Preparation method and application of iron pair and nickel atom co-coordinated nitrogen-doped carbon micro-flower

Abstract

The invention discloses a preparation method and application of nitrogen-doped carbon microflowers co-coordinated with iron pairs and nickel atoms, and belongs to the technical field of oxygen electrocatalysis, a three-atom catalyst is successfully prepared through two-step heat treatment, and the catalyst is composed of nitrogen-doped carbon microflowers which are coordinated with Fe2 and Ni and have carbon vacancies and is named as Fe2 / Ni-N-CCVMFs. The prepared material has Fe2-N6 sites, Ni-N4 sites and carbon vacancies at the same time, so that excellent bifunctional activity and excellent stability are achieved in an alkaline solution, the material has 0.9 V vs. RHE half-wave potential in an oxygen reduction reaction, only 289 mV low overpotential is needed for achieving the current density of 10 mA cm <-2 > in an oxygen evolution reaction, and the material is suitable for being used in the oxygen reduction reaction. And a low delta E (the difference between the potential of an oxygen evolution reaction at 10 mA cm <-2 > and the half-wave potential of an oxygen reduction reaction) value of 0.619 V, and a high initial current retention rate higher than 90% can be maintained in a long-term stability test as long as 100 hours. According to the invention, a new thought is provided for improving the electro-catalytic performance by optimizing the metal site electronic structure.

Description

Technical Field

[0001] This invention belongs to the field of oxygen electrocatalysis technology, specifically a method for preparing and applying nitrogen-doped carbon microflowers with iron pairs and nickel atoms co-coordinated. Background Technology

[0002] Rechargeable zinc-air batteries possess advantages such as high theoretical energy density, low cost, and environmental friendliness, making them a promising green energy storage device. However, the slow oxygen reduction and oxygen evolution reactions on their air electrodes result in actual battery performance far below theoretical values, severely hindering commercialization.

[0003] Although noble metal catalysts exhibit high catalytic activity, their high cost, scarcity, and limited functionality restrict their applications. Therefore, developing efficient and stable non-noble metal bifunctional oxygen electrocatalysts is crucial.

[0004] While atomically dispersed MNC materials have shown potential in the field of catalysis, their single-site configurations make it difficult to efficiently and reversibly drive oxygen electrocatalysis, and the adsorption energies for various oxygen intermediates exhibit a limiting linear relationship, leading to sluggish kinetics. Furthermore, the instability of single-atom sites during the reaction process also affects the durability of the catalyst.

[0005] To address the aforementioned challenges, this study successfully constructed a Fe2 / Ni triatomic catalyst anchored on nitrogen-doped carbon microflora with carbon vacancies through rational electronic structure modulation and defect engineering. In this design, the carbon vacancies and adjacent Ni single atoms synergistically modulate the electronic structure of paired Fe sites, effectively lowering the energy barrier of the rate-determining step in oxygen electrocatalysis, breaking the limitation of intermediate adsorption energy, and significantly enhancing the anti-dissolution ability of the metal sites during long-term operation. The prepared catalyst exhibited excellent activity and stability in both ORR and OER. Summary of the Invention

[0006] The technical solution of this invention is as follows: a method for preparing nitrogen-doped carbon microflowers with iron pairs and nickel atoms co-coordinated, comprising the following steps: S1. Dissolve the zinc source, the nitrogen-containing first ligand and the nitrogen-containing second ligand in the first solvent and react to obtain a metal-organic framework precursor with a flower-like morphology; S2. The metal-organic framework precursor is subjected to high-temperature pyrolysis under an inert atmosphere to obtain a nitrogen-doped carbon micron flower carrier with carbon vacancies. S3. The nitrogen-doped carbon microflower support with carbon vacancies is mixed with iron and nickel sources in a second solvent for metal ion adsorption. Then, the mixture is subjected to reducing heat treatment, acid washing and drying in sequence to obtain nitrogen-doped carbon microflower composite material with iron pairs and nickel atoms co-coordinated.

[0007] Furthermore, the nitrogen-containing first ligand is an imidazole compound, and the nitrogen-containing second ligand is a tetrazolium compound.

[0008] Furthermore, the nitrogen-containing first ligand is 2-methylimidazole, and the nitrogen-containing second ligand is 5-aminotetrazole or its hydrate.

[0009] Furthermore, the molar ratio of the zinc source, the nitrogen-containing first ligand, and the nitrogen-containing second ligand is 1:(3-4):(0.7-1.0).

