A single-atom catalyst based on functionalized MOF, its preparation method and application
By preparing Pt-X bimetallic single-atom catalysts, the problems of slow ORR reaction kinetics and the susceptibility of noble metal catalysts to CO poisoning in fuel cells were solved, achieving efficient, stable and low-cost ORR and HOR reactions, and simplifying the catalyst preparation process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2022-12-14
- Publication Date
- 2026-05-26
Smart Images
Figure CN116130686B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrocatalyst materials technology, and in particular to a single-atom catalyst based on functionalized MOF, its preparation method, and its application. Background Technology
[0002] A fuel cell is a clean energy conversion device that uses hydrogen as fuel, directly converting the chemical energy of hydrogen into electrical energy. During the operation of a fuel cell, the oxygen reduction reaction (ORR) occurs at the cathode, and the hydrogen oxidation reaction (HOR) occurs at the anode. Because the ORR reaction is slow, a precious metal catalyst is required. Currently, the hydrogen used in fuel cells is mostly industrial by-product hydrogen or hydrogen produced through reforming reactions, which contains CO impurities. This can poison the HOR catalyst during use. Therefore, the research on efficient ORR / HOR electrocatalysts has always been a focus of attention.
[0003] Metal-organic frameworks (MOFs) are a class of materials with ordered topological structures formed by the coordination complexation of metal ions and organic ligands. They possess characteristics such as high specific surface area and tunable structure. In recent years, due to their high specific surface area and tunable structure, MOFs have been widely used as support materials for single-atom catalysts. However, some problems still need to be solved, such as poor conductivity and easy structural collapse. Therefore, to address these problems, it is necessary to prepare MOF catalysts with stable structures and excellent conductivity.
[0004] Meanwhile, most current methods for preparing single-atom catalysts have drawbacks such as complex preparation methods, high preparation costs, and difficulty in industrial production. Therefore, it is urgent to develop a general strategy for preparing single-atom catalysts using MOF as a support material with a simple synthesis method. Summary of the Invention
[0005] The purpose of this invention is to provide a single-atom catalyst based on a functionalized MOF for use in HOR and ORR reactions, and its preparation method. This Pt-X bimetallic single-atom catalyst has the advantages of structural stability and excellent electrical conductivity, while its preparation method has the advantages of a short preparation process and low cost.
[0006] To achieve the above objectives, the technical solution of the present invention is as follows:
[0007] This invention provides a method for preparing a Pt-X bimetallic single-atom catalyst, the method comprising the following steps:
[0008] S1. Take the X metal precursor solution, Zn precursor powder, and 2-methylimidazolium organic ligand powder and dissolve them in alcohol solvent I. After ultrasonic mixing, a mixture is obtained. The mixture is then subjected to microwave heating, oven drying, and tube furnace calcination in sequence to finally obtain the MOF material supported on X metal single atoms, i.e., X / MOF material, wherein one or more of Fe, Co, Ir, Ru, and Au are present.
[0009] S2. Dissolve the X / MOF material obtained in step S1 in alcohol solvent II, add carbon powder, sonicate, add Pt precursor solution, stir to obtain Pt adsorbed carbon material.
[0010] S3. Add an alkaline solvent to the carbon material adsorbed by Pt in step S2 to adjust the pH of the solution, and obtain mixture two. Microwave heat mixture two, then wash with deionized water, centrifuge, dry and calcine under an inert atmosphere to finally obtain the Pt-X bimetallic single-atom catalyst.
[0011] In the above technical solution, further, in step S1, based on one volume of the mixed liquid, the concentration of Zn in the Zn precursor powder is 25-30 mmol / L, and the concentration of X in the X metal precursor solution is 0.01-3 mmol / L.
[0012] The X metal precursor in the X metal precursor solution is one or more of the following: iron phosphate (FePO4), iridium chloride (H2IrCl6), ruthenium chloride (RuCl3), and chloroauric acid (HAuCl4);
[0013] The Zn precursor is one or more of diethylzinc, dimethylzinc, and zinc chloride;
[0014] The alcohol solvent I is one or more of ethanol, isopropanol, ethylene glycol, and n-butanol;
[0015] The ultrasound duration is 0.5-1 hour;
[0016] The microwave heating time is 0.5-1 hour, and the microwave heating temperature is 60-80℃.
