Iron and cobalt atom pair co-coordinated nitrogen-doped carbon as well as preparation method and application thereof

Abstract

The invention discloses iron and cobalt atom pair co-coordinated nitrogen-doped carbon and a preparation method and application thereof, and belongs to the technical field of electrocatalysts, and the preparation method comprises the following steps: mixing a zinc source, a nitrogen-containing ligand and a mixed solvent, and carrying out a coordination reaction to obtain a metal organic framework precursor; pyrolyzing the metal organic framework precursor to obtain a nitrogen-doped carbon carrier; the preparation method comprises the following steps: mixing the nitrogen-doped carbon carrier, an iron source, a cobalt source and an organic solvent, carrying out a load reaction, and then sequentially carrying out heat treatment and acid pickling treatment to obtain the Fe2 / Co2-N-C composite material. The composite material has high conductivity, large specific surface area and abundant active sites, the adsorption / desorption energy barrier of an oxygen intermediate is synergistically optimized through the strong electron coupling effect of atomic-scale dispersed iron and cobalt double metal atoms and a nitrogen-doped carbon carrier, and the bifunctional oxygen electrocatalytic activity and stability are remarkably improved. The composite material shows excellent oxygen reduction reaction and oxygen evolution reaction performance, and has a wide application prospect in the field of batteries.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalyst technology, specifically a nitrogen-doped carbon with iron and cobalt atoms co-coordinated, its preparation method, and its application. Background Technology

[0002] Rechargeable zinc-air batteries (ZABs) are considered promising next-generation energy storage devices due to their high theoretical energy density, low cost, and good safety. However, the slow oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics on their air electrodes severely limit the actual performance of the batteries. Currently, although platinum (Pt) and ruthenium (Ru)-based catalysts are highly efficient ORR / OER benchmark materials, their high cost and resource scarcity limit their large-scale application. Therefore, developing high-performance, low-cost non-precious metal bifunctional oxygen electrocatalysts is crucial.

[0003] In recent years, atomically dispersed transition metal-nitrogen-carbon materials have become a research hotspot due to their excellent catalytic performance. However, the linear energy scaling relationship followed by traditional single-atom active sites limits their independent regulation of the adsorption energies of various oxygen-containing intermediates, resulting in sluggish reaction kinetics. In contrast, bi-site reaction mechanisms involving two adjacent metal sites can bypass the formation of the key intermediate (*OOH) and directly break the OO bond, providing a new strategy for overcoming the above bottlenecks and achieving efficient four-electron reaction pathways. However, realizing this mechanism places stringent requirements on the geometry of the active sites (such as precise atomic spacing). Summary of the Invention

[0004] To address this challenge, this invention successfully constructed a nitrogen-doped carbon material with co-coordinated iron and cobalt atom pairs through a stepwise pyrolysis strategy. The precisely constructed Fe-Co atom pair active sites in this material meet the geometric and electronic structure requirements of a two-site mechanism. Experimental characterization and in-situ spectroscopic analysis confirmed that its ORR / OER process follows a highly efficient two-site reaction pathway. The prepared catalyst exhibits excellent bifunctional oxygen electrocatalytic activity, with its oxygen evolution reaction (OER) reaching a response time of 10 mA cm⁻¹. -2 The difference (Δ) between the potential of the oxygen reduction reaction (1.502 V vs RHE) and the half-wave potential of the oxygen reduction reaction (0.919 V vs RHE) E The efficiency is as low as 0.583 V, significantly outperforming commercial Pt / C+RuO2 catalysts. This invention provides a new approach for designing highly efficient non-noble metal electrocatalysts based on a two-atom-site mechanism, and strongly promotes the development of energy devices such as zinc-air batteries.

[0005] The purpose of this invention is to solve the problems of insufficient activity, poor stability, and difficulty in breaking the linear scaling relationship of traditional single-atom sites in the prior art of non-precious metal bifunctional oxygen electrocatalysts.

