Preparation method and application of nitrogen and phosphorus co-doped Fe-N-C catalyst

Abstract

The application discloses a preparation method and application of a nitrogen and phosphorus co-doped Fe-N-C catalyst, and relates to the field of zinc-air batteries. The ZIF-8 encapsulating FePc is used as a precursor, and a high-performance nitrogen and phosphorus dual-doped oxygen reduction electrocatalyst N-P / Fe-N-C is designed by adsorbing organic compounds. The prepared N-P / Fe-N-C catalyst retains a typical granular dodecahedron morphology, and a proper amount of carbon nanotubes is generated, so that an excellent microstructure is formed, and the N-P / Fe-N-C catalyst has an ultrahigh specific surface area (up to 817.02 m 2 ·g ‑1 ) and a hierarchical porous structure. The structural advantages can effectively increase the contact area of the three-phase interface of oxygen, the catalyst and the electrolyte, significantly shorten the diffusion path of the oxygen-containing reactants and products, greatly improve the exposure amount of active sites, and solve the technical defects of the existing Fe-N-C catalyst, such as insufficient exposure of active sites and low mass transfer efficiency, from the structural level.

Description

Technical Field

[0001] This invention relates to the field of zinc-air batteries, specifically to a method for preparing a nitrogen-phosphorus co-doped Fe-NC catalyst and its application. Background Technology

[0002] With the escalating global energy crisis and increasing environmental awareness, the development of efficient, clean, and sustainable energy conversion and storage technologies has become a current research hotspot. Fuel cells, metal-air batteries, and water electrolysis for hydrogen production are promising new energy technologies, but their core performance is highly dependent on the catalytic activity, stability, and selectivity of the catalysts. Currently, the catalysts widely used in these technologies are mainly precious metal catalysts such as platinum (Pt), ruthenium (Ru), and iridium (Ir). Although they possess excellent catalytic performance, precious metal resources are scarce, expensive, and have limited reserves. Furthermore, they are prone to aggregation, dissolution, and loss during long-term use, resulting in high catalyst costs and severely restricting the large-scale industrial application and widespread adoption of these energy technologies. To address these shortcomings of precious metal catalysts, the development of high-performance, low-cost non-precious metal catalysts has become a key research focus in the field of catalysis. Among them, Fe-NC catalysts are considered one of the most promising non-precious metal catalytic materials for replacing precious metal catalysts due to their significant advantages such as high catalytic activity, wide availability of raw materials, low cost, and environmental friendliness. The catalytic activity of Fe-NC catalysts mainly comes from the FeN4 active sites formed on their surface. These active sites can effectively adsorb and activate the reaction substrate, accelerating the reaction process. At the same time, the high specific surface area and good conductivity of the carbon support can further improve the electron transport efficiency and active site utilization of the catalyst.

[0003] However, single nitrogen-doped Fe-NC catalysts still have many shortcomings that limit their practical application: on the one hand, single nitrogen doping is difficult to effectively regulate the local electronic structure of FeN4 active sites, resulting in the intrinsic catalytic activity of the catalyst needing further improvement; on the other hand, the pore structure of the carbon support is prone to agglomeration, resulting in insufficient exposure of active sites, and the catalyst has poor stability in the electrochemical reaction process, with significant catalytic performance degradation after long-term cycling, which cannot meet the requirements of actual working conditions.

[0004] Existing methods for preparing nitrogen-phosphorus co-doped Fe-NC catalysts generally suffer from the following problems: First, the preparation process is cumbersome, involving numerous steps, a long reaction cycle, and low production efficiency. Second, the ratio of doping elements is difficult to precisely control, making it impossible to achieve the optimal match between N and P doping amounts and Fe-NC catalyst performance. Third, the utilization rate of active sites in the catalyst still needs improvement, and its adaptability in different reaction media such as acidic and alkaline media is poor, making it difficult to simultaneously meet the requirements of multiple electrochemical reactions such as oxygen reduction and hydrogen evolution. Fourth, some preparation methods require the use of highly corrosive reagents, placing high demands on equipment and generating waste gas and wastewater, posing environmental pollution risks. Furthermore, the current understanding of the electrocatalytic reaction mechanism and active sites of nitrogen-phosphorus co-doped Fe-NC catalysts is still insufficient, lacking systematic theoretical support, which further restricts the optimization of catalyst performance and the improvement of preparation processes.

[0005] In summary, existing methods for preparing nitrogen-phosphorus co-doped Fe-NC catalysts suffer from numerous drawbacks, including complex processes, high costs, uneven doping, poor performance consistency, difficulties in large-scale production, and insufficient stability. Their catalytic performance and application effects still cannot fully meet the actual operating requirements of emerging energy technologies such as fuel cells and metal-air batteries. Therefore, developing a simple, convenient, low-cost, and environmentally friendly method for preparing nitrogen-phosphorus co-doped Fe-NC catalysts that enables uniform doping of Fe, N, and P elements, precise control of catalyst pore structure and active site distribution, full utilization of the synergistic effect of NP co-doping, and high activity, high stability, high active site exposure, and excellent mass transfer efficiency, while also expanding its application scenarios, is of significant practical importance and application value for promoting the industrialization of non-precious metal catalysts, reducing the application costs of emerging energy technologies, and promoting the transformation and upgrading of the energy structure. This is also a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the aforementioned shortcomings of the prior art, this invention provides a method for preparing a nitrogen-phosphorus co-doped Fe-NC catalyst and its application.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for preparing a nitrogen-phosphorus co-doped Fe-NC catalyst is provided, comprising the following specific steps: S1: Dissolve Zn(NO3)2·6H2O in methanol to obtain solution A, and dissolve 2-methylimidazole in methanol to obtain solution B; S2: After mixing solutions A and B, add phthalocyanine iron and stir the reaction at room temperature for 24 hours. Centrifuge the product and wash and dry it with methanol to obtain ZnFe-ZIF powder. S3: Dissolve ZnFe-ZIF powder in methanol to obtain solution C; dissolve melamine in methanol and then add triphenylphosphine to obtain solution D; S4: Add solution D to solution C and stir rapidly for 12 h. Wash the resulting precipitate with methanol and dry to obtain NP / ZnFe-ZIF. Incubate NP / ZnFe-ZIF under Ar atmosphere at 5 °C·min. -1 The temperature was increased to 950℃ and held for 2 hours. After natural cooling to room temperature, the target product, nitrogen-phosphorus co-doped Fe-NC catalyst, was obtained.

