A method for synthesizing a single-atom catalyst in parallel with structure construction and single atom generation

Abstract

The application belongs to the field of nanomaterials and electrocatalysis, and specifically designs a single-atom electrocatalyst, which is formed by carbonizing a precursor mixed with nitrogen-containing organic matter and transition metal salt in a way parallel to single-atom generation. The nitrogen-doped carbon nanosheet prepared from the metal salt has the characteristics of rich pore structure, large specific surface area and high graphitization degree, and can capture single-atom metal to form a single-atom catalyst. In the preparation process, the transition metal salt acts as a template, a metal source and a pore-forming agent, and has a catalytic effect on the formed carbon material, thereby improving the graphitization degree of the carbon material. The single-atom catalyst prepared by the application has a high specific surface area and a developed pore size structure, which improves the exposure rate of active sites, and the carbon with a high graphitization degree not only improves the conductivity but also improves the corrosion resistance of the catalyst in an alkaline environment, thereby improving the stability of the catalyst.

Description

Technical Field

[0001] This invention belongs to the technical field of catalyst preparation, specifically relating to a method for preparing a single-atom catalyst. Background Technology

[0002] Zinc-air batteries, clean, efficient, and sustainable energy devices, have garnered widespread attention and are considered one of the most promising new energy sources to replace traditional fossil fuels. Zinc-air batteries possess characteristics such as high theoretical output capacity, low manufacturing cost, high safety, and environmental friendliness, and are thus regarded as one of the most promising future power sources.

[0003] However, the slow reaction kinetics of the key reactions in zinc-air batteries, the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), severely hinder the large-scale application of these devices, requiring catalysts for catalytic drive. Currently, ORR and OER catalysts are mainly noble metal catalysts; however, the scarcity and high price of noble metals on Earth significantly impede the large-scale application of zinc-air batteries. Therefore, we need to develop efficient and stable ORR and OER catalysts without noble metals to promote the large-scale application of zinc-air batteries. In the research of zinc-air battery catalysts, single-atom catalysts have attracted widespread attention due to their near 100% atom utilization and high catalytic activity. The uniformity of active sites in single-atom catalysts gives them the advantages of both homogeneous and heterogeneous catalysts, while overcoming the disadvantages of both. Single-atom catalysts greatly reduce the cost of catalysts; only a very low metal content is needed to exhibit catalytic activity comparable to or even better than high-metal-content catalysts, increasing metal utilization by tens or even hundreds of times.

[0004] Currently, commonly used methods for preparing single-atom catalysts include co-precipitation, impregnation, displacement reaction, atomic layer deposition, and reverse Oswald ripening. However, these methods suffer from drawbacks such as low yield, high cost, and complex equipment, which hinder the large-scale application of single-atom catalysts. Given the unparalleled advantages demonstrated by single-atom catalysts in zinc-air batteries, developing a general strategy for preparing single-atom catalysts that is simple to synthesize, low in cost, and effective for multiple metals is particularly important.

[0005] In the research of zinc-air battery catalysts, carbon materials are indispensable. Pure carbon materials lack catalytic activity, often requiring heteroatom doping and morphological configuration. Heteroatom doping often reduces the graphitization degree of carbon materials, while highly graphitized carbon possesses excellent conductivity and corrosion resistance; however, it lacks active sites for catalytic ORR and OER. This raises the question of how to balance the relationship between carbon graphitization degree and heteroatom doping to simultaneously improve the catalyst's catalytic activity and stability. The morphological configuration of carbon materials is also crucial for enhancing catalytic activity. Carbon material morphologies are generally classified into one-dimensional, two-dimensional, and three-dimensional structures. Among these three structures, two-dimensional structures can be effectively exposed to the electrolyte, and most of the active sites on the surface of two-dimensional carbon materials can participate in electrocatalytic reactions, resulting in high efficiency for two-dimensional carbon materials in a series of electrochemical reactions. However, the single-atom dispersion, balancing the degree of graphitization and heteroatom relationship, and two-dimensional structure construction mentioned above can only be implemented individually, and each method has limited effect on improving the catalytic performance of the catalyst. Therefore, it is necessary to explore a new method for preparing single-atom catalysts that can simultaneously achieve the above characteristics. Summary of the Invention

[0006] In view of the current problems of complex and costly preparation processes for single-atom catalysts, the balance between heteroatom doping and graphitization of carbon materials, the complex preparation process of two-dimensional carbon materials and the problems of subsequent processing, and the needs of research and application in this field, one of the objectives of this invention is to provide a method for preparing ultra-stable single-atom catalysts that is simple in process, low in cost, and can be mass-produced. The method is characterized by preparation through a method that combines structure construction and single-atom generation.

