A metal single-atom electrocatalyst, its preparation method and application

Abstract

The present invention relates to a metal single-atom electrocatalyst, a preparation method thereof and an application, belonging to the technical field of new energy materials. The metal single-atom electrocatalyst includes a carrier of zero-dimensional carbon dots and an active center of metal dispersed in a single-atom form supported on the carrier. The specific preparation method includes: S1, preparing a nitrogen-doped carbon dot solution; S2, preparing a carbon black suspension; S3, obtaining carbon black adsorbed with carbon dots; S4, using ultrasonic waves to place the carbon black adsorbed with carbon dots on the filter paper in step S3 into deionized water to obtain a mixed solution, dropping a metal precursor solution into the mixed solution, stirring for 24 h, filtering to obtain a filter residue, and drying the filter residue to obtain the metal single-atom electrocatalyst. The preparation method of the metal single-atom electrocatalyst in the present invention is applicable to the preparation of various types of metal single-atom electrocatalysts, has excellent universality, and the preparation process is simple, facilitating batch synthesis on an industrial scale, and greatly reducing the production cost of the metal single-atom electrocatalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and particularly to a metal single-atom electrocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The problems of excessive consumption of fossil energy and environmental pollution are becoming increasingly severe. Developing new energy technologies is one of the important ways to solve the current energy and environmental problems, such as developing methanol fuel cells, hydrogen fuel cells, etc. that can directly convert chemical energy into electrical energy.

[0003] Reducing metal nanoparticles or clusters to the atomic scale can not only effectively reduce the cost of catalysts (especially precious metals), but also provide uniform active sites. Therefore, metal single-atom catalysts have received extensive attention in recent years. Compared with metal cluster catalysts and alloy catalysts, metal single-atom catalysts are increasingly widely used in new energy technologies including methanol fuel cells due to their high catalytic activity, adjustable coordination environment, and high atomic utilization efficiency. Therefore, developing efficient metal single-atom electrocatalysts and batch synthesis technologies matching them is of great significance for promoting the rapid development of many new energy technologies. However, the synthesis steps of metal single-atom electrocatalysts usually have problems such as cumbersome and complex steps, low metal single-atom loading, and large restrictions on metal types, resulting in the difficulty of mass-producing metal single-atom electrocatalysts and severely restricting their large-scale application.

[0004] The metal atoms in metal single-atom catalysts need to be highly dispersed on a suitable support. However, the sharp increase in specific surface area will lead to a significant rise in the free energy of the metal surface, making isolated metal atoms prone to agglomeration during the preparation and reaction processes, forming clusters, which reduces the active sites and lowers the catalytic efficiency and stability of the methanol oxidation reaction. One of the effective ways to solve this problem is to use a suitable support material to provide abundant anchoring sites for single atoms and prevent their aggregation. As a zero-dimensional carbon nanomaterial with remarkable fluorescence properties, carbon dots (CDs) exhibit excellent performance in the fields of optics and electrochemistry due to their low cost, easy accessibility, unique electron transport ability, and large specific surface area. The surface of carbon dots contains abundant functional groups, such as oxygen-containing functional groups like carboxyl (-COOH) and hydroxyl (-OH), as well as heteroatom functional groups brought about by doping with non-metals such as nitrogen, boron, phosphorus, and fluorine. These functional groups have a strong binding effect on the vast majority of metal species. On the one hand, they can provide abundant binding sites for anchoring and stabilizing isolated metal single atoms, thereby increasing the metal loading; on the other hand, they have a regulatory effect on the structure and electron distribution of carbon dots themselves. They also have a significant impact on the electronic state and structure of metal catalysts. These heteroatom functional groups even have the effect of donating electrons, endowing carbon dots with a certain reducing ability, and enabling the metal single-atom catalyst to be obtained only by simple room-temperature impregnation adsorption without additional high-temperature calcination, chemical reduction and other treatment steps.

[0005] Chinese Patent Application No. 202210817899.0 discloses a nitrogen-containing carbon quantum dot modified platinum-ruthenium bimetallic methanol oxidation electrocatalyst and its preparation method. The specific content includes that the platinum-ruthenium bimetallic alloy cluster electrocatalyst is obtained by reducing metal salts with a strong reducing agent sodium borohydride and loading them on carbon black with the assistance of nitrogen-containing carbon dots. The distribution form of the metal on carbon black is in the form of cluster particles. This disclosure uses the surface functional groups of nitrogen-containing carbon dots to anchor platinum-ruthenium metals, making the platinum-ruthenium agglomeration fully dispersed and improving the catalytic activity. However, this patent does not involve the preparation method of metal single-atom catalysts, let alone the fact that the weak reducibility of carbon dots to metals contributes to the formation of metal single atoms.

