Nitrogen and phosphorus co-doped carbon confinement Fe2P / FeNi / NPC nanoparticle and preparation method and application thereof

Abstract

The invention provides a nitrogen and phosphorus co-doped carbon confinement Fe2P / FeNi / NPC nano-particle as well as a preparation method and an application of the nitrogen and phosphorus co-doped carbon confinement Fe2P / FeNi / NPC nano-particle. A carbon skeleton of the nitrogen and phosphorus co-doped carbon confinement Fe2P / FeNi / NPC nano-particle is in a leaf shape, the nitrogen and phosphorus co-doped carbon confinement Fe2P / FeNi / NPC nano-particle is a bimetallic heterojunction Fe2P / FeNi nano-particle composite material in three-dimensional leaf-shaped nano-carbon interconnected with nitrogen and phosphorus co-doped carbon nano-tubes, and bimetallic heterojunction Fe2P / FeNi nano-particles are uniformly distributed on the carbon skeleton and are packaged in CNTs; according to the corresponding preparation method, a porous organic polymer ZIF-8 is used as a precursor, and an in-situ alloying and phosphating strategy is adopted, so that the leaf-shaped nanocarbon composite material (Fe2P / FeNi / NPC) interconnected with the carbon nanotubes (CNTs) for packaging Fe2P / FeNi heterostructure nanoparticles is successfully prepared. The catalyst has high-density bimetallic active sites, a rich pore structure and excellent electrochemical performance, and shows excellent oxygen reduction (ORR) and oxygen evolution (OER) catalytic performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and particularly relates to a non-noble metal catalyst prepared by an in-situ alloying and phosphating method for encapsulating heterogeneous structure Fe2P / FeNi nanoparticles encapsulated in leaf-shaped nanocarbon encapsulated by nitrogen and phosphorus co-doped carbon nanotubes (CNTs) and its application. Background Art

[0002] Due to its high energy density, environmental friendliness and abundant zinc resources, the zinc-air battery has become an important candidate for the next-generation energy storage device. However, the performance of the zinc-air battery is critically limited by the catalytic efficiency of the electrocatalyst in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Currently, most commercial catalysts use noble metal materials (such as Pt / C and RuO2 catalysts). Although their catalytic performance is excellent, they are expensive, resource-limited and have poor stability, which restricts the large-scale commercial promotion of zinc-air batteries. In addition, although the existing non-noble metal catalysts have low cost, they have obvious deficiencies in catalytic activity and cycle stability and are difficult to meet the requirements of long-life batteries. Therefore, it is particularly important to develop a highly efficient, low-cost and highly durable bifunctional non-noble metal catalyst.

[0003] In recent years, due to the adjustable composition, structure, unique physical and chemical properties and multifunctional active sites of transition metal phosphides (TMPs), their ability to trigger oxygen electrochemical reactions has been systematically studied. Since the electrocatalytic process mainly occurs on the surface or near the surface of the material, strategies such as element doping, surface and interface modulation, crystal plane engineering, phase modulation and structure engineering have been adopted to optimize the electrocatalytic activity of TMPs, thereby reducing the electrochemical overpotential of oxygen.

[0004] Introducing doping elements into transition metal phosphides can change the electronic structure of the original catalyst, thereby improving its catalytic performance. Theoretical calculations can predict the influence of different doping amounts on the adsorption energy of intermediate products, thereby regulating the catalytic performance at the atomic scale. The element doping of transition metal phosphides can be divided into cation doping, anion doping and co-doping of cations and anions. Taking cation doping as an example, zinc-doped cobalt phosphide (Zn-doped CoP) with different doping levels exhibits different hydrogen adsorption free energies (ΔGH) in the hydrogen evolution reaction (HER), which corresponds to its HER performance. Zinc with a doping ratio of 8.3% produces the most moderate ΔGH and optimized Fermi level position, corresponding to the lowest HER reaction overpotential. Doping elements such as manganese (Mn), vanadium (V), cerium (Ce), copper (Cu), chromium (Cr), etc. can also improve ΔGH by changing the electronic interaction. 。Cation doping can change the original coordination environment of elements. After doping ruthenium (Ru) in the Ni@Ni2P sample, the peak intensity of the Ni-Ni bond increases, indicating that more Ni(0) is available for rapid electron transfer. The strong interaction between Ru and Ni prevents the complete phosphidation of nickel. The nickel in the core and ruthenium on the surface improve electron transfer and ΔGH. Therefore, Ni@Ni2P–Ru exhibits superior performance compared to platinum supported on carbon. Cation doping is not only beneficial for improving the HER process but also applicable to the oxygen evolution reaction (OER). For the rate-limiting step of OER (HO→O), the reaction energy barrier of molybdenum-doped cobalt phosphide (Mo-doped CoP) is lower than that of pure cobalt phosphide. Similarly, compared with single-metal NiP / SCW or CoP / SCW, bimetallic NiCoP / SCW exhibits more excellent OER catalytic activity and stability.

