Supported nitrogen and phosphorus co-doped iron single-atom bifunctional electrocatalysts and applications thereof

Abstract

The application relates to a supported nitrogen-phosphorus co-doped iron monatomic bifunctional electrocatalyst and application thereof, wherein the supported nitrogen-phosphorus co-doped iron monatomic bifunctional electrocatalyst is Fe1 / NCP catalyst, the Fe1 / NCP catalyst is obtained by taking ZIF-8 as a precursor, introducing an iron source, coating with a polymer, and then pyrolyzing and phosphorizing to anchor Fe monatomic atoms in N and P co-doped porous carbon, and P is introduced into a second shell of an active center Fe site. The supported nitrogen-phosphorus co-doped iron monatomic bifunctional electrocatalyst has a half-wave potential of 0.91-0.97 V under the condition of 0.1 M KOH, has OER activity in 0.1 M KOH, and has an overpotential of 330-390 mV. The nitrogen-phosphorus co-doped iron monatomic bifunctional electrocatalyst shows excellent electrocatalytic activity under alkaline conditions, and has higher ORR and OER activity, stability and methanol poisoning resistance than commercial Pt / C and RuO2.

Description

Technical Field

[0001] This invention relates to the fields of energy materials and electrocatalysis technology, specifically to supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalysts and their applications. Background Technology

[0002] To address the fossil fuel crisis and environmental pollution, researchers have begun exploring sustainable and efficient new clean energy sources, with fuel cells and metal-air batteries being the most widely studied. However, the slow oxygen reduction reaction kinetics at the cathode severely limit their electrocatalytic performance. Currently, Pt / C catalysts are widely used in the oxygen reduction reaction (ORR), but their high cost and poor stability hinder their widespread application. Water electrolysis is an efficient route for producing green hydrogen and an effective means of producing, storing, and using renewable energy. The design and synthesis of efficient oxygen evolution reaction (OER) catalysts are crucial for improving the efficiency of hydrogen production through water electrolysis. Currently, the most effective OER catalysts are oxides of precious metals such as iridium and ruthenium (IrO2 and RuO2, etc.), but their scarcity and high price severely restrict their application. Therefore, the development of novel, efficient, stable, and readily available electrocatalyst systems is urgently needed.

[0003] Currently, most catalyst systems simply load metal particles onto nitrogen-doped carbon supports, without effectively controlling and optimizing their electronic structure, which significantly limits the improvement of their catalytic activity. Nitrogen-doped carbon materials containing iron single atoms are representative catalysts for oxygen reduction reactions. However, existing techniques for preparing single-atom catalysts are demanding and complex, and the catalysts are prone to aggregation during long-term use, leading to activity decay. Doping with metal and non-metal elements, and controlling the catalyst morphology and size, can effectively improve catalyst activity. For example, introducing heteroatoms and foreign metals into carbon materials can effectively control the electronic structure and physicochemical properties of the carbon materials, improving the chemical stability, regulating the band gap, and enhancing the conductivity. Nitrogen-doped carbon materials possess a unique structure that is more advantageous than traditional catalysts. On the one hand, the introduction of nitrogen components can effectively control the acid-base properties and wettability of the catalyst, improving its activation ability for intermediate product molecules. On the other hand, utilizing the interaction between nitrogen species and metal components can effectively improve the dispersion and stability of metal active sites. Phosphorus-doped carbon has attracted much attention as an anode material. Compared with boron and sulfur doping, phosphorus doping often exhibits moderate adsorption capacity for active intermediates. However, constructing catalyst systems with special coordination structures is quite challenging. Therefore, accurately and cleverly doping within specific shells of metal single atoms is a challenge. Based on this, to improve the electrocatalytic activity and enhance the chemical stability of catalysts, it is urgent to develop a low-cost, high-performance, and long-life method for preparing nitrogen- and phosphorus co-doped non-noble metal porous carbon electrocatalysts, which could enable the widespread application of metal-air batteries. Summary of the Invention

