Preparation of nitrogen-doped carbon supported iron-cobalt nanoparticle bifunctional catalyst and its catalytic application

Abstract

The application discloses a preparation of a nitrogen-doped carbon loaded iron-cobalt nanoparticle bifunctional catalyst and catalytic application thereof, and first prepares a graphene loaded iron metal monatomic atom catalyst; then the catalyst is subjected to iron trichloride intercalation, and is subjected to dry ball milling with a nitrogen source and a cobalt source to obtain a precursor; and the nitrogen-doped carbon loaded iron-cobalt nanoparticle oxygen reduction / oxygen evolution bifunctional catalyst is prepared by pyrolysis of the precursor through programmed temperature rising. The iron source is first introduced to prepare the monatomic atom catalyst with high oxygen reduction performance, and then the cobalt source is introduced to make the catalyst realize efficient bifunctional catalysis of oxygen reduction and oxygen evolution, and the catalytic performance is superior to that of a commercial platinum-carbon catalyst and an iridium oxide catalyst using noble metals, but the preparation cost is greatly reduced, and the catalyst has wide application prospect.

Description

Technical Field

[0001] This invention relates to the preparation of a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst and its application in oxygen reduction / oxygen evolution catalytic reactions, belonging to the field of oxygen reduction and oxygen evolution catalyst technology. Background Technology

[0002] With rapid societal development, the demand for energy is increasing. The overuse of fossil fuels such as oil, coal, and natural gas has placed immense pressure on the environment, and these non-renewable energy sources are gradually facing depletion. The current energy situation is one of too many resources and too few available. Energy shortages and environmental issues are two of the most important problems of the 21st century, and electrochemical energy storage and conversion are effective strategies to alleviate the increasingly severe energy and environmental crisis. Fuel cells and zinc-air batteries, as next-generation energy conversion devices, have been widely studied due to their advantages such as high energy density, safety and pollution-free operation, low cost, and reliability. However, the high reaction barrier of ORR / OER results in relatively low energy conversion efficiency, hindering the large-scale application of zinc-air batteries. Therefore, the search for bifunctional catalysts that can simultaneously catalyze ORR / OER is currently a research hotspot.

[0003] Although noble metal catalysts such as platinum, iridium, and ruthenium exhibit high catalytic activity for ORR / OER, their scarcity and high cost limit the commercialization of zinc-air batteries. There is an urgent need to design and construct non-noble metal catalysts. Transition metals, due to their low cost and abundant reserves, have been extensively studied by researchers, and the combination of nitrogen-doped carbon materials with metals has further broadened their application in electrocatalysts.

[0004] Among carbon-based materials, graphene is known as "black gold." It possesses an extremely high specific surface area, excellent mechanical stability, good flexibility, good electrical conductivity, and is inexpensive, environmentally friendly, and abundant. Graphene is the thinnest known material, a single atom thick, and a two-dimensional material with open planes, composed of carbon atoms arranged in sp... 2 Two-dimensional crystals, densely packed with hybrid components forming a hexagonal honeycomb lattice, are the building blocks of graphite, carbon nanotubes, and fullerenes. Perfectly crystalline graphene combines excellent mechanical strength, thermal conductivity, light transmittance, electrical conductivity, and chemical stability. Monolayer graphene possesses extremely high intrinsic mechanical strength, with a Young's modulus of 1 TPa and a fracture strength of 130 GPa, making it the toughest known material; it also boasts the highest thermal conductivity, approximately 5300 W / (m·K), ten times that of copper and tens of times that of silicon; its room-temperature carrier mobility reaches 2.0 × 10⁵ cm⁻¹. 2 Graphene has a mobility of / (V·S), which is 100 times faster than that of silicon. Graphene also has excellent electrical conductivity, capable of withstanding extremely high current densities.