[0005] In addition, TMP particles directly exposed to the electrolyte are prone to inactivation, which inevitably leads to poor stability during the electrochemical reaction process. Therefore, precisely controlling the regional functionalization and uniformity of bifunctional catalysts is a major challenge.

[0006] Based on the above background, the present invention proposes a simple and direct in-situ alloying and phosphidation method for synthesizing a bimetallic heterojunction encapsulated in leaf-shaped nanocarbon interconnected by nitrogen, phosphorus co-doped carbon nanotubes (CNTs), named Fe2P / FeNi / NPC, which is intended to be used as a bifunctional catalyst in rechargeable zinc-air batteries. Summary of the Invention

[0007] The purpose of the present invention is to provide a process-simple in-situ alloying and phosphidation method for preparing a bimetallic heterojunction Fe2P / FeNi nanoparticle composite material with excellent electrochemical performance, encapsulated in leaf-shaped nanocarbon interconnected by nitrogen, phosphorus co-doped carbon nanotubes (CNTs). Its transition metal phosphide is encapsulated inside the CNTs and is not easily inactivated. Compared with noble metal Pt / C and RuO2 catalysts, Fe2P / FeNi / NPC has a lower cost.

[0008] The technical solution adopted by the present invention to solve its technical problems is as follows: On the one hand, the present invention provides a nitrogen, phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticle, whose carbon skeleton is leaf-shaped, which is a bimetallic heterojunction Fe2P / FeNi nanoparticle composite material in three-dimensional leaf-shaped nanocarbon interconnected by nitrogen, phosphorus co-doped carbon nanotubes (CNTs). The bimetallic heterojunction Fe2P / FeNi nanoparticles are uniformly distributed on the carbon skeleton and encapsulated inside the CNTs; In the X-ray diffraction pattern, the nanoparticle has a characteristic diffraction peak of (0 0 2) of graphite carbon at 24°; at 40.2°, 44.2° and 47.3°, it has characteristic diffraction peaks corresponding to the (1 1 1), (2 0 1) and (2 1 0) crystal planes of hexagonal Fe2P, corresponding to the FeNi alloy phase.

[0009] On the other hand, the present invention also provides a method for preparing nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles. First, a porous organic polymer with a leaf-like nanostructure is selected as a precursor, and through ion exchange, transition metal ions Fe 3+ and Ni 2+ are doped into the metal sites in the porous organic polymer, thereby forming potentially high-density MN x active sites; Secondly, using melamine phosphate (MPP) as a phosphorus source, by means of a high-temperature in-situ phosphidation method, the phase structure is regulated and the catalytic activity of the heterostructure catalyst is optimized by adjusting the molar ratio of Fe 3+ and Ni 2+ During the high-temperature in-situ phosphidation process, transition metals (TM) catalyze the growth of highly graphitized CNTs, and at the same time, a strong coupling is formed between FeNi / Fe2P and nitrogen-doped CNTs, so that the particles are encapsulated inside the CNTs. The release of nitrogen- and phosphorus-containing gaseous species contributes to the formation and uniform distribution of nitrogen and phosphorus co-doping, thereby enhancing the catalytic activity by regulating the charge redistribution within the carbon framework.

[0010] Specifically, a method for preparing nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles, wherein the porous organic polymer is ZIF-8, comprises the following steps: S1. The synthesis method of Fe-Ni-ZIF-8 is as follows: Based on the traditional ZIF-8 synthesis method, zinc nitrate (Zn(NO3)2) is dissolved in water to prepare solution A; 2-methylimidazole, Fe 3+ salt and Ni 2+ salt are dissolved in water to prepare solution B, and a mixed solution is obtained. Solution A is poured into solution B to obtain a mixed solution. The mixed solution is stirred, allowed to stand, and after the reaction is completed, it is centrifuged, washed, and dried to obtain a doped iron-nickel ZIF-8 ionic organic polymer, which is the Fe-Ni-ZIF-8 precursor; S2. The synthesis method of the FeNi / Fe2P / NPC is as follows: After fully mixing the obtained Fe-Ni-ZIF-8 precursor with melamine phosphate (MPP), a high-temperature in-situ phosphidation reaction is carried out in an inert atmosphere to prepare a bimetallic heterostructure Fe2P / FeNi nanoparticle composite encapsulated by leaf-shaped nanocarbon interconnected with N / P co-doped carbon nanotubes (CNTs), namely FeNi / Fe2P / NPC.

[0011] In the present invention, a porous organic polymer with a leaf-shaped nanostructure (such as ZIF-8) is selected as the precursor. Through ion exchange, transition metal ions Fe 3+ and Ni 2+ are doped into the metal sites in ZIF-8, thereby forming potentially high-density MN x active sites. In the present invention, melamine phosphate (MPP) is used as the phosphorus source. By using the in-situ phosphidation method, the phase structure is regulated and the catalytic activity of the heterostructure catalyst is optimized by adjusting the molar ratio of Fe 3+ and Ni 2+ (1:0, 1:0.3, 1:0.5, and 1:1). During the high-temperature carbonization process, transition metals (TM) catalyze the growth of highly graphitized CNTs, and at the same time, a strong coupling is formed between FeNi / Fe2P and nitrogen-doped CNTs, so that the particles are encapsulated inside the CNTs. The release of nitrogen- and phosphorus-containing gaseous species contributes to the formation and uniform distribution of N / P co-doping, thereby enhancing the catalytic activity by regulating the charge redistribution within the carbon framework.

