A carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst for zinc-air batteries and its preparation method

Abstract

The present invention provides a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst for zinc-air batteries and a preparation method thereof. A zinc-based zeolite imidazolate framework material ZIF‑8 is first synthesized by coordination self-assembly, and a layer of cobalt-based zeolite imidazolate framework material ZIF‑67 is coated on the surface of ZIF‑8. Iron acetylacetonate is added during the self-assembly process of ZIF‑67 to finally form a ZIF‑8@ZIF‑67@Fe(acac)3 precursor. The above-mentioned precursor is placed in a tubular furnace filled with an inert gas and pyrolyzed at high temperature. The obtained carbon material is pickled and further pyrolyzed for a second time to finally prepare a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst. The catalyst provided by the present invention can effectively improve the catalytic efficiency of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and has excellent catalytic activity and stability. It is applied to rechargeable zinc-air batteries, with the characteristics of high specific power and low cost.

Description

Technical Field

[0001] The present invention relates to a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst applied to a zinc-air battery and a preparation method thereof, belonging to the scientific and technical field of zinc-air batteries. Background Art

[0002] With the increasing demand for energy and environmental pollution, zinc-air batteries have become one of the most promising devices for providing sustainable and clean energy conversion pathways. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are kinetically slow processes that rely primarily on expensive noble metal catalysts (Pt / Ru). In recent years, metal-nitrogen-carbon (MNC, where M refers to non-noble metals such as Fe and Co) materials, which use nitrogen to anchor dispersed metal atoms, have become promising alternative materials due to their unique electronic properties and high atomic utilization efficiency. However, although the scientific community has synthesized a large number of non-noble metal catalysts, further improving the performance of MNC materials remains a huge uncertainty, mainly for the following reasons: First, the utilization rate of metal active sites is insufficient, and the manufacture of monodisperse metal sites with sufficient availability remains challenging. Second, a single type of transition metal element cannot simultaneously satisfy the forward and reverse reactions in the oxygen catalysis process, and the ORR / OER reaction efficiency cannot be effectively improved simultaneously.

[0003] In acidic or alkaline media, metal-loaded nitrogen-doped carbon materials are becoming one of the most promising candidates to replace precious metal-based catalysts. However, the current preparation methods of bimetallic catalysts are still at the level of simple mixed pyrolysis. The active sites of the catalysts prepared by this method are often not effectively exposed and cannot exert a catalytic effect. It is well known that zeolitic imidazolate frameworks (ZIFs) are composed of metal-containing nodes and organic ligands, and their typical characteristics are atomically dispersed metal sites. The pyrolysis of ZIFs is an important way to prepare metal-loaded nitrogen-doped carbon materials. Since ZIFs have complete and regular pore structure characteristics, filling the internal pores of ZIFs with metal complexes with small molecule characteristics will promote the generation of bimetallic active sites, which is an effective preparation method for bimetallic nitrogen-doped catalysts. For example, Duan et al. developed a simple approach based on MOF (metal organic framework) derived hierarchical Fe,Co@NC materials (FeCo-NCT) for efficient electrocatalysis of oxygen reduction (ORR) and oxygen evolution reaction (OER) based on ZnCo-ZIFs wrapped with iron-doped glucosamine (ZnCo-ZIF@Fe / glucosamine). 1 / 2 =0.877V), OER activity (E j＝10=1.6V) and reversible oxygen overpotential (0.71V) showed excellent electrocatalytic performance (Journal of Materials Chemistry A, 2020, 8(18):9355-9363). He et al. obtained atomically dispersed Fe-Co bimetallic sites (FeCo-NC) from Fe and Co co-doped zeolitic imidazolate framework (ZIF-8) to establish multiple active sites for bifunctional ORR / OER catalysts. In alkaline medium, the atomically dispersed FeCo-NC catalyst has a great effect on ORR (E 1 / 2 =0.877V) and OER (E j＝10 =1.579V) showed excellent bifunctional catalytic activity, and the ORR and OER stability were comparable to those of precious metal catalysts (Pt / C and RuO2) (ACS Catalysis, 2022, 12(2):1216-1227). However, the disadvantages of the above-mentioned methods are that the prepared catalysts all have smooth particle structures, which are prone to agglomeration during pyrolysis, resulting in the inability to fully expose the active sites. At the same time, the material transfer and charge conduction between the particles cannot be carried out efficiently. However, the modification of the particle surface with carbon nanotubes will effectively improve the above-mentioned transport and mass transfer efficiency.