[0005] Meanwhile, graphene possesses a well-defined two-dimensional structure and a large specific surface area, exhibiting high electrical and thermal conductivity, as well as high chemical and electrochemical stability, thus demonstrating broad application prospects. Using graphene as a support to load metal active sites, the combination of transition metals and graphene endows the composite material with bifunctional electrocatalytic activity for both ORR and OER. This invention first introduces an iron source to prepare a graphene-supported single-atom catalyst with high oxygen reduction performance, and then introduces a cobalt source to enable the catalyst to achieve highly efficient bifunctional catalysis for both oxygen reduction and oxygen evolution. Summary of the Invention

[0006] This invention addresses the shortcomings of existing non-precious metal oxygen reduction / oxygen evolution bifunctional catalysts by providing a method for preparing a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst and its application in oxygen reduction / oxygen evolution catalytic reactions. The raw materials used in this invention are readily available, the method is simple to operate, has high yield, and exhibits high catalytic activity for both oxygen reduction and oxygen evolution reactions, thus possessing the potential for large-scale application.

[0007] The present invention discloses a method for preparing a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst, comprising the following steps:

[0008] Step 1: Mix small-sized multilayer graphene with metal chloride and treat at high temperature to obtain a metal-rich graphene intercalation; then heat and mix the obtained graphene intercalation with ferric sulfate, melamine, and formaldehyde aqueous solution (commercially available, concentration 37wt%) to form a graphene-iron salt-hydrogel, which is then freeze-dried and pyrolyzed at high temperature to obtain a graphene-supported metal single-atom catalyst.

[0009] Step 2: The graphene-supported metal single-atom catalyst obtained in Step 1 is mixed with a metal chloride and subjected to high-temperature treatment to obtain a graphene reintercalation product. The graphene reintercalation product in Step 2 is prepared by high-temperature heat treatment and exfoliation of an iron-nitrogen-carbon-iron-graphene (Fe-NC / Fe-G) composite single-atom catalyst and a metal chloride. The graphene reintercalation product is prepared by mixing the metal chloride and the catalyst in a corundum crucible and then intercalating the metal chloride into the catalyst through programmed temperature rise.

[0010] Step 3: The graphene reintercalation material obtained in Step 2, along with nitrogen and cobalt sources, is ball-milled to obtain the precursor;

[0011] Step 4: Place the precursor obtained in Step 3 in an inert or reducing atmosphere and calcine and pyrolyze it to obtain a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst.

[0012] In step 1, the mass ratio of small-sized multilayer graphene to metal chloride is 1:10 to 50; the mass ratio of graphene intercalation product to melamine is 1:5 to 10; and the molar ratio of melamine, formaldehyde, and ferric sulfate is 1:1 to 2:1.

[0013] In step 1, the small-sized multilayer graphene is prepared by a method including the following steps:

[0014] Using 10% sulfuric acid as the electrolyte, artificial graphite powder was placed in a PP bag, with graphite plates as the positive and negative electrodes in a positive and negative array configuration. Sulfate ions were intercalated, and a DC voltage of +5V to -5V was applied between the cathode and anode. Electrolysis was carried out for 48 hours, with the electrodes being exchanged every 4 hours. The resulting graphene-sulfuric acid solution was ball-milled, washed until neutral, and then freeze-dried to obtain small-sized multilayer graphene.

[0015] In step 1, the metal chloride is selected from one or more of anhydrous aluminum chloride, anhydrous copper chloride, sodium chloride, cobalt chloride, nickel chloride, potassium chloride, copper chloride, and ferric chloride.

[0016] In step 1, the high-temperature treatment includes three stages: the first stage is from room temperature to T1, with a heating rate of 5℃ / min to 10℃ / min, and holding at T1 for 2 to 3 hours, with a temperature range of 180℃ to 200℃; the second stage is from T1 to T2, with a heating rate of 5℃ / min to 10℃ / min, with a temperature range of 300℃ to 360℃, and holding at T2 for 1 to 2 hours; the third stage is cooling to room temperature with the furnace, with inert gas protection throughout, including but not limited to argon or nitrogen, and a flow rate of 0.1 to 1 mL / min.

[0017] In step 1, the freeze drying includes two stages: the first stage is freezing at -30°C to -60°C for 3 to 6 hours; the second stage is maintaining a vacuum of 1-30 Pa for 24 to 36 hours.