[0012] Furthermore, in the above preparation method of nitrogen- and phosphorus-codoped carbon-confined Fe2P / FeNi / NPC nanoparticles, in step S1, the concentration of zinc nitrate in the solution A is 10 mmol / L to 20 mmol / L, and the molar ratio of zinc nitrate to 2-methylimidazole is generally controlled at 1:4 to 1:10 to ensure the formation of a good crystal structure of ZIF-8.

[0013] Furthermore, in the above preparation method of nitrogen- and phosphorus-codoped carbon-confined Fe2P / FeNi / NPC nanoparticles, in step S1, the Fe 3+ salt is ferric chloride or ferric nitrate, the Ni 2+ salt is nickel acetate or nickel nitrate, and the molar ratio of Fe 3+ and Ni 2+ is controlled at 1:0.3 to 1:1 to adjust the proportion of bimetallic active sites.

[0014] Further, in the preparation method of the above nitrogen, phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles, in step S1, the reaction temperature of the mixed solution is 20 to 60 °C, the stirring time is 10 to 30 minutes, and the standing time is 12 to 36 hours.

[0015] Further, in the preparation method of the above nitrogen, phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles, in step S2, the mass ratio of melamine phosphate to the Fe-Ni-ZIF-8 precursor is 1:3 to 1:7.

[0016] Further, in the preparation method of the above nitrogen, phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles, in step S2, the heating rate during the high-temperature in-situ phosphidation reaction is 2 to 5 °C / min, the carbonization temperature is 600 to 1000 °C, and the heat preservation time is 1.5 to 3 hours.

[0017] Thirdly, the present invention also provides the application of the nitrogen, phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles prepared by any one of the above in a positive electrode catalyst of a zinc-air battery.

[0018] The reaction mechanism of the present invention: The organic ligand functional sites of ZIF-8 and Fe 3+ , Ni 2+ Through non-covalent bond interactions, metal ions can be effectively anchored, and at the same time, the construction of dual-metal active sites can be realized. During the high-temperature carbonization process, transition metals (TM) catalyze the growth of highly graphitized CNTs, and at the same time, a strong coupling is formed between Fe2P / FeNi and nitrogen-doped CNTs, so that the particles are encapsulated inside the CNTs. The release of nitrogen- and phosphorus-containing gaseous species contributes to the formation and uniform distribution of N, P doping, thereby enhancing the catalytic activity by regulating the charge redistribution within the carbon framework.

[0019] In addition, the hierarchical pore structure formed at high temperature minimizes the diffusion resistance and exposes more active sites during the reaction. During the in-situ alloying and phosphidation processes, the d-d orbital hybridization effect between Fe and P, Fe and Ni optimizes the adsorption / desorption ability of reaction intermediates, enhances the kinetic processes of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), significantly reduces the reaction energy barrier, and improves the catalytic efficiency. The synergistic effect of Fe2P and FeNi nanoalloys not only facilitates the activation of the O=O chemical bond, but also optimizes the catalytic process by adjusting the reaction path of the intermediate.

[0020] Creating a strong interface between carbon nanotubes (CNTs) and transition metal active components can enhance catalytic activity and stability. The tubular structure of CNTs not only helps to reduce the particle size by encapsulation but also effectively prevents the aggregation of active nanoparticles during the reaction. At the same time, encapsulating these active nanoparticles in CNTs can isolate and protect the fragile TMP nanoparticles from the harsh reaction environment, thereby improving the durability of the catalyst. In addition, the "chainmail" carbon layer helps the electron transfer on the TMP nanoparticles to the outer surface, forming an enlarged electrocatalytic active center by inducing charge redistribution.

[0021] Compared with the prior art, the present invention has the following advantages: 1. Construction of highly efficient active centers: By regulating the doping of transition metals and phosphorus, in-situ alloying and phosphating can be achieved to regulate the phase of the catalyst, forming high-density bimetallic active sites and significantly improving the activity of the catalyst. 2. Unique structure of carbon nanotube encapsulated heterogeneous nanoparticles: Using ZIF-8 as the carbon source and transition metals as the catalyst, through in-situ high-temperature carbonization, the transition metals catalyze the growth of highly graphitized CNTs, and at the same time, a strong coupling is formed between Fe2P / FeNiP and nitrogen-doped CNTs, enabling the particles to be encapsulated inside the CNTs. The tubular structure of CNTs not only helps to reduce the particle size by encapsulation but also effectively prevents the aggregation of active nanoparticles during the reaction. At the same time, encapsulating these active nanoparticles in CNTs can isolate and protect the fragile TMP nanoparticles from the harsh reaction environment, thereby improving the durability of the catalyst.