[0006] Chinese Patent Application No. 202310173076.3 discloses a synthesis method of a super-highly dispersed platinum-copper methanol oxidation electrocatalyst. The specific content includes that the platinum-copper bimetallic alloy cluster electrocatalyst is obtained by reducing metal salts with a strong reducing agent sodium borohydride and loading them on carbon black with the assistance of nitrogen-phosphorus-containing carbon dots. The distribution form of the metal on carbon black is in the form of cluster particles. This disclosure uses the functional groups of nitrogen-phosphorus-containing carbon dots to anchor platinum-copper metals and utilizes the structural regulation effect of carbon dots on platinum and copper to improve the electrocatalytic activity. However, this patent does not involve the preparation method of metal single-atom catalysts, let alone the influence of the distribution form of metal single atoms on methanol oxidation.

[0007] Jiahui Liang et al. disclosed a method for enhancing the methanol oxidation reaction activity of platinum-ruthenium cluster catalysts via resonance energy transfer in the article "Boosting the Methanol Oxidation Reaction Activity of Pt-Ru Clusters via Resonance Energy Transfer" (Small 19 (2023) 202302149). The specific content includes that the platinum-ruthenium bimetallic alloy cluster electrocatalyst is formed by reducing metal salts with a strong reducing agent sodium borohydride and is loaded on carbon black with the assistance of resonance energy transfer between nitrogen-containing carbon dots and platinum. Through the fluorescence quenching effect of carbon dots with platinum and ruthenium, it is found that there is resonance energy transfer between carbon dots and metals, which changes the electronic structure of metals, reduces the d-band center of platinum, and improves the catalytic activity of metal catalysts. However, this literature does not disclose the preparation method of metal single-atom catalysts, let alone that the weak reducibility of carbon dots to metals contributes to the formation of metal single atoms.

[0008] Regarding the above technical phenomena, how to synthesize metal single-atom electrocatalysts with the assistance of carbon dots is of great significance for promoting the large-scale production of metal single-atom electrocatalysts and the rapid development of related new energy technology fields. Summary of the Invention

[0009] The purpose of the present invention is to provide a metal single-atom electrocatalyst, its preparation method and application, to solve the technical problems such as the cumbersome preparation process, low metal loading, limited types, and high cost of traditional metal single-atom electrocatalysts.

[0010] On the one hand, a metal single-atom electrocatalyst provided by the present invention adopts the following technical scheme:

[0011] A metal single-atom electrocatalyst includes a carrier and an active center.

[0012] The carrier is zero-dimensional carbon dots.

[0013] The active center is a metal dispersed in the form of single atoms, and the metal is loaded on zero-dimensional carbon dots.

[0014] On the other hand, the present application also provides a preparation method of a metal single-atom electrocatalyst, including the following steps:

[0015] S1. Take a nitrogen source and citric acid, dissolve them in deionized water, mix evenly, place them in a reaction kettle, and after the reaction ends, cool and filter to obtain a nitrogen-doped carbon dot solution.

[0016] S2. Take conductive carbon black and place it in deionized water, and ultrasonically treat it for 1-2 h to obtain a carbon black suspension.

[0017] S3. Mix the nitrogen-doped carbon dot solution prepared in step S1 and the carbon black suspension prepared in step S2, stir for 48 h, filter, and obtain carbon black adsorbed with carbon dots on the filter paper;

[0018] S4. Use ultrasonic waves to place the carbon black adsorbed with carbon dots on the filter paper in step S3 into deionized water to obtain a mixed solution, add a metal precursor solution dropwise to the mixed solution, stir, and immerse and adsorb at room temperature for 24 h, filter to obtain a filter residue, and dry the filter residue in an environment of 50 - 60 °C to obtain a metal single-atom electrocatalyst.

[0019] Preferably, the nitrogen source in step S1 is any one of urea and ethylenediamine.

[0020] Preferably, the reaction temperature of the reaction kettle in step S1 is 160 - 240 °C, and the reaction time is 8 - 12 h.

[0021] Preferably, 50 - 100 mg of nitrogen source is dissolved in each milliliter of deionized water in step S1;

[0022] 25 - 50 mg of citric acid is dissolved in each milliliter of deionized water in step S1.

[0023] 0.6 - 0.8 mg of conductive carbon black is dissolved in each milliliter of deionized water in step S2.

[0024] Preferably, the volume ratio of the nitrogen-doped carbon dot solution to the carbon black suspension in step S3 is (0.09 - 0.2):1.

[0025] Preferably, the metal in the metal precursor solution in step S4 includes any one or more of ruthenium, rhodium, palladium, osmium, iridium, platinum, rhenium, manganese, iron, cobalt, nickel, and zinc.