[0017] The drying time is 8-12 hours, and the drying temperature is 60-80℃;
[0018] The calcination temperature is 900-950℃, and the calcination time is 150-200min.
[0019] In the above technical solution, further, in step S2, the Pt precursor in the Pt precursor solution is one or more of chloroplatinic acid (H2PtCl6), dichlorohexaaminoplatinum Pt(NH3)6Cl2, dichlorotetraaminoplatinum (Pt(NH3)4Cl2), and dinitrosodiaminoplatinum (Pt(NO2)2(NH3)2), and the concentration of Pt in the Pt precursor is 0.01-5 mmol / L;
[0020] The alcohol solvent II is one or more of ethanol, isopropanol, ethylene glycol, and n-butanol;
[0021] The carbon powder is one or more of conductive carbon black, Ketjen black, and graphene, and the amount of carbon powder added is 20%-30% of the mass of the carbon material adsorbed by Pt.
[0022] In the above technical solution, further, in step S3, the alkaline solvent is a sodium hydroxide ethanol solution;
[0023] After adjusting the pH, the pH of the second mixture is 9-12;
[0024] The microwave heating time is 1-2 hours, and the microwave heating temperature is 60-80℃;
[0025] The calcination temperature is 850-950℃, and the calcination time is 150-200min.
[0026] In another aspect, the present invention provides a Pt-X bimetallic single-atom catalyst prepared by the above preparation method, wherein the catalyst has the following structure: the core is a MOF-supported active metal X single atom, and the shell is a carbon-supported active metal Pt single atom.
[0027] In the above technical solution, further, the catalyst has an active metal X single atom loading of 0.1–0.5 wt.% and an active metal Pt single atom loading of 0.1–0.3 wt.%; the catalyst has a specific surface area of 200–300 m². 2 / g; the catalyst has a pore volume of 0.2–0.5 cm³. 3 / g, with a pore size of 0.1–0.3 nm.
[0028] In another aspect, the present invention provides the application of the above-mentioned catalyst in the hydrogenation reaction.
[0029] The present invention also provides an application of the above-mentioned catalyst in oxygen reduction reactions.
[0030] The present invention has the following beneficial effects:
[0031] 1. This invention provides a carbon-coated MOF support for a catalyst carrying Pt-X bimetallic single atoms. This catalyst structure offers several advantages: firstly, the carbon coating protects the MOF core, preventing MOF collapse and thus enhancing catalyst stability; secondly, the carbon shell surface modification results in chemically active properties, exhibiting high activity and high conductivity. Therefore, the catalyst of this invention demonstrates high activity, high stability, and high conductivity, showing significant effects on HOR and ORR reactions, exhibiting high catalyst activity. The catalyst core of this invention consists of an MOF supporting X metal single atoms, while the outer shell is a carbon-supported Pt single atom. Compared to catalysts with two or more metal active components simultaneously supported in the core or shell, this isolated structure facilitates the dispersion of single atoms, preventing agglomeration into large atomic clusters and ensuring structural stability.
[0032] 2. This catalyst structure uses MOF as a support, which has a high specific surface area and regular mesopores. Therefore, it provides single-atom channels that are conducive to the uniform dispersion and mass transfer of X metal active sites. Furthermore, the catalyst structure simultaneously supports dual active sites of Pt and X metal active sites, achieving synergistic catalysis and greatly improving the catalyst activity. Compared with existing core-shell catalysts, a small amount of noble metal Pt is dispersed on the carbon surface in this catalyst, forming a Pt-X single-atom catalyst, which greatly improves the utilization rate of noble metal atoms and reduces the production cost of the catalyst.
[0033] 3. The preparation method of the catalyst of the present invention is simple and mild compared with the ultra-high temperature, ultra-vacuum and displacement methods. It overcomes the problems of harsh or difficult-to-control preparation conditions of existing single-atom catalysts and has good practicality and economy.
[0034] 4. In the preparation method of the present invention, the X / MOF material and carbon powder are added in sequence in steps and each step needs to be stirred. Compared with adding all of them directly and then stirring, a stable core-shell structure can be constructed. The stable core-shell structure protects the core from being destroyed during the reaction process. Attached Figure Description
[0035] Figure 1 The HOR polarization curves for CO poisoning resistance of Sample 1, Sample 2, Sample 3, and a commercial catalyst are shown.