[0022] 3. The present invention adopts the strategies of in-situ alloying and in-situ phosphating to successfully prepare nitrogen- and phosphorus-codoped carbon-confined Fe2P / FeNi / NPC nanoparticles (Fe2P / FeNi / NPC). By adjusting the content of ZIF-8, the molar ratio of Fe 3+ and Ni 2+ and the dosage of MPP to regulate the phase structure and optimize the catalytic activity of the heterogeneous structure catalyst. Thanks to these synergistic effects, the obtained Fe2P / FeNi / NPC exhibits excellent bifunctional activity for oxygen reduction reaction (ORR) / oxygen evolution reaction (OER), surpassing noble metal-based catalysts (such as Pt / C+RuO2) and many recently reported advanced catalysts.

[0023] 4. Excellent electrochemical performance: The Fe2P / FeNi / NPC material shows high specific capacity and excellent cycle stability as the positive electrode catalyst of a zinc-air battery, far superior to traditional non-noble metal catalysts.

[0024] 5. Simple process and scalability: The preparation method is simple and the cost is low, which is suitable for large-scale production. As a catalyst, it has a unique structure and excellent electrochemical performance. Its preparation process is simple and can be applied to large-scale production. Description of the Drawings

[0025] Figure 1 It is the synthesis flow chart of the Fe2P / FeNi / NPC catalyst prepared in Example 1 of the present invention, showing the preparation steps from precursor synthesis to in-situ alloying and phosphating; Figure 2 It is the scanning electron microscope (SEM) image of the Fe2P / FeNi / NPC catalyst prepared in Example 1 of the present invention; Figure 3 It is the X-ray diffraction (XRD) pattern of the composite materials obtained in Examples 1 to 3 and Comparative Example 1; Figure 4 It is the characterization diagram of the Fe2P / FeNi / NPC catalyst prepared in Example 1 of the present invention, where a is the transmission electron microscope (TEM), b and c are high-resolution transmission electron microscope images, d is the selected area electron diffraction (SAED) image, e is the EDS line scan map, f is the high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image, and images g-k are the surface scan images of C, N, P, Fe, and Ni elements respectively; Figure 5 It is the nitrogen adsorption and desorption test BET pattern of the composite materials prepared in Examples 1, 2, and 3 of the present invention; Figure 6 It is the X-ray photoelectron spectroscopy (XPS) pattern of the Fe2P / FeNi / NPC composite material prepared in Example 1 of the present invention, where a is the high-resolution C1s spectrum, b is the high-resolution Fe2p spectrum, c is the high-resolution Ni2p spectrum, d is the high-resolution p2p spectrum, and e is the high-resolution N1s spectrum.

[0026] Figure 7 It is the comparison diagram of the catalytic performance of the composite materials prepared in Examples 1 to 3 and Comparative Example 1 of the present invention with noble metal catalysts for a. oxygen reduction reaction (ORR) and b. oxygen evolution reaction (OER); Figure 8 It is the performance diagram of the rechargeable zinc-air battery assembled with the Fe2P / FeNi / NPC composite material prepared in Example 1 of the present invention and noble metal catalysts, where a is the schematic structural diagram in the aqueous zinc-air battery, b is the constant current discharge diagram, and c is the energy density polarization curve; Figure 9Performance graph of the rechargeable zinc-air battery assembled with the Fe2P / FeNi / NPC composite material prepared in Example 1 of the present invention. Among them, a is the constant current charge-discharge graph of Example 1, Example 2, the comparative example and the noble metal catalyst, and b is the performance curve of different current rates of Example 1; Figure 10 Physical diagram, constant current discharge and charge-discharge cycle performance of the flexible zinc-air battery assembled with the Fe2P / FeNi / NPC composite material prepared in Example 1 of the present invention. Among them, a is the structural schematic diagram of the flexible zinc-air battery, b is the flexible battery power led image, c is the constant current discharge curve, d is the energy density polarization curve, e is the constant current charge-discharge curve, and f is the constant current charge-discharge curve of the battery at different bending angles. Detailed implementation manners

[0027] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can understand the present invention more clearly.

[0028] The following embodiments are only used to illustrate the present invention, but not to limit the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0029] The manufacturers, models and purities of several substances used in the present invention are as follows: Melamine phosphate: Macklin M859615-100g 15541-60-3 ≥99%; 2-Methylimidazole: aladdin M104839-500g, 98%; Nafion: Alfa aesar A175209-10 mL 31175-20-9, 5wt%; Zn(NO3)2·6H2O: aladdin Z190758-500g, 13778-30-8, 98%; Fe(NO3)3·9H2O: aladdin F100208-500g, 7782-61-8, 98%; Ni(AC)2·4H2O: aladdin N112914-500g, 6018-89-9, 99%.

[0030] It should be noted that as long as the corresponding components are contained, products of other manufacturers and other models can also be selected. In addition, the substances not specifically described are common substances and can be purchased in the market.