[0026] Preferably, the metal precursor in the metal precursor solution in step S4 includes one or more of ruthenium chloride, chlororhodic acid, chloropalladic acid, chloroosmic acid, chloroiridic acid, chloroplatinic acid, rhenium chloride, manganese sulfate, manganese chloride, manganese nitrate, iron sulfate, iron chloride, iron nitrate, cobalt sulfate, cobalt chloride, cobalt nitrate, nickel sulfate, nickel chloride, nickel nitrate, zinc sulfate, zinc chloride, and zinc nitrate.

[0027] Preferably, the concentration of the metal precursor solution in step S4 is 0.0025 mol / L;

[0028] The dropping rate of the metal precursor solution in step S4 is 0.1 - 10 mL / min;

[0029] The volume ratio of the mixed solution to the metal precursor solution in step S4 is 4:(1 - 1.5).

[0030] On the other hand, the present invention also provides an application of the above-mentioned metal single-atom electrocatalyst in an electrocatalytic reaction.

[0031] In summary, the present invention includes the following beneficial technical effects:

[0032] 1. For the metal single-atom electrocatalyst provided by the present invention, through the anchoring and reduction of carbon dots, metal single atoms are uniformly loaded on zero-dimensional carbon dots, with good dispersibility, and the abundant heteroatom functional groups provide a large number of anchor points for the single atoms, so that a single-atom electrocatalyst with a high metal loading can be prepared; in addition, compared with other preparation methods of metal single-atom electrocatalysts such as atomic layer deposition and high-temperature pyrolysis, the preparation method of the metal single-atom electrocatalyst has the advantages of simple preparation process, easy operation and low energy consumption. A metal single-atom electrocatalyst with a high metal single-atom loading and uniform dispersion can be prepared only by a simple room-temperature impregnation method, which is convenient for batch synthesis on an industrial scale and greatly reduces the production cost of the metal single-atom electrocatalyst.

[0033] 2. The preparation method of the metal single-atom electrocatalyst provided by the present invention is applicable to the preparation of various types of metal single-atom electrocatalysts, including noble metal-based and non-noble metal-based single-atom electrocatalysts, and at the same time, a single-atom electrocatalyst with multi-metal cooperation can be prepared, having excellent universality.

[0034] 3. By analyzing the Pt L-edge X-ray absorption near-edge structure spectrum of the Ni,Pt-NCDs / C single-atom catalyst, it shows that the coordination environment around the platinum atoms is mainly platinum-chlorine coordination and platinum-nitrogen coordination, and the crystal plane parameters corresponding to nickel and platinum metals do not appear in the X-ray diffraction pattern, indicating the formation and high dispersion of nickel and platinum single atoms; and by analyzing the aberration-corrected electron microscopy image of the Co,Pd,Pt-NCDs / C single-atom catalyst, the formation of cobalt, palladium and platinum metal single atoms is proved.

[0035] 4. A fuel cell is a chemical device that directly converts the chemical energy of a fuel into electrical energy, also known as an electrochemical generator. Since a fuel cell converts the Gibbs free energy part of the chemical energy of a fuel into electrical energy through an electrochemical reaction and is not limited by the Carnot cycle effect, it has high efficiency; in addition, a fuel cell uses fuel and oxygen as raw materials, and at the same time has no mechanical transmission components, so the harmful gases emitted are extremely few and the service life is long; in this application, the electrocatalytic methanol oxidation performance of the Pt-NCDs / C single-atom catalyst is tested in an alkaline medium (1 mol / L KOH + 1 mol / L CH3OH) using a classical three-electrode system, and the optimal mass activity reaches 6611.73 mA / mg Pt 。 Description of the Drawings

[0036] Figure 1It is the Fourier transform infrared spectrum of the Pt-NCDs / C single-atom catalyst and carbon dots prepared in Example 1 of the present invention.

[0037] Figure 2 It is the mass activity diagram of the electrochemical methanol oxidation of the Pt-NCDs / C single-atom catalyst prepared in Example 1 of the present invention, the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1, and the commercial platinum-carbon catalyst.

[0038] Figure 3 It is the i-t (chronoamperometry) curve diagram of the Pt-NCDs / C single-atom catalyst prepared in Example 1 of the present invention, the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1, and the commercial platinum-carbon catalyst.

[0039] Figure 4 It is the X-ray diffraction pattern of the Pt-NCDs / C single-atom catalyst prepared in Example 1 of the present invention, the Pd-NCDs / C single-atom catalyst prepared in Example 2, the Zn-NCDs / C single-atom catalyst prepared in Example 3, the Ni, Pt-NCDs / C single-atom catalyst prepared in Example 4, the Co, Pd, Pt-NCDs / C single-atom catalyst prepared in Example 5, the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1, the Pd, Ru-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 2, as well as conductive carbon black and commercial palladium-carbon catalyst.

