For example, the sweep may be started in a narrow range and gradually or stepwise expanded, or the expanded range may be narrowed. Furthermore, the sweeping potential range (potential difference) may be constant, and examples of such ranges include 3V, 2V, 1.7V, etc. In the manufacturing method of the present invention, the particle size of the platinum group particles produced can be adjusted by adjusting electrochemical conditions such as the sweeping speed, the number of cycles, and the sweeping potential range (potential difference).According to the manufacturing method of the present invention, platinum group particles are produced in the narrow interlayer region of the layered manganese oxide, making it possible to produce platinum group particles with small particle sizes while suppressing aggregation. Furthermore, by changing the potential when electrolyzing the platinum group complex, extremely small particle sizes such as sub-nanometer and single-atom size can be produced. In addition, since the produced platinum group particles are supported in the interlayer region of the layered manganese oxide from the time of production, there is no need to support them on another support, and the layered manganese oxide containing the platinum group particles in the interlayer region can be used as a catalyst. Therefore, the manufacturing method of the present invention is both a method for producing platinum group particles and a method for producing layered manganese oxide containing platinum group particles in the interlayer region. The platinum group particles in the present invention have higher catalytic activity than conventional platinum group catalysts, so the same catalytic effect can be achieved with a smaller amount than conventional methods, and as a result, the amount of platinum group used can be reduced. The layered manganese oxide produced by the manufacturing method of the present invention may be peeled off from the electrode and used, but it can also be used as an electrode as is, and a catalyst electrode can be formed without the need to apply a catalyst to the electrode again. The electrode substrate of the working electrode used in the manufacturing method of the present invention is not particularly limited as long as it is an electrode used in electrolysis, and examples include metal plates such as platinum, carbon paper, carbon cloth, and carbon materials such as graphite. Examples of counter electrodes include platinum, porous carbon, gold, and titanium. [Examples]

[0016] The present invention will be described in detail below with reference to examples of the present invention, but the technical scope of the present invention is not limited to these examples.

[0017] [Example 1] The layered manganese oxide of the present invention was prepared by the following steps 1 to 3. (Step 1) 0.7089 g of 50 mM [CH3(CH2)3]4NCl(TBACl) and 0.024 g of 2 mM MnSO4·5H2O were dissolved in distilled water to make 50 mL. The resulting aqueous solution was bubbling with N2 for 20 minutes to remove oxygen from the solution. Using a salt bridge, the reference electrode was Ag / AgCl, the counter electrode was a Pt mesh, and the working electrode was a 5 mm diameter glassy carbon rotating disk electrode (GC electrode) polished with polishing diamond and alumina. The voltage was maintained at 1.0 V and the flow rate was 200 mC / cm. 2 Electrochemical deposition was performed under the specified conditions, and a precipitate was deposited on the GC electrode. The precipitate after step 1 is referred to as precipitate 1. (Step 2) The precipitate on the GC electrode obtained in Step 1 was lightly washed with distilled water without separating it from the GC electrode, and then vacuum-dried at room temperature for 1 hour. After drying, the GC electrode with the precipitate attached was immersed in a 50 mM Pt(NH3)4Cl2 solution for 24 hours to perform ion exchange. The precipitate after Step 2 (after ion exchange) is referred to as Precipitate 2. (Step 3) A three-electrode cell was constructed using the GC electrode with the precipitate obtained in Step 2 attached as the working electrode, the Pt wire as the counter electrode, and Ag / AgCl as the reference electrode. 0.1M KOH, obtained by bubbling N2 for 20 minutes, was used as the electrolyte. A potentiostat connected to the cell was used to start a potential sweep, setting the working electrode potential to -0.975~0.050V (vs Ag / AgCl). At this time, the potential sweep start potential was -0.974V (vs Ag / AgCl). The sweep speed was set to 50mV / sec, and the potential sweep width was gradually changed to an upper limit potential of 0.7V (vs Ag / AgCl) and a lower limit potential of -1.3V (vs Ag / AgCl). The potential width was 0.01V in each case. Ag / AgCl The potential was gradually changed, and the total number of potential sweep cycles was 100. The precipitate after step 3 (after potential sweep) is referred to as precipitate 3.