[0004] To address these issues, we synthesized a ZIF-8@ZIF-67@Fe(acac)3 precursor as a precursor-derived carbon nanotube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst. This catalyst is simple to prepare, inexpensive, and possesses abundant active sites, which could facilitate the practical application of zinc-air batteries. Summary of the Invention

[0005] The present invention aims to provide a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst for zinc-air batteries and a preparation method thereof. First, ZIF-8 with a dodecahedral structure is prepared, and ZIF-67 is self-assembled on its surface with ZIF-8 as the core. In this process, Fe(acac)3 is encapsulated in the pores of the internal structure of ZIF-67 to prepare a ZIF-8@ZIF-67@Fe(acac)3 precursor. Subsequently, the preparation steps of pyrolysis at a specific temperature-acid washing-drying-pyrolysis are carried out in an inert gas. The final material obtained is the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst.

[0006] The purpose of the present invention is achieved through the following solutions:

[0007] A method for preparing a carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst comprises the following steps:

[0008] (1) Preparation of ZIF-8 core: Dissolve appropriate amounts of 2-methylimidazole and zinc salt in anhydrous methanol solvent, mix the two solutions under stirring at room temperature, let them stand for a certain period of time, filter them through a sand core funnel, and further dry them in a vacuum drying oven. The resulting white powder is the ZIF-8 core;

[0009] (2) Preparation of ZIF-8@ZIF-67@Fe(acac)3 precursor: ZIF-8 and an appropriate amount of cobalt salt were dispersed in methanol solvent and ultrasonically formed into solution A; then an appropriate amount of 2-methylimidazole and Fe(acac)3 were dissolved in methanol solvent to form solution B. The above two solutions A and B were quickly mixed under stirring at room temperature. After a certain reaction time, the mixture was filtered and dried. The obtained purple powder was the ZIF-8@ZIF-67@Fe(acac)3 precursor;

[0010] (3) Preparation of carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst: A certain amount of ZIF-8@ZIF-67@Fe(acac)3 precursor is placed in a high-temperature tubular furnace filled with inert gas, and a certain heating time and heating temperature are set. The obtained black powder is acid-washed and then dried, and then placed in a high-temperature tubular furnace filled with inert gas for secondary pyrolysis. The final product is the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst.

[0011] Furthermore, in step (1), the zinc salt is one or more of zinc chloride (ZnCl2), zinc nitrate hexahydrate (Zn(NO3)2·6H2O), zinc sulfate (ZnSO4), zinc oxalate (ZnC2O4), zinc acetate (Zn(CH3COO)2), and zinc carbonate (ZnCO3).

[0012] Furthermore, in step (1), the molar ratio of 2-methylimidazole to zinc salt is 1 to 8: 1. More preferably, the molar ratio of 2-methylimidazole to zinc salt is 2 to 3:1.

[0013] Furthermore, in step (1), the stirring time is 12 to 48 hours, and the stirring temperature is room temperature.

[0014] Furthermore, in step (1), the vacuum drying time is 8 to 24 hours, and the vacuum drying temperature is 60 to 80°C.

[0015] Furthermore, in step (2), the cobalt salt is one or more of cobalt chloride (CoCl2), cobalt nitrate hexahydrate (Co(NO3)2·6H2O), cobalt sulfate (CoSO4), cobalt oxalate (CoC2O4), cobalt acetate (Co(CH3COO)2), and cobalt carbonate (CoCO3).

[0016] Furthermore, in step (2), the mass ratio of cobalt salt to ZIF-8 is 4 to 20:1.

[0017] Furthermore, in step (2), the molar ratio of 2-methylimidazole to Fe(acac)3 is 1 to 20:1.

[0018] Furthermore, in step (2), the reaction time is 12 to 48 hours, and the reaction temperature is 10 to 40°C.

[0019] Furthermore, in step (3), the inert gas is one of Ar, He, and N2.

[0020] Furthermore, in step (3), the heating time is 1 to 5 hours, and the heating temperature is 900 to 1200°C.

[0021] Furthermore, in step (3), the heating time of the secondary pyrolysis is 1 to 5 hours, and the heating temperature is 900 to 1200°C.

[0022] In the preparation scheme of the present invention, the carbon tubes are bamboo-shaped carbon nanotubes.

[0023] In the preparation scheme of the present invention, the carbon tube grafting is that the carbon tubes are distributed on the surface of the hollow nanoparticles with the morphology of a regular dodecahedron.