[0007] This invention discloses a method for preparing a single-atom catalyst using nitrogen-containing organic matter as a carbon precursor and a metal salt simultaneously as a template, pore-forming agent, metal source, and catalyst for catalytic carbon. The method involves mixing via dissolution or ball milling, washing with hydrochloric acid, and secondary carbonization to ultimately obtain the single-atom catalyst. By utilizing the metal salt as a template, pore-forming agent, dopant, and catalyst for catalytic carbon, the method achieves simultaneous single-atom preparation and controls the pore size, morphology, and graphitization degree of the carbon material. This invention utilizes only nitrogen-containing organic matter as a carbon precursor and a metal salt simultaneously as a template, pore-forming agent, metal source, and catalyst for catalytic carbon, eliminating the need for introducing additional templates, metal templates, pore-forming agents, or catalysts. Therefore, compared to existing single-atom catalyst methods, this method is simpler, lower in cost, and suitable for large-scale production.

[0008] This invention organically combines single-atom preparation, template method, and activation method to achieve simultaneous completion. Metal salts are selected as template agents, activators, and metal sources. The metal salts isolate and separate nitrogen-containing organic matter to form a two-dimensional structure. As the temperature increases, the metal salts are reduced to elemental metals by carbon. This process consumes carbon, causing numerous defects and pores to form. At high temperatures, the elemental metals also act as catalysts for carbon, increasing the graphitization degree of the carbon material. Finally, at high temperatures, the metal volatilizes, and the defects and micropores on the carbon material trap the single-atom metals, fixing them and forming a dispersed single-atom metal structure. During the secondary carbonization process, ammonia is used to dope the carbon material, introducing more nitrogen.

[0009] The single-atom catalyst prepared in this invention is prepared by using a parallel approach of structure building and single-atom generation. During the preparation process, the transition metal salt simultaneously functions as a template agent, metal source, pore-forming agent, and carbon catalyst, simplifying the preparation process of the single-atom catalyst. The obtained single-atom catalyst has advantages such as high stability, good conductivity, low price, and high catalytic activity. The single-atom catalyst prepared in this invention has the following characteristics: (1) Two-dimensional structure, which can effectively improve the contact between the electrolyte and the catalyst; (2) Large specific surface area, which increases the exposure rate of active sites, allowing more active sites to participate in the reaction; (3) Abundant pore structure, which accelerates the transport of reactants and products, thereby improving catalytic activity; (4) High degree of graphitization, which improves conductivity and has anti-corrosion properties in alkaline environments, thereby improving catalyst stability; (5) Single-atom dispersed metal active sites, which improve the activity of the catalyst.

[0010] The specific preparation method of the present invention is as follows:

[0011] (a) Mixing: Mixing nitrogen-containing organic compounds with transition metal salts;

[0012] (b) Carbonization: The well-mixed sample is placed in a tube furnace, heated and held under the protection of an inert gas to carbonize and activate the sample.

[0013] (c) Cleaning: The carbonized sample is acid-washed in hydrochloric acid solution, then filtered with a large amount of deionized water until neutral, and then dried in an oven.

[0014] (d) The dried sample was carbonized again in a mixed atmosphere of nitrogen and ammonia to obtain a single-atom catalyst.

[0015] In the preparation method of the present invention, the nitrogen-containing organic compounds used in step (a) include, but are not limited to: ammonium citrate, dopamine hydrochloride, hexamethylenetetramine, humic acid, etc.; the transition metal salt is one or more of transition metals such as Fe salt, Co salt, Ni salt, Mn salt, etc.

[0016] In the preparation method of the present invention, the mass ratio of nitrogen-containing organic precursor to transition metal salt in step (a) is 1:3.

[0017] In the preparation method of the present invention, in step (a), 10g of nitrogen-containing organic matter is dissolved in 30ml of water, then 30g of transition metal salt is added and stirred for 1h to form a transparent solution. Finally, the solution is rapidly frozen with liquid nitrogen and freeze-dried for 24h to form a uniform solid powder.

[0018] In the preparation method of the present invention, in step (b), the carbonization temperature is 700–1200 °C, and the heating rate is 1–10 °C / min. -1 The heat preservation time is 0 to 10 hours.