[0018] In step 1, the high-temperature pyrolysis includes three stages: the first stage is from room temperature to T1, with a heating rate of 2℃ / min to 10℃ / min, and is maintained at T1 for 2 to 3 hours, with the temperature range of T1 being 180℃ to 300℃; the second stage is from T1 to T2, with a heating rate of 2℃ / min to 10℃ / min, with the temperature range of T2 being 800℃ to 1000℃, and is maintained at T2 for 0.5 to 2 hours; the third stage is cooled to room temperature with the furnace, under ammonia conditions throughout, with a flow rate of 0.1 to 1 mL / min.

[0019] In step 2, the mass ratio of the graphene-supported metal single-atom catalyst obtained in step 1 to the metal chloride is 1:10 to 50.

[0020] In step 2, the parameter settings for the high-temperature treatment are the same as those for the high-temperature treatment process in step 1.

[0021] In step 3, the molar ratio of the graphene reintercalation material, cobalt source, and nitrogen source obtained in step 2 is 1:1:4.

[0022] In step 3, the nitrogen source is graphite carbon nitride; the cobalt source is one of CoCl2·6H2O, Co(NO3)2·6H2O, or Co(CH3COO)2·4H2O.

[0023] Furthermore, the graphitic carbon nitride is obtained by calcining a graphitic carbon nitride precursor. Specifically, the graphitic carbon nitride precursor is calcined at 500–600°C for 2–6 hours to obtain graphitic carbon nitride, with a heating rate of 2–3°C / min. The graphitic carbon nitride precursor is selected from any one of urea, dicyandiamide, melamine, and guanidine hydrochloride.

[0024] In step 3, the grinding time is 2-6 hours, and the particle size of the powder after grinding is ≤60μm.

[0025] In step 4, the inert atmosphere or reducing atmosphere is N2, Ar, a mixture of N2 and H2, or a mixture of Ar and H2.

[0026] In step 4, the calcination temperature is 750–800℃; the holding time during calcination is 1.5–2 hours; and the heating rate during calcination is 3–8℃ / min.

[0027] The application of the nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst of the present invention is to use the nitrogen-doped carbon-supported iron-cobalt nanoparticles as the cathode material of the battery.

[0028] The present invention conducted electrochemical tests on the bifunctional catalytic material using a three-electrode system, and the results demonstrated that the bifunctional catalytic material of the present invention possesses excellent bifunctional catalytic activity. The bifunctional catalytic activity refers to oxygen reduction and oxygen evolution catalytic activity.

[0029] Furthermore, the bifunctional catalytic material can be used as a cathode bifunctional catalytic material in a flexible solid-state zinc-air battery, and the battery performance was tested. The results show that the flexible solid-state zinc-air battery has excellent battery performance.

[0030] Due to the various structural advantages of the bifunctional catalytic material prepared in this invention, it also exhibits highly efficient catalytic activity for oxygen reduction and oxygen evolution reactions. The half-wave potential for oxygen reduction and the overpotential for oxygen evolution are 0.88 V and 321 mV, respectively. When the bifunctional catalytic material prepared in this invention is applied to the cathode catalysis of an all-solid-state flexible zinc-air battery, the charge-discharge polarization curves and charge-discharge cycle life are superior to those of commercial 20% Pt / C catalysts.

[0031] Finally, the raw materials used in this invention are all readily available. Furthermore, the method of this invention has advantages such as simple operation, safety, and low cost. Attached Figure Description

[0032] Figure 1 SEM image of the nitrogen-doped carbon-supported iron-cobalt nanoparticles prepared in Example 1 as a bifunctional catalyst for oxygen reduction / oxygen evolution.

[0033] Figure 2 The oxygen reduction / oxygen evolution bifunctional catalyst TEM is prepared from nitrogen-doped carbon-supported iron-cobalt nanoparticles in Example 1.

[0034] Figure 3 The image shows the XRD pattern of the oxygen reduction / oxygen evolution bifunctional catalyst of Example 1, which is a single-atom catalyst, ferric chloride reintercalation, ball milling, and nitrogen-doped carbon-supported iron-cobalt nanoparticles.