[0018] [Example 2] After performing steps 1 and 2 as in Example 1, the sweep speed was set to 90 mV / sec, and the potential sweep width was gradually changed to an upper potential of 0.475 V (vs Ag / AgCl) and a lower potential of -1.175 V (vs Ag / AgCl) (each with a potential width of 0.01 V). Ag / AgClStep 3 was performed in the same manner as in Example 1, except that the voltage was changed gradually, and the total number of potential sweep cycles was 100 cycles. The precipitate after step 3 in Example 2 is called precipitate 3(2).

[0019] [Example 3] The layered manganese oxide of the present invention was prepared by the following steps 1 to 3. (Step 1) 0.7089 g of 50 mM [CH3(CH2)3]4NCl(TBACl) and 0.024 g of 2 mM MnSO4·5H2O were dissolved in distilled water to make 50 mL. The resulting aqueous solution was bubbling with N2 for 20 minutes to remove oxygen from the solution. Using a salt bridge, the reference electrode was Ag / AgCl, the counter electrode was Pt mesh, and the working electrode was an FTO electrode, with a voltage of 1.0 V and a flow rate of 200 mC / cm². 2 Electrochemical deposition was carried out under the specified conditions, and precipitates were deposited on the FTO electrode. The precipitate after step 1 is designated as precipitate 1(3). (Step 2) The precipitate on the FTO electrode obtained in Step 1 was lightly washed with distilled water without separating it from the FTO electrode, and then vacuum-dried at room temperature for 1 hour. After drying, the FTO electrode with the precipitate attached was immersed in a 50 mM Pd(NH3)4Cl2 solution for 24 hours to perform ion exchange. The precipitate after Step 2 (after ion exchange) is referred to as Precipitate 2 (3). (Step 3) A three-electrode cell was constructed using the FTO electrode with the precipitate obtained in Step 2 attached as the working electrode, a Pt wire as the counter electrode, and Ag / AgCl as the reference electrode. 0.1M KOH, obtained by bubbling N2 for 20 minutes, was used as the electrolyte. A potentiostat connected to the cell was used to start a potential sweep, setting the working electrode potential to -0.975~0.050V (vs Ag / AgCl). At this time, the potential sweep start potential was -0.974V (vs Ag / AgCl). The sweep speed was set to 50mV / sec, and the potential sweep width was gradually changed to an upper limit potential of 0.7V (vs Ag / AgCl) and a lower limit potential of -1.2V (vs Ag / AgCl). The potential width was 0.05V in each case. Ag / AgCl The potential was gradually changed, and the total number of potential sweep cycles was 30. The precipitate after step 3 (after potential sweep) is referred to as precipitate 3(3).

[0020] [Example 4] The layered manganese oxide of the present invention was prepared by the following steps 1 to 3. (Step 1) 0.7089 g of 50 mM [CH3(CH2)3]4NCl(TBACl) and 0.024 g of 2 mM MnSO4·5H2O were dissolved in distilled water to make 50 mL. The resulting aqueous solution was bubbling with N2 for 20 minutes to remove oxygen from the solution. Using a salt bridge, the reference electrode was Ag / AgCl, the counter electrode was a Pt mesh, and the working electrode was a 5 mm diameter glassy carbon rotating disk electrode (GC electrode) polished with polishing diamond and alumina. The voltage was maintained at 1.0 V and the flow rate was 200 mC / cm. 2 Electrochemical deposition was performed under the specified conditions, and a precipitate was deposited on the GC electrode. The precipitate after step 1 is referred to as precipitate 1. (Step 2) The precipitate on the GC electrode obtained in Step 1 was lightly washed with distilled water without separating it from the GC electrode, and then vacuum-dried at room temperature for 1 hour. After drying, the GC electrode with the precipitate attached was immersed in a 50 mM Pt(NH3)4Cl2 solution for 3 hours to perform ion exchange. The precipitate after Step 2 (after ion exchange) is referred to as Precipitate 2. (Step 3) A three-electrode cell was constructed using the GC electrode with the precipitate obtained in Step 2 attached as the working electrode, a carbon rod as the counter electrode, and Ag / AgCl as the reference electrode. 0.05 M [CH3(CH2)3]4NOH(TBAOH) obtained by bubbling N2 for 20 minutes was used as the electrolyte. Using a potentiostat connected to the cell, the potential of the working electrode was set to -0.1 to 1.5 V (vs RHE) and a potential sweep was started. The sweep rate was set to 10 mV / second and the potential sweep was performed for 40 hours. The precipitate after Step 3 (after potential sweep) is referred to as precipitate 3 (4). Note that -0.1 to 1.5 V (vs RHE) can be converted to -1.013 to 0.587 V (vs Ag / AgCl) using the conversion formula "E(Ag / AgCl) = E(RHE) - 0.059 pH - 0.199".

