Preparation method and application of carbon-loaded cobalt nanoparticle and iron monatomic electro-catalytic material

Abstract

The invention discloses a preparation method and application of a carbon-loaded cobalt nanoparticle and iron monatomic electro-catalytic material, relates to a preparation and regulation method of a zinc air battery cathode catalyst, and solves the problems of low electricity generation performance and poor stability of an existing rechargeable zinc air battery cathode. Specifically, a high-efficiency and stable-catalysis carbon-loaded cobalt nanoparticle and iron monatomic electro-catalysis material is reasonably designed and successfully synthesized by utilizing the adsorption effect of a metal organic framework (MOFs) and polyvinylpyrrolidone as an ion adsorption layer, and under the condition that active sites are not sacrificed, the high-efficiency and stable-catalysis carbon-loaded cobalt nanoparticle and iron monatomic electro-catalysis material can be used for preparing a high-efficiency and stable-catalysis carbon-loaded cobalt nanoparticle / iron monatomic electro-catalysis material. And the dispersity of cobalt nanoparticles and the catalytic activity of iron monatomic are improved. The obtained material is used as a zinc air battery cathode material, the overall performance of a rechargeable zinc air battery can be improved, and efficient and oriented conversion of the zinc air battery is achieved.

Description

Technical Field

[0001] The invention belongs to the field of zinc-air battery redox electrocatalysts, and specifically relates to a preparation method and application of carbon-supported cobalt nanoparticles and iron single-atom electrocatalytic materials. Background Art

[0002] In order to achieve the goals of carbon peak and carbon neutrality, it is necessary to develop devices that can effectively convert / store clean energy. This is not only a necessary condition for promoting high-quality development, but also an important direction for our future development. Rechargeable batteries such as metal-air batteries, fuel cells and lithium-ion batteries have the characteristics of efficient reversible conversion of electrical energy to chemical energy. Due to its advantages such as high theoretical energy density, environmental friendliness, safety and reliability, and low production cost, RZAB technology has become one of the most promising energy storage technologies today, far surpassing fuel cells. Although the theoretical energy density of RZAB can reach 1350 Wh kg −1 , but the actual energy density is only 40-50% of the theoretical level. This is mainly due to the kinetic characteristics of the oxygen evolution reaction (OER) and the oxygen reduction reaction in the cathode. Therefore, in order to improve the operating efficiency of RZAB, effective measures must be taken to develop a highly active bifunctional catalyst that can drive efficient ORR and OER simultaneously. Single atom catalysts (SACs) are considered to be the most promising oxygen electrocatalysts to replace precious metal (platinum, palladium, ruthenium, etc.) catalysts due to their high atomic utilization, high selectivity, adjustable coordination environment, and extraordinary activity in many reactions. Iron atoms in the Fe-Nx configuration usually have high surface free energy and are easy to aggregate into metal clusters or nanoparticles, which seriously reduces the number of single atom active sites. Therefore, it is difficult to further improve the catalytic performance by simply increasing the content of metal single atoms. Therefore, the reaction activity of the Fe-Nx site can be regulated by adjacent Co nanoparticles to achieve higher oxygen electrocatalytic performance. Summary of the invention

[0003] The purpose of the present invention is to solve the problem of low electrocatalytic activity caused by low catalytic activity and poor stability of the cathode of rechargeable zinc-air batteries in the prior art, and provide a preparation method and application of carbon-supported cobalt nanoparticles and iron single-atom electrocatalytic materials. The method first prepares nano-scale MIL-88B, uses PVP as an ion adsorption layer to adsorb Co ions in the solution, forms a CoFe-MOF precursor through strong coordination with 2-methylimidazole, and calcines in a nitrogen atmosphere at 900°C. The Co ions adsorbed on the surface are converted into Co nanoparticles, and the MIL-88B therein is converted into Fe-Nx active sites, thereby completing the preparation of the Fe SAs / Co zinc-air battery cathode catalyst. The highly dispersed metal nanoparticles obtained by the present invention regulate the single-atom catalyst, and the catalyst ORR / OER activity and stability are enhanced through the regulation of Fe-Nx by the highly dispersed Co nanoparticles. The single-atom electrocatalytic material prepared by the present invention exhibits superior ORR / OER activity and improves the overall performance of the rechargeable zinc-air battery.