[0035] Figure 4 LSV curves were used to test the oxygen reduction / oxygen evolution bifunctional catalyst and single-atom catalyst of nitrogen-doped carbon-supported iron-cobalt nanoparticles prepared in Example 1. The horizontal axis represents voltage in volts (V), and the vertical axis represents current density in mA / cm². 2 .

[0036] Figure 5 The LSV curves for testing the oxygen reduction / oxygen evolution bifunctional catalyst and the single-atom catalyst of nitrogen-doped carbon-supported iron-cobalt nanoparticles prepared in Example 1 are shown, where the horizontal axis represents voltage in volts (V) and the vertical axis represents current density in mA / cm². 2 .

[0037] Figure 6 The graphs show the charge-discharge polarization curves and power density curves of the bifunctional catalytic material catalyst prepared in Example 1 in an all-solid-state flexible zinc-air battery, where the horizontal axis represents the current density in mA / cm². 2 The left vertical axis represents voltage, in volts (V), and the right vertical axis represents power density, in mW / cm². 2 .

[0038] Figure 7 This indicates that the bifunctional catalytic material prepared in Example 1 performs well in an all-solid-state flexible zinc-air battery at a current density of 5 mA / cm². 2 Cyclic life test diagrams were performed under different bending conditions and at 3mA / cm. 2 Cyclic life test graph under current density, where the horizontal axis represents time in hours (h) and the vertical axis represents voltage in volts (V).

[0039] Figure 8LSV curves were used to test the oxygen reduction / oxygen evolution bifunctional catalyst and single-atom catalyst oxygen reduction catalytic activity of nitrogen-doped carbon-supported iron-cobalt nanoparticles prepared in Example 5. The horizontal axis represents voltage in volts (V), and the vertical axis represents current density in mA / cm². 2 .

[0040] Figure 9 The LSV curves for testing the oxygen reduction / oxygen evolution bifunctional catalyst and single-atom catalyst oxygen evolution catalytic activity of nitrogen-doped carbon-supported iron-cobalt nanoparticles prepared in Example 5 are shown, where the horizontal axis represents voltage in volts (V) and the vertical axis represents current density in mA / cm². 2 .

[0041] Figure 10 The results are shown in the test of the FeCo-NC catalyst prepared in Example 5 in an all-solid-state flexible ZAB. Detailed Implementation

[0042] The technical solution of the present invention will be further analyzed and described below through specific embodiments, but is not limited to the following embodiments.

[0043] Example 1:

[0044] Using 10% sulfuric acid as the electrolyte, artificial graphite powder was placed in a PP bag, with graphite plates as the positive and negative electrodes in a positive and negative array configuration. Sulfate ions were intercalated. A DC voltage of +5V to -5V was applied between the cathode and anode, and electrolysis was performed for 48 hours, with the electrodes being swapped every 4 hours. The resulting graphene-sulfuric acid solution was ball-milled, washed until neutral, and then freeze-dried to obtain small-sized multilayer graphene. Then, 0.5g of the dried small-sized multilayer graphene and 7.5g of anhydrous ferric chloride were mixed in a corundum crucible and placed in a tube furnace. The temperature was programmed, increasing to 180℃ at a rate of 5℃ / min and holding for 2 hours, then increasing to 360℃ at a rate of 5℃ / min and holding for 2 hours. After that, the temperature was cooled to room temperature with the furnace temperature, all under an argon atmosphere at a gas flow rate of 0.1mL / min. The resulting product is a precursor to a single-atom catalyst.