[0004] One objective of this invention is to provide a supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst, which addresses the problems of traditional homogeneous palladium catalysts being difficult to separate and recover, suffering severe palladium loss, and easily generating palladium black contamination products. A second objective of this invention is to provide applications of this supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: This supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst is an Fe1 / NCP catalyst. It uses ZIF-8 as a precursor, introduces an iron source, coats it with a polymer, and then anchors Fe single atoms in N and P co-doped porous carbon through pyrolysis and phosphating. Specifically, P is introduced into the second shell of the active Fe site, as detailed below: Step 1: Disperse ZIF-8 in an ethanol solution containing metallic iron salts, and evaporate it to dryness using a rotary evaporator to obtain a solid powder; Step 2: Disperse dopamine hydrochloride and hexadecyltrimethylammonium bromide in deionized water, adjust the pH to 8-10 with ammonia water to form a mixed solution. The mass ratio of dopamine hydrochloride to hexadecyltrimethylammonium bromide is 1:1, and the concentrations of dopamine hydrochloride and hexadecyltrimethylammonium bromide are both 0.4-0.8 mg / mL. Step 3: Add the solid powder obtained in Step 1 to the mixture obtained in Step 2, disperse it by ultrasonication, stir it magnetically for 12-36 hours, and then centrifuge to obtain a solid precipitate. Step 4: Wash the solid precipitate 3-6 times with deionized water and then vacuum dry it; Step 5: Obtain Fe1 / NC by programmed temperature rise method: Calcine the solid dried in Step 4 at a temperature of 900-1200 °C for 1-4 hours, with a heating rate of 3-10 °C / min. The inert gas used during calcination is 99.9% Ar or N2, to obtain black solid powder Fe1 / NC. Step 6: Place Fe1 / NC powder in a ceramic boat and position it at the lower tuyer of a tube furnace. Place sodium hypophosphite in another ceramic boat and position it at the upper tuyer of a tube furnace. Both boats are opened opposite each other and calcined in the same tube furnace. The mass ratio of Fe1 / NC to sodium hypophosphite is 1:3 to 1:10. The calcination temperature is 300 to 500 °C, the calcination time is 1 to 4 hours, and the heating rate during calcination is 3 to 10 °C / min. The inert gas used during calcination is 99.9% Ar or N2. This yields the Fe1 / NCP catalyst. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst has a half-wave potential of 0.91 to 0.97 V under 0.1 M KOH conditions, exhibits OER activity in 0.1 M KOH, and has an overpotential of 330 to 390 mV.

[0006] The preparation method of ZIF-8 in the above scheme includes the following steps: Step (1): Dissolve zinc nitrate hexahydrate in a solvent to obtain solution A; disperse 2-methylimidazole in a solvent to obtain solution B. The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:4 to 1:8. The solvent is one of methanol solution, ethanol solution, or deionized water. Step (2): Under ultrasonic conditions, add solution B to solution A, let stand for 12-24 hours, centrifuge to obtain solid precipitate, wash several times with solvent, vacuum dry into solid powder, and grind it to obtain ZIF-8.

[0007] In the above scheme, the molar concentration of 2-methylimidazole in step (1) is 0.1-0.4 mol / L; the volume ratio of solvent A to solution B is 1:1.

[0008] In step (2) of the above scheme, the vacuum drying temperature is 60-90 ℃ and the drying time is 12-72 hours.

[0009] In step one of the above scheme, the iron salt is one of ferric acetylacetone, ferric acetate, ferric chloride, or ferric nitrate.

[0010] In step one of the above scheme, the metal content of iron salt loaded on ZIF-8 is 0.4 wt% to 1.2 wt%; the concentration of ZIF-8 dispersion is 4 mg / mL to 10 mg / mL; and the rotary evaporation temperature is 40 to 80 ℃.

[0011] In step five of the above scheme, the calcination temperature is 900-1000 ℃, the heating rate is preferably 3-6 ℃ / min, and the calcination time is 2-4 hours; in step six, the calcination temperature is 300-400 ℃, the heating rate is preferably 3-6 ℃ / min, and the calcination time is preferably 1-3 hours.

[0012] In step two of the above scheme, the pH is adjusted to 9 with ammonia water; in step three, a magnetic stirrer is used for stirring for 24 hours; in step five, the heating rate is 3 ℃ / min and the calcination time is 3 hours; in step six, the heating rate is 3 ℃ / min and the calcination time is 2 hours.

[0013] The aforementioned supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalysts were used to assemble zinc-air batteries, achieving peak power densities as high as 180–250 mW / cm². -2 .

[0014] The above-described supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst is used for ORR and OER reactions. Beneficial effects

[0015] 1. The method of this invention uniformly anchors iron single atoms into porous carbon materials co-doped with nitrogen and phosphorus. Phosphating treatment can increase the specific surface area of ​​the catalyst, generate abundant mesopores, and introduce P into the second coordination layer at the Fe sites, resulting in a highly efficient bifunctional electrocatalyst with a special electronic structure.