[0006] The technical solution of this invention is as follows: a method for preparing nitrogen-doped carbon with iron and cobalt atom pairs co-coordinated, characterized by comprising the following steps: S1. A zinc source, a nitrogen-containing ligand, and a mixed solvent are mixed to carry out a coordination reaction to obtain a metal-organic framework precursor. S2. The metal-organic framework precursor is pyrolyzed under an inert atmosphere to obtain a nitrogen-doped carbon support. S3. Mix the nitrogen-doped carbon support, iron source, cobalt source and organic solvent, and carry out the loading reaction under a protective atmosphere; S4. The product after the loading reaction is subjected to heat treatment and acid washing in sequence to obtain a nitrogen-doped carbon composite material with iron and cobalt atoms co-coordinated.

[0007] Furthermore, the molar ratio of zinc source to nitrogen-containing ligand is 1:(1-1.5); the mass ratio of nitrogen-doped carbon support, iron source to cobalt source is (8-12):(0.8-1.2):(0.8-1.2).

[0008] Furthermore, the zinc source is zinc chloride; the nitrogen-containing ligand is 1H-1,2,3-triazole; the iron source is dodecyl diferric; and the cobalt source is nonacarbonyl dicobalt.

[0009] Furthermore, the mixed solvent includes ethanol, water, ammonia, and N,N-dimethylformamide; the organic solvent includes methanol and tetrahydrofuran.

[0010] Furthermore, the coordination reaction is carried out at room temperature for 20-28 hours; the pyrolysis temperature is 950-1050℃ and the pyrolysis time is 1-3 hours.

[0011] Furthermore, the loading reaction temperature is 110-130 ℃, and the reaction time is 2-4 hours.

[0012] Furthermore, the heat treatment is carried out under an inert atmosphere at a temperature of 750-850 ℃ for 2-4 hours; the pickling treatment uses a 0.05-0.15 mol / L sulfuric acid solution for 20-28 hours.

[0013] A nitrogen-doped carbon composite material with co-cobalt atom pairs co-coordinated includes a nitrogen-doped carbon support and active sites anchored on the nitrogen-doped carbon support. The active sites are atomically dispersed iron-cobalt bimetallic atom pairs. In aberration-corrected high-angle annular dark-field scanning transmission electron microscope images, the iron-cobalt bimetallic atom pairs appear as a pair of bright spots with a spacing of 0.18 nm to 0.25 nm.

[0014] Furthermore, when the composite material is used as a bifunctional oxygen electrocatalyst, its bifunctional activity index ΔE≤0.65 V, where ΔE is defined as the difference between the potential of the oxygen evolution reaction at a current density of 10 mA cm⁻² in an oxygen-saturated 1 M KOH solution and the half-wave potential of the oxygen reduction reaction in an oxygen-saturated 0.1 M KOH solution.

[0015] Furthermore, in the X-ray diffraction pattern, no characteristic diffraction peaks belonging to metallic iron, metallic cobalt, or their oxides were observed in the 2θ range of 20°–80° for the composite material.

[0016] Application of a nitrogen-doped carbon composite material with iron and cobalt atom pairs co-coordinated in the field of oxygen electrocatalysis.

[0017] The beneficial effects of this invention are as follows: The nitrogen-doped carbon material with co-cobalt iron-cobalt atom pairs provided by this invention effectively breaks the linear scaling limitations of traditional single-atom sites by precisely constructing Fe-Co atom pair active centers. Its dual-site reaction mechanism bypasses the formation of the *OOH intermediate, directly promoting the breaking of the OO bond, thereby significantly improving the bifunctional catalytic kinetics of oxygen reduction and oxygen evolution reactions. This material exhibits excellent conductivity, high specific surface area, and abundant active sites, demonstrating activity and superior long-term operational stability compared to commercial platinum-based / ruthenium-based catalysts. Zinc-air batteries assembled with this material exhibit high power density, high specific capacity, and ultra-long cycle life, showing broad application prospects in the field of energy storage and conversion. Attached Figure Description

[0018] Figure 1 This is a transmission electron microscope (TEM) image of Fe2 / Co2-NC obtained in Example 1 with a scale bar of 50 nm.

[0019] Figure 2 The image shows the HAADF-STEM image of Fe2 / Co2-NC obtained in Example 1 and the corresponding EDX elemental mapping of C, N, O, Fe, and Co elements.

[0020] Figure 3 The image is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope (AC HAADF-STEM) image of Fe2 / Co2-NC obtained in Example 1.

[0021] Figure 4 The image shows the X-ray diffraction (XRD) pattern of Fe2 / Co2-NC obtained in Example 1.