[0040] Figure 5 It is the Pt L-edge X-ray absorption near-edge structure spectrum of the Ni, Pt-NCDs / C single-atom catalyst prepared in Example 4 of the present invention.

[0041] Figure 6 It is the aberration-corrected electron microscopy image of the Co, Pd, Pt-NCDs / C single-atom catalyst prepared in Example 5 of the present invention. Detailed implementation manners

[0042] The following further elaborates on the present invention in conjunction with Examples 1-5, Comparative Examples 1-2 and the attached Figure 1-6 for a more detailed description.

[0043] Example 1

[0044] A preparation method of a metal single-atom electrocatalyst, wherein metal platinum is loaded on zero-dimensional carbon dots in the form of single atoms, and the specific preparation method is as follows:

[0045] S1. Take 2 g of urea and 0.5 g of citric acid and dissolve them in 20 mL of deionized water. After mixing evenly, place them in a polytetrafluoroethylene reaction kettle. Set the reaction temperature of the polytetrafluoroethylene reaction kettle to 200 °C and the reaction time to 12 h. After the reaction is completed, cool the obtained product to room temperature and filter to remove insoluble impurities to obtain an orange-yellow nitrogen-doped carbon dot solution;

[0046] S2. Take 30 mg of conductive carbon black BP20000 and add it to 50 mL of deionized water. Ultrasonically treat it for 1.5 h to obtain a carbon black suspension;

[0047] S3. Take the carbon black suspension prepared in step S2 and mix it with 4.5 mL of the nitrogen-doped carbon dot solution prepared in step S1. Stir at room temperature for 48 h and filter. The carbon black adsorbed with carbon dots is obtained on the filter paper;

[0048] S4. Use ultrasound to place the carbon black adsorbed with carbon dots on the filter paper in step S3 into 40 mL of deionized water to obtain a mixed solution. Add 10 mL of 0.0025 mol / L chloroplatinic acid solution dropwise to the mixed solution, maintain a dropping rate of 0.15 mL / min, stir at room temperature for 24 h, filter to obtain a filter residue, and dry the filter residue in a constant temperature oven set at 50 °C to obtain a Pt-NCDs / C single-atom catalyst loaded with platinum single atoms.

[0049] The proportion of Pt atoms in the Pt-NCDs / C single-atom catalyst prepared in Example 1 was determined by inductively coupled plasma atomic emission spectrometry to be 5.6%.

[0050] Refer to Figure 1 , Figure 1 is the Fourier transform infrared spectrum of the Pt-NCDs / C single-atom catalyst and carbon dots prepared in this Example 1. At 550 cm -1 , a strong signal related to N-Pt stretching vibration appears in the Pt-NCDs / C single-atom catalyst, while the initial stretching vibration absorption peak of N-H at 3190 cm -1 in the carbon dots disappears, proving that the heteroatom functional group (amino group) in the carbon dots is the binding site of platinum.

[0051] Refer to Figure 2 , Figure 2It is a mass activity diagram of the electrochemically catalyzed methanol oxidation of the Pt-NCDs / C single-atom catalyst prepared in Example 1 and the commercial platinum-carbon catalyst. A fuel cell is a chemical device that directly converts the chemical energy of a fuel into electrical energy, also known as an electrochemical generator. It is the fourth power generation technology after hydraulic power generation, thermal power generation, and nuclear power generation. Since a fuel cell converts the Gibbs free energy part of the chemical energy of a fuel into electrical energy through an electrochemical reaction and is not restricted by the Carnot cycle effect, it has high efficiency; in addition, a fuel cell uses fuel and oxygen as raw materials and has no mechanical transmission components, so the harmful gases emitted are extremely few and the service life is long. From the perspective of saving energy and protecting the ecological environment, fuel cells are the most promising power generation technologies. The electrochemically catalyzed methanol oxidation performance of the Pt-NCDs / C single-atom catalyst prepared in Example 1 and the commercial platinum-carbon catalyst was tested using a classical three-electrode system in an alkaline medium (1 mol / L KOH + 1 mol / L CH3OH). It can be seen that the mass activity of the commercial platinum-carbon catalyst is 1363.11 mA / mg Pt The mass activity of the Pt-NCDs / C single-atom catalyst obtained in this example is 6611.73 mA / mg Pt which is 4.85 times that of the commercial platinum-carbon catalyst.