[0008] Furthermore, in step S1, the ratio of Zn(NO3)2·6H2O to 2-methylimidazole is 2.5g:6.568g; and when preparing solution A, the ratio of Zn(NO3)2·6H2O to methanol is 2.5g:80mL; and when preparing solution B, the ratio of 2-methylimidazole to methanol is 6.568g:80mL.

[0009] Furthermore, in step S2, the ratio of iron phthalocyanine to Zn(NO3)2·6H2O is 100mg:2.5g.

[0010] Furthermore, in step S3, when preparing solution C, the ratio of ZnFe-ZIF powder to methanol is 300mg:100mL; when preparing solution D, the ratio of melamine to methanol is 100mg:50mL, and the ratio of ZnFe-ZIF powder, melamine, and triphenylphosphine is 300mg:100mg:90~110mg.

[0011] The present invention also provides a nitrogen-phosphorus co-doped Fe-NC catalyst prepared by the above preparation method. The nitrogen-phosphorus co-doped Fe-NC catalyst has a granular dodecahedral morphology, carries carbon nanotubes, has a high specific surface area and a hierarchical porous structure, increases the contact area between the three-phase interface of oxygen, catalyst and electrolyte, shortens the diffusion path of oxygen-containing reactants and products, and exposes more active sites.

[0012] This invention also provides the application of the above-mentioned nitrogen-phosphorus co-doped Fe-NC catalyst in the preparation of zinc-air batteries. The preparation method of the zinc-air battery adopts the following steps: A1: Nitrogen-phosphorus co-doped Fe-NC catalyst, acetylene black, water, isopropanol and 5% Nafion solution were added sequentially to the reactor vessel; ultrasonic treatment was then performed to obtain a uniform suspension. A2: Add the suspension droplets onto the current collector and dry under vacuum; A3: Press the gas diffusion layer, the dry catalyst-containing current collector prepared in A2, and the diaphragm together to obtain an air cathode; A4: A zinc-air battery was prepared by using a polished zinc sheet as the air anode and a mixed solution of KOH and Zn(Ac)2 as the electrolyte.

[0013] Furthermore, in step A1, the ratio of nitrogen-phosphorus co-doped Fe-NC catalyst, acetylene black, water, isopropanol, and 5% Nafion solution is 5 mg: 2 mg: 600 μL: 360 μL: 40 μL.

[0014] Furthermore, in step A2, the current collector is nickel foam, and the loading of the suspension on the nickel foam is 1 mg·cm³. -2 .

[0015] Furthermore, in step A4, the concentration of KOH in the electrolyte is 6 mol·L⁻¹. -1 The concentration of Zn(Ac)₂ in the electrolyte is 0.2 mol·L⁻¹. -1 .

[0016] This invention also provides the application of the above-mentioned nitrogen-phosphorus co-doped Fe-NC catalyst in the preparation of zinc-air batteries. The preparation method of the zinc-air battery adopts the following steps: B1: Nitrogen-phosphorus co-doped Fe-NC catalyst, RuO2 catalyst, acetylene black, water, isopropanol, and 5% Nafion solution were added sequentially to the reactor vessel; a homogeneous suspension was obtained by ultrasonic treatment; the ratio of the volume of nitrogen-phosphorus co-doped Fe-NC catalyst, RuO2 catalyst, acetylene black, water, isopropanol, and 5% Nafion solution was 5 mg: 5 mg: 2 mg: 600 μL: 360 μL: 40 μL; B2: Add the suspension droplets onto the current collector and dry under vacuum; B3: Press the gas diffusion layer, the dry catalyst-containing current collector prepared in B2, and the diaphragm together to obtain an air cathode; B4: A zinc-air battery was prepared by using a polished zinc sheet as the air anode and a mixed solution of KOH and Zn(Ac)₂ as the electrolyte. The concentration of KOH in the electrolyte was 6 mol·L⁻¹. -1 The concentration of Zn(Ac)₂ in the electrolyte is 0.2 mol·L⁻¹. -1 .

[0017] The beneficial effects of this invention are as follows: This invention utilizes ZIF-8 encapsulated with FePc as a precursor to design a high-performance nitrogen-phosphorus binary-doped oxygen reduction electrocatalyst, NP / Fe-NC, through the adsorption of organic compounds. The NP / Fe-NC catalyst prepared by this invention retains a typical granular dodecahedral morphology and exhibits the accompanying formation of a suitable amount of carbon nanotubes, resulting in an excellent microstructure and an ultra-high specific surface area (up to 817.02 m²). 2 ·g-1 The structure features a hierarchical porous structure. This structure effectively increases the contact area at the interface between oxygen, catalyst, and electrolyte, significantly shortens the diffusion path of oxygen-containing reactants and products, and greatly enhances the exposure of active sites. This structurally addresses the technical shortcomings of existing Fe-NC catalysts, such as insufficient exposure of active sites and low mass transfer efficiency. Simultaneously, the additional N atoms incorporated into the carbon matrix induce uneven surface charge distribution, optimizing oxygen adsorption performance and promoting positive charging of adjacent carbon atoms, thus increasing the graphitization degree of the carbon support. The introduction of P elements increases topological defects in the carbon framework, inducing charge delocalization and further improving the catalyst's conductivity. The synergistic effect of these two elements effectively improves the problems of insufficient electronic structure regulation and poor conductivity in single-doped catalysts, laying the structural and electronic foundation for the catalyst's excellent electrocatalytic performance.