[0022] Figure 5 This is a TEM image of Fe2-NC obtained in Example 2 with a scale bar of 50 nm.

[0023] Figure 6 The image shows the AC HAADF-STEM image of Fe2-NC obtained in Example 2.

[0024] Figure 7 This is a TEM image of Co2-NC obtained in Example 3 with a scale bar of 50 nm.

[0025] Figure 8 The image shows the AC HAADF-STEM image of Co2-NC obtained in Example 3.

[0026] Figure 9 The N2 adsorption / desorption isotherms and pore size distributions of the materials obtained in Examples 1-4 are shown.

[0027] Figure 10 Linear sweep voltammetry (LSV) curves of the materials obtained in Examples 1-4 and Comparative Example 1 in KOH electrolyte.

[0028] Figure 11 Accelerated durability testing (ADT) of the materials obtained in Examples 1-4 and Comparative Example 1 in KOH electrolyte.

[0029] Figure 12 The zinc-air battery (ZAB) based on the Fe2 / Co2-NC obtained in Example 1 was tested at 5 mA cm⁻¹. -2 Constant current charge-discharge cycle test. Detailed Implementation

[0030] In one embodiment of the present invention, an oxygen electrocatalytic composite material is provided, which is a structure in which atomically dispersed iron-cobalt atom pairs are anchored on a nitrogen-doped carbon framework as active sites; wherein, the nitrogen-doped carbon framework serves as a conductive support and provides abundant nitrogen coordination sites, and the atomically dispersed Fe2 / Co2 atom pairs serve as catalytic active centers. The unique electronic structure formed by the two together can optimize the adsorption / desorption behavior of oxygen intermediates, thereby significantly improving catalytic performance.

[0031] 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 highly reproducible. By constructing atom-pair active sites, the resulting composite material exhibits excellent bifunctional activity and stability in ORR and OER. Specifically, the method for preparing the composite material includes the following steps: S1. Preparation of nitrogen-doped carbon support: A zinc source, a nitrogen-containing organic ligand, and a mixed solvent are reacted to obtain a metal-organic framework precursor; the precursor is then pyrolyzed at high temperature under an inert atmosphere to obtain a porous nitrogen-doped carbon material. S2, Construction of iron-cobalt atom pair sites: The nitrogen-doped carbon material, iron source, cobalt source and organic solvent are mixed and loaded under a protective atmosphere; the resulting product is then subjected to heat treatment and acid washing to obtain the final product Fe2 / Co2-NC.

[0032] The zinc source is zinc chloride, the nitrogen-containing organic ligand is 1H-1,2,3-triazole, the iron source is dodecyltriferric, and the cobalt source is nonacarbonyldicobalt. The molar ratio of zinc source to ligand can be adjusted between 1:1 and 1:1.5 to optimize the precursor structure. The mass ratio of nitrogen-doped carbon support, iron source and cobalt source can be adjusted between (8-12):(0.8-1.2):(0.8-1.2) to optimize the loading of active sites and the coordination configuration of atomic pairs.

[0033] In practical applications, the mixed solvent in step S1 is preferably a mixed system containing ethanol, water, ammonia and N,N-dimethylformamide; the organic solvent in step S2 is preferably a mixed solvent of methanol and tetrahydrofuran.

[0034] In a preferred embodiment of the present invention, in step S1, the coordination reaction is carried out at room temperature for 20-28 hours; the pyrolysis is carried out under an argon atmosphere, with the temperature increased to 950-1050 °C at a rate of 5-10 °C / min and held for 1-3 hours.

[0035] In a preferred embodiment of the present invention, in step S2, the loading reaction is carried out under nitrogen protection at a reaction temperature of 110-130 °C for 2-4 hours; the subsequent heat treatment is carried out under an argon atmosphere at 750-850 °C for 2-4 hours; the acid washing treatment uses a sulfuric acid solution with a concentration of 0.05-0.15 mol / L for 20-28 hours.

[0036] In the embodiments of the present invention, the Fe2 / Co2-NC composite material prepared by the above preparation method has high conductivity, high specific surface area and uniformly distributed atomic-level active sites, and exhibits excellent bifunctional oxygen electrocatalytic activity and long-term operational stability.

[0037] In another embodiment of the present invention, the application of the above-mentioned Fe2 / Co2-NC composite material in the field of oxygen electrocatalysis is also provided, which is particularly suitable as an air cathode catalyst for rechargeable zinc-air batteries.