[0052] Refer to Figure 3 , Figure 3 It is an i-t (chronoamperometry) curve diagram including the Pt-NCDs / C single-atom catalyst prepared in Example 1 and the commercial platinum-carbon catalyst. The electrochemically stability of the Pt-NCDs / C single-atom catalyst prepared in Example 1 and the commercial platinum-carbon catalyst was tested in an alkaline medium (1 mol / L KOH + 1 mol / L CH3OH). After 5000 s of constant voltage operation, the current density of the Pt-NCDs / C single-atom catalyst is higher than that of the commercial platinum-carbon catalyst, indicating that the Pt-NCDs / C single-atom catalyst has better stability.

[0053] Refer to Figure 4 , Figure 4 It is an X-ray diffraction pattern including the Pt-NCDs / C single-atom catalyst prepared in Example 1, conductive carbon black, and the commercial palladium-carbon catalyst. The peak shape of the Pt-NCDs / C single-atom catalyst is similar to that of the conductive carbon black, and no crystal plane parameters corresponding to platinum metal appear, indicating the formation and high dispersion of platinum single atoms.

[0054] Example 2

[0055] A method for preparing a metal single-atom electrocatalyst, wherein the metal palladium is loaded on zero-dimensional carbon dots in the form of single atoms. The specific preparation method is as follows:

[0056] S1. Take 2 g of urea and 1 g of citric acid and dissolve them in 20 mL of deionized water. After mixing evenly, place them in a polytetrafluoroethylene reaction kettle. Set the reaction temperature of the polytetrafluoroethylene reaction kettle to 220 °C and the reaction time to 8 h. After the reaction is completed, cool the obtained product to room temperature and filter to remove insoluble impurities to obtain an orange-red nitrogen-doped carbon dot solution;

[0057] S2. Take 30 mg of conductive carbon black BP2000 and add it to 50 mL of deionized water. Ultrasonically treat it for 1 h to obtain a carbon black suspension;

[0058] S3. Take the carbon black suspension prepared in step S2 and mix it with 6 mL of the nitrogen-doped carbon dot solution prepared in step S1. Stir at room temperature for 48 h and filter. The carbon black adsorbed with carbon dots is obtained on the filter paper;

[0059] S4. Use ultrasound to place the carbon black adsorbed with carbon dots on the filter paper in step S3 into 40 mL of deionized water to obtain a mixed solution. Add 10 mL of 0.0025 mol / L palladium chloride solution dropwise to the mixed solution, maintain a dropping rate of 0.1 mL / min, stir at room temperature for 24 h, filter to obtain a filter residue, and dry the filter residue in a constant temperature oven set at 50 °C to obtain a Pd-NCDs / C single-atom catalyst loaded with palladium single atoms.

[0060] Refer to Figure 4 , Figure 4 is the X-ray diffraction pattern including the Pd-NCDs / C single-atom catalyst prepared in Example 2, conductive carbon black, and commercial palladium-carbon catalyst. The peak shape of the Pd-NCDs / C single-atom catalyst is similar to that of conductive carbon black, and no crystal plane parameters corresponding to palladium metal appear, indicating the formation and high dispersion of palladium single atoms.

[0061] Example 3

[0062] A preparation method of a metal single-atom electrocatalyst, wherein metal zinc is loaded on zero-dimensional carbon dots in the form of single atoms. The specific preparation method is as follows:

[0063] S1. Take 1 g of ethylenediamine and 1 g of citric acid and dissolve them in 20 mL of deionized water. After mixing evenly, place them in a polytetrafluoroethylene reaction kettle. Set the reaction temperature of the polytetrafluoroethylene reaction kettle to 180 °C and the reaction time to 12 h. After the reaction is completed, cool the obtained product to room temperature and filter to remove insoluble impurities to obtain a reddish-brown nitrogen-doped carbon dot solution;

[0064] S2. Take 40 mg of conductive carbon black BP2000 and add it to 50 mL of deionized water. Ultrasonically treat it for 1 h to obtain a carbon black suspension;

[0065] S3. Take the carbon black suspension obtained in step S2 and mix it with 8 mL of the nitrogen-doped carbon dot solution obtained in step S1, stir for 48 h at room temperature, filter, and the carbon black adsorbed with carbon dots is obtained on the filter paper;

[0066] S4. Use ultrasound to place the carbon black adsorbed with carbon dots on the filter paper in step S3 into 40 mL of deionized water to obtain a mixed solution, and add 10 mL of 0.0025 mol / L zinc nitrate solution dropwise to the mixed solution, maintaining a dropping rate of 5 mL / min, stir for 24 h at room temperature, filter to obtain a filter residue, and dry the filter residue in a constant temperature oven set at 60 °C to obtain a zinc single-atom loaded Zn-NCDs / C single-atom catalyst.