[0024] In the preparation scheme of the present invention, the iron element of the catalyst is generated by thermal decomposition of Fe(acac)3.

[0025] In the preparation scheme of the present invention, the Fe loading amount in the catalyst is related to the mass of Fe(acac)3 encapsulated in the precursor.

[0026] In the preparation scheme of the present invention, the precursor is a double-layer heterostructure, which is composed of a double-layer ZIFs (ZIF-8 as the core and ZIF-67 as the shell) and Fe(acac)3.

[0027] The preparation method of the present invention is to prepare a carbon nanotube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst by pyrolysis of a ZIF-8@ZIF-67@Fe(acac)3 precursor. The catalyst obtained after pyrolysis has a large number of carbon nanotubes distributed on its surface.

[0028] The present invention also provides the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst for use in zinc-air battery materials.

[0029] The electrochemical test mainly uses a three-electrode test system consisting of a reversible hydrogen electrode (RHE) as the reference electrode, a Pt wire as the counter electrode, and a glassy carbon electrode with a diameter of 3 mm coated with a catalyst as the working electrode. A series of electrochemical tests are carried out with 0.1M KOH solution (ORR), 1M KOH solution (OER) or 6M KOH / 0.2M (CH3COO)2Zn mixed solution (zinc-air battery) as the electrolyte. The linear voltammetry method, chronoamperometry and potential step method are used to investigate the ORR / OER catalytic activity of the catalyst and the zinc-air battery performance.

[0030] The technical solution of the present invention has the following advantages and beneficial effects:

[0031] (1) The catalyst prepared by the present invention has a large number of bamboo-shaped carbon nanotubes distributed on the particle surface, which is beneficial to improving the charge transfer and mass transfer rate during the catalytic process. At the same time, the carbon nanotubes distributed on the catalyst surface can prevent the catalyst particles from agglomerating during the pyrolysis process, which is more conducive to the exposure of active sites. The Fe element is beneficial to improving the ORR reaction during the zinc-air battery reaction process, while the Co element is beneficial to improving the OER reaction. The combination of the two improves the charge and discharge behavior of the zinc-air battery.

[0032] (2) Based on the above advantages, the catalyst prepared by the present invention has excellent ORR and OER catalytic performance. When the catalyst is applied to zinc-air batteries, its peak output power reaches 114mW / cm 2 , surpassing the currently commercially available precious metal catalysts Pt / C and RuO2.

[0033] (3) The present invention uses cheap raw materials, simple preparation steps, and a short synthesis cycle, which is conducive to the commercial application of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a scanning electron microscope (SEM) image of the ZIF-8@ZIF-67@Fe(acac)3 precursor prepared in Example 1.

[0035] Figure 2 This is the transmission electron microscopy (TEM) image of the ZIF-8@ZIF-67@Fe(acac)3 precursor prepared in Example 1.

[0036] Figure 3 This is the X-ray diffraction (XRD) pattern of the ZIF-8@ZIF-67@Fe(acac)3 precursor prepared in Example 1.

[0037] Figure 4 This is an SEM image of the carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared in Example 1.

[0038] Figure 5 This is the XRD pattern of the carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared in Example 1.

[0039] Figure 6 This is the linear sweep voltammetry (LSV) curve (ORR) of the carbon tube grafted nitrogen-doped carbon supported iron / cobalt-based catalyst prepared in Example 1.

[0040] Figure 7 This is the LSV curve (OER) of the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared in Example 1.

[0041] Figure 8 This is a graph showing the electrical output performance of a zinc-air battery prepared in Example 1 and equipped with a carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst. DETAILED DESCRIPTION

[0042] Example 1

[0043] A method for preparing a carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst for zinc-air batteries comprises the following steps:

[0044] (1) Preparation of ZIF-8 core: 2-Methylimidazole (6.16 g) and Zn(NO3)2·6H2O (5.95 g) were dissolved in 150 ml of anhydrous methanol solvent, respectively. The two solutions were mixed under stirring at room temperature, allowed to stand for 24 h, and then filtered through a sand core funnel. The mixture was further dried in a vacuum drying oven at 80°C for 12 h. The resulting white powder was the ZIF-8 core.

[0045] (2) Preparation of ZIF-8@ZIF-67@Fe(acac)3 precursor: 0.5 g ZIF-8 and 5.82 g Co(NO3)2·6H2O were dispersed in 200 ml methanol solvent and ultrasonicated for 1 h to form solution A; 6.16 g 2-methylimidazole and 0.5 g Fe(acac)3 were dissolved in 100 ml methanol solvent to form solution B. The two solutions were quickly mixed under stirring at room temperature, reacted for 24 h, and then filtered and dried. The resulting purple powder was the ZIF-8@ZIF-67@Fe(acac)3 precursor.

