A manganese single-atom carbon-based electrocatalyst with a core-shell structure and a preparation method and application thereof

Abstract

The application discloses a manganese monatomic carbon-based electrocatalyst with a core-shell structure and a preparation method and application thereof. A solvent thermal reaction is carried out by adding manganese nitrate solution and 1H-1,2,3 triazole into N,N dimethylformamide solvent, and MET-2 mixed dicyandiamide prepared through the solvent thermal reaction is pyrolyzed in a vacuum environment. In the application, dicyandiamide is first heat-induced polymerized on the surface of MET-2 crystals to generate a graphene-like shell, and then gas molecules generated in the pyrolysis process can adjust the pore structure. The manganese monatomic carbon-based electrocatalyst with the core-shell structure prepared through the method has more excellent ORR activity than a Pt / C catalyst, and when the manganese monatomic carbon-based electrocatalyst is applied to a zinc-air battery, the zinc-air battery has higher energy density and stability than a zinc-air battery assembled by the Pt / C.

Description

Technical Field

[0001] This invention relates to electrochemical catalyst technology, specifically to a manganese single-atom carbon-based electrocatalyst with a core-shell structure, its preparation method, and its application. Background Technology

[0002] The world is facing a climate and energy crisis, making it crucial to reshape the current fossil fuel-driven development model by utilizing clean, economical, and reliable new energy sources. Metal-air batteries, with their advantages of safety, environmental friendliness, and high energy density, offer an important direction for the development of next-generation energy storage systems. However, the slow kinetics of the oxygen reduction reaction (ORR) at the cathode severely limit the advantages of metal-air batteries. Platinum group metals (PGMs) have become the primary catalysts for ORR due to their high catalytic activity. Unfortunately, their scarcity and stability significantly limit their large-scale application in energy conversion devices. Driven by the need to reduce PGMs, transition metal-intercalated nitrogen-carbon composites (MNCs) show great promise due to their ORR catalytic activity comparable to Pt / C.

[0003] Metal-organic frameworks (MOFs) possess unique advantages, such as ultra-high specific surface area, well-defined pore structure, and tunable composition, leading to their widespread development in the field of electrocatalysis. Furthermore, single-atom catalysts (SACs) based MNCs can be prepared from MOFs as self-adsorbed precursors / templates. Fe-NCs exhibit good activity, but their unfavorable Fenton reaction reduces stability. Conversely, Mn-NCs demonstrate activity comparable to Fe-NCs in the ORR process, but with negligible Fenton reaction activity. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a manganese single-atom carbon-based electrocatalyst with a core-shell structure, its preparation method, and its application, in order to solve the problem that existing oxygen reduction catalysts cannot simultaneously satisfy the requirements of high catalytic activity, good stability, and abundant reserves.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention provides a method for preparing a manganese single-atom carbon-based electrocatalyst with a core-shell structure, comprising the following steps:

[0007] (1) Add 600-800 μL of 1H-1,2,3-triazole and 400-600 μL of 50% manganese nitrate aqueous solution to 30-50 mL of N,N-dimethylformamide and mix evenly by ultrasonication. Then transfer it to a constant temperature of 80-120℃ for 12-24 hours for a solvothermal reaction.

[0008] (2) After the reaction is complete, filter the mixture and then dry it in a constant temperature drying oven at 60-80℃ to obtain MET-2;

[0009] (3) Weigh 200-400mg of the powder material MET-2 after drying in step (2), mix it with 400-1200mg of dicyandiamide and grind it evenly, and then carry out a pyrolysis in a tube furnace under vacuum at 800-1000℃ for 1-2 hours.

[0010] (4) The product after the first pyrolysis is placed in a 0.5-1 mol / L sulfuric acid solution and stirred at 60-80℃ for 10-12 hours. Then, it is washed with ultrapure water, filtered, and dried to obtain a first-stage manganese single-atom core-shell carbon-based oxygen reduction catalyst.

[0011] (5) The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst is transferred to a tube furnace filled with N2 and subjected to secondary pyrolysis at the same temperature as in step (3) for 1-2 hours to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

[0012] The present invention also relates to a manganese single-atom carbon-based electrocatalyst with a core-shell structure prepared by the above method.

[0013] This invention also relates to the application of a core-shell structured manganese single-atom carbon-based electrocatalyst prepared by the above method in primary zinc-air batteries and rechargeable zinc-air batteries.