[0021] [Example 5] After performing steps 1 and 2 as in Example 4, step 3 was performed, which is the same as in Example 4 except that the sweep speed was set to 50 mV / sec. The precipitate after step 3 in Example 5 is referred to as precipitate 3(5).

[0022] [Example 6] After performing steps 1 and 2 as in Example 4, step 3 was performed, which is the same process as in Example 4 except that the sweeping speed was set to 150 mV / sec. The precipitate after step 3 in Example 6 is referred to as precipitate 3(6).

[0023] [Examples 7-10] The layered manganese oxide of the present invention was prepared by the following steps 1 to 3. (Step 1) 0.7089 g of 50 mM [CH3(CH2)3]4NCl(TBACl) and 0.024 g of 2 mM MnSO4·5H2O were dissolved in distilled water to make 50 mL. The resulting aqueous solution was bubbling with N2 for 20 minutes to remove oxygen from the solution. Using a salt bridge, the reference electrode was Ag / AgCl, the counter electrode was a Pt mesh, and the working electrode was a 5 mm diameter glassy carbon rotating disk electrode (GC electrode) polished with polishing diamond and alumina. The voltage was maintained at 1.0 V and the flow rate was 200 mC / cm. 2 Electrochemical deposition was performed under the specified conditions, and a precipitate was deposited on the GC electrode. The precipitate after step 1 is referred to as precipitate 1. (Step 2) The precipitate on the GC electrode obtained in Step 1 was lightly washed with distilled water without separating it from the GC electrode, and then vacuum-dried at room temperature for 1 hour. After drying, the GC electrode with the precipitate attached was immersed in a 50 mM Pt(NH3)4Cl2 solution for 3 hours to perform ion exchange. The precipitate after Step 2 (after ion exchange) is referred to as Precipitate 2. (Step 3) A three-electrode cell was constructed using the GC electrode with the precipitate obtained in Step 2 attached as the working electrode, a carbon rod as the counter electrode, and Ag / AgCl as the reference electrode. 0.1M KOH obtained by bubbling N2 for 20 minutes was used as the electrolyte. Using a potentiostat connected to the cell, a potential sweep was started with the working electrode potential set to 0.05~1.5V (vs RHE). Potential sweeps were performed with sweep speeds of 10mV / sec, 30mV / sec, 50mV / sec, and 150mV / sec, with sweep cycles of 100, 94, 100, and 132 cycles, respectively, resulting in Examples 7-10. The precipitates after Step 3 (after potential sweep) in Examples 7-10 are designated as Precipitate 3(7), Precipitate 3(8), Precipitate 3(9), and Precipitate 3(10), respectively. Note that 0.05~1.5V (vs RHE) can be converted using the conversion formula "E(Ag / AgCl)=E(RHE)-0.059pH-0.199" to -0.975~0.475V (vs Ag / AgCl).

[0024] [Comparative Example 1] After performing steps 1 and 2 as in Example 1, the potential of the working electrode was fixed at 0.475V (vs Ag / AgCl) for 30 minutes using a three-electrode cell with the same configuration as in Example 1.

[0025] [Comparative Example 2] After performing steps 1 and 2 as in Example 1, the potential of the working electrode was fixed at -1.175V (vs Ag / AgCl) for 30 minutes using a three-electrode cell with the same configuration as in Example 1.