[0038] The following embodiments are some specific implementation examples of the present invention in practical applications, but are not limited thereto.

[0039] Example 1: This example provides a method for preparing Fe2 / Co2-NC composite material, specifically including the following steps: S1. Dissolve 5.0 g ZnCl2 in a mixed solvent consisting of 50 mL ethanol, 75 mL water, 20 mL ammonia (25-28%), and 50 mL DMF. While stirring, add 6.26 mL of 1H-1,2,3-triazole dropwise to the solution and continue stirring at room temperature for 24 hours. Filter the resulting white suspension, wash several times with ethanol, and dry under vacuum at 80 °C for 12 hours to obtain the MET-6(Zn) precursor.

[0040] S2. The obtained MET-6(Zn) precursor was placed in a ceramic boat and heated to 1000 °C at a rate of 5 °C / min under an argon atmosphere. The temperature was maintained at this temperature for 2 hours. After cooling with the furnace, a nitrogen-doped carbon support was obtained, denoted as NC.

[0041] S3. Take 20 mg of the NC powder obtained in step S2 and disperse it uniformly in a mixed solvent consisting of 10 mL of methanol and 2 mL of tetrahydrofuran. Add 2.00 mg of Fe2(CO) to the dispersion. 12 And 2.00 mg Co2(CO)8. Under nitrogen protection, the mixture was heated under reflux in an oil bath at 120 °C for 3 hours. After the reaction was complete, the product was collected by centrifugation, washed three times with ethanol, and dried.

[0042] S4. Place the dried powder in a porcelain boat and heat-treat at 800 °C for 3 hours under an argon atmosphere. After cooling, immerse the resulting black powder in a 0.1 mol / L H2SO4 solution for 24 hours to remove unstable substances. Then wash with distilled water until neutral, and dry to obtain the final Fe2 / Co2-NC composite material.

[0043] Example 2: This example provides a method for preparing the control material Fe2-NC. The specific steps are basically the same as in Example 1, except that in step S3, Co2(CO)8 is not added, but only 2.00 mg of Fe2(CO) is added. 12 .

[0044] Example 3: This example provides a method for preparing the control material Co2-NC. The specific steps are basically the same as in Example 1, except that Fe2(CO) is not added in step S3. 12 Only 2.00 mg of Co2(CO)8 was added.

[0045] Example 4: This example provides a method for preparing the control material NC. The specific steps are basically the same as in Example 1, except that Fe2(CO) is not added in step S3. 12 It does not add Co2(CO)8.

[0046] Comparative Example 1: A commercial Pt / C (20wt%) catalyst and RuO2 catalyst were used as benchmark comparative examples for ORR and OER performance evaluation.

[0047] Structural characterization and performance testing: The Fe2 / Co2-NC obtained in Example 1 was characterized by transmission electron microscopy (TEM) and corresponding energy-dispersive X-ray spectroscopy (EDX) elemental distribution maps of carbon (C), nitrogen (N), oxygen (O), iron (Fe), and nickel (Ni), 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 1-4 As shown.

[0048] in, Figure 1 This is a TEM image of the Fe2 / Co2-NC material. The TEM image reveals a three-dimensional integrated network structure with interconnected channels and a carbon skeleton, and abundant pores, which facilitates the exposure of catalytically active sites and is beneficial for improving oxygen catalytic performance.

[0049] Figure 2 The images show HAADF-STEM images of the Fe2 / Co2-NC material and corresponding X-ray energy dispersive X-ray (EDX) elemental mapping diagrams. The images indicate that C, N, O, Fe, and Co elements are uniformly distributed in the material.

[0050] Figure 3 The ACHAADF-STEM image of the Fe2 / Co2-NC material reveals its morphology and fine atomic-scale structure, showing numerous paired bright spots. This indicates that a simple pyrolysis method may lead to the formation of a large number of Fe / Co atom pair sites within the NC, providing more OER / ORR active sites for Fe2 / Co2-NC. Numerous paired bright atomic bright spots can be observed, and statistical measurements show that the spacing between the two atoms in these pairs is mainly concentrated in the range of 0.20 nm ± 0.02 nm.