[0004] The preparation method of the carbon-supported cobalt nanoparticles and iron single atom electrocatalytic material of the present invention is achieved by the following steps: (1) Preparation of carbon-supported cobalt nanoparticles and iron single-atom electrocatalytic materials: ① Dissolve a certain amount of F127 in deionized water and disperse by ultrasonic to obtain a uniformly dispersed solution; ② Add a certain amount of ferric chloride hexahydrate to the solution. Stir the mixed solution to obtain a uniformly dispersed solution; ③ Add a certain amount of acetic acid to the solution in step ②. After sufficient stirring, slowly add a certain amount of 2-aminoterephthalic acid to the solution and stir to form a uniform mixture; ③ The mixture obtained in step ② was transferred to an autoclave, heated for 24 hours and then centrifuged and dried to obtain MIL-88B; ④ Disperse a certain amount of MIL-88B obtained in step ③ in methanol, then add a certain amount of PVP suspension to the suspension, stir and wash thoroughly to obtain the desired MIL-88B@PVP sample; ⑤ Disperse a certain amount of MIL-88B@PVP in a certain amount of methanol to form a uniform suspension; ⑥ Dissolve a certain amount of cobalt nitrate hexahydrate in deionized water to form solution A. Then, add a certain amount of the suspension obtained in step ⑤ to solution A, stir for 5 minutes to form a uniform suspension, and then quickly inject it into the aqueous solution of 2-methylimidazole; ⑦ Stir the mixture obtained in step ⑥ thoroughly at room temperature. After aging, collect the product by centrifugation and wash it several times with ethanol and water. Finally, dry it in a vacuum oven to obtain the desired CoFe-ZIF-L; ⑧ The product synthesized from step ⑦ is placed in a quartz boat and then placed in a tube furnace. The sample is calcined at high temperature and kept in a nitrogen environment for a period of time to obtain a black Fe SAs / Co powder.

[0005] (2) Preparation of electrocatalyst cathode electrode and assembly of rechargeable zinc-air battery reactor: The present invention uses carbon paper coated with CoNi / C-coated hydrophobic carbon cloth as the air cathode (mass loading: 1.0 mg cm -2 ), Zn plate as anode (thickness: 0.5 mm), 6 M KOH as electrolyte, and a homemade Zn-air battery was constructed. To prepare the working electrode, 4.0 mg of the prepared material was ultrasonically dispersed in a mixed solution of deionized water, ethanol, and Nafion (5%, SigmaAldrich) with a volume ratio of 49:49:2; then, 14 μL of the catalyst ink was deposited on the polished RDE and dried naturally, with a catalyst loading of 0.12566 mg cm -2 . For comparison, commercial catalysts of RuO2 (50%, Sinero) for OER and Pt / C (20%, Sigma Aldrich) for ORR were measured under the same conditions. For comparison, a 1:1 mass ratio of Pt / C + RuO2 mixture was tested at the same loading. The performance of CoNi / C cells and Pt / C + RuO2 cells was tested without oxygen extraction. Polarization curves were obtained on a CHI 760E electrochemical workstation at 5 mV s -1 The static charge and discharge data were collected at a scan rate of 10 mA cm using a LANHE CT2001A battery test system. -2 The current density obtained.

[0006] Preferably, in step (1)①, the amount of F127 used is 0.16 g, and the amount of deionized water used is 15 ml.

[0007] Preferably, the amount of ferric chloride hexahydrate used in step (1) ② is 0.179 g.

[0008] Preferably, 0.25 mL of acetic acid is added in step (1) ③. After stirring for 1 hour, 0.06 g of 2-aminoterephthalic acid is slowly added to the solution.

[0009] Preferably, the hydrothermal process in step (1) ④ is to heat at 110 ° C for 24 hours to improve the crystallinity.

[0010] Preferably, in step (1) ⑤, the amount of MIL-88B used is 30 mg, the amount of methanol used is 20 ml, the amount of polyvinyl pyrrolidone used is x=0.5, 1 and 1.5 g respectively, and stirring is performed for 12 hours.

[0011] Preferably, in step (1)⑥, the amount of methanol used is 15 ml, and the amount of MIL-88B@PVP used is 50 mg.

[0012] Preferably, in step (1) ⑦, the amount of cobalt nitrate hexahydrate in solution A is 1 mmol, the amount of deionized water is 40 ml, the amount of dimethylimidazole in solution B is 8 mmol, and the amount of deionized water is 40 ml.