[0046] (3) Preparation of carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst: 1 g of ZIF-8@ZIF-67@Fe(acac)3 precursor was placed in a high-temperature tube furnace filled with argon, heated to 900°C and kept at this temperature for 2 h. The obtained black powder was acid-washed and then dried, and then placed in a high-temperature tube furnace filled with argon for secondary pyrolysis (900°C for 2 h). The final product was a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst.

[0047] Figure 1 and Figure 2 The SEM and TEM images of the ZIF-8@ZIF-67@Fe(acac)3 precursor prepared in Example 1 respectively show that the particle size of the precursor is between 300 nm and 1 μm, and the dispersion is good.

[0048] Figure 3 The X-ray diffraction (XRD) pattern of the ZIF-8@ZIF-67@Fe(acac)3 precursor prepared in Example 1 shows that the precursor exhibits a highly normalized crystal structure, which is the same as that of ZIF-8 and ZIF-67. At the same time, the incorporation of Fe(acac)3 does not affect the structure of the crystal.

[0049] Figure 4 This is an SEM image of the carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared in Example 1. It can be seen that the catalyst particle size is 200-800 nm, a large number of bamboo-shaped carbon nanotubes are distributed on the particle surface, and the particles are interconnected by carbon nanotubes to form a mass transfer network.

[0050] Figure 5 This is the XRD pattern of the carbon tube grafted nitrogen-doped carbon supported iron / cobalt-based catalyst prepared in Example 1. It can be seen that the catalyst contains iron, cobalt metal elements and amorphous carbon.

[0051] Figure 6 This is the LSV curve (ORR) of the carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared in Example 1. The material exhibits good ORR catalytic performance, with an onset potential of 0.956 V and a half-wave potential of 0.775 V.

[0052] Figure 7 The LSV curve (OER) of the carbon tube grafted nitrogen-doped carbon supported iron / cobalt-based catalyst prepared in Example 1. The material showed good OER catalytic performance with a current density of 10 mA / cm 2 The potential at this time is 1.515V.

[0053] The carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared in Example 1 is used as a zinc-air battery material. The specific operation steps are as follows:

[0054] The carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared above was dispersed in ethanol and then drop-coated onto a composite electrode as an air electrode, a zinc sheet as a metal electrode, and a 6M potassium hydroxide + 0.2M zinc acetate mixed solution as an electrolyte to assemble a rechargeable zinc-air battery.

[0055] Figure 8This is the electrical output performance diagram of the zinc-air battery equipped with carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared in Example 1. It can be seen that the battery peak power density is 114mW / cm 2 .

[0056] Example 2

[0057] A method for preparing a carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst for zinc-air batteries comprises the following steps:

[0058] (1) Preparation of ZIF-8 core: A certain amount of 2-methylimidazole (6.16 g) and Zn(NO3)2·6H2O (5.95 g) were dissolved in 150 ml of anhydrous methanol solvent. The two solutions were mixed under stirring at room temperature, allowed to stand for 18 h, and then filtered through a sand core funnel. The mixture was further dried in a vacuum drying oven at 80°C for 12 h. The resulting white powder was the ZIF-8 core.

[0059] (2) Preparation of ZIF-8@ZIF-67@Fe(acac)3 precursor: 0.5g ZIF-8 and 5.82g Co(NO3)2·6H2O were dispersed in 200ml methanol solvent and ultrasonicated for 1h to form solution A; 6.16g 2-methylimidazole and 1g Fe(acac)3 were dissolved in 100ml methanol solvent to form solution B. The two solutions were quickly mixed under stirring at room temperature, reacted for 12h, and then filtered and dried. The resulting purple powder was the ZIF-8@ZIF-67@Fe(acac)3 precursor;

[0060] (3) Preparation of carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst: 1 g of ZIF-8@ZIF-67@Fe(acac)3 precursor was placed in a high-temperature tube furnace filled with argon, heated to 1000°C and kept at this temperature for 2 h. The obtained black powder was acid-washed and then dried, and then placed in a high-temperature tube furnace filled with argon for secondary pyrolysis (1000°C for 2 h). The final product was a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst.