[0051] Figure 4 The XRD pattern of Fe2 / Co2-NC is shown. Only two weak diffraction peaks appear at 25.0° and 43.1°, which are attributed to the (002) and (101) crystal planes of graphitized carbon. No other peaks of any metal species were found, which further confirms the existence of atomically dispersed Fe and Co sites, consistent with the results of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM).

[0052] The Fe2-NC material prepared in Example 2 and the Co2-NC material prepared in Example 3 were characterized by TEM and HAADF-STEM. The results are as follows: Figures 5-8 As shown.

[0053] in, Figure 5 This is a TEM image of Fe2-NC material. Fe2-NC has a three-dimensional hierarchical porous nitrogen-doped carbon network structure.

[0054] Figure 6 This is the HAADF-STEM spectrum of Fe2-NC material; the spectrum shows that paired bright spots appear in Fe2-NC, indicating the presence of metal atom pairs in the sample.

[0055] Figure 7 This is a TEM image of the Co2-NC material. Co2-NC has a three-dimensional hierarchical porous nitrogen-doped carbon network structure.

[0056] Figure 8 This is the HAADF-STEM spectrum of the Co2-NC material; as can be seen from the spectrum, paired bright spots appear in Co2-NC, indicating the presence of metal atom pairs in the sample.

[0057] The Fe2 / Co2-NC materials prepared in Example 1, the Fe2-NC materials prepared in Example 2, the Co2-NC materials prepared in Example 3, and the NC materials prepared in Example 4 were subjected to BET testing. The test results... Figure 9 The N2 adsorption-desorption isotherms show that all materials prepared in the examples have abundant mesoporous structures. Although the specific surface area of ​​the Fe2 / Co2-NC catalyst Brunauer-Emmett-Teller (BET) prepared in Example 1 is smaller than that of the materials obtained in other examples, it has the largest cumulative pore volume, which is beneficial to the exposure of active sites, high accessibility and rapid reaction-related mass transfer during electrocatalysis.

[0058] The Fe2 / Co2-NC prepared in Example 1, the Fe2-NC prepared in Example 2, the Co2-NC prepared in Example 3, the NC prepared in Example 4, and the Pt / C+RuO2 material obtained in Comparative Example 1 were directly used as working electrodes, with a graphite rod as the counter electrode and an Hg / HgO electrode as the reference electrode. Electrochemical measurements and electrocatalytic tests of the standard three-electrode system were performed in 0.1 mol / L KOH aqueous solution and 1 mol / L KOH aqueous solution. During the tests, oxygen was continuously introduced into the electrolyte to maintain oxygen saturation. The test results are as follows: Figures 10-11 As shown.

[0059] in, Figure 10a shows the linear sweep voltammetry (LSV) curves of different materials in oxygen-saturated 0.1 MKOH electrolyte. The curves compare the catalytic activities of Fe2 / Co2-NC, Co2-NC, Co2-NC, the NC material prepared in Example 4, and Pt / C+RuO2. At the same potential, Fe2 / Co2-NC prepared in Example 1 exhibits superior ORR activity, with a more positive half-wave potential than Fe2-NC prepared in Example 2, Co2-NC prepared in Example 3, NC prepared in Example 4, and Pt / C material obtained in Comparative Example 1. This confirms that Fe2 / Co2-NC possesses superior ORR activity. Figure 10 b shows the linear sweep voltammetry (LSV) curves of different materials in an oxygen-saturated 1 MkOH electrolyte. At the same potential, the Fe2 / Co2-NC prepared in Example 1 showed linear sweep voltammetry (LSV) curves at 10 mA / cm². -2 At the current density, the overpotential is only 272 mV, which is much lower than that of Fe2-NC prepared in Example 2, Co2-NC prepared in Example 3, NC prepared in Example 4, and RuO2 obtained in Comparative Example 1.

[0060] Figure 11 The accelerated durability test (ADT) of the Fe2 / Co2-NC material prepared in Example 1 is shown, demonstrating that Fe2 / Co2-NC has excellent durability. Figure 11 In 0.1 M KOH solution, after 10,000 cycles of cyclic voltammetry (CV), the half-wave potential of the ORR decreased by only 0.013 V. In 1 M KOH solution, after 8,000 cycles of CV, the ORR increased at 10 mA cm⁻¹. -2 The potential (1.502 V vs RHE) hardly changed, demonstrating that the prepared Fe2 / Co2-NC material has excellent electrocatalytic ORR and OER durability.