[0019] In the preparation method of the present invention, the single-atom catalyst is composed of a single-atom transition metal and nitrogen-doped carbon nanosheets with abundant pore structure, large specific surface area and high degree of graphitization.

[0020] In the preparation method of the present invention, in step (c), the carbonized sample is acid-washed in 2M hydrochloric acid solution at 90°C for 24 hours, then filtered with a large amount of deionized water until neutral, and dried in an oven at 80°C.

[0021] A zinc-air battery is provided, wherein a single-atom catalyst prepared by the preparation method of the present invention is assembled into a zinc-air battery, and its charge-discharge cycle curve shows that it can remain stable after 16,000 cycles.

[0022] It should be noted that the mass of the transition metal salt is much greater than that of the nitrogen-containing organic precursor. Here, the transition metal salt acts as a template, metal source, and pore-forming agent. The catalytic effect of transition metals on carbon endows carbon with abundant defects, which can capture over-volatile metal atoms to form single-atom catalysts.

[0023] This application discloses a method for preparing single-atom catalysts. The single-metal catalysts obtained by this method have good quality and high stability, and therefore can be applied to various fields where single-atom catalysts are applicable, especially for energy conversion devices, such as metal-air batteries.

[0024] Compared with the prior art, the main beneficial effects and advantages of this invention are as follows:

[0025] 1) The method of parallel structure construction and single-atom generation adopted in this invention simultaneously forms a two-dimensional sheet structure and a single-atom catalyst during the preparation process.

[0026] 2) The preparation process of this invention is simpler, lower in cost, and can be mass-produced compared with existing single-atom catalyst methods.

[0027] 3) The transition metal salts used in this invention serve as templates, create pores, improve the graphitization degree of carbon materials, and act as a cobalt source.

[0028] 4) The catalyst obtained by the preparation method described in this invention has a rich pore structure, a large specific surface area, a large interlayer spacing and a high degree of graphitization.

[0029] 5) The catalyst prepared by the method described in this invention exhibits extremely high stability, which is significantly better than that of single-atom catalysts prepared by traditional methods. Attached image description:

[0030] Figure 1 Scanning electron microscope image of the catalyst prepared in Example 1

[0031] Figure 2 Scanning electron microscope image of the catalyst prepared in Comparative Example 1

[0032] Figure 3 Aberration-corrected electron micrograph of the catalyst prepared in Example 1

[0033] Figure 4 Transmission electron microscopy image of the catalyst prepared in Example 1

[0034] Figure 5 The XRD pattern of the catalyst prepared in Example 1.

[0035] Figure 6 Nitrogen adsorption-desorption curves and pore size distribution diagrams of the catalysts prepared in Example 1 and Comparative Example 1.

[0036] Figure 7 Linear sweep voltammetry plots of oxygen reduction performance of the catalyst in Example 1, the catalyst in Comparative Example 1, and commercial Pt / C.

[0037] Figure 8 Linear sweep voltammetry curves of oxygen evolution performance for the catalyst of Example 1, the catalyst of Comparative Example 1, and commercial IrO2.

[0038] Figure 9 The discharge curves and power density diagrams for the catalyst in Example 1 and commercial Pt / C+IrO2 are shown.

[0039] Figure 10 The above is a charge-discharge cycle curve of the catalyst in Example 1 and commercial Pt / C+IrO2.

[0040] Figure 11 Scanning electron microscope image of the catalyst obtained in Example 2

[0041] Figure 12 The XRD pattern of the catalyst obtained in Example 2.

[0042] Figure 13 The nitrogen adsorption-desorption curves and pore size distribution diagrams of the catalysts prepared in Example 2 and Comparative Example 2 are shown.

[0043] Figure 14 Linear sweep voltammetry plots of oxygen reduction performance of the catalyst in Example 2, the catalyst in Comparative Example 1, and commercial Pt / C.

[0044] Figure 15 The discharge curves and power density diagrams for the catalyst in Example 2 with commercial Pt / C+IrO2 are shown.

[0045] Figure 16 Scanning electron microscope image of the catalyst obtained in Example 3

[0046] Figure 17 Linear sweep voltammetry plots of oxygen reduction performance of the catalyst in Example 3, the catalyst in Comparative Example 2, and commercial Pt / C.

[0047] Figure 18 Linear sweep voltammetry curves of the oxygen evolution performance of the catalyst in Example 3, the catalyst in Comparative Example 2, and commercial IrO2.