[0031] Example 1: Preparation of Fe2P / FeNi / NPC-0.5 catalyst S1. Dissolve 0.4314 g of zinc nitrate (Zn(NO3)2·6H2O) in 14.5 mL of deionized water to prepare solution A; dissolve 1.174 g of 2-methylimidazole, 173 mg of iron nitrate (Fe(NO3)3·9H2O), and 53.28 mg of nickel acetate (Ni(AC)2·4H2O) in 28.5 mL of deionized water to prepare solution B, such that the molar ratio of Fe 3+ and Ni 2+ is 1:0.5. Quickly pour solution A into solution B, stir at room temperature for 10 minutes, and then let it stand for 24 hours to complete the reaction. After the reaction is completed, centrifuge to collect the product (8000 rpm, 8 minutes), wash it several times with deionized water and 95% ethanol, and dry it at 60°C for 12 hours to obtain the Fe-Ni-ZIF-8 precursor.

[0032] S2. Mix 200 mg of the obtained Fe-Ni-ZIF-8 evenly with 50 mg of melamine phosphate (MPP), put it into a tubular furnace, heat it to 900°C at a heating rate of 5°C / min under the protection of argon (Ar), and hold for 2 hours, and then cool it to room temperature. The product after calcination is the Fe2P / FeNi / NPC-0.5 composite material with a three-dimensional nanosheet structure.

[0033] Example 2: Preparation of Fe2P / FeNi / NPC-0.3 catalyst S1. Dissolve 0.4314 g of zinc nitrate (Zn(NO3)2·6H2O) in 14.5 mL of deionized water to prepare solution A; dissolve 1.174 g of 2-methylimidazole, 173 mg of iron nitrate (Fe(NO3)3·9H2O), and 31.97 mg of nickel acetate (Ni(AC)2·4H2O) in 28.5 mL of deionized water to prepare solution B, such that the molar ratio of Fe 3+ and Ni 2+ is 1:0.3. Quickly pour solution A into solution B, stir at room temperature for 10 minutes, and then let it stand for 24 hours to complete the reaction. After the reaction is completed, centrifuge to collect the product (8000 rpm, 8 minutes), wash it several times with deionized water and 95% ethanol, and dry it at 60°C for 12 hours to obtain the Fe-Ni-ZIF-8 precursor.

[0034] S2. Mix 200 mg of the obtained Fe-Ni-ZIF-8 evenly with 50 mg of melamine phosphate (MPP), put it into a tubular furnace, and under the protection of argon (Ar), heat it to 900 °C at a heating rate of 5 °C / min and hold for 2 hours, then cool it to room temperature. The calcined product is the Fe2P / FeNi / NPC-0.3 composite material with a three-dimensional nanosheet structure.

[0035] Example 3: Preparation of Fe2P / FeNi / NPC-1 catalyst S1. Dissolve 0.4314 g of zinc nitrate (Zn(NO3)2·6H2O) in 14.5 mL of deionized water to prepare solution A; dissolve 1.174 g of 2-methylimidazole, 173 mg of iron nitrate (Fe(NO3)3·9H2O), and 106.5 mg of nickel acetate (Ni(AC)2·4H2O) in 28.5 mL of deionized water to prepare solution B, so that the molar ratio of Fe 3+ and Ni 2+ is 1:1. Quickly pour solution A into solution B, stir at room temperature for 10 minutes, and then let it stand for 24 hours to complete the reaction. After the reaction is completed, centrifuge to collect the product (8000 rpm, 8 minutes), wash it several times with deionized water and 95% ethanol, and dry it at 60 °C for 12 hours to obtain the Fe-Ni-ZIF-8 precursor.

[0036] S2. Mix 200 mg of the obtained Fe-Ni-ZIF-8 evenly with 50 mg of melamine phosphate (MPP), put it into a tubular furnace, and under the protection of argon (Ar), heat it to 900 °C at a heating rate of 5 °C / min and hold for 2 hours, then cool it to room temperature. The calcined product is the Fe2P / FeNi / NPC-1 composite material with a three-dimensional nanosheet structure.

[0037] Example 4: Preparation of Fe2P / FeNi / NPC-0.8 catalyst S1. Dissolve 1.66 g (10 mmol) of 1,4-BDC (dioxane terephthalate), 2.70 g (10 mmol) of ferric chloride (FeCl3·6H2O), and 2.33 g of nickel nitrate (Ni(NO3)3·6H2O) in 50 mL of DMF under magnetic stirring. Fe 3+ and Ni 2+The molar ratio is 1:0.8. Then, 4 mL of NaOH solution (2 mol / L) was added dropwise under rapid stirring. After some time, a clear solution was obtained, which was then transferred to a 100 mL autoclave and heated at 100 °C for 14 h. The product was washed repeatedly with DMF and ethanol and soaked in ethanol for 24 hours. After that, the obtained product (MIL-88B) was freeze-dried for 5 hours and then collected. The Fe-Ni-MIL-88b precursor was obtained.

[0038] S2. 200 mg of the obtained Fe-Ni-MIL-88b was mixed evenly with 50 mg of melamine phosphate (MPP), placed in a tube furnace, and heated to 900 °C at a heating rate of 2 °C / min under the protection of argon (Ar) and held for 3 hours, followed by cooling to room temperature. The calcined product was the Fe2P / FeNi / NPC-0.8 composite material with a three-dimensional nanosheet structure.