[0061] Figure 12 This demonstrates a zinc-air battery assembled with Example 1 as the cathode, at 5 mA cm⁻¹ -2 At the specified current density, the Fe2 / Co2-NC-based battery can operate stably for over 1000 hours. After 1000 hours of cycling, the charge-discharge voltage difference of the Fe2 / Co2-NC-based zinc-air battery only increases by 9 mV. This result indicates that Fe2 / Co2-NC can be used not only as a bifunctional oxygen electrode but also as a reversible oxygen electrode.

[0062] In summary, the preparation method provided by the embodiments of the present invention is simple and successfully embeds diatomic iron and cobalt sites into a nitrogen-doped carbon network, constructing a cathode catalyst Fe2 / Co2-NC for rechargeable zinc-air batteries. The Fe2 / Co2-NC catalyst exhibits excellent bifunctional oxygen reduction reaction (ORR) / oxygen evolution reaction (OER) performance, with an ultra-small Δ... E Value (0.583 V). This invention provides important insights into the fundamental exploration of dual single-atom stabilization mechanisms and the design of self-supporting air cathodes.

[0063] 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 with iron and cobalt atom pairs co-coordinated, characterized in that, Includes the following steps: S1. A zinc source, a nitrogen-containing ligand, and a mixed solvent are mixed to carry out a coordination reaction to obtain a metal-organic framework precursor. S2. The metal-organic framework precursor is pyrolyzed under an inert atmosphere to obtain a nitrogen-doped carbon support. S3. Mix the nitrogen-doped carbon support, iron source, cobalt source and organic solvent, and carry out the loading reaction under a protective atmosphere; S4. The product after the loading reaction is subjected to heat treatment and acid washing in sequence to obtain a nitrogen-doped carbon composite material with iron and cobalt atoms co-coordinated.

2. The preparation method according to claim 1, characterized in that, The molar ratio of zinc source to nitrogen-containing ligand is 1:(1-1.5); the mass ratio of nitrogen-doped carbon support, iron source and cobalt source is (8-12):(0.8-1.2):(0.8-1.2).

3. The preparation method according to claim 2, characterized in that, The zinc source is zinc chloride; the nitrogen-containing ligand is 1H-1,2,3-triazole; the iron source is dodecyl diferric; and the cobalt source is nonacarbonyl dicobalt.

4. The preparation method according to claim 3, characterized in that, The mixed solvents include ethanol, water, ammonia, and N,N-dimethylformamide; the organic solvents include methanol and tetrahydrofuran.

5. The preparation method according to claim 4, characterized in that, The coordination reaction is carried out at room temperature for 20-28 hours; the pyrolysis temperature is 950-1050 ℃ and the pyrolysis time is 1-3 hours.

6. The preparation method according to claim 5, characterized in that, The loading reaction temperature is 110-130 ℃, and the reaction time is 2-4 hours.

7. The preparation method according to claim 6, characterized in that, The heat treatment is carried out under an inert atmosphere at a temperature of 750-850 ℃ for 2-4 hours; the pickling treatment uses a 0.05-0.15 mol / L sulfuric acid solution for 20-28 hours.

8. A nitrogen-doped carbon composite material with iron and cobalt atom pairs co-coordinated, characterized in that, It includes a nitrogen-doped carbon support and active sites anchored on the nitrogen-doped carbon support. The active sites are atomically dispersed iron-cobalt bimetallic atom pairs. In aberration-corrected high-angle annular dark-field scanning transmission electron microscope images, the iron-cobalt bimetallic atom pairs appear as a pair of bright spots with a spacing of 0.18 nm-0.25 nm.

9. The composite material according to claim 8, characterized in that, When the composite material is used as a bifunctional oxygen electrocatalyst, its bifunctional activity index ΔE≤0.65 V, where ΔE is defined as the difference between the potential of the oxygen evolution reaction at a current density of 10 mA cm⁻² in an oxygen-saturated 1 M KOH solution and the half-wave potential of the oxygen reduction reaction in an oxygen-saturated 0.1 M KOH solution.

10. The application of a nitrogen-doped carbon composite material with iron and cobalt atom pairs co-coordinated as described in claim 9 in the field of oxygen electrocatalysis.

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