[0036] Figure 2 ORR polarization curves for Sample 2 and the commercial PtC catalyst;
[0037] Figure 3 This is a structural diagram of the single-atom catalyst of the present invention. Detailed Implementation
[0038] The present invention will be further described in detail below with reference to the accompanying drawings.
[0039] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available.
[0040] In one specific embodiment, the preparation method of the Pt-X bimetallic single-atom catalyst includes:
[0041] 1) Dissolve Zn precursor powder, X metal precursor solution and 2-methylimidazolium organic ligand powder in alcohol to obtain a mixture. Sonicate, microwave, and dry the mixture, and then calcine it in a tube furnace to obtain a zinc-based zeolite imidazolium ester framework structure material containing metal X. The zinc concentration in the zinc precursor is 25 mmol / L, and the concentration of X in the metal X precursor is 0.01-5 mmol / L, preferably 0.01-3.3 mmol / L, based on the volume of the mixed solution.
[0042] 2) Dissolve the material obtained in step 1) in alcohol, add a certain amount of carbon powder, sonicate until homogeneous, add Pt precursor solution, and stir until homogeneous;
[0043] 3) Add alkaline solvent to adjust the pH of the solution, microwave the mixture, centrifuge and wash with deionized water in sequence, dry and then calcine under an inert atmosphere to obtain the Pt-X / MOF single-atom catalyst.
[0044] The zinc precursor may be zinc chloride; the metal X precursor may be an acid containing metal X and / or a salt containing metal X, such as at least one of FePO4, CoCl2, H2IrCl6, RuCl3, and HAuCl4.
[0045] Nitrogen atmosphere can be selected as the protective atmosphere.
[0046] The calcination temperature can be selected from 900-950℃, and the calcination time can be selected from 150-200min; for example, calcining at 900℃ for 150min.
[0047] Wherein, metal X can be at least one of Fe, Co, Ir, Ru, and Au; for example, metal X is selected as Ru.
[0048] Example 1
[0049] This embodiment provides a Pt-Fe binary single-atom catalyst, which is prepared by the following method:
[0050] S1. Take 0.005 mmol of iron phosphate metal precursor solution, 12.5 mmol of Zn precursor powder, and 2-methylimidazole organic ligand powder and dissolve them in 500 ml of ethanol solvent. After ultrasonic mixing for 0.5 h, obtain mixture one. Then, microwave heating of mixture one at 60 °C for 0.5 h, oven drying for 8 h at 60 °C, and tube furnace calcination at 900 °C for 150 min are performed to finally obtain MOF material supported on X metal single atoms, i.e., Fe / MOF material.
[0051] S2. Dissolve the X / MOF material obtained in S1 in 500 ml of ethanol solvent, add 50 mg of conductive carbon black, sonicate, add 0.005 mmol of chloroplatinic acid solution, stir, and obtain carbon material adsorbed by Pt.
[0052] S3. Add sodium hydroxide ethanol solution dropwise to the Pt-adsorbed carbon material in S2 to adjust the pH to 9 to obtain mixture two. Microwave-heat mixture two for 1 hour at a temperature of 60°C. Then wash with deionized water, centrifuge, dry, and calcine under an inert atmosphere at a temperature of 850°C for 150 minutes to obtain a Pt-Fe bimetallic single-atom catalyst, designated as sample 1.
[0053] The catalyst prepared in Example 1 was dispersed in anhydrous ethanol and sonicated for 30 min to obtain a homogeneous dispersion. 20 μL of this dispersion was pipetted onto a 5 mm diameter glassy carbon electrode and dried at 60 °C. Then, 1 μL of 0.5 wt.% Nafion solution was pipetted onto the catalyst layer and dried in air to obtain the working electrode. Cyclic voltammetry was performed in a high-purity N2-saturated 0.1 mol / L HClO4 solution at a scan rate of 50 mV / s and a scan range of 0.0–1.10 V (vs. RHE) for 30 cycles. Table 1 shows that the electrochemical active area is 64.5 m². 2 / g, after cyclic voltammetry scanning of the working electrode until the catalyst surface is clean and stable, it is removed for LSV testing. The solution is 0.1 mol / L HClO4 saturated with H2 containing 5 ppm CO gas, with a scan rate of 10 mV / s, a scan range of 0–0.5 V, and a rotating disk electrode speed of 1600 r / min. Table 1 shows that its HOR mass activity against CO poisoning is 142 A / g, and the current retention rate after 20,000 cycles is 68%.