[0039] Comparative Example 1: Preparation of Fe2P / NPC catalyst (without adding nickel acetate) S1. 0.4314 g of zinc nitrate (Zn(NO3)2·6H2O) was dissolved in 14.5 mL of deionized water to prepare solution A; 1.174 g of 2-methylimidazole and 173 mg of iron nitrate (Fe(NO3)3·9H2O) were dissolved in 28.5 mL of deionized water to prepare solution B. Solution A was quickly poured into solution B, and after stirring at room temperature for 10 minutes, it was left standing for 24 hours to complete the reaction. After the reaction was completed, the product was collected by centrifugation (8000 rpm, 8 minutes), washed several times with deionized water and 95% ethanol, and dried at 60 °C for 12 hours to obtain the Fe-ZIF-8 precursor.

[0040] S2. 200 mg of the obtained Fe-ZIF-8 was mixed evenly with 50 mg of melamine phosphate (MPP), placed in a tube furnace, and heated to 900 °C at a heating rate of 5 °C / min under the protection of argon (Ar) and held for 2 hours, followed by cooling to room temperature. The calcined product was the Fe2P / NPC composite material with a three-dimensional nanosheet structure.

[0041] Comparative Example 2: Preparation of catalyst (without adding 2-methylimidazole) Compared with Example 1, the difference was that 2-methylimidazole was not added, and the result was that without adding 2-methylimidazole, ZIF could not be synthesized, that is, the composite catalytic material could not be obtained.

[0042] Performance characterization of the product: As attached Figure 2In Example 1 shown, the carbon skeleton presents a blade-like structure, and the Fe2P / FeNi bimetallic heterogeneous nanoparticles are uniformly distributed on the carbon skeleton and encapsulated inside the CNTs.

[0043] As shown in the Figure 3 accompanying drawings, the composites prepared in Comparative Example 1, Example 3, Example 2, and Example 1 all exhibit a "bread-like peak" at 24°, which belongs to the (0 0 2) of graphite carbon. The characteristic diffraction peaks that appear at 40.2°, 44.2°, and 47.3° in Example 3, Example 2, and Example 1 respectively correspond to the (1 1 1), (2 0 1), and (2 1 0) crystal planes of hexagonal Fe2P. The diffraction peaks at 43.9° and 52.5° correspond to the (111) and (200) crystal planes of the FeNi alloy phase. There is no FeNi alloy phase in Comparative Example 1.

[0044] As shown in the Figure 4 accompanying TEM image (Figure (a)) shows that Example 1 has obvious Fe2P / FeNi nanoparticles encapsulated in the nano-carbon structure interconnected by carbon nanotubes. The average particle size of the nanoparticles is 10 - 15 nm. The HRTEM image (Figure (b)) shows that the d lattice fringe spacings are 0.207 nm and 0.223 nm respectively (Figure (c)), corresponding to the (111) crystal plane of FeNi and the (111) crystal plane of Fe2P respectively. The SAED pattern (Figure (d)) shows the diffraction rings of the (311) crystal plane of FeNi and the (210) crystal plane of Fe2P, confirming the coexistence of Fe2P and FeNi. The results of EDS line scanning and area scanning (element mapping, Figure (e)) show that the distributions of Fe, Ni, and P elements highly overlap, and the distributions of C and N elements highly overlap, indicating the existence of the Fe2P / FeNi heterogeneous structure. N and P atoms are dispersed in the C region, confirming the existence of Fe2P / FeNi heterogeneous crystals in the nitrogen and phosphorus co-doped carbon matrix. The high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image (Figure f) shows that the Fe2P / FeNi nanoparticles are encapsulated in the nano-carbon structure interconnected by carbon nanotubes. The element distribution maps (Figures g-k) show that nitrogen species are dispersed in the carbon region, while the signals of Fe, Ni, and P overlap and are distributed within the carbon region, confirming the existence of Fe2P / FeNi nanocrystals in the nitrogen and phosphorus doped carbon matrix.

[0045] As shown in the Figure 5The nitrogen adsorption and desorption test results shown in the figure show that at extremely low relative pressure (P / P0<0.1), the sample exhibits significant adsorption capacity for N2. In the relative pressure range of 0.5 to 1.0, a large number of micropores and mesopores exist in the sample. Examples 1-3 exhibit typical type IV isotherms and H4 type hysteresis loops, indicating that the sample has stacked pores. The pore size distribution shows that the pore sizes of Examples 1-3 are mainly distributed in the micropore and mesopore range.