[0048] Figure 19 Scanning electron microscope image of the catalyst obtained in Example 4

[0049] Figure 20 Linear sweep voltammetry plots of the oxygen reduction performance of the catalyst in Example 4, the catalyst in Comparative Example 3, and commercial Pt / C. Detailed implementation method:

[0050] To further understand the present invention, the following description, in conjunction with the accompanying drawings and embodiments, will further illustrate the present invention, but does not limit the present invention in any way.

[0051] Example 1:

[0052] First, 10g of ammonium citrate was dissolved in 30ml of water, then 30g of CoCl2·6H2O was added and stirred for 1 hour to form a transparent solution. Finally, the solution was rapidly frozen with liquid nitrogen and freeze-dried for 24 hours to form a uniform solid powder. The solid powder was then calcined in a tube furnace at 900℃ for 2 hours under a nitrogen atmosphere to obtain a black powder. The black powder was then acid-washed with 2M HCl at 90℃ for 24 hours. The acid-washed sample was then calcined at 900℃ for 1 hour under a mixed atmosphere of nitrogen and ammonia to obtain the final catalyst.

[0053] Comparative Example 1:

[0054] 10g of ammonium citrate was dissolved in 30ml of water, then the solution was frozen with liquid nitrogen and freeze-dried for 24 hours to form a powder. The powder was then calcined in a tube furnace at 900℃ for 2 hours under a nitrogen atmosphere to obtain a black powder. The black powder was then acid-washed with 2M HCl at 90℃ for 24 hours. The acid-washed sample was then calcined at 900℃ for 1 hour under a mixed atmosphere of nitrogen and ammonia to obtain the final catalyst.

[0055] Figure 1 and Figure 2 The images shown are scanning electron microscope (SEM) images of the catalysts obtained in Example 1 and Comparative Example 1, respectively. Figure 1 The image shows the microstructure of Example 1, which reveals that Example 1 is a large, complete sheet of two-dimensional material. Figure 2 The image shows the microstructure of Comparative Example 1, which is mainly composed of large, blocky structures. This indicates that CoCl2·6H2O is crucial for the formation of two-dimensional sheet-like structures.

[0056] Figure 3 The aberration electron microscope image of Example 1 shows a large number of bright spots on the carbon sheet, which directly proves the existence of single-atom cobalt.

[0057] Figure 4 The image shows a transmission electron microscope (TEM) image of Example 1. Analysis of the image reveals a distinct graphite lattice in Example 1, indicating a high degree of graphitization. Furthermore, the interlayer spacing of the graphite is 0.401 nm, which is significantly larger than that of traditional graphite interlayers.

[0058] Figure 5 The XRD pattern of the catalyst prepared in Example 1 is shown. As shown in the figure, only two broad diffraction peaks appear in the XRD pattern at 26° and 43°, corresponding to the (002) and (100) crystal planes of graphitic carbon. No characteristic peaks related to metallic cobalt are observed.

[0059] Figure 6 The figures show the nitrogen adsorption-desorption curves and pore size distribution of Example 1 and Comparative Example 1. From the figures, it can be seen that Example 1 has a larger specific surface area and a well-developed pore structure. The specific surface area of ​​Example 1 is 1538.6 m². 2 g -1 The pore size is 1.311 cm³. 3 g -1 This has a much larger specific surface area and pore capacity than the catalyst obtained from Comparative Example 1.

[0060] Figure 7The ORR catalytic performance of the catalyst in Example 1 was compared with that of Comparative Example 1 and commercial Pt / C. It was found that the ORR catalytic performance of Example 1 was significantly improved compared to Comparative Example 1, and even better than that of commercial Pt / C. The half-wave potential of Example 1 was 0.87 V, and the limiting current was 5.2 mA cm⁻¹. -2 .

[0061] Figure 8 The OER activities of the catalyst in Example 1, the catalyst in Comparative Example 1, and IrO2 are demonstrated. Example 1 was tested at 10 mA cm⁻¹. -2 The potential at the current density is 1.533V, which is better than the OER catalytic performance of the catalyst in Comparative Example 1 and IrO2.

[0062] Figure 9 The discharge curves and power density curves of the zinc-air battery assembled with the catalyst prepared in Example 1 were compared with those of a commercial Pt / C+RuO2 battery. Figure 9 It can be seen that the limiting power density of the catalyst material of this invention is approximately 255 mW / cm³. -2 Higher than the 170mW cm⁻¹ of commercial catalysts -2 . Figure 10 The charge-discharge cycle curves of a zinc-air battery assembled with the catalyst material prepared in Example 1 and commercial Pt / C+RuO2 as a catalyst are shown. The catalyst material of this invention remained stable after 16,000 cycles, while commercial Pt / C+RuO2 showed significant degradation after 170 cycles.