[0016] 2. The nitrogen- and phosphorus-co-doped iron single-atom catalyst described in this invention, through a unique coordination environment (P in the second shell), regulates the electronic structure and properties of the active sites, exhibiting excellent electrocatalytic activity under alkaline conditions. It possesses higher ORR and OER activity, stability, and resistance to methanol poisoning than commercial Pt / C and RuO2. When the Fe single-atom catalyst described in this invention is used in zinc-air battery testing, it demonstrates high energy density and ultra-long cycle life, solving the common problems of poor round-trip efficiency and short cycle life in zinc-air batteries, thus enabling the widespread application of zinc-air batteries.

[0017] 3. The single-atom catalyst preparation method described in this invention is simple and effective, with abundant and readily available raw materials. Moreover, its electrocatalytic performance under alkaline conditions is far superior to that of commercial Pt / C and RuO2. This synthesis method can be applied to the development of related materials in other electrocatalytic fields.

[0018] 4. This invention precisely and ingeniously utilizes heteroatoms (phosphorus) to dope the second shell of iron single atoms to prepare a highly active, long-lived, and low-cost single-atom catalyst system. The synthesis method is simple to operate, economical and readily available, and provides a bifunctional electrocatalyst for efficient ORR and OER.

[0019] 5. This invention provides a nitrogen- and phosphorus-doped porous carbon support anchoring iron single atoms to improve the intrinsic activity and stability of the catalyst. Introducing phosphorus atoms into the second coordination layer successfully enhances its ORR and OER activities in alkaline electrolytes. When assembled into a zinc-air battery, it exhibits high energy density and excellent operational stability.

[0020] 6. This invention uses anisotropically grown zeolite-like imidazole ester framework material (ZIF-8) at room temperature as a precursor. After introducing an iron source, it is coated with a polymer, and then Fe single atoms are anchored in N and P co-doped porous carbon through pyrolysis and phosphating. Experimental and theoretical calculations show that P is successfully introduced into the second shell of the Fe site at the active center, causing changes in the local electronic structure and properties of the Fe site, improving the adsorption strength of the oxygen intermediate, reducing the reaction energy barrier, and enhancing the electrocatalytic activity. In addition, the catalyst has a large specific surface area and abundant mesoporous structure, which is beneficial to mass transfer and electron transport in the electrocatalytic process.

[0021] 7. This invention exhibits excellent ORR activity under alkaline conditions, with a half-wave potential of 0.91–0.97 V in 0.1 M KOH, and demonstrates excellent stability and resistance to methanol poisoning. Furthermore, this catalyst possesses OER activity in 0.1 M KOH, with an overpotential of only 330–390 mV. In zinc-air battery performance tests, the peak power density reaches as high as 180–250 mW / cm². -2 It has good operational stability. Attached Figure Description

[0022] Figure 1 The XRD pattern of the catalyst prepared according to Example 1 of the present invention; Figure 2 The SEM image of the catalyst prepared according to Example 1 of the present invention; Figure 3 The X-ray near-edge absorption structure spectrum of the catalyst prepared according to Example 1 of the present invention; Figure 4ORR linear sweep voltammetric curves of the catalyst prepared according to Example 1 of the present invention and the control sample in 0.1 M KOH.

[0023] Figure 5 The OER linear sweep voltammetry curves of the catalyst prepared according to Example 1 of the present invention and the control sample in 0.1 M KOH.

[0024] Figure 6 Discharge polarization curves and power density curves of the catalyst prepared according to Example 1 of the present invention and commercial Pt / C+RuO2 as the positive electrode material of zinc-air batteries. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings: Example

[0026] This supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst is an Fe1 / NCP catalyst. It anchors Fe single atoms within N and P co-doped porous carbon by introducing ZIF-8 as a precursor, followed by polymer coating, pyrolysis, and phosphating. Specifically, P is introduced into the second shell of the active Fe sites, as detailed below: 1. Dissolve 1.29 g of zinc nitrate hexahydrate in 100 mL of methanol solution to obtain solution A; disperse 1.62 g of 2-methylimidazole in 100 mL of methanol solution to obtain solution B. Sonicate until uniformly dispersed.

[0027] 2. Add solution B to solution A under ultrasonic conditions, mix the two solutions obtained in step one, and let them stand for 24 hours.