[0018] This invention achieves uniform doping of Fe, N, and P elements through the rational design of the precursor system and doping method, fully leveraging the synergistic effect of NP binary heteroatoms. It effectively solves the defects of existing nitrogen-phosphorus co-doped Fe-NC catalysts, such as complex preparation process, low catalytic activity, poor stability, and insufficient performance in practical applications. The prepared catalyst has significant advantages in structure, electrocatalytic performance, and practical applications. It can efficiently replace precious metal catalysts and be applied in electrochemical energy conversion fields such as zinc-air batteries. It can reduce the application cost of new energy technologies, promote the industrialization of non-precious metal catalysts, and has important practical application value and industrial promotion prospects. Attached Figure Description

[0019] Figure 1 The image shows the microstructure of the NP / Fe-NC prepared in Example 1. Figure 2 These are microscopic characterization diagrams of the different catalysts in Example 2; Figure 3 The X-ray diffraction pattern is shown in Example 3; Figure 4 The Raman spectrum is shown in Example 3; Figure 5 This is a comparison diagram of specific surface area and pore properties in Example 3; Figure 6 Cyclic voltammetry curves for different catalysts in Example 4; Figure 7 The graph shows the polarization results of different catalysts in Example 4; Figure 8 Tafel slope plots for different catalysts in Example 4; Figure 9 The polarization curves of the catalysts under different preparation conditions in Example 5 are shown. Figure 10 The results of the RRDE electron transfer number and H2O2 yield capacity tests for different catalysts in Example 6 are as follows; Figure 11 The LSV and KL curves for the different catalysts in Example 6 are shown. Figure 12 The CV curves for different catalysts in Example 6 are shown. Figure 13The results are compared to the aging test in Example 7; Figure 14 The open-circuit voltage test results are for the air battery prepared in Example 8; Figure 15 The actual power supply test results are from Example 8; Figure 16 The discharge polarization curves and power density curves of different zinc-air batteries in Example 9 are shown. Figure 17 The results of rate performance tests for different zinc-air batteries in Example 9; Figure 18 The results of the constant current charge-discharge performance test in Example 9; Figure 19 This is a comparison chart of specific capacity under constant current in Example 9; Figure 20 The results of the cyclic charge-discharge test of the zinc-air battery in Example 9; Figure 21 This is a SEM image of the catalyst layer after cyclic charge-discharge testing in Example 9. Detailed Implementation

[0020] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0021] The specifications of the reagents and equipment used in the examples are shown in Table 1 below; Table 1

[0022] Example 1 Preparation of nitrogen-phosphorus co-doped Fe-NC catalyst The specific steps are as follows: 2.5 g of Zn(NO3)2·6H2O and 6.568 g of 2-methylimidazole were dissolved in 80 mL of methanol to obtain solutions A and B, respectively. The two solutions were then mixed thoroughly, and 100 mg of ferrophthalocyanine was added. The mixture was stirred at room temperature for 24 hours to obtain a dark green product. The dark green product was centrifuged with methanol and washed three times, then dried in a vacuum oven at 60 °C for twelve hours to obtain ZnFe-ZIF powder.

[0023] Weigh 300 mg of the prepared ZnFe-ZIF powder and add it to a beaker containing 100 mL of methanol. Sonicate and stir until completely dissolved to obtain solution C. Separately, add 300 mg of melamine to a beaker containing 50 mL of methanol and stir for 10 minutes until homogeneous. Then add 100 mg of triphenylphosphine to obtain solution D. In practice, the amount of triphenylphosphine can also be 90 mg or 110 mg. Solution D was poured into solution C and stirred rapidly for 12 hours. The resulting precipitate was washed three times with methanol by centrifugation and dried at 60 °C for 12 hours to obtain NP / ZnFe-ZIF. The prepared NP / ZnFe-ZIF was heated to 950 °C at a heating rate of 5 °C·min⁻¹ under Ar atmosphere and held at that temperature for 2 hours. After naturally cooling to room temperature, the nitrogen-phosphorus co-doped Fe-NC catalyst was obtained, hereinafter referred to as NP / Fe-NC.

[0024] The microstructure of the prepared NP / Fe-NC was characterized using scanning electron microscopy, and the results are as follows: Figure 1 As shown, where, Figure 1 In the image, 'a' represents the SEM image of NP / Fe-NC. Figure 1 In the image, b is the TEM image of NP / Fe-NC. Figure 1 c in Figure 1 Enlarged view of the area highlighted in box b; Figure 1 In the diagram, d represents the HAADF-STEM image and elemental distribution map; Depend on Figure 1 It can be seen that, due to the presence of both N and P doping, the surface roughness of NP / Fe-NC is between that of N / Fe-NC and P / Fe-NC. TEM images of NP / Fe-NC confirmed the synthesis of NP / Fe-NC with an average particle size of 100 nm. NP / Fe-NC exhibits a disordered carbon structure with randomly oriented graphite domains and no iron agglomeration. HAADF-STEM and elemental distribution maps show the uniform distribution of C, Fe, N, and P elements in the NP / Fe-NC catalyst.