[0026] (X-ray diffraction measurement) Precipitates 1-3 from Example 1 were detached from the GC electrode, and each was subjected to X-ray diffraction measurements (Cu-Ka emission, Rigaku UltimaIV, Rigaku Corporation). X-ray diffraction measurements were also performed on the GC and the glass. The obtained X-ray diffraction patterns are shown in Figure 1. In all of the precipitates 1-3, equally spaced diffraction peaks characteristic of layered manganese dioxide were observed at 2θ = 7°, 14°, 21° (precipitate 1), 12°, 24° (precipitate 2), 12.7°, 23.2°, 25.8° (precipitate 3). The MnO2 peaks in precipitates 2 and 3 were shifted to higher angles compared to precipitate 1. This indicates that the interlayer distance decreased while maintaining the structure. Furthermore, using the Bragg condition (nλ=2dsinθ) to determine the interlayer distance of the thin film from the peak angular position θ of the diffracted X-rays and the X-ray wavelength λ (=1.54051 Å), we obtained 1.24 nm (precipitate 1) and 0.74 nm (precipitate 2). The latter corresponds to the sum of the NH3 molecular diameter and the crystallographic thickness of the MnO2 sheet (1 layer) (0.45 nm). This corresponds to the TBA that supported the interlayer of precipitate 1. + However, through the processing in step 2, Pt(NH3)4 2+ This is thought to be because it was replaced by [another substance]. Similarly, calculations showed that the interlayer distance of precipitate 3 was 0.69 nm. Step 3 reduced the interlayer distance, and since NH3 cannot exist at this interlayer distance, the treatment in step 3 resulted in the formation of Pt(NH3)4 2+ It is thought that the ligand NH3 was eliminated. Considering the crystallographic thickness of the MnO2 sheet, the particle size of the Pt particles generated by the elimination of NH3 can be estimated to be about 0.24 nm. This is very close to the reported single atomic diameter of Pt (about 0.27 nm), suggesting that Pt single atom particles were synthesized. Since diffraction peaks attributed to Pt nanoparticles were observed around 39 and 47 degrees, it is thought that Pt nanoparticles coexist in addition to the aforementioned Pt single atom particles.

[0027] X-ray diffraction measurements were performed on the FTO electrodes with the precipitates obtained in steps 1-3 of Example 3 attached (Cu-Ka emission, Rigaku UltimaIV, Rigaku Corporation). X-ray diffraction measurements were also performed on the FTO. The obtained X-ray diffraction patterns are shown in Figure 5. In all of the precipitates 1(3) to 3(3), equally spaced diffraction peaks characteristic of layered manganese dioxide were observed at 2θ = 7°, 14°, 21° (precipitate 1), 12°, 24° (precipitate 2), 12.5°, 25.1° (precipitate 3). The MnO2 peaks in precipitates 2(3) and 3(3) were shifted to higher angles compared to precipitate 1(3). This indicates that the interlayer distance decreased while maintaining the structure. Furthermore, using the Bragg condition (nλ=2dsinθ) to determine the interlayer distance of the thin film from the peak angular position θ of the diffracted X-rays and the X-ray wavelength λ (=1.54051 Å), we obtained 1.25 nm (precipitate 1) and 0.75 nm (precipitate 2). The latter corresponds to the sum of the NH3 molecular diameter and the crystallographic thickness of the MnO2 sheet (1 layer) (0.45 nm). This corresponds to the TBA that supported the interlayer of precipitate 1. + However, through the processing in step 2, Pd(NH3)4 2+ This is thought to be because it was replaced by [another substance]. Similarly, calculations showed that the interlayer distance of precipitate 3 was 0.71 nm. Step 3 reduced the interlayer distance, and since NH3 cannot exist at this interlayer distance, the treatment in step 3 resulted in the formation of Pd(NH3)4 2+ It is thought that the ligand NH3 was desorbed. Considering the crystallographic thickness of the MnO2 sheet, the particle size of the Pd particles generated by the desorption of NH3 can be estimated to be about 0.26 nm. This is very close to the reported single atomic diameter of Pd (about 0.27 nm), suggesting that Pd single atom particles were synthesized. Diffraction peaks attributed to Pd nanoparticles are known to be observed around 40° and 46°, but these were not observed in this case. From this, it is thought that precipitate 3 contains only the aforementioned Pd single atom particles.