[0028] 3. Centrifuge the sample obtained in step 2 above to obtain a solid precipitate, wash it three times with methanol solution, dry it in a vacuum drying oven at 80 ℃ for 12 hours, and grind it to obtain solid powder ZIF-8.

[0029] 4. Take 100 mg of the sample obtained in step 3 above, disperse it in 15 mL of ethanol solution containing 100 uL of 10 mg / mL iron acetylacetone, and dry it by rotary evaporation at 60 °C to obtain a solid powder.

[0030] 5. Disperse 15 mg of dopamine hydrochloride and 15 mg of cetyltrimethylammonium bromide in 30 mL of deionized water, and adjust the pH to 9 with ammonia.

[0031] 6. Add the solid powder obtained in step 4 to the mixture obtained in step 5 above, disperse it by ultrasonication, and stir it magnetically for 24 hours.

[0032] 7. Centrifuge the sample obtained in step 6 to obtain a solid precipitate, wash it three times with deionized water, and dry it in a vacuum drying oven at 80°C for 12 hours to obtain a solid powder.

[0033] 8. The above solid powder was calcined using a programmed temperature rise method. The calcination temperature was 950 ℃, the calcination time was 2 hours, the heating rate was 3 ℃ / min, and the inert gas used during calcination was 99.9% argon. The resulting black solid powder was named Fe1 / NC.

[0034] 9. Take 10 mg of the Fe1 / NC obtained in step 8 and place it in one porcelain boat, and take 80 mg of sodium hypophosphite and place it in another porcelain boat. Place the two porcelain boats with opposite openings in the same tube furnace for calcination at 350 ℃ for 2 hours. The heating rate during calcination is 3 ℃ / min. The inert gas used during calcination is 99.9% argon. This yields the Fe1 / NCP catalyst. Sodium hypophosphite is reduced at high temperature in an inert atmosphere to generate low-valence P, and the material is etched to create abundant pores, improving the catalyst porosity and specific surface area, and achieving effective doping of P atoms in specific regions.

[0035] The catalysts obtained in the above examples were subjected to a series of structural characterizations to obtain their coordination structures.

[0036] like Figure 1 The figure shows the XRD pattern of the catalyst in Example 1. The horizontal axis represents the diffraction angle and the vertical axis represents the diffraction peak intensity. The figure shows two carbon diffraction peaks at approximately 26.0° and 44.0°, with no metal characteristic diffraction peaks appearing.

[0037] like Figure 2 The image shown is an SEM image of the catalyst of Example 1, which shows that the catalyst obtained in Example 1 is dodecahedral and has a distinct porous structure.

[0038] like Figure 3 The image shows the Fe K-edge XANES pattern of the catalyst in Example 1, revealing the valence state of individual Fe atoms. Through extended X-ray absorption fine structure fitting, a coordination structure with FeN4 as the first shell was obtained, and P was successfully introduced into the second shell, forming a special Fe-NC-P coordination structure. Example

[0039] The only difference between this embodiment and Embodiment 1 is that in this embodiment, the amount of 2-methylimidazole added in step one is 2.63 g. Example

[0040] The only difference between this embodiment and Embodiment 1 is that in this embodiment, 150 mL of methanol solution is added in step one. Example

[0041] The only difference between this embodiment and Embodiment 1 is that in this embodiment, the solvent added in step one is deionized water. Example

[0042] The only difference between this embodiment and Embodiment 1 is that in this embodiment, the salt solution added in step four is ferric nitrate. Example

[0043] The difference between this embodiment and Embodiment 1 is that in this embodiment, step four involves constant-temperature rotary evaporation and drying at 80°C to form a solid powder. Example

[0044] The only difference between this embodiment and Embodiment 1 is that in this embodiment, the mass of dopamine hydrochloride and hexadecyltrimethylammonium bromide added in step five is 20 mg. Example

[0045] The only difference between this embodiment and Embodiment 1 is that in this embodiment, the pH of the solution is adjusted to 8.5 in step five, and the salt solution added in step four is ferric chloride. Example

[0046] The only difference between this embodiment and Embodiment 1 is that in this embodiment, carbonization is carried out in a tube furnace at 950 °C for 3 hours in step eight, with a heating rate of 5 °C / min.

[0047] Example 10: The only difference between this embodiment and Embodiment 1 is that in this embodiment, carbonization is carried out in a tube furnace at 350 °C for 2 h in step nine, with a heating rate of 5 °C / min.