[0025] Example 2: Comparison of Microscopic Characterization of Catalysts To investigate the influence of nonmetallic elements on the local electronic structure of NP / Fe-NC, N / Fe-NC, P / Fe-NC, and NP were prepared using the approximate method described in Example 1. 110 / Fe-NC; wherein, the preparation method of N / Fe-NC differs from that of Example 1 in that melamine is not added; the preparation method of P / Fe-NC differs from that of Example 1 in that triphenylphosphine is not added; NP 110 The difference between the preparation method of / Fe-NC and Example 1 is that the amount of triphenylphosphine used is 110 mg.

[0026] Scanning electron microscopy was used to study ZnFe-ZIF, Fe-NC, N / Fe-NC, P / Fe-NC, NP / Fe-NC, and NP... 110 The microstructure of Fe-NC was characterized, and the results are as follows: Figure 2 As shown in a~f, by Figure 2It can be seen that the four samples—NP / Fe-NC, N / Fe-NC, P / Fe-NC, and Fe-NC—all inherited the morphology of the ZnFe-ZIF dodecahedron. After calcination at 950℃, due to the escape of zinc nodes, all samples showed slight morphological collapse, with significant shrinkage of the outer wall and numerous wrinkles. Since Fe-NC did not contain any non-metallic elements, its decomposition temperature was lower, resulting in a more disordered morphology. Comparing the morphologies of N / Fe-NC and P / Fe-NC, it can be observed that the surface of N / Fe-NC is rougher, indicating that the addition of nitrogen-containing organic matter increases the disorder of the surface morphology, while the addition of phosphorus-containing organic matter protects the morphology. In NP / Fe-NC, the smaller dodecahedral particles are tightly packed together, forming many carbon nanotubes of different sizes (approximately 100–500 nm) that are intertwined. The presence of the carbon nanotube structure further increases the hierarchical porosity of the specific surface area, thereby greatly increasing the contact area between the catalyst and oxygen-containing reactants, which is beneficial for accelerating the ORR reaction. Simultaneously, increasing the amount of triphenylphosphine added to 110 mg yielded NP. 110 / Fe-NC, and nanotube structures of different sizes were also observed.

[0027] Example 3: Comparison of Phase Characterization of Catalysts The ZnFe-ZIF, NP / Fe-NC, N / Fe-NC, P / Fe-NC, and Fe-NC particles prepared using the methods of Examples 1 and 2 were characterized using a Rigaku Smartlab X-ray diffractometer at 5°·min⁻¹ within the range of 10–90°. -1The obtained samples were scanned at a high scanning speed to obtain information on the phase composition and structure of the catalyst samples. The elemental composition and valence states of the samples were analyzed using an ESCALAB 250Xi X-ray photoelectron spectroscopy system, and the peaks were fitted using XPS peaks fitting software. Thermo Fischer DXR Raman spectrometer was used to measure the frequency and intensity changes of light generated after the interaction of the substance with the laser to further obtain structural information of the samples; the excitation wavelength was 532 nm. The Kubo-X1000 automated gas adsorption analyzer utilizes the adsorption characteristics of solid materials, using gas molecules as a "measuring tool" to measure the surface area and pore structure of the material, and can obtain the specific surface area, pore size distribution, and adsorption-desorption curve data of the samples. After the sample was adhered to conductive adhesive, it was placed in the vacuum chamber of a ZEISS SUPRA 55 scanning electron microscope. A small amount of sample powder was directly adhered to the sample stage containing conductive adhesive, and excess powder was blown off the surface with a high-pressure air gun. Subsequently, the catalyst was subjected to a 90-second gold sputtering treatment to improve its conductivity. The morphology of the sample was observed at a working voltage of 15 kV, and the elemental distribution on the sample was analyzed using a JSM-6490LV energy-dispersive X-ray spectroscopy system. The microstructure and structure of the sample were further observed and analyzed using a JEM-2100F transmission electron microscope, and the area distribution of elements in the catalyst was analyzed using the equipped energy dispersive X-ray spectroscopy system.

[0028] X-ray diffraction results are as follows Figure 3 As shown, where, Figure 3 In the figure, 'a' represents a comparison of the XRD patterns of ZnFe-ZIF and the fitted ZIF-8. Figure 3 In the diagram, b represents the XRD comparison charts of NP / Fe-NC, N / Fe-NC, P / Fe-NC, and Fe-NC; from Figure 3 As can be seen from 'a' in Example 1, ZnFe-ZIF can be successfully synthesized using the method described in Example 1. The iron phthalocyanine (FePc) molecule is encapsulated within ZIF-8, thus shifting the curve to the left overall. Figure 3 As shown in b, in NP / Fe-NC, N / Fe-NC, P / Fe-NC and Fe-NC, apart from the two typical broad peaks at about 25° and 44° which belong to amorphous carbon, no metal diffraction peaks were detected, indicating that the iron species are highly dispersed in the catalyst.

[0029] Raman spectroscopy results as follows Figure 4 As shown, by Figure 4 It can be seen that all samples are at approximately 1350cm. -1 (D belt) and 1590cm -1 Two distinct peaks appear at the (G band), corresponding to disordered carbon and graphitized carbon, respectively. Fitting the peaks, the relative area ratio of the D band and the G band ( ID / I G This can be used to reflect the degree of defects and graphitization in carbon materials. The area ratio of the two peaks in Fe-NC is 3.740, higher than that of N / Fe-NC (2.886), but lower than that of P / Fe-NC (3.947). This indicates that the presence of N exacerbates graphitization, while P doping increases the degree of defects. High-N content NP / Fe-NC... I D / I G The lower N content compared to Fe-NC and P / Fe-NC, but higher than N / Fe-NC, further demonstrates that more N contributes to the formation of graphitized carbon, thereby improving the stability of the intercalation sites during operation. Due to the significant loss of non-C elements caused by high-temperature heat treatment, NP / Fe-NC catalysts tend to be highly graphitized. The larger atomic radius and lower electronegativity of P atoms form CP bonds and polarize C / C bonds, thus forcing the carbon lattice to... E 2g More defects are generated in the vibrational mode. It is through the doping strategy that an effective structural evolution is achieved, so that NP / Fe-NC has a suitable degree of graphitization and number of defects, and provides anchoring sites for additional iron atoms, thereby effectively preventing iron agglomeration and achieving effective exposure of active sites and high utilization of metal atoms.