[0014] Furthermore, the preparation method of the primary zinc-air battery cathode is as follows: 2 mg of Mn-N@8Gra-L catalyst is weighed and uniformly dispersed in a mixed solution of 195 μL ethanol and 5 μL naphthol, and then uniformly coated on a 4 cm thick substrate. 2 On carbon cloth;

[0015] The primary zinc-air battery uses a 0.2 mm thick Zn sheet as the negative electrode and a 6 mol / L KOH solution as the electrolyte.

[0016] Furthermore, the preparation method of the rechargeable zinc-air battery positive electrode is as follows: 2 mg of Mn-N@8Gra-L catalyst and 2 mg of RuO2 are weighed and uniformly dispersed in a mixed solution of 390 μL ethanol and 10 μL naphthol, and then uniformly coated on a 4 cm thick substrate. 2 On carbon cloth;

[0017] The rechargeable zinc-air battery uses a 0.2 mm thick Zn sheet as the negative electrode and a mixed solution of KOH and Zn(Ac)2 as the electrolyte; wherein the concentration of KOH is 6 mol / L and the concentration of Zn(Ac)2 is 0.2 mol / L.

[0018] Compared with the prior art, the present invention has the following technical effects:

[0019] This invention utilizes an in-situ thermal erosion strategy to prepare a core-shell structured manganese single-atom carbon-based electrocatalyst, which exhibits a high specific surface area (1062.6 m²). 2 / g). The Mn-N@8Gra-L catalyst prepared in this invention exhibits superior ORR activity (E) compared to the Pt / C catalyst. 1 / 2 =0.875V vs. RHE), and using it as a positive electrode oxygen reduction catalyst in the assembly of a primary zinc-air battery has Its high energy density is far higher than that of a primary zinc-air battery assembled with Pt / C. The rechargeable zinc-air battery based on the Mn-N@8Gra-L catalyst also exhibited superior long-term stability (ΔE = 82.7 mV) compared to the rechargeable zinc-air battery assembled with the Pt / C catalyst. To the applicant's knowledge, this is the first time in the art that a core-shell structured carbon-based catalyst has been formed in one step through a pyrolysis process and applied to the ORR field, achieved through very low-temperature surface modification. This patent application provides new ideas for the subsequent design of various highly efficient single-atom-site catalysts with core-shell structures.

[0020] This invention employs an in-situ thermal erosion strategy to load transition metal manganese in single-atom form onto a core-shell structured, mesoporous, hierarchical nitrogen-doped carbon material and applies it to the oxygen reduction reaction (ORR). In the initial stage of pyrolysis, dicyandiamide thermally induces the formation of a polymer shell coating the MET-2 carbon matrix on the MET-2 crystal surface under heating conditions. As the pyrolysis temperature increases, the polymer shell decomposes into a graphene-like shell. Subsequently, the 1H-1,2,3-triazole organic ligand and the graphene-like shell undergo thermal self-decomposition to generate ammonia and CxNy. + The carbon matrix of the core is eroded by gases, resulting in a manganese single-atom core-shell carbon-based oxygen reduction catalyst with a high specific surface area and a hierarchical pore structure rich in mesopores. Simultaneously, ammonia and CxNy are produced by the decomposition of the graphene-like shell. + The presence of this gas not only replenishes the nitrogen content in the carbon matrix but also inhibits the loss of nitrogen sources from the organic ligands, thereby increasing the loading of anchored transition metal manganese single atoms and improving the electrocatalytic activity of the catalyst. The presence of the core-shell structure further enhances the catalyst's stability. The mesoporous hierarchical pore structure and the synergistic effect of single-atom sites are beneficial to improving the catalyst's catalytic activity and battery performance. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope (SEM) image of the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of the present invention.

[0022] Figure 2 This is a transmission electron microscope (TEM) image of the manganese single-atom carbon-based electrocatalyst with a core-shell structure prepared in Example 1 of the present invention.

[0023] Figure 3 This is a high-resolution transmission electron microscope (HR-TEM) image of the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of the present invention.

[0024] Figure 4 The annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of this invention.

[0025] Figure 5 The Mn-K edge XANES spectra of the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of this invention, and MnPc and Mnfoil.

[0026] Figure 6 The Mn-K edge FT-EXAFS spectra of the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of this invention, along with MnPc and Mnfoil;

[0027] Figure 7 The N2 adsorption-desorption isotherm of the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of this invention (inset shows the pore distribution);

[0028] Figure 8 This is a comparison diagram of the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of the present invention and the commercial Pt / C catalyst oxygen reduction LSV;

[0029] Figure 9 A comparison of the energy densities of a primary zinc-air battery assembled with the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of this invention and a commercial Pt / C catalyst.