[0013] Preferably, in step (1)⑧, the room temperature is 25 degrees Celsius and the stirring time is 3 hours.

[0014] Preferably, in step (1) ⑨, the heating temperature is 900 degrees Celsius, the insulation time in the nitrogen atmosphere is 2 hours, and the heating rate is 5 degrees Celsius / min.

[0015] Compared with the prior art, the advantages of the present invention are: (1) The carbon-supported cobalt nanoparticles and iron single atom electrocatalytic materials prepared by the method of the present invention are used as cathode catalysts for zinc-air rechargeable batteries. Cobalt nanoparticles with suitable particle size and high OER activity are used to modulate the ORR / OER catalytic performance of individually dispersed iron single atoms to obtain a composite material with good conductivity, stability and high catalytic activity. (2) The carbon-supported cobalt nanoparticles and iron single atom electrocatalytic materials prepared by the method of the present invention are used as cathode catalysts for zinc-air rechargeable batteries. Inexpensive polyvinyl pyrrolidone is used as a cation adsorbent to controllably synthesize cobalt nanoparticles and iron single atoms, and no metal agglomeration is generated during the high-temperature synthesis process.

[0016] (3) The carbon-supported cobalt nanoparticles and iron single-atom electrocatalytic materials prepared by the method of the present invention are used as cathode catalysts for zinc-air rechargeable batteries. By regulating the Fe SAs by adjacent Co NPs, high ORR / OER performance is achieved, thereby obtaining reaction performance superior to that of precious metal catalysts such as Pt / C, and the assembled zinc-air battery exhibits a higher open circuit voltage and better durability. At the same time, the catalyst production cost can be effectively reduced, providing a theoretical basis for the large-scale production and application of rechargeable zinc-air batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 SEM images of MIL-88B@PVP and Fe SAs / Co-1 catalysts; Figure 2 It is a series of TEM images of Fe SAs / Co-1 catalyst; Figure 3 is the XRD pattern of Fe SAs / Co-1 catalyst; Figure 4 ORR linear scanning cycle curves of the series of catalysts; Figure 5 ORR linear sweep voltammetry curves of a series of catalysts; Figure 6 Linear sweep voltammetry curves of OER of a series of catalysts; Figure 7 The open circuit voltage, charge-discharge curves and power density diagram of the assembled rechargeable zinc-air battery of Fe SAs / Co-1 catalyst; Figure 8 Schematic diagram of the cycling stability of the assembled rechargeable zinc-air battery with Fe SAs / Co-1 and Pt / C+RuO2 catalysts; DETAILED DESCRIPTION

[0018] (1) Preparation of carbon-supported cobalt nanoparticles and iron single-atom electrocatalytic materials ① Dissolve 0.16 g F127 in 15 mL deionized water, and then add 0.179 g ferric chloride hexahydrate (FeCl3-6H2O) to the solution. Stir the mixed solution at room temperature (25 °C) for 1 hour to ensure thorough mixing; ② Add 0.25 mL acetic acid to the solution in step ①. After stirring for 1 hour, slowly add 0.06 g 2-aminoterephthalic acid to the solution and stir for 2 hours to form a uniform mixture; ③ Transfer the mixture to an autoclave and heat at 110 degrees Celsius for 24 hours to improve crystallinity. After the reaction is completed, wash the product with ethanol several times to remove residual impurities, and then dry it in an oven at 60 °C to obtain nano-scale MIL-88B; ④ Disperse 30 mg of MIL-88B obtained in step ③ in 20 mL of methanol, and then add 0.5, 1.0 or 1.5 g of PVP suspension to the suspension, and then stir for 12 hours. Finally, the excess PVP was removed by centrifugal washing with methanol and dried in an oven at 60 °C to obtain the desired MIL-88B@PVP sample; ⑤ 50 mg of MIL-88B@PVP was dispersed in 15 mL of methanol to form a uniform suspension A; ⑥ 1 mmol of cobalt nitrate hexahydrate was dissolved in 40 mL of deionized water to form solution A. Subsequently, 3 mL of suspension A was added to solution A and stirred for 5 minutes to form a uniform suspension B, which was then quickly injected into 40 mL of an aqueous solution containing 8 mmol of 2-methylimidazole; ⑦ The resulting mixture was stirred at room temperature (25 °C) for 3 hours and then aged for 12 hours. After aging, the product was collected by centrifugation and washed several times with ethanol and water. Finally, it was dried in a vacuum oven at 60 °C to obtain the desired CoFe-ZIF-L; ⑧ The synthesized CoFe-ZIF-L was placed in a quartz boat and then placed in a tube furnace. The sample was heated to 900 °C and maintained in a nitrogen environment for 2 h with a heating rate controlled at 5 °C / min-1 to obtain black Fe SAs / Co powder.