[0048] Comparative Example 1: The only difference between this comparative example and Example 1 is that in this comparative example, the sample is obtained after calcination in step eight. No further processing is performed, and step nine is omitted.

[0049] Comparative Example 2: The difference between this embodiment and Embodiment 1 is that, in this comparative example, acetylacetone iron is not added in step four, and no further processing is performed after calcination in step eight.

[0050] Comparative Example 3: In this example, 5 mg of commercial Pt / C (Pt mass fraction of 20 wt%) catalyst was ultrasonically dispersed for 30 min to obtain a solution.

[0051] Comparative Example 4: In this example, 5 mg of commercial RuO2 (Ru mass fraction of 20 wt%) catalyst was ultrasonically dispersed for 30 min to obtain a solution.

[0052] To evaluate the performance of the nitrogen- and phosphorus-co-doped Fe single-atom catalysts prepared in the embodiments of the present invention, this application also provides electrochemical performance test information of the catalysts in Preparation Example 1 and the comparative example.

[0053] Preparation of catalyst ink: Weigh 5 mg of catalyst and place it in a 1.5 mL centrifuge tube, add 960 uL of isopropanol solution and 40 uL of 5 wt% Nafion solution, and sonicate for one hour to obtain the solution.

[0054] Electrochemical ORR performance testing: The test was conducted in a three-electrode system. 8 μL of catalyst was drop-coated onto the surface of a rotating disk electrode and allowed to air dry to serve as the working electrode. A platinum wire was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The electrolyte was 0.1 M potassium hydroxide solution. Linear sweep voltammetry was performed on a Shanghai Chenhua CHI760E electrochemical workstation connected to a PINE rotating disk instrument (USA). The scan rate was 10 mV / s, and the electrode rotation speed was 1600 r.

[0055] The electrochemical testing environment is as follows: room temperature and one atmosphere of pressure. Before the test, high-purity oxygen is introduced into the electrolyte for 30 minutes to saturate the electrolyte with oxygen.

[0056] like Figure 4 The catalyst prepared in Example 1 and other comparative samples were subjected to electrocatalytic ORR tests in 0.1 M KOH. The catalyst prepared in Example 1 showed an oxygen reduction onset potential of 1.10 V and a half-wave potential of 0.95 V, indicating that it has superior ORR activity compared to Pt / C. Furthermore, its cycling performance is also better than Pt / C, demonstrating excellent stability.

[0057] like Figure 5 The OER activity of the catalyst prepared in Example 1 and other comparative catalysts was evaluated in 0.1 M KOH electrolyte. The results show that the catalyst prepared in Example 1 has an overpotential of 370 mV, which is slightly better than that of the commercial RuO2 catalyst (378 mV), indicating that it has excellent OER activity.

[0058] The catalyst was used in a zinc-air battery with Zn as the negative electrode and Preparation Example 1 as the positive electrode. The electrolyte was a solution of 6 mol / L KOH and 0.2 mol / L zinc acetate.

[0059] like Figure 6 The figures show the depolarization and power density curves of the catalyst in Example 1, Comparative Example 1, and commercial Pt / C+RuO2. As can be seen from the figures, the power density of the prepared catalyst is significantly better than that of commercial Pt / C.

[0060] This invention precisely and ingeniously introduces heteroatoms of phosphorus into the second shell of iron single atoms, thereby influencing the adsorption strength of oxygen-containing intermediates and improving catalytic reaction activity by regulating the electronic structure and properties of the iron atom sites. This synthetic method is used to prepare highly active, long-lived, and low-cost single-atom catalyst systems, and is simple to operate and readily available.

[0061] The nitrogen- and phosphorus co-doped iron single-atom catalyst prepared in this invention exhibits superior ORR performance and OER performance compared to commercial Pt / C catalysts in alkaline electrolytes. When used in zinc-air batteries, the catalyst demonstrates peak power density exceeding that of most non-noble metal catalysts and exhibits excellent charge-discharge cycle stability at a charge-discharge current of 10 mA cm⁻¹. -2 Under these conditions, the performance remained stable after 700 charge-discharge cycles (350 hours) with no significant degradation.