[0010] Furthermore, in step S2, the temperature of high-temperature pyrolysis is 900-1000 ℃.

[0011] Furthermore, in step S3, the reducing heat treatment is carried out in a hydrogen-containing atmosphere at a temperature of 350-370 °C.

[0012] Furthermore, the mass ratio of the nitrogen-doped carbon microflower support with carbon vacancies, the iron source, and the nickel source is (4-6):(0.8-1.2):(0.5-1.0).

[0013] Furthermore, the iron source is ferrous chloride, and the nickel source is nickel chloride.

[0014] The iron source is ferrous chloride, and the nickel source is nickel chloride.

[0015] A nitrogen-doped carbon microflower composite material with iron pairs and nickel atoms co-coordinated includes a nitrogen-doped carbon microflower carrier, and iron pair sites and nickel single-atom sites atomically dispersed on the carrier, wherein the iron pair sites have an Fe2-N6 configuration and the nickel single-atom sites have a Ni-N4 configuration.

[0016] Application of a nitrogen-doped carbon microflower composite material with iron pairs and nickel atoms co-coordinated in the oxygen electrocatalytic electrode of a rechargeable zinc-air battery.

[0017] The beneficial effects of this invention are as follows: The Fe2 / Ni-NC provided by this invention CV The MFs composite material effectively modulates the electronic structure of paired Fe sites through the synergistic effect of carbon vacancies and single Ni sites, promoting the direct breaking of oxygen-oxygen bonds and breaking the limitations of traditional linear scaling relationships. This significantly enhances the bifunctional catalytic activity of oxygen reduction and oxygen evolution reactions. Simultaneously, the introduction of carbon vacancies effectively enhances the stability of metal sites during long-term catalysis. In rechargeable zinc-air batteries, this material exhibits high open-circuit voltage, excellent power density, and ultra-long cycle life, significantly outperforming commercial noble metal catalysts and showing broad application prospects in energy conversion and storage. Attached Figure Description

[0018] Figure 1 The Fe2 / Ni-NC obtained in Example 1CV SEM and TEM images of MFs; in the figure, a is a SEM image with a scale bar of 1 μm; b is a TEM image with a scale bar of 200 nm.

[0019] Figure 2 The Fe2 / Ni-NC obtained in Example 1 CV HRTEM image of MFs.

[0020] Figure 3 The Fe2 / Ni-NC obtained in Example 1 CV AC HAADF-STEM image of MFs.

[0021] Figure 4 The Fe2 / Ni-NC obtained in Example 1 CV XRD patterns of MFs.

[0022] Figure 5 Fe2-NC obtained in Example 2 CV SEM and TEM images of MFs; in the figure, a is a SEM image with a scale bar of 1 μm; b is a TEM image with a scale bar of 200 nm.

[0023] Figure 6 Fe2-NC obtained in Example 2 CV AC HAADF-STEM image of MFs.

[0024] Figure 7 The Ni-NC obtained in Example 3 CV SEM and TEM images of MFs; in the figure, a is a SEM image with a scale bar of 1 μm; b is a TEM image with a scale bar of 200 nm.

[0025] Figure 8 The Ni-NC obtained in Example 3 CV AC HAADF-STEM image of MFs.

[0026] Figure 9 The images show the EPR spectra of the materials obtained in Examples 1-4.

[0027] Figure 10 The images show the Raman spectra of the materials obtained in Examples 1-4.

[0028] Figure 11 The C 1s spectrum is shown in the X-ray photoelectron spectroscopy (XPS) of the materials obtained in Examples 1-3.

[0029] Figure 12 The LSV curves of the materials obtained in Examples 1-4 and Comparative Example 1 in the electrolyte are shown.

[0030] Figure 13 ADT tests were conducted on the materials obtained in Examples 1-4 and Comparative Example 1 in the electrolyte.

[0031] Figure 14 The it test results are for the materials obtained in Examples 1-4 and Comparative Example 1 in the electrolyte. Detailed Implementation

[0032] It should be noted that in the description of this invention, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation.

[0033] In this invention, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; a connection can be a mechanical connection or an electrical connection; a link can be a direct connection or an indirect connection through an intermediate medium, and can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] In one embodiment of the present invention, an oxygen electrocatalytic composite material is provided, which anchors atomically dispersed Fe pairs and single Ni sites on nitrogen-doped carbon microflora with carbon vacancies; wherein, NC CV MFs serve as the support and conductive framework, Fe2-N6 and Ni-N4 sites act as dual active centers, and carbon vacancies regulate the electronic structure of metal sites. The three work synergistically to enhance oxygen electrocatalytic performance.