[0028] (X-ray photoelectron spectroscopy measurement) Precipitates 1-3 from Example 1 were detached from the GC electrode and each was subjected to X-ray photoelectron spectroscopy (XPS) (K-Alpha, Thermo Scientific). The results are shown in Figures 2-4. The presence of Mn was confirmed because spectral peaks in the Mn2p range were observed in precipitates 1-3 (Figure 2). A spectral peak of cationic N species was observed in precipitate 1, therefore TBA + We confirmed that it had been introduced (Figure 3). In addition, in precipitate 2, the spectral peak of cationic N species disappeared and a peak derived from NH3 was observed (Figure 3), and in the range of Pt4f, Pt that was not observed in precipitate 1 was observed. 2+ and Pt 4+ Since a peak was observed (Figure 4), precipitate 2 is TBA + Pt(NH3)4 2+ Replaced with Pt(NH3)4 2+ It was confirmed that it had been introduced. In precipitate 3, Pt 2+ and Pt 4+ Not the peak of Pt, but Pt derived from bulk Pt 0 A peak was observed. Also, Pt from bulk Pt 0 In addition to the peak, two types of Pt4f peaks were observed. The Pt4f peak shifts to the higher energy side as the particle size decreases, indicating that precipitate 3 contains Pt particles of multiple sizes, and in addition to Pt aggregates, extremely small Pt particles (Pt sub It is thought that (as indicated) is being formed. From the results of X-ray diffraction and X-ray photoelectron spectroscopy measurements, precipitate 1 is TBA + / MnO2, precipitate 2 is Pt(NH3)4 2+ Precipitate 3 was identified as Pt / MnO2. The mass ratio of MnO2 to Pt in Precipitate 3 was determined from the ratio of atoms obtained from XPS measurement, and it was found to be MnO2:Pt 1:0.45.

[0029] X-ray photoelectron spectroscopy (XPS) was performed on the FTO electrodes with the precipitates obtained in steps 1-3 of Example 3 (K-Alpha, Thermo Scientific). The results are shown in Figures 6-8. The presence of Mn was confirmed because spectral peaks in the Mn2p range were observed in precipitates 1(3)-3(3) (Figure 6). Since a spectral peak of cationic N species was observed in precipitate 1(3), TBA was identified. + We confirmed that it had been introduced (Figure 7). In addition, in precipitate 2(3), the spectral peak of cationic N species disappeared and a peak derived from NH3 was observed (Figure 7), and in the range of Pd3d, Pd that was not observed in precipitate 1 was observed. 2+ A peak was observed (Figure 8), therefore, in precipitate 2(3) TBA + Pd(NH3)4 2+ Replaced with Pd(NH3)4 2+ It was confirmed that it had been introduced. In precipitate 3(3), Pd 2+ It's not a peak, but rather extremely small Pd particles (Pd sub (Notation) Pd 0 A peak was observed (Figure 8). Here, the Pd3d peak shifts to the higher energy side as the particle size decreases, so precipitate 3 contains extremely small Pd particles (Pd sub It is thought that (as indicated) is being formed. From the results of X-ray diffraction and X-ray photoelectron spectroscopy, precipitate 1(3) is TBA + / MnO2, precipitate 2(3) is Pd(NH3)4 2+ Precipitate 3(3) was identified as Pd / MnO2. The mass ratio of MnO2 to Pd in ​​precipitate 3(3) was determined from the ratio of atoms obtained from XPS measurement, and it was found to be MnO2:Pd 1:0.07.