Claims

1. A supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst, characterized in that: This supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst is an Fe1 / NCP catalyst. It uses ZIF-8 as a precursor, introduces an iron source, coats it with a polymer, and then anchors Fe single atoms in N and P co-doped porous carbon through pyrolysis and phosphating. Specifically, P is introduced into the second shell of the active Fe site, as detailed below: Step 1: Disperse ZIF-8 in an ethanol solution containing metallic iron salts, and evaporate it to dryness using a rotary evaporator to obtain a solid powder; Step 2: Disperse dopamine hydrochloride and hexadecyltrimethylammonium bromide in deionized water, adjust the pH to 8-10 with ammonia water to form a mixed solution. The mass ratio of dopamine hydrochloride to hexadecyltrimethylammonium bromide is 1:1, and the concentrations of dopamine hydrochloride and hexadecyltrimethylammonium bromide are both 0.4-0.8 mg / mL. Step 3: Add the solid powder obtained in Step 1 to the mixture obtained in Step 2, disperse it by ultrasonication, stir it magnetically for 12-36 hours, and then centrifuge to obtain a solid precipitate. Step 4: Wash the solid precipitate 3-6 times with deionized water and then vacuum dry it; Step 5: Obtain Fe1 / NC by programmed temperature rise method: Calcine the solid dried in Step 4 at a temperature of 900-1200℃ for 1-4 hours, with a heating rate of 3-10℃ / min. The gas used during calcination is 99.9% Ar or N2, to obtain black solid powder Fe1 / NC. Step 6: Place Fe1 / NC powder in a ceramic boat and position it at the lower tuyer of a tube furnace. Place sodium hypophosphite in another ceramic boat and position it at the upper tuyer of a tube furnace. Both boats are opened opposite each other and calcined in the same tube furnace. The mass ratio of Fe1 / NC to sodium hypophosphite is 1:3 to 1:

10. The calcination temperature is 300 to 500 °C, the calcination time is 1 to 4 hours, and the heating rate during calcination is 3 to 10 °C / min. The gas used during calcination is 99.9% Ar or N2. This yields the Fe1 / NCP catalyst. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst has a half-wave potential of 0.91 to 0.97 V under 0.1 M KOH conditions, exhibits OER activity in 0.1 M KOH, and has an overpotential of 330 to 390 mV.

2. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst according to claim 1, characterized in that: The preparation method of ZIF-8 includes the following steps: Step (1): Dissolve zinc nitrate hexahydrate in a solvent to obtain solution A; disperse 2-methylimidazole in a solvent to obtain solution B. The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:4 to 1:

8. The solvent is one of methanol solution, ethanol solution, or deionized water. Step (2): Under ultrasonic conditions, add solution B to solution A, let stand for 12-24 hours, centrifuge to obtain solid precipitate, wash several times with solvent, vacuum dry into solid powder, and grind it to obtain ZIF-8.

3. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst according to claim 2, characterized in that: In step (1), the molar concentration of 2-methylimidazole is 0.1–0.4 mol / L; the volume ratio of solvent A to solution B is 1:

1.

4. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst according to claim 3, characterized in that: In step (2), the vacuum drying temperature is 60-90 °C and the drying time is 12-72 hours.

5. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst according to claim 4, characterized in that: In step one, the iron salt is one of ferric acetylacetone, ferric acetate, ferric chloride, or ferric nitrate.

6. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst according to claim 5, characterized in that: In step one, the metal content of the iron salt loaded on ZIF-8 is 0.4 wt% to 1.2 wt%; the concentration of the ZIF-8 dispersion is 4 mg / mL to 10 mg / mL; and the rotary evaporation temperature is 40 to 80 °C.

7. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst according to claim 6, characterized in that: In step five, the calcination temperature is 900–1000 °C, the heating rate is 3–6 °C / min, and the calcination time is 2–4 hours; in step six, the calcination temperature is 300–400 °C, the heating rate is 3–6 °C / min, and the calcination time is 1–3 hours.

8. The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst according to claim 7, characterized in that: In step two, the pH is adjusted to 9 with ammonia water; in step three, a magnetic stirrer is used for stirring for 24 hours; in step five, the heating rate is 3 ℃ / min and the calcination time is 3 hours; in step six, the heating rate is 3 ℃ / min and the calcination time is 2 hours.

9. The application of any one of the supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalysts according to claims 1 to 8, characterized in that: The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst is used to assemble zinc-air batteries, achieving peak power densities as high as 180–250 mW / cm². -2 .

10. The application of any one of the supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalysts according to claims 1 to 8, characterized in that: The supported nitrogen-phosphorus co-doped iron single-atom bifunctional electrocatalyst is used for ORR and OER reactions.

Images