[0035] In another embodiment of the present invention, a method for preparing an oxygen electrocatalytic composite material is also provided. This method is simple to operate, and through precursor pyrolysis and metal coordination modification, the resulting composite material exhibits excellent bifunctional catalytic activity and stability in ORR and OER. Specifically, the method for preparing the composite material includes the following steps: S1. Synthesis of flower-like zeolite-type zinc-tetrazole framework precursor: Zinc source, first ligand, second ligand and first solvent are mixed and subjected to first reaction to obtain Zn-ZTF precursor; S2. Preparation of nitrogen-doped carbon microflora: The Zn-ZTF precursor is pyrolyzed to obtain nitrogen-doped carbon microflora (NC) with carbon vacancies. CV MFs; S3, Anchoring of the metal site: The NC CV MFs, iron source, nickel source, and a second solvent are mixed to carry out a second reaction, followed by heat treatment, acid washing, and drying to obtain Fe2 / Ni-NC. CV MFs composite materials.

[0036] The first ligand is 2-methylimidazole, and the second ligand is 5-aminotetrazole monohydrate; the molar ratio of zinc source, first ligand, and second ligand is 1:(3-4):(0.7-1.0); NC CV The mass ratio of MFs, iron source and nickel source is (4-6):(0.8-1.2):(0.5-1.0); the embodiments of the present invention can optimize the electronic structure of the composite material by adjusting the metal loading.

[0037] In practical applications, the zinc source is zinc acetate dihydrate; the iron source is anhydrous ferrous chloride; the nickel source is anhydrous nickel chloride; and the first and second solvents are independently methanol or ethanol.

[0038] In a preferred embodiment of the present invention, the first solvent is methanol, the temperature of the first reaction is 60-70 °C, and the reaction time is 100-120 minutes; the pyrolysis is carried out under an argon atmosphere, the pyrolysis temperature is 900-940 °C, and the pyrolysis time is 1-3 hours.

[0039] In a preferred embodiment of the present invention, the second solvent is ethanol, the second reaction is carried out at room temperature for 20-28 hours, the heat treatment is carried out in a 10 vol% H2 / Ar mixed atmosphere at a temperature of 350-370 °C for 4-6 hours, and the pickling is carried out using a 1 M hydrochloric acid solution for 10-14 hours.

[0040] In the embodiments of the present invention, Fe2 / Ni-NC is prepared by the above-described preparation method. CV MFs composites possess abundant carbon vacancies and atomically dispersed metal sites, while also exhibiting high electrical conductivity and good catalytic stability.

[0041] In another embodiment of the present invention, the above-mentioned Fe2 / Ni-NC is also provided. CV The application of MFs composite materials in the field of oxygen electrocatalysis can be specifically applied to rechargeable zinc-air batteries. This Fe2 / Ni-NC composite material... CV When MFs composite materials are used as air electrode catalysts, they exhibit excellent bifunctional catalytic activity for ORR and OER under alkaline conditions.

[0042] The following embodiments are specific implementation examples of the present invention in practical applications, but are not limited thereto.

[0043] Example 1: This example provides a method for preparing an oxygen electrocatalytic composite material, specifically including the following steps: S1. Dissolve 246.0 mg of 2-methylimidazole and 77.0 mg of 5-aminotetrazole monohydrate in 10 mL of methanol to form solution A, and dissolve 214.0 mg of zinc acetate dihydrate in 10 mL of methanol to form solution B. Pour solution A into solution B with stirring, react at room temperature for 5 min, transfer the suspension to a 50 mL test tube, and let it stand at 60 °C for 100 min. After the reaction is complete, centrifuge, wash three times with ethanol, and vacuum dry at 80 °C for 12 hours to obtain the Zn-ZTF precursor. S2. The above Zn-ZTF precursor was subjected to an argon atmosphere at 5 °C for min. -1 The temperature was raised to 920 °C and pyrolyzed for 2 hours to obtain NC. CV MFs; S3, 20 mg NC CV MFs were added to 10 mL of an ethanol solution containing 4.0 mg anhydrous FeCl2 and 3.0 mg anhydrous NiCl2, and ultrasonically dispersed. The mixture was then stirred at room temperature for 24 hours. After centrifugation, the mixture was vacuum dried at 80 °C for 12 hours, followed by heat treatment at 360 °C for 5 hours in a 10 vol% H2 / Ar atmosphere. Finally, it was soaked in 1 M HCl for 12 hours, washed, and dried to obtain Fe2 / Ni-NC. CV MFs composite materials.