[0045] 0.02 mol melamine, 0.06 mol formaldehyde aqueous solution (37 wt%), and 15 mL ultrapure water were heated to 70 °C in a three-necked flask equipped with a condenser. The solution was observed to be clear and transparent. 0.02 mol ferric sulfate and 0.5 g of graphene intercalation product were added sequentially, stirred thoroughly, and then freeze-dried. A portion of the freeze-dried product was placed in a tube furnace and heated to 180 °C at a rate of 5 °C / min, held for 1 hour, then increased to 900 °C at a rate of 5 °C / min, held for 30 minutes, and then cooled to room temperature with the furnace temperature. The entire process was carried out under an argon atmosphere at a gas flow rate of 0.1 mL / min. The resulting pyrolysis product was stirred with 0.5 M H₂SO₄ at room temperature for 6 hours. The mixed solution was then poured into a vacuum filtration flask, and the solvent was removed using a 0.22 μm microporous membrane and water. The solid was dried in a vacuum drying oven at 0.085 MPa–0.1 MPa at a temperature of 60 °C for 6 hours. The dried product was heated to 180°C at a rate of 5°C / min under an ammonia atmosphere and held for 1 hour. Then, it was heated to 900°C at a rate of 5°C / min and held for 30 minutes. After cooling to room temperature with the furnace temperature, the resulting product was a graphene-supported single-atom iron catalyst.

[0046] The intercalation process was repeated to obtain the intercalated product. 0.1 g of the intercalated product, 0.4 g of graphitic carbon nitride, and 0.05 g of cobalt nitrate hexahydrate were then dry-ball-milled for 6 hours. The milled product was placed in a tube furnace and heated to 750°C at a rate of 5°C / min. After holding at this temperature for 30 minutes, the temperature was allowed to cool to room temperature with the furnace, all under an argon atmosphere at a flow rate of 0.1 mL / min. The temperature was then again increased to 750°C at a rate of 5°C / min in the tube furnace and held for 30 minutes, followed by cooling to room temperature with an ammonia atmosphere at a flow rate of 0.1 mL / min. This yielded a nitrogen-doped carbon-supported iron-cobalt nanoparticle-based oxygen reduction / oxygen evolution bifunctional catalyst.

[0047] Example 2:

[0048] First, a graphene-supported single-atom iron catalyst was prepared, and then the catalyst was intercalated to obtain the intercalated product. The steps were the same as in Example 1. 0.05 g of the intercalated product, 0.2 g of graphitic carbon nitride, 0.05 g of ferric nitrate nonahydrate, and 39 mg of anhydrous cobalt chloride were ball-milled for 6 h, yielding a mass of 279 mg after ball milling.

[0049] The ball-milled product was placed in a tube furnace and heated to 900°C at a rate of 5°C / min. After holding at this temperature for 30 minutes, it was cooled to room temperature along with the furnace temperature. The entire process was carried out under an argon atmosphere with a gas flow rate of 0.1 mL / min. This yielded a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst for oxygen reduction / oxygen evolution.

[0050] Example 3:

[0051] First, a graphene-supported single-atom iron catalyst was prepared, and then the catalyst was intercalated to obtain an intercalated product. The steps were the same as in Example 1. 0.1 g of the intercalated product, 0.4 g of graphitic carbon nitride, 0.1 g of ferric nitrate nonahydrate, and 20 mg of anhydrous cobalt chloride were ball-milled for 6 h, and the mass after ball-milling was 0.53 g.

[0052] The ball-milled product was placed in a tube furnace and heated to 900°C at a rate of 5°C / min. After holding at this temperature for 30 minutes, it was cooled to room temperature along with the furnace temperature. The entire process was carried out under an argon atmosphere with a gas flow rate of 0.1 mL / min. This yielded a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst for oxygen reduction / oxygen evolution.

[0053] Example 4:

[0054] First, a graphene-supported single-atom iron catalyst was prepared, and then the catalyst was intercalated to obtain the intercalated product. The steps were the same as in Example 1. 0.05 g of the intercalated product, 0.2 g of graphitic carbon nitride, and 33 mg of anhydrous cobalt chloride were ball-milled for 6 h, yielding a mass of 134 mg after ball milling.

[0055] The ball-milled product was placed in a tube furnace and heated to 750°C at a rate of 5°C / min. After holding at this temperature for 30 minutes, it was cooled to room temperature along with the furnace temperature. The entire process was carried out under an ammonia atmosphere with a gas flow rate of 0.1 mL / min. This yielded a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst for oxygen reduction / oxygen evolution.