[0030] Figure 10 This is a comparison chart of the charge / discharge cycle tests of a rechargeable zinc-air battery assembled with the core-shell structured manganese single-atom carbon-based electrocatalyst prepared in Example 1 of this invention and a commercial Pt / C catalyst. Detailed Implementation

[0031] The specific content of the present invention will be further explained in detail below with reference to Embodiment 1.

[0032] Example 1

[0033] 740 μL of 1H-1,2,3-triazole and 585 μL of 50% manganese nitrate aqueous solution were added to 50 mL of N,N-dimethylformamide and ultrasonically mixed to obtain solution A. Solution A was then transferred to a constant temperature of 120 °C for a solvothermal reaction for 24 hours. After the reaction, the mixture was filtered and dried in a constant temperature drying oven at 60 °C to obtain white powder MET-2. 300 mg of MET-2 and 800 mg of dicyandiamide were weighed, mixed, and ground. The homogenized powder was then subjected to a single pyrolysis in a tube furnace at 900 °C under vacuum for 2 hours. The product after the first pyrolysis was placed in a 0.5 mol / L sulfuric acid solution and stirred at 80 °C for 12 hours. After washing with ultrapure water, the mixture was filtered and dried to obtain a single-atom manganese core-shell carbon-based oxygen reduction catalyst. The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst was subjected to secondary high-temperature pyrolysis in a tube furnace filled with N2 atmosphere at 900℃ for 1 hour to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

[0034] Application of the core-shell structured manganese single-atom carbon-based electrocatalyst (Mn-N@8Gra-L) prepared in this embodiment in a primary zinc-air battery:

[0035] Weigh 2 mg of the Mn-N@8Gra-L catalyst prepared in this example and uniformly disperse it in a mixed solution of 195 μL ethanol and 5 μL naphthol, and then uniformly coat it on a 4 cm thick surface. 2 A primary zinc-air battery was assembled using carbon cloth as the positive electrode oxygen reduction catalyst, a 0.2 mm thick Zn sheet as the negative electrode, and a 6 mol / L KOH solution as the electrolyte.

[0036] As a comparison, a primary zinc-air battery was prepared using a commercial Pt / C catalyst instead of the Mn-N@8Gra-L catalyst prepared in this example. Specifically, 2 mg of the commercial Pt / C catalyst was weighed and uniformly dispersed in a mixed solution of 195 μL ethanol and 5 μL naphthol, and then uniformly coated onto a 4 cm thick substrate. 2 A primary zinc-air battery was assembled using carbon cloth as the positive electrode oxygen reduction catalyst, a 0.2 mm thick Zn sheet as the negative electrode, and a 6 mol / L KOH solution as the electrolyte.

[0037] Application of the core-shell structured manganese single-atom carbon-based electrocatalyst (Mn-N@8Gra-L) prepared in this embodiment in a rechargeable zinc-air battery:

[0038] Weigh 2 mg of Mn-N@8Gra-L catalyst and 2 mg of RuO2 prepared in this example and uniformly disperse them in a mixed solution of 390 μL ethanol and 10 μL naphthol, and then uniformly coat it on a 4 cm thick surface.2 A zinc-air battery was assembled using carbon cloth as the positive electrode oxygen reduction catalyst, a 0.2 mm thick Zn sheet as the negative electrode, and a mixed solution of KOH and Zn(Ac)2 as the electrolyte. The concentration of KOH was 6 mol / L and the concentration of Zn(Ac)2 was 0.2 mol / L.

[0039] As a comparison, a rechargeable zinc-air battery was prepared by replacing the Mn-N@8Gra-L catalyst prepared in this example with a commercial Pt / C catalyst. The specific method was as follows: 2 mg of commercial Pt / C catalyst and 2 mg of RuO2 were weighed and uniformly dispersed in a mixed solution of 390 μL of ethanol and 10 μL of naphthol, and then the solution was uniformly coated on a 4 cm thick substrate. 2 A zinc-air battery was assembled using carbon cloth as the positive electrode oxygen reduction catalyst, a 0.2 mm thick Zn sheet as the negative electrode, and a mixed solution of KOH and Zn(Ac)2 as the electrolyte. The concentration of KOH was 6 mol / L and the concentration of Zn(Ac)2 was 0.2 mol / L.