[0030] The specific surface area and pore properties of the four catalysts are as follows: Figure 5 As shown, where Figure 5 In the figure, 'a' represents the nitrogen adsorption / desorption isotherms for the four catalysts. Figure 5 In the diagram, b represents the pore size distribution of the four catalysts; from Figure 5 It can be seen that the specific surface areas of NP / Fe-NC, N / Fe-NC, P / Fe-NC, and Fe-NC are 817.02 m². 2 ·g -1 626.98m 2 ·g -1 893.57m 2 ·g -1 532.63m 2 ·g -1 It is worth noting that the adsorption / desorption isotherms of all samples are at... p / p A significant hysteresis loop is present in the 0.8–1.0 range, indicating the presence of mesoporous structures in the samples. P / Fe-NC and Fe-NC exhibit distinct peaks near 3 nm and 60 nm, suggesting that their pores are predominantly mesopores and macropores. The prominent surface area of ​​the P / Fe-NC sample is attributed to its relatively small morphological variation, but due to… Figure 5 As indicated by b in the figure, it lacks the necessary micropores, which may be the reason why it did not exhibit the best catalytic performance. In contrast, due to the rapid evaporation of Zn, the N / Fe-NC and NP / Fe-NC samples formed abundant microporous and mesoporous structures. It is precisely because the NP / Fe-NC sample has both a relatively large specific surface area and abundant micropores that it shows outstanding advantages in ORR. The large specific surface area is conducive to mass transport, promotes the adsorption of oxygen-containing reactants, and improves the selectivity of ORR products. At the same time, the continuous mesoporous network accelerates the desorption of reaction products and effectively avoids the blockage of active sites.

[0031] Example 4 Electrochemical performance testing of the catalyst The electrochemical performance of NP / Fe-NC, N / Fe-NC, P / Fe-NC, and Fe-NC prepared using the method in Example 2 was tested. All electrochemical performance tests were performed on an Ivium VC electrochemical workstation. ORR and OER measurements were conducted using a classic three-electrode system, with Hg / HgO as the reference electrode, a Pt wire as the counter electrode, and a catalyst-coated RDE / RRDE as the working electrode. The voltage involved was converted to a reversible hydrogen electrode (V vs. RHE). Furthermore, all electrochemical tests were performed at room temperature. In the ORR test, all linear sweep voltammetry (LSV) curves were within 10 mV·s. -1 The scan was performed at a scanning rate of 1600 rpm, with a test voltage range of 0.2–1.2 V and a rotation speed of 1600 rpm. The electrolyte was 0.1 mol·L⁻¹ oxygen-saturated solution. -1 KOH or HClO4 solution. LSV was measured at different rotation speeds (400, 625, 900, 1225, 1600, 2025 and 2500 rpm), and the number of transferred electrons was calculated using the Koutecky-Levich (KL) equation. n The specific equation is shown in the following formula; ; ; In the formula, J , J k , J L These represent the measured current density, kinetic current density, and limiting current density, respectively, all in mA·cm². -2 . ω , n , F , C , D O2 , vThese represent the electrode rotation speed (rpm), electron transfer number, and Faraday constant (96485 C·mol⁻¹), respectively. -1 The volume concentration of O2 in the electrolyte (1.2 × 10⁻⁶) -6 mol·cm -3 The diffusion coefficient of O2 is 1.9 × 10⁻⁶. - 5 mol·s -1 ) and the kinematic viscosity of the electrolyte (0.1 cm⁻¹) 2 ·s -1 The catalytic activity can be estimated through RRDE testing. n The calculation equation for hydrogen peroxide yield (H2O2%) is shown below; ; ; In the formula, I D , I R , N The values ​​represent the collection efficiency of the disk current, the ring current, and the Pt ring (0.42).

[0032] At different scan rates (10, 20, 30, 40, 50, 60 mV·s) -1 Cyclic voltammetry (CV) curves were measured under voltage sweep conditions ranging from 1.065 to 1.165 V. The current density difference corresponding to the median voltage was plotted against the sweep rate, and the results were fitted to determine the electrochemical double-layer capacitance. C dl ),in, C dl It is positively correlated with the electrochemical active surface area (ECSA). ECSA reflects the number of active sites on the electrode surface that can participate in electrochemical reactions. The higher the ECSA of the catalyst, the more active sites on its surface are available for reactants to adsorb and react, thus exhibiting better catalytic activity.

[0033] In a three-electrode system, the ORR activities of NP / Fe-NC, N / Fe-NC, P / Fe-NC, and Fe-NC materials were tested in a 0.1 M KOH solution (saturated with O2). Simultaneously, 20% Pt / C was used as the reference catalyst, and the cyclic voltammetry (CV) curves are shown below. Figure 6 As shown, by Figure 6 It can be seen that the NP / Fe-NC catalyst exhibits a larger scanning area and a more outstanding redox peak during the activation process compared to other catalysts. This means that more active sites on the catalyst surface are rapidly activated, the catalyst can transfer more charge, and has higher electrochemical activity.