[0054] Example 2
[0055] This embodiment provides a Pt-Ir two-component single-atom catalyst, which is prepared by the following method:
[0056] S1. Take 1.5 mmol of chloroiridium metal precursor solution, 15 mmol of Zn precursor powder, and 2-methylimidazolium organic ligand powder and dissolve them in 500 ml of ethylene glycol solvent. After ultrasonic mixing for 1 h, obtain mixture one. Then, the mixture one is successively subjected to microwave heating at 80 °C for 1 h, oven drying for 12 h at 80 °C, and tube furnace calcination at 950 °C for 200 min to finally obtain MOF material supported on X metal single atoms, i.e., Ir / MOF material.
[0057] S2. Dissolve the Ir / MOF material obtained in S1 in 500 ml of ethanol solvent, add 50 mg of Ketjen black, sonicate, add 2.5 mmol of dichlorohexaaminoplatinum solution, stir, and obtain carbon material adsorbed by Pt.
[0058] S3. Add sodium hydroxide ethanol solution dropwise to the Pt-adsorbed carbon material in S2 to adjust the pH to 12 to obtain mixture two. Microwave-heat mixture two for 2 hours at a temperature of 80°C. Then wash with deionized water, centrifuge, dry, and calcine under an inert atmosphere at a temperature of 950°C for 200 minutes to finally obtain the Pt-Ir bimetallic single-atom catalyst.
[0059] The catalyst prepared in Example 2 was designated as Sample 2. Using the same testing methods and conditions as in Example 1, CV testing was performed. As shown in Table 1, its electrochemical active area was 68.5 m². 2 As shown in Table 1, its HOR activity against CO poisoning is 148 A / g, and the retention rate after 20,000 cycles of current is 76%, as determined by LSV testing. Figure 2 It can be seen that its ORR quality activity is 540 A / g, which is much higher than the quality activity of commercial PtC of 115 A / g.
[0060] Example 3
[0061] This embodiment provides a Pt-Ru single-atom catalyst, which is prepared by the following method:
[0062] S1. Take 0.75 mmol of ruthenium chloride precursor solution, 13.5 mmol of Zn precursor powder, and 2-methylimidazolium organic ligand powder and dissolve them in 500 ml of isopropanol solvent. After ultrasonic mixing for 0.75 h, obtain mixture one. Then, the mixture one is successively subjected to microwave heating at 70 °C for 0.75 h, oven drying for 10 h at 70 °C, and tube furnace calcination at 925 °C for 175 min to finally obtain MOF material supported on Ru metal single atoms, i.e., Ru / MOF material.
[0063] S2. Dissolve the Ru / MOF material obtained in S1 in 500 ml of isopropanol solvent, add 50 mg of graphene, sonicate, add 1.25 mmol of chloroplatinic acid solution, stir, and obtain Pt-adsorbed carbon material.
[0064] S3. Add sodium hydroxide ethanol solution dropwise to the Pt-adsorbed carbon material in S2 to adjust the pH to 11 to obtain mixture two. Microwave-heat mixture two for 1.5 hours at a temperature of 70°C. Then wash with deionized water, centrifuge, dry, and calcine under an inert atmosphere at 900°C for 175 minutes to finally obtain the Pt-Ru bimetallic single-atom catalyst.
[0065] The catalyst prepared in Example 3 is designated as Sample 3. Using the same testing methods and conditions as in Example 1, CV testing was performed. As shown in Table 1, its electrochemical active area is 63.5 m². 2 As shown in Table 1 by LSV testing, its HOR mass activity against CO poisoning is 138 A / g, and the retention rate after 20,000 cycles of current is 66%.