[0040] like Figure 1 As shown, the Mn-N@8Gra-L catalyst prepared in this embodiment maintains a uniformly dispersed polyhedral morphology, thanks to the dispersibility brought about by the graphene-like layer generated by the addition of dicyandiamide.

[0041] like Figure 2 As shown in the transmission electron microscope image of the Mn-N@8Gra-L catalyst prepared in this embodiment, it has a core-shell structure with internal cavities.

[0042] Figure 3 The high-resolution transmission electron microscope image of the Mn-N@8Gra-L catalyst prepared in this embodiment shows that the irregular lattice fringes indicate that both the core and shell have amorphous properties, indicating that metallic manganese is successfully embedded in the core and shell in the form of single atoms.

[0043] Figure 4 The image shows an aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the Mn-N@8Gra-L catalyst prepared in this embodiment. The single bright spot directly proves the dispersion of manganese atoms, demonstrating that the synthesized Mn-N@8Gra-L catalyst has uniformly dispersed single-atom Mn sites.

[0044] X-ray absorption spectroscopy (XAS) was used to analyze the electronic valence state and coordination structure of the transition metal Mn. Figure 5 The Mn-K edge X-ray absorption near-edge (XANES) spectra shown reveal that the Mn-N@8Gra-L catalyst is significantly different from Mnfoil, but its energy absorption threshold is very close to that of MnPc, indicating that the valence state of the Mn atoms is approximately 2+. Figure 6 As shown, in the Fourier transform diagram of the extended edge X-ray absorption fine structure spectrum (EXAFS), the Mn-N@8Gra-L catalyst exhibits [significance / performance]. There is a distinct characteristic peak at this point, which is in good agreement with the scattering of the Mn-N bond in MnPc and is different from the scattering of the Mn-Mn bond in Mn foil. This further indicates that the Mn atoms in this catalyst are dispersed in the form of single atoms with the conventional Mn-Nx configuration.

[0045] like Figure 7 As shown, the Mn-N@8Gra-L catalyst prepared in this embodiment exhibits a typical type IV nitrogen adsorption-desorption isotherm. The pore size distribution indicates that the Mn-N@8Gra-L catalyst has a mesoporous-dominated hierarchical pore structure with a specific surface area as high as 1062.6 m². 2 g -1 The presence of mesoporous hierarchical structures can accelerate electron transfer and mass transport.

[0046] like Figure 8 The LSV curves shown demonstrate the excellent electrochemical performance of the catalyst. As can be seen from the figure, the Mn-N@8Gra-L catalyst prepared in Example 1 exhibits better performance than Pt / C (E 1 / 2 =0.86V vs. RHE,J L =5.81mA cm -2 Superior ORR activity (E) 1 / 2 =0.875V vs. RHE, J L =5.71mA cm -2 ).

[0047] Figure 9 This is a comparison of the energy densities of a primary zinc-air battery assembled with the Mn-N@8Gra-L catalyst prepared in this embodiment and a commercial Pt / C catalyst; as shown in the figure, at a fixed current density of 50 mA / cm², the energy density of the primary zinc-air battery is significantly higher than that of the commercial Pt / C catalyst prepared in this embodiment. 2 During low discharge, the primary zinc-air battery assembled with Mn-N@8Gra-L catalyst exhibits... Its high energy density far exceeds that of primary zinc-air batteries assembled with Pt / C.

[0048] like Figure 10As shown, the rechargeable zinc-air battery assembled with Mn-N@8Gra-L catalyst and RuO2 maintained a discharge voltage of 1.182V and a charging voltage of 2.009V during a charge-discharge process lasting over 100 hours, with a charge-discharge voltage difference of 82.7mV. In contrast, the rechargeable zinc-air battery assembled with Pt / C and RuO2 exhibited a larger charge-discharge voltage difference (90mV), indicating that the Mn-N@8Gra-L catalyst has better long-term cycling stability than the Pt / C catalyst when used in rechargeable zinc-air batteries.