[0034] The polarization results of the catalyst are as follows Figure 7 As shown, where, Figure 7 In the figure, 'a' represents the linear sweep voltammetry (LSV) curves of the five catalysts. Figure 7 In this context, 'b' represents the calculated performance results of the five catalysts; from Figure 7 As shown in 'a', the NP / Fe-NC has the most positive onset potential at 1.051V, indicating that NP / Fe-NC is more likely to initiate the ORR reaction. The onset potentials of N / Fe-NC (1.009V), P / Fe-NC (1.061V), Fe-NC (0.992V), and Pt / C (0.999V) are lower, indicating that their ORR reaction kinetics are slower. Figure 7 As can be seen from b in the figure, compared to Fe-NC ( E 1 / 2 =0.830V, J L =5.566mA·cm -2 ) catalyst, N / Fe-NC ( E 1 / 2 =0.858V, J L =4.947mA·cm -2 ), P / Fe-NC ( E 1 / 2 =0.857V, J L =6.015mA·cm -2 )of E 1 / 2 and J L All have increased significantly. Among them, P / Fe-NC J L The most significant improvement can be attributed to changes in electronic structure, which increase carrier concentration and conductivity in the material. Simultaneously, P doping promotes the formation of abundant pyridine nitrogen, and the strong interaction between N atoms and metal atoms results in a more uniform dispersion of metal atoms on the material surface. This not only increases the active sites of the catalyst but also optimizes the charge transport path between the metal and the carbon substrate. Therefore, during the ORR process, when oxygen-containing reactants react at the active sites, efficient charge transfer can be achieved, accelerating the reaction rate. Compared to N / Fe-NC, P / Fe-NC, and Fe-NC samples, the NP / Fe-NC sample exhibits the most positive [positive charge / discharge]. E 1 / 2 (0.884V) and the highest J L (6.015mA·cm) -2Clearly, the combined addition of N and P can synergistically regulate the coordination structure and porosity distribution, thereby accelerating electron transfer.

[0035] The Tafel slope results for the five catalysts are as follows: Figure 8 As shown, by Figure 8 It can be seen that, with N / Fe-NC (72mV·dec) -1 ), P / Fe-NC (82mV·dec) -1 ), Fe-NC (92mV·dec) -1 ) and commercial Pt / C (95mV·dec -1 Compared to ), the NP / Fe-NC (64mV·dec) prepared in this invention -1 The Tafel slope is the smallest, indicating that the highly coordinated configuration contributes to accelerating the ORR process. Kinetic current density ( J k This is also a key parameter for evaluating ORR activity. The NP / Fe-NC catalyst at 0.85V... J k Reaching 25.1 mA·cm -2 While N / Fe-NC, P / Fe-NC and Fe-NC and commercial Pt / C J k Only 9.88 mA·cm -2 7.71 mA·cm -2 3.42mA·cm -2 and 4.42 mA·cm -2 Therefore, NP / Fe-NC exhibits optimal ORR reaction kinetics.

[0036] Example 5: Effects of different treatment methods on the electrochemical performance of NP / Fe-NC Samples with different P doping levels and at different temperatures were prepared using the method described in Example 1; including samples with NP doping levels of 90 mg triphenylphosphine. 90 / Fe-NC, NP with a triphenylphosphine content of 110 mg 110 / Fe-NC; NP / Fe-NC-800℃, NP / Fe-NC-900℃, and NP / Fe-NC-1000℃ were prepared with 100 mg of triphenylphosphine added and a heat treatment temperature of 800℃, 900℃, and 1000℃, respectively. The method of Example 4 was used to detect the following: Figure 9 The polarization curves of the catalyst under different preparation conditions are shown; among them, Figure 9 In the figure, 'a' represents the LSV curves for different amounts of triphenylphosphine added. Figure 9 In the figure, b represents the LSV curves at different heat treatment temperatures, derived from... Figure 9 As can be seen from 'a' in the figure, compared with NP / Fe-NC, NP 90 / Fe-NC、NP 110 The ORR activity of / Fe-NC decreased, mainly due to NP 90 The P content provided by / Fe-NC is insufficient to meet the requirements of active sites, while NP 110 Excessive P accumulation in Fe-NC affects the exposure of active sites. Figure 9 As indicated by b in the figure, 950℃ is the optimal heat treatment temperature. At temperatures too low, zinc ions cannot completely evaporate, thus failing to form well-developed pores during pyrolysis and providing sufficient sites for the migration of phthalocyanine iron, making it difficult to form an ideal coordination structure. Therefore, the number of active sites decreases, and the activity declines, significantly reducing the catalyst's catalytic ability. Furthermore, pyrolysis below 950℃ results in low graphitization of carbon materials, poor electrical conductivity, and severe electron scattering during electron transport, affecting the electron transfer efficiency in the electrochemical reaction. Conversely, excessively high temperatures cause the electrocatalyst network structure to collapse, reducing the dispersion of Fe atoms and leading to Fe-N... x The alteration of the site's structure and electronic properties significantly reduces the catalyst's catalytic activity for ORR.

[0037] Example 6: Comparison of the number of electrons transferred and the H2O2 yield of the catalyst. The number of transferred electrons and the H2O2 yield of NP / Fe-NC, N / Fe-NC, P / Fe-NC and Fe-NC prepared by the method of Example 2 were detected by rotating ring disk electrode, with 20% Pt / C as the reference catalyst. The electrode preparation method is as follows: Weigh 2.5 mg of the catalyst to be tested into a small glass bottle, and add 300 μL of water, 180 μL of isopropanol, and 20 μL of 5% Nafion solution sequentially. During this process, ensure the accuracy of the amount of each liquid added to guarantee the precise ratio of the catalyst slurry. Then, transfer the suspension containing the catalyst and solvent to an ultrasonic instrument and sonicate for at least 0.5 hours to ensure the catalyst is fully dispersed in the solution and forms a uniform catalyst slurry. After ultrasonic treatment, use a pipette to drop an appropriate amount of catalyst slurry onto a rotating disk electrode (RDE) or a rotating ring electrode (RRDE), where the diameter of the RDE is 3 mm and the diameter of the RRDE is 4 mm. After drying at room temperature, perform electrochemical testing. The catalyst loading is 0.42 mg·cm³. -2 .