[0019] (2) Preparation of electrocatalyst cathode electrode and assembly of rechargeable zinc-air battery reactor: The present invention uses carbon paper coated with CoNi / C-coated hydrophobic carbon cloth as the air cathode (mass loading: 1.0 mg cm -2 ), Zn plate as anode (thickness: 0.5 mm), 6 M KOH as electrolyte, and a homemade Zn-air battery was constructed. To prepare the working electrode, 4.0 mg of the prepared material was ultrasonically dispersed in a mixed solution of deionized water, ethanol, and Nafion (5%, SigmaAldrich) with a volume ratio of 49:49:2; then, 14 μL of the catalyst ink was deposited on the polished RDE and dried naturally, with a catalyst loading of 0.12566 mg cm -2. For comparison, commercial catalysts of RuO2 (50%, Sinero) for OER and Pt / C (20%, Sigma Aldrich) for ORR were measured under the same conditions. For comparison, a 1:1 mass ratio of Pt / C + RuO2 mixture was tested at the same loading. The performance of CoNi / C cells and Pt / C + RuO2 cells was tested without oxygen extraction. Polarization curves were obtained on a CHI 760E electrochemical workstation at 5 mV s -1 The static charge and discharge data were collected at a scan rate of 10 mA cm using a LANHE CT2001A battery test system. -2 The current density obtained.

[0020] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the amount of polyvinyl pyrrolidone used in step (1) ⑤ is 0.5 g. The other steps and parameters are the same as those in specific embodiment 1.

[0021] Specific embodiment 3: This embodiment differs from the specific embodiment 1 in that the amount of polyvinyl pyrrolidone used in step (1) ⑤ is 1.5 g. The other steps and parameters are the same as those in the specific embodiment 1.

[0022] Specific embodiment 4: This embodiment differs from specific embodiment 1 in that the amount of hexahydrate and ferric chloride used in step (1) ② is 0 g. The other steps and parameters are the same as those in specific embodiment 1.

[0023] Specific embodiment 5: This embodiment differs from specific embodiment 1 in that the powder obtained after calcination in step (1) ⑨ is acid-washed in 0.5 mM HCl solution for 12 hours to remove Co nanoparticles. The other steps and parameters are the same as those in specific embodiment 1.

[0024] Specific embodiments 1 to 5 of the catalytic materials and their corresponding characterization and performance analysis: Figure 1 This is a scanning electron microscope (SEM) image of MIL-88B@PVP and Fe SAs / Co-1 catalysts. It can be directly observed that the surface of MIL-88B@PVP becomes rough due to the uniform coating of PVP. The particle size distribution diagram shows that the diameter of the MIL-88B module after PVP functionalization is about 60 nm. After high-temperature carbonization, Fe SAs / Co-1 retains its original morphology and forms a large number of carbon nanotubes on the surface. The formation of these carbon nanotubes is attributed to the high solubility of carbon in Co / Fe metal at high temperature, which causes carbon to precipitate from the Fe / Co matrix during the formation of Co nanoparticles and eventually form carbon nanotubes. The presence of these carbon nanotubes improves the conductivity of the catalyst (i.e., the electron transfer efficiency).

[0025] Figure 2 The transmission electron microscopy (TEM) image of Fe SAs / Co-1 further reveals the structural characteristics of Fe SAs / Co-1. The catalyst exhibits a nanoflower-like structure with highly dispersed Co nanoparticles in the carbon matrix, which is attributed to the adsorption of Co on the surface under the action of the MIL-88B@PVP module. 2+ The abundant amino and carbonyl groups on the surface of polyvinyl pyrrolidone help to coordinate the adsorbed Co 2+ The Co nanoparticles are dispersed around the core, while the subsequent high-temperature carbonization causes Co to aggregate in the nanoparticles wrapped in the N-doped carbon layer. In addition, high-resolution TEM images show lattice fringes with a plane spacing of approximately 0.201 nm, which is consistent with the (111) crystal plane characteristics of metallic Co, further confirming the existence of Co nanoparticles.