[0049] Example 2

[0050] 600 μL of 1H-1,2,3-triazole and 600 μL of 50% manganese nitrate aqueous solution were added to 40 mL of N,N-dimethylformamide and ultrasonically mixed to obtain solution A. Solution A was then transferred to a constant temperature of 100℃ for 18 hours for a solvothermal reaction. After the reaction, the mixture was filtered and dried in a constant temperature drying oven at 70℃ to obtain white powder MET-2. 200 mg of MET-2 and 1200 mg of dicyandiamide were weighed, mixed, and ground. The homogenized powder was then subjected to a single pyrolysis in a tube furnace at 1000℃ under vacuum for 1 hour. The product after the first pyrolysis was placed in a 0.5 mol / L sulfuric acid solution and stirred at 80℃ for 10 hours. After washing with ultrapure water, the mixture was filtered and dried to obtain a single-atom manganese core-shell carbon-based oxygen reduction catalyst. The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst was subjected to secondary high-temperature pyrolysis in a tube furnace filled with N2 atmosphere at 1000℃ for 2 hours to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

[0051] Example 3

[0052] 800 μL of 1H-1,2,3-triazole and 400 μL of 50% manganese nitrate aqueous solution were added to 45 mL of N,N-dimethylformamide and ultrasonically mixed to obtain solution A. Solution A was then transferred to a constant temperature of 80 °C for a solvothermal reaction for 12 hours. After the reaction, the mixture was filtered and dried in a constant temperature drying oven at 80 °C to obtain white powder MET-2. 400 mg of MET-2 and 400 mg of dicyandiamide were weighed, mixed, and ground. The homogenized powder was then subjected to a single pyrolysis in a tube furnace at 800 °C under vacuum for 1 hour. The product after the first pyrolysis was placed in a 0.5 mol / L sulfuric acid solution and stirred at 60 °C for 10 hours. After washing with ultrapure water, the mixture was filtered and dried to obtain a primary manganese single-atom core-shell carbon-based oxygen reduction catalyst. The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst was subjected to secondary high-temperature pyrolysis in a tube furnace filled with N2 atmosphere at 800℃ for 1 hour to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

[0053] Example 4

[0054] 650 μL of 1H-1,2,3-triazole and 420 μL of 50% manganese nitrate aqueous solution were added to 30 mL of N,N-dimethylformamide and ultrasonically mixed to obtain solution A. Solution A was then transferred to a constant temperature of 90 °C for a solvothermal reaction for 22 hours. After the reaction, the mixture was filtered and dried in a constant temperature drying oven at 60 °C to obtain white powder MET-2. 300 mg of MET-2 and 500 mg of dicyandiamide were weighed, mixed, and ground. The homogenized powder was then subjected to a single pyrolysis in a tube furnace at 800 °C under vacuum for 2 hours. The product after the first pyrolysis was placed in a 0.5 mol / L sulfuric acid solution and stirred at 60 °C for 12 hours. After washing with ultrapure water, the mixture was filtered and dried to obtain a primary manganese single-atom core-shell carbon-based oxygen reduction catalyst. The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst was subjected to secondary high-temperature pyrolysis in a tube furnace filled with N2 atmosphere at 800℃ for 2 hours to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

[0055] Example 5

[0056] 600 μL of 1H-1,2,3-triazole and 400 μL of 50% manganese nitrate aqueous solution were added to 30 mL of N,N-dimethylformamide and ultrasonically mixed to obtain solution A. Solution A was then transferred to a constant temperature of 110 °C for a solvothermal reaction for 20 hours. After the reaction, the mixture was filtered and dried in a constant temperature drying oven at 70 °C to obtain white powder MET-2. 200 mg of MET-2 and 800 mg of dicyandiamide were weighed, mixed, and ground. The homogenized powder was then subjected to a single pyrolysis in a tube furnace at 1000 °C under vacuum for 2 hours. The product after the first pyrolysis was placed in a 1 mol / L sulfuric acid solution and stirred at 80 °C for 12 hours. After washing with ultrapure water, the mixture was filtered and dried to obtain a primary manganese single-atom core-shell carbon-based oxygen reduction catalyst. The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst was subjected to secondary high-temperature pyrolysis in a tube furnace filled with N2 atmosphere at 1000℃ for 2 hours to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

[0057] Example 6

[0058] 800 μL of 1H-1,2,3-triazole and 600 μL of 50% manganese nitrate aqueous solution were added to 50 mL of N,N-dimethylformamide and ultrasonically mixed to obtain solution A. Solution A was then transferred to a constant temperature of 80 °C for a solvothermal reaction for 24 hours. After the reaction, the mixture was filtered and dried in a constant temperature drying oven at 80 °C to obtain white powder MET-2. 200 mg of MET-2 and 1000 mg of dicyandiamide were weighed, mixed, and ground. The homogenized powder was then subjected to a single pyrolysis in a tube furnace at 900 °C under vacuum for 1 hour. The product after the first pyrolysis was placed in a 1 mol / L sulfuric acid solution and stirred at 60 °C for 10 hours. After washing with ultrapure water, the mixture was filtered and dried to obtain a single-atom manganese core-shell carbon-based oxygen reduction catalyst. The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst was subjected to secondary high-temperature pyrolysis in a tube furnace filled with N2 atmosphere at 900℃ for 2 hours to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