[0061] Example 3

[0062] A method for preparing a carbon tube-grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst for zinc-air batteries comprises the following steps:

[0063] (1) Preparation of ZIF-8 core: A certain amount of 2-methylimidazole (6.16 g) and ZnCl2 (2.72 g) were dissolved in 150 ml of anhydrous methanol solvent. The two solutions were mixed under stirring at room temperature, allowed to stand for 18 h, and then filtered through a sand core funnel. The mixture was further dried in a vacuum drying oven at 80°C for 12 h. The resulting white powder was the ZIF-8 core.

[0064] (2) Preparation of ZIF-8@ZIF-67@Fe(acac)3 precursor: 0.5g ZIF-8 and 5.82g Co(NO3)2·6H2O were dispersed in 200ml methanol solvent and ultrasonicated for 1h to form solution A; 6.16g 2-methylimidazole and 1g Fe(acac)3 were dissolved in 100ml methanol solvent to form solution B. The two solutions were quickly mixed under stirring at room temperature, reacted for 12h, and then filtered and dried. The resulting purple powder was the ZIF-8@ZIF-67@Fe(acac)3 precursor;

[0065] (3) Preparation of carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst: 1 g of ZIF-8@ZIF-67@Fe(acac)3 precursor was placed in a high-temperature tube furnace filled with argon, heated to 1000°C and kept at this temperature for 2 h. The obtained black powder was acid-washed and then dried, and then placed in a high-temperature tube furnace filled with argon for secondary pyrolysis (1000°C for 2 h). The final product was a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst.

[0066] The above embodiments are only preferred implementation modes of the present invention and are only used to explain the present invention rather than to limit the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst, characterized in that: The following steps are involved: (1) Preparation of ZIF-8 core: 2-Methylimidazole and zinc salt were dissolved in anhydrous methanol solvent, respectively. The two solutions were mixed under stirring at room temperature, allowed to stand, and then filtered through a sand core funnel and vacuum dried. The resulting white powder was the ZIF-8 core. (2) Preparation of ZIF-8@ZIF-67@Fe(acac)3 precursor: ZIF-8 and cobalt salt were dispersed in methanol solvent and ultrasonically formed into solution A; 2-methylimidazole and Fe(acac)3 were then dissolved in methanol solvent to form solution B. The above two solutions A and B were quickly mixed under stirring at room temperature. After the reaction, the solution was filtered and dried. The purple powder obtained was the ZIF-8@ZIF-67@Fe(acac)3 precursor; (3) Preparation of carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst: The ZIF-8@ZIF-67@Fe(acac)3 precursor was placed in a high-temperature tube furnace filled with inert gas and heated. The obtained black powder was acid-washed and then dried. It was then placed in a high-temperature tube furnace filled with inert gas for secondary pyrolysis. The final product was the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst. In step (2), the mass ratio of cobalt salt to ZIF-8 is 4 to 20:1; the molar ratio of 2-methylimidazole to Fe(acac)3 is 1 to 20:1; In step (3), the heating time is 1 to 5 hours, and the heating temperature is 900 to 1200°C; the heating time of the secondary pyrolysis is 1 to 5 hours, and the heating temperature is 900 to 1200°C.

2. The method for preparing the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst according to claim 1, characterized in that: In step (1), the zinc salt is one or more of zinc chloride, zinc nitrate hexahydrate, zinc sulfate, and zinc acetate; and the molar ratio of 2-methylimidazole to the zinc salt is 1 to 8:

1.

3. The method for preparing the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst according to claim 1, characterized in that: In step (1), the stirring time is 12 to 48 hours, and the stirring temperature is room temperature; the vacuum drying time is 8 to 24 hours, and the vacuum drying temperature is 60 to 80°C.

4. The method for preparing the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst according to claim 1, characterized in that: In step (2), the cobalt salt is one or more of cobalt chloride, cobalt nitrate hexahydrate, cobalt sulfate, cobalt oxalate, and cobalt acetate.

5. The method for preparing the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst according to claim 1, characterized in that: In step (2), the reaction time is 12 to 48 hours, and the reaction temperature is 10 to 40°C.

6. The method for preparing the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst according to claim 1, characterized in that: In step (3), the inert gas is one of Ar, He, and N2.

7. A carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The precursor is a double-layer heterogeneous structure, and a large number of carbon nanotubes are distributed on the surface of the catalyst obtained after pyrolysis.

8. Use of the carbon tube grafted nitrogen-doped carbon-supported iron / cobalt-based catalyst according to claim 7 in zinc-air batteries.

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