[0044] Example 2: This example provides a method for preparing an oxygen electrocatalytic composite material, specifically including the following steps: S1, Same as Example 1; S2, Same as Example 1; S3, 20 mg NC CV MFs were added to 10 mL of an ethanol solution containing 4.0 mg of anhydrous FeCl2, without adding NiCl2. The other steps were the same as in Example 1 to obtain Fe2-NC. CV MFs control materials.

[0045] Example 3: This example provides a method for preparing an oxygen electrocatalytic composite material, specifically including the following steps: S1, Same as Example 1; S2, Same as Example 1; S3, 20 mg NC CV MFs were added to 10 mL of an ethanol solution containing 3.0 mg of anhydrous NiCl2, without adding FeCl2. The other steps were the same as in Example 1 to obtain Ni-NC. CV MFs control materials.

[0046] Example 4: This example provides a method for preparing an oxygen electrocatalytic composite material, specifically including the following steps: S1, Same as Example 1; S2, Same as Example 1; Comparative Example 1: A commercial Pt / C (20 wt%) catalyst and RuO2 catalyst were used as benchmark comparative examples for ORR and OER performance evaluation.

[0047] Structural characterization and performance testing: I. The Fe2 / Ni-NC obtained in Example 1 CV The MFs composite material was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM), and X-ray diffraction (XRD). The results are as follows: Figures 1-3 As shown.

[0048] in, Figure 1 a is Fe2 / Ni-NC CV SEM images of MFs Figure 1 b is Fe2 / Ni-NC CV TEM images of MFs. SEM images show Fe2 / Ni-NC CV MFs retain their parent nitrogen-doped carbon microflowers (NC) very well. CV The morphology of the MFs was observed, but the nanosheets constituting the petals were thinner. Additionally, SEM images showed that Fe2 / Ni-NC... CV MFs possess a large specific surface area and a highly open porous structure, which is beneficial for exposing active sites and facilitating the transport of reaction-related species during oxygen electrocatalysis. Fe2 / Ni-NC CV TEM images of MFs ( Figure 1 b) indicates that these microflowers are all composed of ultrathin wrinkled nanosheets, and no metal particles or clusters were observed in the spectra, which further confirms the atomic-level dispersion of Fe / Ni.

[0049] Figure 2 Fe2 / Ni-NC CV High-resolution transmission electron microscopy images of MFs clearly show discontinuous carbon lattice fringes in these graphene-like ultrathin nanosheets, and no metal particles or clusters were found in the HRTEM images, indicating that they are defective graphitic carbon structures.

[0050] Figure 3 Fe2 / Ni-NC CVAC HAADF-STEM image of MFs. In addition to many individual bright spots, pairs of bright spots (red circles) are also clearly visible in the image.

[0051] Figure 4 Fe2 / Ni-NC was demonstrated CV Powder XRD patterns of MFs. The patterns show only two broadened diffraction peaks at 2θ = 25.0° and 43.3°, corresponding to the (002) and (101) crystal plane characteristic peaks of graphitic carbon, respectively. No diffraction peaks corresponding to crystalline Fe or Ni species were observed, which is consistent with the results of high-resolution transmission electron microscopy (HRTEM).

[0052] The Fe2-NC prepared in Example 2 CV MFs material, Ni-NC prepared in Example 1 CV The MFs material was characterized by SEM, TEM, and AC HAADF-STEM, and the results are as follows: Figures 5-8 As shown.

[0053] in, Figure 5 Fe2-NC CV SEM and TEM images of MFs. The SEM image shows Fe2-NC CV MFs also exhibit a flower-like appearance, similar to Fe2 / Ni-NC. CV MFs are very similar. The synthesized Fe2-NC CV Transmission electron microscopy (TEM) images of the MFs further revealed that these microflowers are all composed of ultrathin folded nanosheets.

[0054] Figure 6 It is the synthesized Fe2-NC CV MFs AC HAADF-STEM image. The image shows only pairs of bright spots (red circles).