[0026] Figure 3 The powder X-ray diffraction pattern (XRD) confirmed the crystal structure of Fe SAs / Co-1. For Fe SAs / Co, the peak broadening near 25° is attributed to the (002) plane of graphitized carbon, and the peaks near 44.13, 51.52 and 75.76° are attributed to the (1 1 1), (2 0 0) and (2 2 0) and (2 2 0) crystal planes of metallic cobalt (JCPDS No. 15-0806). It is worth noting that the XRD pattern of Fe SAs / Co-1 does not show the metallic iron phase, which indicates that no aggregation of metallic iron occurs during the pyrolysis process.

[0027] Figure 4 The CV curves of Pt / C, Fe SAs, Co NPs and Fe SAs / Co-x (x=0.5, 1 and 1.5) in 0.1M KOH solution. As shown in the figure, the series of materials have a reduction peak between 0.80-0.90V, which symbolizes ORR, and the peak positions are higher than that of Pt / C catalyst.

[0028] Figure 5 The LSV curve in 0.1 M KOH (5 mV s -1 and 1600 rpm), it can be observed that Fe SAs / Co-1 has the highest half-wave potential (E 1 / 2 ) is 0.881 V, which is much higher than 0.847 V of Pt, indicating that the FeSAs / Co-1 material has an ORR performance far beyond that of Pt / C. At the same time, the high ORR activity achieved by Fe SAs / Co-1 mainly comes from the synergistic effect between Co nanoparticles and Fe-Nx sites to promote electron transfer, thereby improving the catalytic efficiency and kinetics of ORR.

[0029] Figure 6 RuO2, Fe SAs, Co NPs and Fe SAs / Co-x (x = 0.5, 1 and 1.5) in 1 M KOH solution at a scan rate of 2 mV s -1 The LSV test of OER was performed in the range of 1.0 to 2.0 V. FeSAs / Co-1 only needs 327 mV overpotential to drive 10 mA cm -2 The current density is better than that of Co NPs (404 mV), Fe SAs (434 mV), and RuO2 (517 mV) catalysts, as well as Fe SAs / Co-x (x = 0.5 and 1.5). The interaction of Co nanoparticles with Fe-Nx sites should promote the in situ formation of highly active CoOOH / FeOOH, thereby accelerating the reaction kinetics.

[0030] Figure 7 The open circuit voltage output and power density diagram of the homemade rechargeable zinc-air battery of Fe SAs / Co-1 and Pt / c+RuO2 catalysts show the voltage output performance of Fe SAs / Co-1 and Pt / c+RuO2 catalysts during the test period. It can be directly seen from the figure that the open circuit voltage of Fe SAs / Co-1-based ZAB is 1.48 V and the maximum power density is 204.4 mWcm -2 At 10 mA cm -2 The specific capacity is 700.3 mAh g -1 , which is higher than that of Pt / C+RuO2-based ZAB (1.35 V, 52 mW cm -2 and 657.1 mAh g -1 ). This indicates that the Fe SAs / Co-1 based batteries have better charging capability with a smaller voltage difference between the discharge and charge polarization curves.

[0031] Figure 8 is 10 mA cm -2The continuous constant current charge and discharge test diagram of Fe SAs / Co-1 and Pt / C+RuO2 catalyst at a current density of 1000 Å was used to evaluate the performance and durability of Fe SAs / Co-1-based ZAB. The cycle included 10 minutes of discharge and 10 minutes of charge. The charge and discharge stability of Fe SAs / Co-1-based ZAB showed only 2.5% round-trip efficiency decay in the 180 h cycle test, indicating that the long-term cycle stability of ZAB with Fe SAs / Co-1 cathode is good. In contrast, the voltage difference of the battery based on Pt / C+RuO2 increased significantly after 20 hours of cycling. The above results indicate that Fe SAs / Co-1 with excellent ORR / OER bifunctional electrocatalytic activity shows good practical applicability in ZAB, thereby achieving efficient and long-lasting cycle life.