[0063] Example 2:

[0064] First, 10g of ammonium citrate was dissolved in 30ml of water, then 30g of MnCl2·4H2O was added and stirred for 1 hour to form a transparent solution. Finally, the solution was rapidly frozen with liquid nitrogen and freeze-dried for 24 hours to form a uniform solid powder. The solid powder was then calcined in a tube furnace at 900℃ for 2 hours under a nitrogen atmosphere to obtain a black powder. The black powder was then acid-washed with 2M HCl at 90℃ for 24 hours. The acid-washed sample was then calcined at 900℃ for 1 hour under a mixed atmosphere of nitrogen and ammonia to obtain the final catalyst.

[0065] Figure 11 This is a scanning electron microscope (SEM) image of the catalyst obtained in Example 2. (The image is obtained through...) Figure 11 It can be observed that the catalyst obtained in Example 2 has a two-dimensional sheet-like structure.

[0066] Figure 12 The XRD pattern of the catalyst prepared in Example 2 is shown. As shown in the figure, only two broad diffraction peaks appear in the XRD pattern, located at 21° and 43°, corresponding to the (002) and (100) crystal planes of graphitic carbon. No characteristic peaks related to metallic manganese are present.

[0067] Figure 13 The nitrogen adsorption-desorption curves and pore size distribution of the catalyst prepared in Example 2 are shown in the figures. From the figures, it can be concluded that Example 2 has a large specific surface area and a well-developed pore structure. Calculations revealed that the specific surface area of ​​the catalyst obtained in Example 2 is 1967.2 m². 2 g -1 The pore size is 3.827 cm³. 3 g -1 .

[0068] Figure 14 A comparison of the ORR catalytic performance of the catalyst in Example 2 with that of Comparative Example 1 and commercial Pt / C revealed that Example 2 exhibited significantly improved ORR catalytic performance compared to Comparative Example 1, and even outperformed commercial Pt / C. The half-wave potential of Example 2 was 0.9 V, and the limiting current was 5.2 mA cm⁻¹. -2 .

[0069] Figure 15 The discharge curves and power density curves of the zinc-air battery assembled with the catalyst prepared in Example 2 were compared with those of a commercial Pt / C+RuO2 battery. Figure 15 It can be seen that the limiting power density of the catalyst material of the present invention is approximately 190 mW / cm³. -2 Higher than the 170mW cm⁻¹ of commercial catalysts -2 .

[0070] Example 3:

[0071] 10g of dopamine hydrochloride was dissolved in 30ml of water, then 15g of MnCl2·4H2O and 15g of CoCl2·6H2O were added and stirred for 1 hour to form a transparent solution. The solution was then rapidly frozen with liquid nitrogen and freeze-dried for 24 hours to form a uniform solid powder. The solid powder was calcined in a tube furnace at 800℃ for 2 hours under a nitrogen atmosphere to obtain a black powder. The black powder was then acid-washed with 2M HCl at 90℃ for 24 hours. The acid-washed sample was then calcined at 800℃ for 1 hour under a mixed atmosphere of nitrogen and ammonia to obtain the final catalyst.

[0072] Comparative Example 2:

[0073] 10g of dopamine hydrochloride was dissolved in 30ml of water, then the solution was frozen with liquid nitrogen and freeze-dried for 24 hours to form a powder. The powder was then calcined in a tube furnace at 800℃ for 2 hours under a nitrogen atmosphere to obtain a black powder. The black powder was then acid-washed with 2M HCl at 90℃ for 24 hours. The acid-washed sample was then calcined at 800℃ for 1 hour under a mixed atmosphere of nitrogen and ammonia to obtain the final catalyst.

[0074] Figure 16This is a scanning electron microscope (SEM) image of the catalyst obtained in Example 3. Figure 16 It can be observed that the catalyst obtained in Example 3 has a two-dimensional sheet-like structure.

[0075] Figure 17 The ORR catalytic performance of the catalyst in Example 3 was compared with that of Comparative Example 2 and commercial Pt / C. It was found that the ORR catalytic performance of Example 3 was significantly improved compared to Comparative Example 2, and even better than that of commercial Pt / C. The half-wave potential of Example 3 was 0.85 V, and the limiting current was 5.5 mA cm⁻¹. -2 .