[0066] Comparative Example 1
[0067] S1. Take 0.005 mmol of iron phosphate metal precursor solution, 12.5 mmol of Zn precursor powder, and 2-methylimidazole organic ligand powder and dissolve them in 500 ml of ethanol solvent. After ultrasonic mixing for 0.5 h, obtain mixture one. Then, microwave heating of mixture one at 60 °C for 0.5 h, oven drying for 8 h at 60 °C, and tube furnace calcination at 900 °C for 150 min are performed to finally obtain MOF material supported on X metal single atoms, i.e., Fe / MOF material.
[0068] S2. Dissolve the X / MOF material obtained in S1 in 500 ml of ethanol solvent, sonicate, add 0.005 mmol of chloroplatinic acid solution, stir, and obtain Pt-adsorbed MOF material.
[0069] S3. Add sodium hydroxide ethanol solution dropwise to the Pt-adsorbed MOF material in S2 to adjust the pH to 9 to obtain mixture two. Microwave-heat mixture two for 1 hour at a temperature of 60°C. Then wash with deionized water, centrifuge, dry, and calcine under an inert atmosphere at a temperature of 850°C for 150 minutes to finally obtain the Pt-Fe bimetallic single-atom catalyst.
[0070] Using the same testing methods and conditions as in Example 1, the catalyst prepared in Comparative Example 1 was subjected to CV and LSV tests, and the relevant data are recorded in Table 1. Since the MOF material in Comparative Example 1 was not coated with carbon, the conductivity and catalytic activity of the catalyst prepared by it were not as good as those of this application. At the same time, the structure prepared by this method cannot guarantee stability.
[0071] Comparative Example 2
[0072] S1. Take 0.005 mmol of iron phosphate metal precursor solution, 12.5 mmol of Zn precursor powder, and 2-methylimidazole organic ligand powder and dissolve them in 500 ml of ethanol solvent. After ultrasonic mixing for 0.5 h, obtain mixture one. Then, microwave heating of mixture one at 60 °C for 0.5 h, oven drying for 8 h at 60 °C, and tube furnace calcination at 900 °C for 150 min are performed to finally obtain MOF material supported on X metal single atoms, i.e., Fe / MOF material.
[0073] S2. Add sodium hydroxide ethanol solution dropwise to the Fe / MOF material in S1 to adjust the pH to 9 to obtain mixture two. Microwave-heat mixture two for 1 hour at a temperature of 60°C. Then wash with deionized water, centrifuge, dry, and calcine under an inert atmosphere at a temperature of 850°C for 150 minutes to finally obtain the Fe single-atom catalyst.
[0074] Using the same testing methods and conditions as in Example 1, the catalyst prepared in Comparative Example 2 was subjected to CV and LSV tests, and the relevant data are recorded in Table 1. Since Comparative Example 2 uses a single-metal single-atom catalyst, the conductivity and catalytic activity of the catalyst prepared in it are not as good as those of this application. Compared with the comparative example, the bimetallic single-atom catalyst in Example 2 has a synergistic catalytic effect, and the type and ratio of active metals can be adjusted according to needs.
[0075] Comparative Example 3
[0076] S1. Take 0.005 mmol of iron phosphate metal precursor solution, dissolve it in 500 ml of ethanol solvent, add 50 mg of conductive carbon black, sonicate, add 0.005 mmol of chloroplatinic acid solution, stir and sonicate for 0.5 h to obtain mixture one. Then, the mixture one is successively subjected to microwave heating at 60℃ for 0.5 h, oven drying for 8 h at 60℃, and tube furnace calcination at 900℃ for 150 min to finally obtain carbon material supported on Pt-Fe metal single atoms.
[0077] S2. Add sodium hydroxide ethanol solution dropwise to the carbon material supporting the metal single atom in S1, adjust the pH to 9 to obtain mixture two. Microwave-heat mixture two for 1 hour at a temperature of 60°C. Then wash with deionized water, centrifuge, dry, and calcine under an inert atmosphere at a temperature of 850°C for 150 minutes to finally obtain the Pt-Fe bimetallic single-atom catalyst.
[0078] Using the same test methods and conditions as in Example 1, the catalyst prepared in Comparative Example 3 was subjected to CV and LSV tests, and the relevant data are recorded in Table 1. Since Comparative Example 3 does not use a core-shell structure and does not introduce MOF materials, the conductivity and catalytic activity of the catalyst prepared in it are not as good as those of this application. In this method, single atoms cannot be effectively dispersed, and a large number of single atoms agglomerate into clusters or form nanoparticles.