[0030] Precipitates 3(4) to 3(6) from Examples 4 to 6 were exfoliated from the GC electrode and each was subjected to X-ray photoelectron spectroscopy (XPS) (K-Alpha, Thermo Scientific). The results are shown in Figure 9. In precipitates 3(4) to 3(6), in precipitate 3(4), Pt originated from the Pt bulk. 0 In addition to the peak, there are two types of Pt4f peaks (Ptsub (as indicated) was observed. In addition, in precipitates 3(5) and 3(6), Pt originated from the Pt bulk. 0 No peak was observed, Pt sub Only the Pt4f peak was observed. In addition, precipitates 1 and 2 from Example 4 and precipitates 3(4) to 3(6) from Examples 4 to 6 were peeled off from the GC electrode and X-ray diffraction measurements were performed on each (Cu-Ka emission, Rigaku UltimaIV, manufactured by Rigaku Corporation). The obtained X-ray diffraction patterns are shown in Figure 10. From top to bottom in Figure 10, precipitates 1, 2, 3(4), 3(5), and 3(6) are shown. In Figure 9, Pt 10 / MnO2, Pt 50 / MnO2 and Pt 150 / MnO2 is Pt in Figure 10. (10) / MnO2, Pt (50) / MnO2 and Pt (150) / MnO2 represents precipitates 3(4), 3(5), and 3(6), respectively. In precipitate 1, equally spaced diffraction peaks characteristic of layered manganese dioxide were observed at 2θ = 7°, 14°, and 21°, respectively, originating from the diffraction of the (001), (002), and (003) planes. In precipitate 2, equally spaced diffraction peaks characteristic of layered manganese dioxide were observed at 11.59° and 24.21°, respectively, originating from the diffraction of the (001) and (002) planes. In precipitate 3(4), equally spaced diffraction peaks characteristic of layered manganese dioxide originating from the diffraction of the (001) and (002) planes were observed at 2θ = 11.97°, 18.36°, and 24.75°, in precipitate 3(5), at 12.19° and 25.11°, and in precipitate 3(6), at 12.45° and 25.18°, respectively, as shown in Figure 10. The interlayer distances of the thin films were determined using the Bragg condition (nλ=2dsinθ) based on the peak angular position θ of the diffracted X-rays and the X-ray wavelength λ (=1.54051 Å). For precipitate 3(4), the interlayer distances were 0.72 nm and 0.96 nm, for precipitate 3(5) it was 0.73 nm, and for precipitate 3(6) it was 0.71 nm. For precipitate 3(4), since the diffraction peak of the (001) plane (2θ=11.97°) was broad, the interlayer distance was calculated from the diffraction peaks of the (002) plane (18.36°, 24.75°). In other cases, the interlayer distance was determined from the diffraction peak of the (001) plane. Considering the crystallographic thickness (0.45 nm) of the MnO2 sheet (layer), the particle sizes of the generated platinum particles were calculated to be 0.27 nm and 0.51 nm for precipitate 3(4), 0.28 nm for precipitate 3(5), and 0.26 nm for precipitate 3(6). Since the calculated particle sizes of 0.27 nm and 0.28 nm are very close to the single atomic diameter of Pt (approximately 0.27 nm), it is thought that the platinum particles exist as single-atom particles. Furthermore, in the case of the calculated particle size of 0.51 nm (i.e., when the gap between layers is 0.51 nm), it is possible that platinum particles with a particle size of 0.51 nm are present, that platinum particles with a particle size of less than 0.51 nm are partially overlapping (aggregated), or that both of these are present. The results shown in Figures 9 and 10 indicate that a layered manganese oxide with platinum particles contained between layers is obtained, and that the particle size of the contained platinum particles changes depending on the sweep rate in step 3.

[0031] Precipitates 3(7) to 3(10) from Examples 7 to 10 were peeled from the GC electrode and each was subjected to X-ray photoelectron spectroscopy (XPS) (K-Alpha, Thermo Scientific). The results are shown in Figure 11. The interlayer distance of the thin films was determined using the Bragg condition (nλ=2dsinθ) from the peak angular position θ of the diffracted X-rays and the X-ray wavelength λ (=1.54051 Å), and was found to be 0.951 nm for precipitate 3(7), 0.726 nm for precipitate 3(8), 0.693 nm for precipitate 3(9), and 0.690 nm for precipitate 3(10). Considering the crystallographic thickness of the MnO2 sheet (0.45 nm), the particle sizes of the synthesized platinum particles were calculated to be 0.501 nm for precipitate 3(7), 0.276 nm for precipitate 3(8), 0.243 nm for precipitate 3(9), and 0.240 nm for precipitate 3(10). These results also show that as the sweep rate increases, the particle size of the synthesized platinum particles decreases or aggregation decreases.