[0046] As attached Figure 6 In the XPS spectra shown, the three peaks of the high-resolution C1s spectrum (Figure a) can be attributed to CC / C=C, CO / CN / CP and O=CO. The high-resolution XPS spectra of Fe and Ni (Figure b, c) show peaks of Fe(0) and Fe-P, as well as peaks of Ni(0) and Ni-N, confirming the Fe2P and FeNi alloys and the active site Fe-P x (2≤x≤4),Ni-N x (2≤x≤4). The high-resolution P2p spectrum (Figure d) shows peaks of PC, Fe-P and PO. In the high-resolution N 1s XPS spectrum (Figure e), pyridinic nitrogen, pyrrolic nitrogen / MN can be observed. x , graphitic nitrogen and nitrogen oxides.

[0047] Application Example 1 The application of the electrocatalyst obtained in Examples 1-3 and Comparative Example 1 is as follows: a slurry is prepared using the catalyst as the active material, isopropanol as the dispersion solution, and Nafion (5 wt.%) as the binder. The mass ratio of the active material, isopropanol, and Nafion is determined to be 4:15:435. After the components are fully mixed, 10 μL of the slurry is dropped on the working electrode of the rotating disk electrode to test the electrocatalytic performance.

[0048] Attached Figure 7 The electrocatalytic performance results of Examples 1-3 and Comparative Example 1 are shown. The linear potential scanning curve (LSV) measured in the voltage range of 0.2 ~ 1.0 V shows that the prepared Example 1 has a higher half-wave potential (0.84 V), which is better than the commercial 20 wt% Pt / C catalyst (0.78 V) and Example 2, Example 3 and the comparative example. The linear potential scanning curve (LSV) measured in the voltage range of 1.0 ~ 1.8 V shows that Example 1 has a higher half-wave potential (0.84 V) at 10 mA cm -2 The catalyst has a lower overpotential (1.64 V), which is better than that of Example 2, Example 3 and the comparative example, but slightly higher than that of the commercial RuO2 catalyst (1.56 V).

[0049] Application Example 2 Application of the Fe2P / FeNi / NPC-0.5 composite material prepared in Example 1 as a cathode material for rechargeable metal-air batteries is as follows: In the process of preparing the battery, 10 mg of the Fe2P / FeNi / NPC-0.5 composite material (bifunctional electrocatalyst) was ultrasonically dispersed in 850 μL of isopropanol, and 50 μL of 5 wt.% Nafion solution was added, followed by ultrasonic dispersion for 30 minutes to prepare the catalyst slurry. The slurry was evenly coated on a carbon cloth (4 cm × 4 cm) and dried at 70 °C for 6 hours, and the loading amount of the catalyst reached 2.5 mg cm -2 A polished zinc plate (purity 99.99%, 3 × 3 cm) was used as the anode, the carbon cloth loaded with the catalyst was used as the air cathode, and 6 M KOH was used as the electrolyte solution with zinc acetate added. The polarization curve, power density, constant current discharge, constant current charge-discharge cycle and other performances of the battery were tested on a Blue Electric Battery Test System (LAND CT2001A) system to evaluate its energy storage capacity. To further illustrate the excellent performance of the prepared Fe2P / FeNi / NPC-0.5 composite material in assembling metal-air batteries, a commercial noble metal ruthenium oxide + platinum carbon was assembled into a reference zinc-air battery for comparison.

[0050] Attached Figure 8 are the performance results of the zinc-air battery. The zinc-air battery (ZAB) assembled in Example 1 maintained a voltage of 1.20 V after constant current discharge at 5 mA cm -2 for 208 hours, and the specific capacity of the battery reached 755.08 mAh g -1 . The discharge life (177 h) of the Pt / C + RuO2-based ZAB was significantly lower than that of Example 1, and the battery capacity was only 663.62 mAh g -1 . The power density of the assembled zinc-air battery was tested, and the results showed that the zinc-air battery assembled in Example 1 had a higher power density of 158.4 mW cm -2 , which was better than that of the zinc-air electrode assembled from noble metal platinum carbon / ruthenium oxide (130.1 mWcm -2 ).

[0051] Attached Figure 9 is the charge-discharge curve of the zinc-air battery assembled with the Fe2P / FeNi / NPC-0.5 composite material at a current density of 5 mA cm -2 . After 1400 h of charge and discharge, it was still able to maintain a narrow voltage window without obvious electrode polarization behavior, and its cycling performance was much better than that of the zinc-air electrode assembled from noble metal ruthenium oxide / platinum carbon. Moreover, the zinc-air battery assembled in Example 1 had excellent rate performance.

[0052] Application Example 3 The preparation of the positive electrode of the flexible zinc-air battery is the same as that of the aqueous system. The electrolyte membrane is a PVA-KOH hydrogel membrane. A sandwich structure is adopted to stack the carbon cloth coated with the catalyst, the electrolyte membrane, and the zinc negative electrode in sequence to form a sandwich structure, and a flexible zinc metal-air battery is assembled.