[0055] Figure 7 It is Ni-NC CV SEM and TEM images of MFs. The SEM image shows Ni-NC CV MFs also exhibit a flower-like appearance, similar to Fe2 / Ni-NC. CV MFs are very similar. The synthesized Ni-NC CV Transmission electron microscopy (TEM) images of the MFs further revealed that these microflowers are all composed of ultrathin folded nanosheets.

[0056] Figure 8 It is the synthesized Ni-NC CV MFs AC HAADF-STEM image. The image shows only individual bright spots.

[0057] The Fe2 / Ni-NC prepared in Example 1 CV MFs material, Fe2-NC prepared in Example 2 CV MFs material, Ni-NC prepared in Example 3 CV MFs material and NC prepared in Example 4 CV Electron paramagnetic resonance (EPR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were performed on the MFs material. The results are shown below. Figure 9 , Figure 10 as well as Figure 11 As shown.

[0058] Figure 9 The spectrum is an EPR spectrum, indicating that Fe2 / Ni-NC CV MFs show better performance than Fe2-NC at a g value of 2.004. CV MFs, Ni-NC CV The stronger signal peaks in the MFs material confirm the successful introduction of carbon vacancies and the presence of Fe2 / Ni-NC. CV MFs have the highest number of carbon vacancies.

[0059] Figure 10 These are the Raman spectra of the materials obtained in Examples 1-4. Fe2 / Ni-NC CV The Raman spectra of MFs and other materials in the embodiments are at approximately 1346 cm⁻¹. -1 and 1575 cm -1 Distinct characteristic peaks appear at these points, corresponding to the D band (disordered carbon) and the G band (graphite carbon), respectively. This is consistent with Fe2-NC. CV MFs, Ni-NC CV MFs and NC CV Compared to MFs, Fe2 / Ni-NC CV MFs of I D / I G The highest ratio indicates the highest degree of defect.

[0060] Figure 11 The C 1s spectra of the materials obtained in Examples 1-3 are shown in the X-ray photoelectron spectroscopy (XPS). Quantitative XPS analysis showed that the high-resolution XPS C 1s spectra of the material could be deconvoluted into three characteristic peaks with binding energies of 284.6 eV, 285.3 eV, and 286.9 eV, respectively, corresponding to the chemical states of C=C, CN, and CO bonds.

[0061] The Fe2 / Ni-NC prepared in Example 1 were respectively CVMFs material, Fe2-NC prepared in Example 2 CV MFs material, Ni-NC prepared in Example 3 CV MFs material, NC prepared in Example 4 CV The MFs material and the Pt / C+RuO2 material obtained in Comparative Example 1 were directly used as the working electrode, the graphite rod as the counter electrode, and the Hg / HgO electrode as the reference electrode. Electrochemical measurements and electrocatalytic tests of the standard three-electrode system were performed in aqueous solutions containing 0.1 M KOH and 1 M KOH. During the tests, oxygen was continuously introduced into the electrolyte to maintain oxygen saturation. The test results are as follows: Figures 12-14 As shown.

[0062] in, Figure 12 a represents the linear sweep voltammetry (LSV) curves of different materials in an oxygen-saturated 0.1 M KOH electrolyte. The curves compare Fe2 / Ni-NC. CV MFs materials, Fe2-NC CV MFs materials, Ni-NC CV MFs material, NC prepared in Example 4 CV The catalytic activity of MFs materials and Pt / C+RuO2 materials was compared. At the same potential, the Fe2 / Ni-NC material prepared in Example 1... CV MFs exhibited superior ORR activity, with a more corrected onset potential of 1.03 V vs RHE and a more corrected half-wave potential (0.90 V vs RHE). Figure 12 b shows the linear sweep voltammetry (LSV) curves of different materials in an oxygen-saturated 1 M KOH electrolyte. At the same potential, the Fe2 / Ni-NC prepared in Example 1... CV MFs require only 289 mV of overpotential (η) 10 It can reach 10 mAcm -2 The current density is much lower than that of Fe2-NC. CV MFs (514 mV), Ni-NC CV MFs (300 mV), NC CV MFs (343 mV) and RuO2 (334 mV).