[0038] The results are as follows Figure 10 As shown, where, Figure 10 In this context, 'a' represents the RRDE test result for NP / Fe-NC. Figure 10 In this context, 'b' represents a comparison of the number of electrons transferred and the hydrogen peroxide yield for the five catalysts; according to Figure 10 Calculations in section a show that, within a potential range of 0.2 to 0.8 V, the electron transfer number of NP / Fe-NC is consistently higher than 3.95, the peroxide yield is less than 1%, and the Faraday efficiency is higher than 99%. (From...) Figure 10 As shown in b, the selectivity of NP / Fe-NC is significantly better than that of other reference samples, further confirming its efficient four-electron ORR reaction pathway, which is beneficial for achieving efficient energy conversion.

[0039] Furthermore, the selectivity of the ORR reaction pathway was further evaluated using Koutecky-Levich (KL) curves, which were derived from LSV curves at different RDE speeds. The results are as follows: Figure 11 As shown, where, Figure 11 In the figure, 'a' represents the LSV curves of NP / Fe-NC at different RDE speeds. Figure 11 In this context, b represents the KL curve for NP / Fe-NC. Figure 11 In the figure, c represents the LSV curves of N / Fe-NC at different RDE speeds. Figure 11 In this context, d represents the KL curve for N / Fe-NC. Figure 11 In the figure, 'e' represents the LSV curves of P / Fe-NC at different RDE speeds. Figure 11 f in the figure represents the KL curve of P / Fe-NC. Figure 11 In the figure, g represents the LSV curves of Fe-NC at different RDE speeds. Figure 11 In this context, h represents the KL curve for Fe-NC; according to Figure 11 Calculations based on the KL equation revealed electron transfer numbers of NP / Fe-NC, N / Fe-NC, P / Fe-NC, and Fe-NC to be 4, 3.97, 3.98, and 3.8, respectively, indicating that NP / Fe-NC exhibits excellent four-electron reaction pathway selectivity. The electron transfer number of NP / Fe-NC reaching the theoretical value may be due to the thicker catalyst layer causing the KL equation to deviate from the ideal hydrodynamic model, or it may be influenced by the background current. Furthermore, there may be deviations between the actual test conditions and the empirical constants involved in the KL equation (e.g., O2 concentration, O2 diffusion coefficient, solution viscosity, etc.).

[0040] Meanwhile, to gain a deeper understanding of the intrinsic activity of the prepared samples, different scan rates (10, 20, 30, 40, 50, 60 mV·s) were applied within the voltage range of 1.065–1.165 V.-1 CV curves for NP / Fe-NC, N / Fe-NC, P / Fe-NC, Fe-NC, and Pt / C were measured. The results are as follows: Figure 12 As shown, where, Figure 12 In the figure, 'a' represents the CV curve of NP / Fe-NC. Figure 12 In the figure, b represents the CV curve of N / Fe-NC. Figure 12 In the figure, c represents the CV curve of P / Fe-NC. Figure 12 In the figure, d represents the CV curve of Fe-NC. Figure 12 In this context, 'e' represents the CV curve of Pt / C. Figure 12 In this context, f represents the relationship between the sweep rate and the current density; from Figure 12 It can be seen that the current density increases with the increase of the scan rate. A graph is plotted between the current density difference at the median voltage of 1.115V and the scan rate, and the double-layer capacitance is obtained by fitting the graph. (NP / Fe-NC) C dl 25.5 mF·cm -2 Higher than N / Fe-NC (19.8 mF·cm) -2 ), P / Fe-NC (22.3 mF·cm) -2 ), Fe-NC (15.3 mF·cm) -2 ) and Pt / C (8.2 mF·cm -2 This indicates that the optimal sample NP / Fe-NC not only exposes more active sites during the electrochemical process, but also has a high utilization rate of active sites.

[0041] Example 7: Determination of catalyst stability Accelerated aging tests were applied to determine the stability of the catalysts. NP / Fe-NC and Pt / C catalysts were subjected to 5000 CV cycles, respectively, and the performance changes after cycling were detected. The accelerated aging test for ORR requires a temperature of 0.1 mol·L⁻¹. -1 The test is performed in KOH or HClO4 solution, while the OER test requires 1 mol·L⁻¹ solution. -1 The reaction was carried out in KOH solution. The performance degradation process of the catalyst during long-term operation was simulated by applying continuous CV tests. The ORR scan rate was 100 mV·s. -1 The voltage range is set between 0.5 and 1.1 V. The OER scan rate is 50 mV·s. -1 The voltage range is between 0.9 and 1.5V, and the LSV curve needs to be tested before and after cycling. The results are as follows... Figure 13 As shown, where, Figure 13 In the figure, 'a' represents the LSV curves before and after the accelerated aging test. Figure 13In the image, b represents the SEM image of NP / Fe-NC at a 400 nm scale after 5000 CV cycles. Figure 13 In the image, 'c' represents the SEM image of NP / Fe-NC at a 200 nm scale after 5000 CV cycles; Figure 13 It can be seen that after 5000 CV cycles, the NP / Fe-NC E 1 / 2 The loss of only 10 mV was significantly better than that of the Pt / C catalyst (47 mV), indicating that NP / Fe-NC exhibits good cyclic stability. Furthermore, SEM images after 5000 CV cycles showed that the structure of NP / Fe-NC remained well-preserved, with no obvious signs of iron agglomeration, further demonstrating the high stability of this atomically dispersed active site and the robustness of the catalyst structure.