[0053] Appendix Figure 10 are the performance results of the flexible zinc-air battery. A flexible zinc-air battery can light up an LED screen. The flexible zinc-air battery assembled with the nanoparticles obtained in Example 1 can be discharged for 10.5 h at a current density of 2 mA cm -2 and exhibits a high open-circuit voltage of 1.36 V. The physical diagram, constant-current discharge, and charge-discharge cycle performance of the flexible zinc-air battery assembled with the Fe2P / FeNi / NPC composite material prepared in Example 1. The power density of the flexible zinc-air battery reaches 158.02 mW cm -2 . At a current density of 2 mA cm -2 , the flexible zinc-air battery can be cycled for 17 h, which is better than the metal-air electrode assembled with noble metal ruthenium oxide / platinum carbon (7 h). At different bending angles (0°, 60°, 90°, 120°, 180°), the flexible zinc-air battery assembled with Example 1 still maintains a stable voltage window, indicating that the battery has good flexible stability.

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticle, characterized in that, Its carbon skeleton is leaf-shaped, which is a bimetallic heterojunction Fe2P / FeNi nanoparticle composite in a three-dimensional leaf-shaped nanocarbon interconnected by nitrogen and phosphorus co-doped carbon nanotubes. The bimetallic heterojunction Fe2P / FeNi nanoparticles are uniformly distributed on the carbon skeleton and encapsulated inside the CNTs; In the X-ray diffraction pattern, the nanoparticles have a characteristic diffraction peak of (0 0 2) of graphite carbon at 24°; At 40.2°, 44.2° and 47.3°, there are characteristic diffraction peaks corresponding to the (1 1 1), (2 0 1) and (2 1 0) crystal planes of hexagonal Fe2P, corresponding to the FeNi alloy phase.

2. The preparation method of the nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles according to claim 1, characterized in that First, a porous organic polymer with a leaf-like nanostructure is selected as a precursor. Through ion exchange, transition metal ions Fe 3+ and Ni 2+ are doped into the metal sites in the porous organic polymer, thereby forming potentially high-density MN x active sites, where 2 ≤ x ≤ 4; Secondly, using melamine phosphate as the phosphorus source, through the high-temperature in-situ phosphating method, by adjusting the molar ratio of Fe 3+ and Ni 2+ to regulate the phase structure and optimize the catalytic activity of the heterostructure catalyst. During the high-temperature in-situ phosphating process, transition metals catalyze the growth of highly graphitized CNTs, and at the same time, a strong coupling is formed between FeNi / Fe2P and nitrogen-doped CNTs, encapsulating the particles inside the CNTs.

3. The preparation method of the nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles according to claim 2, characterized in that, The porous organic polymer is ZIF-8, ZIF-67, MIL-88B or COF-102.

4. The preparation method of the nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles according to claim 2, wherein The porous organic polymer is ZIF-8, and it includes the following steps: S1. The synthesis method of the Fe-Ni-ZIF-8 is as follows: Dissolve zinc nitrate in water to prepare solution A; dissolve 2-methylimidazole, Fe 3+ salt and Ni 2+ salt in water to prepare solution B to obtain a mixed solution. Pour solution A into solution B to obtain a mixed solution. After the mixed solution is stirred and left standing, after the reaction is completed, centrifuge, wash, and dry to obtain a ZIF-8 ion organic polymer doped with iron and nickel, which is the Fe-Ni-ZIF-8 precursor; S2. The synthesis method of FeNi / Fe2P / NPC is: after fully mixing the obtained Fe-Ni-ZIF-8 precursor with melamine phosphate, perform a high-temperature in-situ phosphidation reaction in an inert atmosphere to prepare a bimetallic heterostructure Fe2P / FeNi nanoparticle composite encapsulated by a leaf-shaped nanocarbon interconnected by N / P co-doped carbon nanotubes, that is, FeNi / Fe2P / NPC is obtained.

5. The preparation method of the nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles according to claim 4, characterized in that, In step S1, the concentration of zinc nitrate in solution A is 10 mmol / L to 20 mmol / L, and the molar ratio of zinc nitrate to 2-methylimidazole is controlled at 1:4 to 1:10 to ensure the formation of a good crystal structure of ZIF-8.

6. The preparation method of the nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles according to claim 4, characterized in that, In step S1, the Fe 3+ salt is ferric chloride or ferric nitrate, and the Ni 2+ salt is nickel acetate or nickel nitrate. The molar ratio of Fe 3+ to Ni 2+ is controlled to be 1:0.3 to 1:1 to adjust the proportion of bimetallic active sites.

7. The preparation method of a nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticle according to claim 4, characterized in that, In step S1, the reaction temperature of the mixed solution is 20 to 60 °C, the stirring time is 10 to 30 minutes, and the standing time is 12 to 36 hours.

8. The preparation method of the nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles according to claim 4, characterized in that, In step S2, the mass ratio of melamine phosphate to the Fe-Ni-ZIF-8 precursor is 1:3 to 1:

7.

9. The preparation method of the nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles according to claim 4, characterized in that, In step S2, the heating rate during the high-temperature in-situ phosphidation reaction is 2 to 5 °C / min, the carbonization temperature is 600 to 1000 °C, and the heat preservation time is 1.5 to 3 hours.

10. The nitrogen and phosphorus co-doped carbon-confined Fe2P / FeNi / NPC nanoparticles prepared by any one of claims 2 to 9 are used as a positive electrode catalyst for a zinc-air battery.

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