[0067] Refer to Figure 4 , Figure 4 Figure

[0068] Example 4

[0069] A preparation method of a metal single-atom electrocatalyst, wherein metal nickel and platinum are loaded on zero-dimensional carbon dots in the form of single atoms, and the specific preparation method is as follows:

[0070] S1. Take 2 g of urea and 0.5 g of citric acid and dissolve them in 20 mL of deionized water. After mixing evenly, place them in a polytetrafluoroethylene reaction kettle, set the reaction temperature of the polytetrafluoroethylene reaction kettle to 180 °C, and the reaction time to 12 h. After the reaction is completed, cool the obtained product to room temperature, filter to remove insoluble impurities, and obtain an orange-yellow nitrogen-doped carbon dot solution;

[0071] S2. Take 40 mg of conductive carbon black BP2000 and add it to 50 mL of deionized water, and ultrasonically treat for 2 h to obtain a carbon black suspension;

[0072] S3. Take the carbon black suspension obtained in step S2 and mix it with 10 mL of the nitrogen-doped carbon dot solution obtained in step S1, stir for 48 h at room temperature, filter, and the carbon black adsorbed with carbon dots is obtained on the filter paper;

[0073] S4. Use ultrasound to place the carbon black adsorbed with carbon dots on the filter paper in step S3 into 40 mL of deionized water to obtain a mixed solution, and add 5 mL of a mixed solution of 0.0025 mol / L nickel nitrate and 5 mL of 0.0025 mol / L chloroplatinic acid dropwise to the mixed solution, maintaining a dropping rate of 10 mL / min, stir for 24 h at room temperature, filter to obtain a filter residue, and dry the filter residue in a constant temperature oven set at 60 °C to obtain a nickel and platinum bimetal single-atom loaded Ni, Pt-NCDs / C single-atom catalyst.

[0074] Refer to Figure 4 , Figure 4 Figure 1 is the X-ray diffraction pattern of the Ni, Pt-NCDs / C single-atom catalyst prepared in Example 4, conductive carbon black, and commercial palladium-on-carbon catalyst. The peak shape of the Ni, Pt-NCDs / C single-atom catalyst is similar to that of conductive carbon black, and no crystal plane parameters corresponding to nickel and platinum metals appear, indicating the formation and high dispersion of nickel and platinum single atoms.

[0075] Refer to Figure 5 , Figure 5 Figure 2 is the X-ray absorption near-edge structure spectrum of the Pt L-edge of the Ni, Pt-NCDs / C single-atom catalyst prepared in Example 4, showing that the coordination environment around the platinum atoms is mainly platinum-chlorine coordination and platinum-nitrogen coordination, that is, platinum-chlorine bonds and platinum-nitrogen bonds are formed, and no metal bonds such as platinum-platinum bonds and platinum-nickel bonds appear, further proving the formation of platinum single atoms and their loading on carbon dots and remaining independent of each other.

[0076] Example 5

[0077] A preparation method of a metal single-atom electrocatalyst, wherein metal cobalt, palladium, and platinum are loaded on zero-dimensional carbon dots in the form of single atoms. The specific preparation method is as follows:

[0078] S1. Take 2 g of urea and 0.5 g of citric acid and dissolve them in 20 mL of deionized water. After mixing evenly, place them in a polytetrafluoroethylene reaction kettle. Set the reaction temperature of the polytetrafluoroethylene reaction kettle to 220 °C and the reaction time to 8 h. After the reaction is completed, cool the obtained product to room temperature and filter to remove insoluble impurities to obtain an orange-yellow nitrogen-doped carbon dot solution;

[0079] S2. Take 40 mg of conductive carbon black BP2000 and add it to 50 mL of deionized water, and ultrasonically treat it for 1 h to obtain a carbon black suspension;

[0080] S3. Take the carbon black suspension prepared in step S2 and mix it with 10 mL of the nitrogen-doped carbon dot solution prepared in step S1, stir at room temperature for 48 h, and filter to obtain carbon black adsorbed with carbon dots on the filter paper;

[0081] S4. Use ultrasound to place the carbon black adsorbed with carbon dots on the filter paper in step S3 in 40 mL of deionized water to obtain a mixed solution, and add a mixed solution of 5 mL of 0.0025 mol / L cobalt nitrate, 5 mL of 0.0025 mol / L chloroplatinic acid, and 5 mL of 0.0025 mol / L palladium chloride to the mixed solution, maintain a dropping rate of 5 mL / min, stir at room temperature for 24 h, filter to obtain a filter residue, and dry the filter residue in a constant-temperature oven set at 60 °C to obtain a Co, Pd, Pt-NCDs / C single-atom catalyst loaded with cobalt, palladium, and platinum trimetal single atoms.