[0032] (Cyclic voltammetry) Cyclic voltammetry (CV) was performed using the GC electrode (with a layer of precipitate 3 formed on its surface) and platinum electrode obtained in step 3 of Example 1 as working electrodes, respectively. A Pt wire was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M KOH as the electrolyte. The temperature was set to 25°C. The results are shown in Figures 9 and 10. For the GC electrode obtained in step 3, the values ​​ranged from 0.05 to 1.725 V. RHE Measurements were performed within the range (sweep speed 50 mV / sec) (Figure 9). For the platinum electrode, the range was 0.05~1.725V. RHE Measurements were taken within this range (sweep speed 50 mV / sec) (Figure 10). Figure 9 shows the range of 0.05~1.175V for the GC electrode obtained in step 2 of Example 1. RHE The results of CV performed within the specified range are also shown. The presence of electrochemically active Pt in the interlayer of Pt / MnO2 was indicated by the confirmation of a Pt-specific redox peak in precipitate 3. The shaded areas in Figures 9 and 10 represent the total amount of electricity due to hydrogen desorption, and the amount of electricity obtained from the shaded areas is the amount of electricity for hydrogen desorption per unit platinum surface area, which is 210 μC / cm². 2By dividing by , the active surface area (ECSA) was determined to be 0.085 cm² for the GC electrode obtained in step 3. 2 Next, using the GC electrode obtained in step 3 of Example 2 (with a layer of precipitate 3(2) formed on its surface), -0.15~1.5V was measured in the same manner as above. RHE Measurements were performed within the specified range (sweep speed 90 mV / sec). The results are shown in Figure 11. From Figure 11, an increase in the reduction current originating from the hydrogen evolution reaction was confirmed in the region below 0V, and metallization of Pt due to repeated cycles was confirmed.

[0033] Cyclic voltammetry (CV) was performed using the FTO electrodes (with a layer of precipitate 1(3) or 3(3) formed on the surface) and Pd electrodes obtained in steps 1 and 3 of Example 3 as working electrodes, respectively. A Pt wire was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M KOH as the electrolyte. The results are shown in Figures 12 and 13. For the FTO electrodes obtained in steps 1 and 3, the voltage range was -0.175 to 1.725 V. RHE Measurements were taken within the range (sweep speed 50 mV / sec) (Figure 12). For the Pd electrode, the range was -0.175 to 1.725 V. RHE Measurements were performed within the specified range (sweep rate 50 mV / sec) (Figure 13). The presence of electrochemically active Pd in ​​the Pd / MnO2 interlayer was indicated by the confirmation of a Pd-specific redox peak in precipitate 3(3). The shaded area in Figure 13 represents the total charge due to PdO reduction. The active surface area (ECSA) was estimated from the charge obtained from the area of ​​the peak at a similar position in Figure 12, and the ECSA of the FTO electrode obtained in step 3 was found to be 0.076 cm². 2 That was the case.

[0034] Using the GC electrodes obtained in Comparative Examples 1 and 2, the same method as in Example 1 was used, with Comparative Example 1 measuring -0.11 to 0.3V. RHE Measurements were taken within the range (sweep speed 90mV / sec), and for Comparative Example 2, the range was -0.15 to 0.3V. RHEMeasurements were performed within the specified range (sweep speed 90 mV / sec). The results for Comparative Example 1 are shown in Figure 14, and the results for Comparative Example 2 are shown in Figure 15. From Figures 14 and 15, it can be seen that almost no reduction current originating from the hydrogen evolution reaction was observed even in the region below 0 V. This indicates that Pt was not metallized in Comparative Examples 1 and 2, where constant potential was maintained.

[0035] (Hydrogen evolution reaction) To evaluate the activity for the hydrogen evolution reaction (HER), the GC electrode (with a layer of precipitate 3 formed on its surface) and the platinum electrode obtained in step 3 of Example 1 were used as working electrodes, and linear sweep voltammetry (LSV) was performed at -0.175 to 1.725 V. RHE The test was performed within the specified range (sweep speed 50 mV / sec). A Pt wire was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M KOH as the electrolyte. The current value was normalized by the calculated ECSA. The results are shown in Figures 16-18. Figure 16 shows the results for the GC electrode obtained in step 3 of Example 1, Figure 17 shows the results for the platinum electrode, and Figure 18 is a superimposed view of Figures 16 and 17. The HER start potential was 0.0942 V for the GC electrode obtained in step 3. RHE Therefore, the platinum electrode yielded 0.114V. RHE Therefore, the GC electrode obtained in step 3 showed improved HER activity because it reacted faster.