[0056] Example 5:

[0057] First, a graphene-supported single-atom iron catalyst was prepared, and then the catalyst was intercalated to obtain the intercalated product. The steps were the same as in Example 1. 0.1 g of the intercalated product, 0.4 g of graphitic carbon nitride, and 0.1 g of ferric sulfate were ball-milled for 6 hours, yielding a mass of 0.52 g after ball milling. The ball-milled product was placed in a tube furnace, and the temperature was programmed to rise to 900 °C at a rate of 5 °C / min. After holding at this temperature for 30 minutes, it was cooled to room temperature with the furnace temperature. The entire process was carried out under an argon atmosphere with a gas flow rate of 0.1 mL / min.

[0058] 60 mg of the treated product and 15 mg of cobalt nitrate hexahydrate were ultrasonically dispersed in 20 ml of ultrapure water. The product was then freeze-dried and placed in a tube furnace. The temperature was programmed to rise to 750 °C at a rate of 5 °C / min, held at that temperature for 15 minutes, and then cooled to room temperature with the furnace temperature. The entire process was carried out under an ammonia atmosphere with a gas flow rate of 0.1 mL / min. This yielded a nitrogen-doped carbon-supported iron-cobalt nanoparticle-based oxygen reduction / oxygen evolution bifunctional catalyst.

[0059] Example 6: Electrochemical Testing of a Three-Electrode System

[0060] The oxygen reduction / oxygen evolution bifunctional catalytic material prepared by nitrogen-doped carbon-supported iron-cobalt nanoparticles in Example 1 was subjected to three-electrode electrochemical tests to test its oxygen reduction catalytic activity and oxygen evolution catalytic activity.

[0061] The oxygen reduction reaction test conditions were as follows: oxygen-saturated 0.1M KOH solution as the electrolyte, Ag / AgCl electrode as the reference electrode, platinum wire as the counter electrode, and glassy carbon electrode as the working electrode. The loading of the catalyst material on the glassy carbon during the test was 500 μg / cm³. 2 The rotating disk electrode rotates at 1600 rpm.

[0062] The oxygen evolution reaction test conditions were as follows: oxygen-saturated 1M KOH solution as the electrolyte, Hg / HgO electrode as the reference electrode, platinum wire as the counter electrode, and glassy carbon electrode as the working electrode. The loading of the catalyst material on the glassy carbon during the test was 500 μg / cm³. 2 The rotating disk electrode rotates at 1600 rpm.

[0063] The LSV curve for oxygen reduction catalytic activity testing is shown in the figure. Figure 4 As shown, according to Figure 4 It can be seen that the oxygen reduction reaction half-wave potential of the bifunctional catalytic material of the present invention is 0.88V, while the oxygen reduction reaction half-wave potential of the commercial 20% Pt / C catalyst is 0.84V.

[0064] The LSV curve for oxygen evolution catalytic activity testing is shown below. Figure 5 As shown, according to Figure 5 It can be seen that the bifunctional catalytic material of the present invention operates at a current density of 10 mA / cm². 2 The overpotential at this point is 321 mV, while that of a commercial 20% Pt / C catalyst at a current density of 10 mA / cm² is much higher. 2 The overpotential at that point is 400mV.

[0065] Figure 8 , Figure 9 The results are for the FeCo-NC catalyst prepared in Example 5. The half-wave potential for oxygen reduction and the overpotential for oxygen evolution of the catalyst prepared in Example 5 are 0.88 V and 347 mV, respectively.

[0066] Example 7: Performance Testing of All-Solid-State Flexible Zinc-Air Battery

[0067] The prepared FeCo-NC catalyst was tested in an all-solid-state flexible ZAB. The catalyst was coated on carbon cloth as an air cathode, and zinc foil was assembled as the anode. Unlike liquid ZABs, the all-solid-state flexible ZAB uses gel-based alkaline polyvinyl alcohol (PVA) as the electrolyte. Figure 6 As shown. The maximum power density of the FeCo-NC catalyst cathode is 105 mW / cm².-2 At 3mAcm -2 At a current density of 5.0 mA cm⁻¹, the all-solid-state flexible ZAB can be charged and discharged for 60 hours without significant degradation. Using an FeCo-NC air cathode at a current density of 5.0 mA cm⁻¹... -2 Cyclic stability performance tests were conducted under different bending conditions, and a stable charge-discharge process was achieved under any bending condition, such as... Figure 7 As shown.