[0082] Refer to Figure 4 , Figure 4 Figure 2 is the X-ray diffraction pattern of the Co, Pd, Pt-NCDs / C single-atom catalyst prepared in Example 5, conductive carbon black, and commercial palladium-carbon catalyst. The peak shape of the Co, Pd, Pt-NCDs / C single-atom catalyst is similar to that of conductive carbon black, and no crystal plane parameters corresponding to cobalt, palladium, and platinum metals appear, indicating the formation and high dispersion of cobalt, palladium, and platinum single atoms.

[0083] Refer to Figure 6 , Figure 6 Figure 3 is the aberration-corrected electron microscopy image of the Co, Pd, Pt-NCDs / C single-atom catalyst prepared in Example 5. In aberration-corrected electron microscopy, the electron beam passes through the sample, and atoms with higher atomic numbers scatter electrons more strongly, resulting in more electrons being scattered to high angles, thus forming brighter regions in the image. That is, the isolated bright spots in the figure are cobalt, palladium, and platinum with higher atomic numbers (the bright spots marked by the gray circles in the figure are some metal single atoms on the support), which are evenly dispersed on the carbon support, proving the formation of cobalt, palladium, and platinum metal single atoms.

[0084] Comparative Example 1

[0085] A method for preparing a metal cluster electrocatalyst, wherein platinum metal is loaded on zero-dimensional carbon dots in the form of clusters. The specific preparation method is as follows:

[0086] Compared with Example 1, step S4 is changed to use ultrasound to place the carbon black adsorbed with carbon dots in step S3 in 40 mL of deionized water to obtain a mixed solution. Then, 10 mL of 0.0025 mol / L chloroplatinic acid solution is added dropwise to the mixed solution, and then 0.05 mol / L sodium borohydride solution is slowly added dropwise at a dropping rate of 0.15 mL / min, and the final dropping volume is about 10 mL. Stir at room temperature for 6 h, filter to obtain a filter residue, and dry the filter residue in a constant-temperature oven set at 50 °C. The other steps are the same. The Pt-NCDs / C-Cluster cluster catalyst loaded with platinum clusters is obtained.

[0087] The Pt atomic ratio in the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1 is determined to be 7.9% by inductively coupled plasma atomic emission spectrometry.

[0088] Refer to Figure 2 , Figure 2Figure showing the mass activities of the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1 and the commercial platinum-carbon catalyst for electrochemically catalyzed methanol oxidation. Using a classical three-electrode system, the electrocatalytic performance of the Pt-NCDs / C-Cluster cluster catalyst and the commercial platinum-carbon catalyst prepared in Comparative Example 1 was tested for electrochemically catalyzed methanol oxidation in an alkaline medium (1 mol / L KOH + 1 mol / L CH3OH). It can be seen that the mass activity of the commercial platinum-carbon catalyst is 1363.11 mA / mg Pt , and the mass activity of the Pt-NCDs / C-Cluster cluster catalyst obtained in this comparative example is 3167.49 mA / mg Pt , which is 2.32 times that of the commercial platinum-carbon catalyst.

[0089] Refer to Figure 2 , Figure 2 The mass activity of the Pt-NCDs / C single-atom catalyst prepared in Example 1 in Pt (6611.73 mA / mg Pt ) is 2.09 times that of the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1 (3167.49 mA / mg

[0090] Refer to Figure 3 , Figure 3 Figure showing the i-t (chronoamperometry) curves of the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1 and the commercial platinum-carbon catalyst. The electrochemical stability of the Pt-NCDs / C-Cluster cluster catalyst and the commercial platinum-carbon catalyst prepared in Comparative Example 1 was tested in an alkaline medium (1 mol / L KOH + 1 mol / L CH3OH). After 5000 s of constant-voltage operation, the current density of the Pt-NCDs / C-Cluster catalyst is lower than that of the commercial platinum-carbon catalyst, indicating that the stability of the Pt-NCDs / C-Cluster catalyst is poorer than that of the commercial platinum-carbon catalyst.

[0091] Refer to Figure 3 , Figure 3 In

[0092] Refer to Figure 4 , Figure 4X-ray diffraction patterns of the Pt-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 1, conductive carbon black, and commercial palladium-carbon catalyst are shown. The crystal plane parameters corresponding to platinum metal appear in the Pt-NCDs / C-Cluster cluster catalyst, indicating that platinum exists in the form of clusters and has poorer dispersion than single-atom catalysts.