[0063] Figure 13 The Fe2 / Ni-NC prepared in Example 1 is shown. CV Accelerated durability testing (ADT) of MFs materials indicates that Fe2 / Ni-NC CVMFs exhibit excellent durability. In 0.1 M KOH solution, after 15,000 cycles of cyclic voltammetry (CV) testing, the half-wave potential of the ORR decreased by only 0.017 V. In 1 M KOH solution, after 10,000 cycles of CV testing, the OER remained stable at 10 mA cm⁻¹. -2 The potential (1.519 V vs RHE) remained almost unchanged, demonstrating that the prepared Fe2 / Ni-NC CV MFs catalysts exhibit excellent electrocatalytic ORR and OER durability.

[0064] Figure 14 The Fe2 / Ni-NC prepared in Example 1 is shown. CV MFs material, Fe2-NC prepared in Example 2 CV MFs material, Ni-NC prepared in Example 3 CV IT testing of MFs materials. After 100 hours of IT testing, Fe2 / Ni-NC CV The ORR / OER current on the MFs remained at 98.3% / 93.5% of its initial current, significantly higher than that of the Fe2-NC sample. CV MFs and Ni-NC CV The presence of MFs indicates that the synergistic effect between Fe and Ni further enhances the long-term operational stability of the catalyst we prepared.

[0065] In summary, the preparation method provided by the embodiments of the present invention is simple and successfully prepared a novel material in which three-atom Fe2 / Ni sites are coordinated on nitrogen-doped carbon microflowers containing carbon vacancies, which is named Fe2 / Ni-NC. CV Characterization results confirmed the simultaneous presence of Fe2-N6 sites, Ni-N4 sites, and carbon vacancy sites in this material. These structural features endow it with excellent electrocatalytic activity in both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) (OER at 10 mA cm⁻¹). -2 The difference Δ between the potential and the half-wave potential of the oxygen reduction reaction E It has a voltage of only 0.619 V and excellent stability.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be included within the scope of protection of the present invention. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A method for preparing nitrogen-doped carbon microflowers with iron pairs co-coordinated with nickel atoms, characterized in that, Includes the following steps: S1. Dissolve the zinc source, the nitrogen-containing first ligand and the nitrogen-containing second ligand in the first solvent and react to obtain a metal-organic framework precursor with a flower-like morphology; S2. The metal-organic framework precursor is subjected to high-temperature pyrolysis under an inert atmosphere to obtain a nitrogen-doped carbon micron flower carrier with carbon vacancies. S3. The nitrogen-doped carbon microflower support with carbon vacancies is mixed with iron and nickel sources in a second solvent for metal ion adsorption. Then, the mixture is subjected to reducing heat treatment, acid washing and drying in sequence to obtain nitrogen-doped carbon microflower composite material with iron pairs and nickel atoms co-coordinated.

2. The preparation method according to claim 1, characterized in that, The nitrogen-containing first ligand is an imidazole compound, and the nitrogen-containing second ligand is a tetrazolium compound.

3. The preparation method according to claim 2, characterized in that, The nitrogen-containing first ligand is 2-methylimidazole, and the nitrogen-containing second ligand is 5-aminotetrazole or its hydrate.

4. The preparation method according to claim 3, characterized in that, The molar ratio of the zinc source, the nitrogen-containing first ligand, and the nitrogen-containing second ligand is 1:(3-4):(0.7-1.0).

5. The preparation method according to claim 4, characterized in that, In step S2, the temperature of high-temperature pyrolysis is 900-1000 ℃.

6. The preparation method according to claim 5, characterized in that, In step S3, the reducing heat treatment is carried out in a hydrogen-containing atmosphere at a temperature of 350-370 °C.

7. The preparation method according to claim 6, characterized in that, The mass ratio of the nitrogen-doped carbon microflower support with carbon vacancies to the iron source and the nickel source is (4-6):(0.8-1.2):(0.5-1.0).

8. The preparation method according to claim 7, characterized in that, The iron source is ferrous chloride, and the nickel source is nickel chloride.

9. A nitrogen-doped carbon microflower composite material with iron pairs and nickel atoms co-coordinated, characterized in that, The composite material prepared by any one of claims 1-8 includes a nitrogen-doped carbon micron flower carrier, and iron pair sites and nickel single-atom sites atomically dispersed on the carrier, wherein the iron pair sites are of the Fe2-N6 configuration and the nickel single-atom sites are of the Ni-N4 configuration.

10. The application of the nitrogen-doped carbon microflower composite material with iron pairs and nickel atoms co-coordinated as described in claim 9 in the oxygen electrocatalytic electrode of a rechargeable zinc-air battery.

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