[0076] Figure 18 The OER activities of the catalyst in Example 3, the catalyst in Comparative Example 2, and IrO2 are demonstrated. Example 3 was tested at 10 mA cm⁻¹. -2 The potential at the current density is 1.508V, which is better than the OER catalytic performance of the catalyst in Comparative Example 1 and IrO2.

[0077] Example 4:

[0078] 10g of hexamethylenetetramine was dissolved in 30ml of water, then 15g of MnCl₂·4H₂O and 15g of CoCl₂·6H₂O were added and stirred for 1 hour to form a transparent solution. The solution was then rapidly frozen with liquid nitrogen and freeze-dried for 24 hours to form a uniform solid powder. The solid powder was calcined in a tube furnace at 800℃ for 2 hours under a nitrogen atmosphere to obtain a black powder. The black powder was then acid-washed with 2M HCl at 90℃ for 24 hours. The acid-washed sample was then calcined at 800℃ for 1 hour under a mixed atmosphere of nitrogen and ammonia to obtain the final catalyst.

[0079] Comparative Example 3:

[0080] 10g of hexamethylenetetramine was dissolved in 30ml of water, then the solution was frozen with liquid nitrogen and freeze-dried for 24 hours to form a powder. The powder was then calcined in a tube furnace at 800℃ for 2 hours under a nitrogen atmosphere to obtain a black powder. The black powder was then acid-washed with 2M HCl at 90℃ for 24 hours. The acid-washed sample was then calcined at 800℃ for 1 hour under a mixed atmosphere of nitrogen and ammonia to obtain the final catalyst.

[0081] Figure 19 This is a scanning electron microscope (SEM) image of the catalyst obtained in Example 4. (The image is obtained through...) Figure 19 It can be observed that the catalyst obtained in Example 3 has a two-dimensional sheet-like structure.

[0082] Figure 20The ORR catalytic performance of the catalyst in Example 4 was compared with that of Comparative Example 3 and commercial Pt / C. It was found that the ORR catalytic performance of Example 4 was significantly improved compared to Comparative Example 3, and even comparable to that of commercial Pt / C. The half-wave potential of Example 4 was 0.84 V, and the limiting current was 5 mA cm⁻¹. -2 .

Claims

1. A method for the parallel synthesis of single-atom catalysts through structure construction and single-atom generation, characterized in that: Using nitrogen-containing organic matter as a carbon precursor and transition metal salts as templates, pore-forming agents, metal sources, and catalysts for carbon, the mixture is prepared by dissolution or ball milling, followed by carbonization, hydrochloric acid washing, and secondary carbonization to obtain a single-atom catalyst. The transition metal salts serve as both templates and metal sources, and can also alter the graphitization degree and pore structure of the carbon material. This method organically combines single-atom preparation, template method, and activation method, achieving simultaneous completion. The specific steps are as follows: (a) Mixing: Mixing nitrogen-containing organic matter with transition metal salts; the nitrogen-containing organic matter used is: ammonium citrate, dopamine hydrochloride, hexamethylenetetramine or humic acid; the transition metal salt is one or more of Fe salt, Co salt, Ni salt, Mn salt transition metals; the mass ratio of nitrogen-containing organic matter precursor to transition metal salt is 1:3; (b) Carbonization: The well-mixed sample is placed in a tube furnace, heated and held under the protection of an inert gas to carbonize and activate the sample; the carbonization temperature is 700~1200 ℃, the heating rate is 1~10 ℃ min-1, and the holding time is 0~10h. (c) Cleaning: The carbonized sample is acid-washed in hydrochloric acid solution, then filtered with a large amount of deionized water until neutral, and then dried in an oven. (d) The dried sample was carbonized again in a mixed atmosphere of nitrogen and ammonia to obtain a single-atom catalyst.

2. The method according to claim 1, characterized in that: In step (a), 10 g of nitrogen-containing organic matter was dissolved in 30 ml of water, and then 30 g of transition metal salt was added and stirred for 1 h to form a transparent solution. Finally, the solution was rapidly frozen with liquid nitrogen and freeze-dried for 24 h to form a uniform solid powder.

3. The method according to claim 1, characterized in that: In step (c), the carbonized sample is acid-washed in 2 M hydrochloric acid solution at 90 °C for 24 h, then filtered with a large amount of deionized water until neutral, and dried in an oven at 80 °C.

4. A zinc-air battery, wherein, Assemble the single-atom catalyst prepared by any one of the methods in claims 1-3 into a zinc-air battery.

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