[0079] Table 1
[0080]
[0081]
[0082] The specific embodiments of this invention are merely illustrative of the invention and are not intended to limit it. After reading this specification, those skilled in the art can make modifications to the embodiments of this invention without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this invention.
Claims
1. A method for preparing a Pt-X bimetallic single-atom catalyst, characterized in that: The method includes the following steps: S1. Take the X metal precursor solution, Zn precursor powder, and 2-methylimidazolium organic ligand powder and dissolve them in alcohol solvent I. After ultrasonic mixing, a mixture is obtained. The mixture is then subjected to microwave heating, oven drying, and tube furnace calcination in sequence to finally obtain the MOF material supported on X metal single atoms, i.e., X / MOF material, where X is one or more of Fe, Co, Ir, Ru, and Au. S2. Dissolve the X / MOF material obtained in step S1 in alcohol solvent II, add carbon powder, sonicate, add Pt precursor solution, stir to obtain Pt adsorbed carbon material. S3. Add an alkaline solvent to the carbon material adsorbed by Pt in step S2 to adjust the pH of the solution, and obtain mixture two. Microwave heat mixture two, then wash with deionized water, centrifuge, dry and calcine under an inert atmosphere to finally obtain the Pt-X bimetallic single-atom catalyst.
2. The preparation method according to claim 1, characterized in that: In step S1, based on one volume of the mixed solution, the concentration of Zn in the Zn precursor powder is 25-30 mmol / L, and the concentration of X in the X metal precursor solution is 0.01-3 mmol / L. The X metal precursor in the X metal precursor solution is one or more of the following: iron phosphate (FePO4), chloroiridium acid (H2IrCl6), ruthenium chloride (RuCl3), chloroauric acid (HAuCl4), and hexahydroxypentacobalt dicarbonate (CHCoO4); The Zn precursor is one or more of diethylzinc, dimethylzinc, and zinc chloride; The alcohol solvent I is one or more of ethanol, isopropanol, ethylene glycol, and n-butanol; The ultrasound duration is 0.5-1 hour; The microwave heating time is 0.5-1 hour, and the microwave heating temperature is 60-80℃. The drying time is 8-12 hours, and the drying temperature is 60-80℃; The calcination temperature is 900-950℃, and the calcination time is 150-200min.
3. The preparation method according to claim 1, characterized in that: In step S2, the Pt precursor in the Pt precursor solution is one or more of chloroplatinic acid (H2PtCl6), dichlorohexaaminoplatinum Pt(NH3)6Cl2, dichlorotetraaminoplatinum (Pt(NH3)4Cl2), and dinitrosodiaminoplatinum (Pt(NO2)2(NH3)2), and the concentration of Pt in the Pt precursor is 0.01-5 mmol / L; The alcohol solvent II is one or more of ethanol, isopropanol, ethylene glycol, and n-butanol; The carbon powder is one or more of conductive carbon black, Ketjen black, and graphene, and the amount of carbon powder added is 20%-30% of the mass of the carbon material adsorbed by Pt.
4. The preparation method according to claim 1, characterized in that: In step S3, the alkaline solvent is a sodium hydroxide ethanol solution; After adjusting the pH, the pH of the second mixture is 9-12; The microwave heating time is 1-2 hours, and the microwave heating temperature is 60-80℃; The calcination temperature is 850-950℃, and the calcination time is 150-200min.
5. A Pt-X bimetallic single-atom catalyst prepared by the method according to any one of claims 1-4, characterized in that: The catalyst has the following structure: the core is a MOF-supported active metal X single atom, and the outer shell is a carbon-supported active metal Pt single atom.
6. The catalyst according to claim 5, characterized in that: In the catalyst, the loading of active metal X single atoms is 0.1–0.5 wt.%, and the loading of active metal Pt single atoms is 0.1–0.3 wt.%; the specific surface area of the catalyst is 200–300 m². 2 / g; the catalyst has a pore volume of 0.2–0.5 cm³. 3 / g, with a pore size of 0.1–0.3 nm.
7. The use of the catalyst according to any one of claims 5-6 in a hydrogenation reaction.
8. The use of the catalyst according to any one of claims 5-6 in the oxygen reduction reaction.