[0068] Figure 10 Discharge polarization curves and corresponding power density plots were plotted. The peak power density of the all-solid-state air battery based on the FeCo-NC catalyst prepared in Example 5 was 70 mW cm⁻¹. -2 At a current density of 5 mA cm⁻², the all-solid-state flexible ZAB can be charged and discharged for about 25 hours without significant changes.

Claims

1. A method for preparing a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst, characterized in that... Includes the following steps: Step 1: Mix small-sized multilayer graphene with metal chloride and treat at high temperature to obtain a metal-rich graphene intercalation; then heat and mix the obtained graphene intercalation with ferric sulfate, melamine, and formaldehyde aqueous solution to form a graphene-iron salt-hydrogel, which is then freeze-dried and pyrolyzed at high temperature to obtain a graphene-supported metal single-atom catalyst. Step 2: Mix the graphene-supported metal single-atom catalyst obtained in Step 1 with a metal chloride and treat it at high temperature to obtain the graphene reintercalation product. Step 3: The graphene reintercalation material obtained in Step 2, along with nitrogen and cobalt sources, is ball-milled to obtain the precursor; Step 4: Place the precursor obtained in Step 3 in an inert or reducing atmosphere and calcine and pyrolyze it to obtain a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of small-sized multilayer graphene to metal chloride is 1:10~50; the mass ratio of graphene intercalation product to melamine is 1:5~10; and the molar ratio of melamine, formaldehyde and ferric sulfate is 1:1~2:

1.

3. The preparation method according to claim 1, characterized in that: In step 1, the metal chloride is selected from one or more of anhydrous aluminum chloride, sodium chloride, cobalt chloride, nickel chloride, potassium chloride, copper chloride, and ferric chloride.

4. The preparation method according to claim 1, characterized in that: In steps 1 and 2, the high-temperature treatment includes three stages: the first stage is from room temperature to T1, with a heating rate of 5℃ / min to 10℃ / min, and holding at T1 for 2 to 3 hours, with a temperature range of 180℃ to 200℃; the second stage is from T1 to T2, with a heating rate of 5℃ / min to 10℃ / min, with a temperature range of 300℃ to 360℃, and holding at T2 for 1 to 2 hours; the third stage is cooling to room temperature in the furnace; the entire process is protected by inert gas, with a flow rate of 0.1 to 1 mL / min.

5. The preparation method according to claim 1, characterized in that: In step 2, the mass ratio of the graphene-supported metal single-atom catalyst obtained in step 1 to the metal chloride is 1:10 to 50.

6. The preparation method according to claim 1, characterized in that: In step 3, the molar ratio of the graphene reintercalation material, cobalt source, and nitrogen source obtained in step 2 is 1:1:

4.

7. The preparation method according to claim 1, characterized in that: In step 3, the nitrogen source is graphite carbon nitride; the cobalt source is one of CoCl2·6H2O, Co(NO3)2·6H2O, or Co(CH3COO)2·4H2O.

8. The preparation method according to claim 7, characterized in that: The graphite carbon nitride is obtained by calcining a graphite carbon nitride precursor. Specifically, the graphite carbon nitride precursor is calcined at 500~600℃ for 2~6h to obtain graphite carbon nitride, with a heating rate of 2~3℃ / min. The graphite carbon nitride precursor is selected from any one of urea, dicyandiamide, melamine, and guanidine hydrochloride.

9. The application of a nitrogen-doped carbon-supported iron-cobalt nanoparticle bifunctional catalyst prepared by any one of the preparation methods of claims 1-8, characterized in that: The nitrogen-doped carbon-supported iron-cobalt nanoparticles were used as the cathode material for the battery.

10. The application according to claim 9, characterized in that: The nitrogen-doped carbon-supported iron-cobalt nanoparticles are used as a cathode bifunctional catalytic material in flexible solid-state zinc-air batteries.

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