[0059] Example 7

[0060] 750 μL of 1H-1,2,3-triazole and 450 μL of 50% manganese nitrate aqueous solution were added to 40 mL of N,N-dimethylformamide and ultrasonically mixed to obtain solution A. Solution A was then transferred to a constant temperature of 120 °C for a solvothermal reaction for 16 hours. After the reaction, the mixture was filtered and dried in a constant temperature drying oven at 60 °C to obtain white powder MET-2. 350 mg of MET-2 and 600 mg of dicyandiamide were weighed, mixed, and ground. The homogenized powder was then subjected to a single pyrolysis in a tube furnace at 900 °C under vacuum for 1.5 hours. The product after the first pyrolysis was placed in a 1 mol / L sulfuric acid solution and stirred at 70 °C for 11 hours. After washing with ultrapure water, the mixture was filtered and dried to obtain a primary manganese single-atom core-shell carbon-based oxygen reduction catalyst. The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst was subjected to secondary high-temperature pyrolysis in a tube furnace filled with N2 atmosphere at 900℃ for 1 hour to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

Claims

1. A method for preparing a manganese single-atom carbon-based electrocatalyst with a core-shell structure, characterized in that, Includes the following steps: (1) Add 600-800 μL of 1H-1,2,3-triazole and 400-600 μL of 50% manganese nitrate aqueous solution to 30-50 mL of N,N-dimethylformamide and mix evenly by ultrasonication. Then transfer it to a constant temperature of 80-120℃ for 12-24 hours for a solvothermal reaction. (2) After the reaction is complete, filter the sample and then dry it in a constant temperature drying oven at 60-80℃ to obtain MET-2. (3) Weigh 200-400mg of the powder material MET-2 after drying in step (2), mix it with 400-1200mg of dicyandiamide and grind it evenly, and then carry out a pyrolysis in a tube furnace under vacuum at 800-1000℃ for 1-2 hours. (4) The product after the first pyrolysis is placed in a 0.5-1 mol / L sulfuric acid solution and stirred at 60-80℃ for 10-12 hours. Then, it is washed with ultrapure water, filtered, and dried to obtain a first-stage manganese single-atom core-shell carbon-based oxygen reduction catalyst. (5) The primary manganese single-atom core-shell carbon-based oxygen reduction catalyst is transferred to a tube furnace filled with N2 and subjected to secondary pyrolysis at the same temperature as in step (3) for 1-2 hours to obtain the Mn-N@8Gra-L catalyst, which is a manganese single-atom carbon-based electrocatalyst with a core-shell structure.

2. A manganese single-atom carbon-based electrocatalyst with a core-shell structure prepared by the method described in claim 1.

3. The application of a core-shell structured manganese single-atom carbon-based electrocatalyst prepared by the method described in claim 1 in primary zinc-air batteries and rechargeable zinc-air batteries.

4. The application as described in claim 3, characterized in that, The preparation method of the primary zinc-air battery positive electrode is as follows: 2 mg of Mn-N@8Gra-L catalyst is uniformly dispersed in a mixed solution of 195 μL of ethanol and 5 μL of naphthol, and then uniformly coated on 4 cm 2 carbon cloth; The primary zinc-air battery uses a 0.2 mm thick Zn sheet as the negative electrode and a 6 mol / L KOH solution as the electrolyte.

5. The application as described in claim 3, characterized in that, The preparation method of the rechargeable zinc-air battery positive electrode is as follows: 2 mg of Mn-N@8Gra-L catalyst and 2 mg of RuO2 are uniformly dispersed in a mixed solution of 390 μL of ethanol and 10 μL of naphthol, and then uniformly coated on 4 cm 2 carbon cloth; The rechargeable zinc-air battery uses a 0.2 mm thick Zn sheet as the negative electrode and a mixed solution of KOH and Zn(Ac)2 as the electrolyte; wherein the concentration of KOH is 6 mol / L and the concentration of Zn(Ac)2 is 0.2 mol / L.

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