[0036] Using the GC electrode obtained in step 3 of Examples 4-6 (with a layer of precipitate 3 formed on its surface) as the working electrode, linear sweep voltammetry (LSV) was performed at -0.1 to 0.2V. RHE The experiment was conducted within the specified range (sweep speed 50 mV / sec). A carbon rod was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M KOH as the electrolyte. The results are shown in Figure 23. Figure 23 shows Pt 10 / MnO2, Pt 50 / MnO2 and Pt 150 / MnO2 represents precipitate 3(4) from Example 4, precipitate 3(5) from Example 5, and precipitate 3(6) from Example 6, respectively. As shown in Figure 23, precipitates 3(4), 3(5), and 3(6) all exhibit HER activity, but while precipitates 3(4) and 3(5) show similar HER activity, precipitate 3(6) shows lower HER activity. From this, it can be seen that HER activity can be adjusted by adjusting the sweep rate when reduction is performed by electrolysis in step 3.

[0037] (Oxygen reduction reaction) To evaluate the activity in the oxygen reduction reaction (ORR), the GC electrode obtained in step 3 of Example 1 (with a layer of precipitate 3 formed on its surface), the GC electrode without precipitates on its surface, and the platinum electrode were used as working electrodes, and linear sweep voltammetry (LSV) was performed at 1.50 to 0.05 V. RHE The procedure was performed within the specified range. The sweep speed was set to 10 mV / sec, and the rotation speed to 4000 rpm to remove oxygen bubbles on the working electrode. A Pt wire was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M KOH as the electrolyte. The current value was normalized by the calculated ECSA. The results are shown in Figure 19. It was confirmed that the GC electrode obtained in step 3 showed an earlier start of ORR and improved ORR activity compared to the platinum electrode.

[0038] Using the GC electrode obtained in step 3 of Examples 4-6 (with a layer of precipitate 3 formed on its surface) as the working electrode, linear sweep voltammetry (LSV) was performed at 0.7-1.2V. RHE The experiment was conducted within the specified range. The sweep speed was set to 10 mV / sec, and the rotation speed was set to 4000 rpm to remove oxygen bubbles on the working electrode. A Pt wire was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.1 M KOH as the electrolyte. The results are shown in Figure 24. Pt in Figure 24 10 / MnO2, Pt 50 / MnO2 and Pt 150 / MnO2 represents precipitate 3(4) from Example 4, precipitate 3(5) from Example 5, and precipitate 3(6) from Example 6, respectively. In the results shown in Figure 24, precipitates 3(4), 3(5), and 3(6) all exhibit ORR activity, but while precipitates 3(4) and 3(5) show similar ORR activity, precipitate 3(6) shows lower ORR activity. From this, it can be seen that ORR activity can be adjusted by adjusting the sweep rate when reduction is performed by electrolysis in step 3. [Industrial applicability]

[0039] The layered manganese oxide of the present invention exhibits excellent catalytic activity and can therefore be suitably used as a catalyst for oxygen reduction reactions, hydrogen evolution reactions, and the like. Furthermore, the manufacturing method of the present invention can produce sub-nanometer and single-atom-sized platinum group particles, as well as layered manganese oxides containing such platinum group particles between layers, making it suitable for producing catalysts with excellent catalytic activity for oxygen reduction reactions, hydrogen evolution reactions, and the like.

Claims

1. Layered manganese oxide containing platinum group metal particles between layers.

2. The layered manganese oxide according to claim 1, characterized in that the particle size of the platinum group metal particles is such that the atomic diameter of the platinum group in the platinum group metal particles is ~0.7 nm, and the particle size is determined by subtracting the crystallographic thickness of the layer included in the interlayer distance, which is 0.45 nm, from the interlayer distance of the layered manganese oxide determined by X-ray diffraction measurement.

3. The layered manganese oxide according to claim 1, characterized in that the size of the gaps between layers in the layered manganese oxide is such that the atomic diameter of the platinum group metals is approximately 1 nm.

4. An electrode having a layered manganese oxide on its surface according to any one of claims 1 to 3.

5. A method for producing layered manganese oxide containing platinum group metal particles between layers, comprising introducing a platinum group complex into the interlayers of layered manganese oxide, and reducing the introduced platinum group complex by electrolysis, the method comprising the steps of changing the potential applied to the platinum group complex in the positive direction and changing it in the negative direction.

6. The manufacturing method according to claim 5, characterized by comprising the steps of forming a layered manganese oxide with a platinum group complex introduced between the layers on the surface of an electrode, and changing the potential of the electrode in the positive direction and changing it in the negative direction.

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