Claims

1. A method for preparing carbon-supported cobalt nanoparticles and iron single-atom electrocatalytic materials and their application, characterized in that The preparation of the cathode material for rechargeable zinc-air batteries is achieved by the following steps: (1) Preparation of carbon-supported cobalt nanoparticles and iron single-atom electrocatalytic materials: ① Dissolve a certain amount of F127 in deionized water and disperse by ultrasonic to obtain a uniformly dispersed solution; ② Add a certain amount of ferric chloride hexahydrate to the solution. Stir the mixed solution to obtain a uniformly dispersed solution; ③ Add a certain amount of acetic acid to the solution in step ②. After sufficient stirring, slowly add a certain amount of 2-aminoterephthalic acid to the solution and stir to form a uniform mixture; ④ Transfer the mixture obtained in step ③ into an autoclave, heat for 24 hours and then centrifuge and dry to obtain MIL-88B; ⑤ Disperse a certain amount of MIL-88B obtained in step ④ in methanol, then add a certain amount of PVP suspension to the suspension, stir and wash thoroughly to obtain the desired MIL-88B@PVP sample; ⑥ Disperse a certain amount of MIL-88B@PVP in a certain amount of methanol to form a uniform suspension; ⑦ Dissolve a certain amount of cobalt nitrate hexahydrate in deionized water to form solution A. Then, add a certain amount of the suspension obtained in step ⑥ to solution A, stir for 5 minutes to form a uniform suspension, and then quickly inject it into the aqueous solution of 2-methylimidazole; ⑧ The mixture obtained in step ⑦ was stirred at room temperature. After aging, the product was collected by centrifugation and washed several times with ethanol and water. Finally, it was dried in a vacuum oven to obtain the desired CoFe-MOF; ⑨ The product synthesized in step ⑧ is placed in a quartz boat and then placed in a tube furnace. The sample is calcined at high temperature and kept in a nitrogen environment for a period of time to obtain a black Fe SAs / Co powder.

2. (2) Preparation of electrocatalytic cathode electrode and assembly of rechargeable zinc-air battery reactor: The present invention uses carbon paper coated with CoNi / C-coated hydrophobic carbon cloth as the air cathode (mass loading: 1.0 mgcm -2 ), Zn plate as anode (thickness: 0.5 mm), 6 M KOH as electrolyte, and a homemade Zn-air battery was constructed. To prepare the working electrode, 4.0 mg of the prepared material was ultrasonically dispersed in a mixed solution of deionized water, ethanol, and Nafion (5%, SigmaAldrich) with a volume ratio of 49:49:2; then, 14 μL of the catalyst ink was deposited on the polished RDE and dried naturally, with a catalyst loading of 0.12566 mg cm -2 . For comparison, commercial catalysts of RuO2 (50%, Sinero) for OER and Pt / C (20%, Sigma Aldrich) for ORR were measured under the same conditions. For comparison, a 1:1 mass ratio of Pt / C + RuO2 mixture was tested at the same loading. The performance of CoNi / C cells and Pt / C + RuO2 cells was tested without oxygen extraction. Polarization curves were obtained on a CHI 760E electrochemical workstation at 5 mV s -1 The static charge and discharge data were collected at a scan rate of 10 mA cm using a LANHE CT2001A battery test system. -2 The current density obtained.

3. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that In step (1)①, the amount of F127 used is 0.16 g, and the amount of deionized water used is 15 ml.

4. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that The amount of ferric chloride hexahydrate used in step (1) ② is 0.179 g.

5. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that 0.25 mL of acetic acid was added to step (1) ③. After stirring for 1 hour, the amount of 2-aminoterephthalic acid used was 0.06 g.

6. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that The process of the hydrothermal autoclave in step (1) ④ is to heat at 110°C for 24 hours to improve the crystallinity.

7. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that In step (1) ⑤, the amount of MIL-88B used is 30 mg, the amount of methanol used is 20 ml, and the amount of polyvinyl pyrrolidone used is x=0.5, 1 and 1.5 g respectively, and stirring is carried out for 12 hours.

8. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that In step (1)⑥, the amount of methanol used is 15 ml, and the amount of MIL-88B@PVP used is 50 mg.

9. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that In step (1) ⑦, the amount of cobalt nitrate hexahydrate in solution A is 1 mmol, and the amount of deionized water is 40 ml. The amount of dimethylimidazole in solution B is 8 mmol, and the amount of deionized water is 40 ml.

10. A self-assembled rechargeable zinc-air battery cathode catalyst according to claim 1, characterized in that In step (1) ⑨, the heating temperature is 900 degrees Celsius, the insulation time in the nitrogen atmosphere is 2 hours, and the heating rate is 5 degrees Celsius / min.

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