[0093] Comparative Example 2

[0094] A preparation method of a metal cluster electrocatalyst, in which palladium and ruthenium metals are loaded on zero-dimensional carbon dots in the form of clusters. The specific preparation method is as follows:

[0095] Compared with Example 4, step S4 is changed to use ultrasound to place the carbon black adsorbed with carbon dots in step S3 in 40 mL of deionized water to obtain a mixed solution. Add 5 mL of 0.0025 mol / L palladium chloride solution and 5 mL of 0.0025 mol / L ruthenium chloride solution to the mixed solution, and then slowly add 0.05 mol / L sodium borohydride solution while maintaining a dropping rate of 0.15 mL / min. The final dropping volume is about 10 mL. Stir at room temperature for 12 h, filter to obtain the filter residue, and dry the filter residue in a constant-temperature oven set at 50 °C. The remaining steps are the same. The Pd, Ru-NCDs / C-Cluster cluster catalyst loaded with palladium and ruthenium clusters is obtained.

[0096] Refer to Figure 4 , Figure 4 X-ray diffraction patterns of the Pd, Ru-NCDs / C-Cluster cluster catalyst prepared in Comparative Example 2 and commercial palladium-carbon catalyst are shown. The peak shape of the Pd, Ru-NCDs / C-Cluster cluster catalyst shows the crystal plane parameters corresponding to palladium metal, but the crystal plane parameters corresponding to ruthenium metal do not appear. This indicates that ruthenium metal has been doped into the palladium lattice or exists in an amorphous form, indicating that ruthenium and palladium form a palladium-ruthenium alloy nanostructure or palladium-ruthenium clusters, and the dispersion is poorer than that of single-atom catalysts.

[0097] The above are all preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a metal single-atom electrocatalyst, characterized in that, It includes the following steps: S1. Take a nitrogen source and citric acid, dissolve them in deionized water, mix evenly, place them in a reaction kettle. After the reaction ends, cool and filter to obtain a nitrogen-doped carbon dot solution; S2. Take conductive carbon black and place it in deionized water, ultrasonically treat it for 1 - 2 h to obtain a carbon black suspension; S3. Mix the nitrogen-doped carbon dot solution prepared in step S1 and the carbon black suspension prepared in step S2, stir for 48 h, filter, and obtain carbon black adsorbed with carbon dots on the filter paper; S4. Use ultrasound to place the carbon black adsorbed with carbon dots on the filter paper in step S3 in deionized water to obtain a mixed solution, add a metal precursor solution dropwise to the mixed solution, stir, immerse and adsorb at room temperature for 24 h, filter to obtain a filter residue, and dry the filter residue in an environment of 50 - 60 °C to obtain a metal single-atom electrocatalyst; The metal in the metal precursor solution includes any one or more of ruthenium, rhodium, palladium, osmium, iridium, platinum, rhenium, manganese, iron, cobalt, nickel, zinc; the metal precursor includes one or more of ruthenium chloride, chlororhodic acid, chloropalladic acid, chloroosmic acid, chloroiridic acid, chloroplatinic acid, rhenium chloride, manganese sulfate, manganese chloride, manganese nitrate, iron sulfate, iron chloride, iron nitrate, cobalt sulfate, cobalt chloride, cobalt nitrate, nickel sulfate, nickel chloride, nickel nitrate, zinc sulfate, zinc chloride, zinc nitrate; The metal single-atom electrocatalyst includes a carrier and an active center; The carrier is zero-dimensional carbon dots; The active center is a metal dispersed in the form of single atoms, and the metal is loaded on the zero-dimensional carbon dots.

2. The preparation method of a metal single-atom electrocatalyst according to claim 1, wherein, The nitrogen source in step S1 is any one of urea and ethylenediamine.

3. The preparation method of a metal single-atom electrocatalyst according to claim 1, characterized in that, In step S1, the reaction temperature of the reaction kettle is set to 160 - 240 °C, and the reaction time is 8 - 12 h.

4. The preparation method of a metal single-atom electrocatalyst according to claim 1, wherein, In step S1, 50 - 100 mg of nitrogen source is dissolved in each milliliter of deionized water; In step S1, 25 - 50 mg of citric acid is dissolved in each milliliter of deionized water; In step S2, 0.6 - 0.8 mg of conductive carbon black is dissolved in each milliliter of deionized water.

5. The preparation method of a metal single-atom electrocatalyst according to claim 1, characterized in that, In step S3, the volume ratio of the nitrogen-doped carbon dot solution to the carbon black suspension is (0.09 - 0.2):

1.

6. The preparation method of a metal single-atom electrocatalyst according to claim 1, characterized in that, In step S4, the concentration of the metal precursor solution is 0.0025 mol / L; In step S4, the dropping rate of the metal precursor solution is 0.1 - 10 mL / min; In step S4, the volume ratio of the mixed solution to the metal precursor solution is 4:(1 - 1.5).

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