[0042] Example 8: Preparation of Zinc-Air Batteries using NP / Fe-NC Zinc-air batteries were prepared using the NP / Fe-NC catalyst from Example 1. The specific preparation method was as follows: 5 mg of catalyst and 2 mg of acetylene black were weighed and dispersed in a mixed solution of 600 μL water, 360 μL isopropanol, and 40 μL of 5% Nafion solution. The solution was then sonicated for at least 0.5 hours to form a uniformly dispersed suspension. Nickel foam was selected as the current collector, and the dispersed slurry was dropped onto the nickel foam at a loading of 1 mg / cm³. -2 The mixture was dried overnight in a vacuum drying oven at 60°C. Subsequently, the gas diffusion layer, nickel foam with dripped slurry, and diaphragm were sequentially pressed into a sheet to serve as the air cathode, and a polished zinc sheet was used as the anode. (6 mol·L⁻¹) -1 KOH and 0.2 mol·L -1 A mixed solution of Zn(Ac)2 was used as the electrolyte.

[0043] Commercial Pt / C-based zinc-air batteries were assembled using the same steps, employing an air electrode of Pt / C+RuO2, wherein the mass ratio of Pt / C to RuO2 catalyst was 1:1.

[0044] The open-circuit voltages of the two types of air batteries were tested, and the results are as follows: Figure 14 As shown, due to their excellent electrocatalytic activity and highly promising energy conversion capabilities, the open-circuit voltage of NP / Fe-NC-based ZABs is 1.49V, significantly better than that of Pt / C-based ZABs (1.46V). To further verify the performance and feasibility of ZABs prepared based on NP / Fe-NC in practical applications, actual power supply tests were conducted, and the results are as follows. Figure 15As shown, ZABs made with NP / Fe-NC as the air cathode successfully lit a 1V LED lamp. This experimental result confirms that the NP / Fe-NC catalyst in ZABs can effectively convert chemical energy into electrical energy and provide a stable power supply for external load devices.

[0045] Performance testing of the zinc-air battery prepared in Example 9 Performance tests of the zinc-air battery were conducted using a VPM-300 electrochemical workstation at a scan rate of 5 mV·s. -1 Furthermore, the open-circuit voltage, charge-discharge voltage difference, and power density curves of the assembled zinc-air battery were tested using a French VPM-300 workstation, while the catalyst was tested at different current densities (1, 2, 5, 10, 15, and 20 mA·cm⁻¹) using a Shenzhen Xinwei CT-4008T charge-discharge tester. -2 Rate performance and constant current charge / discharge performance under these conditions.

[0046] The discharge polarization curves and power density curves of NP / Fe-NC and Pt / C based zinc-air batteries are as follows: Figure 16 As shown, by Figure 16 It can be seen that the peak power density of the Pt / C-based zinc-air battery is 114.4 mW·cm⁻¹. -2 (204.9mA·cm) -2 ), while the NP / Fe-NC based zinc-air battery achieves a current density of 260.8 mA·cm⁻¹. -2 It reached a peak power density of 166.4 mW·cm⁻¹. -2 .

[0047] Rate performance test results at different current densities are as follows Figure 17 As shown, by Figure 17 It can be seen that the discharge voltage of both NP / Fe-NC and Pt / C-based zinc-air batteries decreases with increasing current density. However, the NP / Fe-NC assembled zinc-air battery maintains a higher discharge voltage than the Pt / C assembled zinc-air battery at all current densities. Even at 20 mA·cm⁻¹ -2 At high current densities, the NP / Fe-NC-based zinc-air battery can still maintain an average discharge voltage of 1.239V, far exceeding the discharge voltage of Pt / C (1.228V). Furthermore, as the current density returns to 15 mA·cm⁻¹... -2 and 10mA·cm -2 The voltage can also basically recover to its original level. This shows that the zinc-air battery assembled by NP / Fe-NC has good reversibility and recovery, and can cope with high load operation, which provides an important guarantee for its widespread use in practical applications.

[0048] At 10 mA·cm -2 and 20mA·cm -2 Constant current charge-discharge performance was tested at the density, and the results are as follows: Figure 18 As shown, where, Figure 18 In this context, 'a' is 10 mA·cm. -2 The test results Figure 18 b in the figure is 20 mA·cm -2 The test results; by Figure 18 It is observed that during discharge, the discharge potential plateau continuously decreases, but the discharge voltage of the NP / Fe-NC assembled zinc-air battery is significantly higher than that of the Pt / C-based zinc-air battery. Specifically, the discharge voltage of the NP / Fe-NC-based zinc-air battery is 1.288V, while the discharge voltage of the Pt / C-based zinc-air battery is only 1.267V. After continuous operation for more than 125 hours, the voltage of the NP / Fe-NC-based zinc-air battery decreases slightly and can continue discharging for 157.5 hours. However, the voltage plateau of the Pt / C-based zinc-air battery shows a significant voltage drop after 115 hours of discharge. The current density is extended to 25 mA·cm². -2 The NP / Fe-NC-based zinc-air battery can still maintain a voltage plateau of 1.253V and can discharge stably for about 68 hours, while the Pt / C zinc-air battery can only reach a discharge plateau of 1.254V and discharge for 64 hours.

[0049] To comprehensively evaluate the discharge performance of zinc-air batteries, at 10 mA·cm -2 Under constant current, the specific capacity of zinc-air batteries assembled with NP / Fe-NC and Pt / C plates was calculated based on the mass of anode zinc plate loss. The results are as follows: Figure 19 As shown, by Figure 19 It can be seen that the specific capacity of the zinc-air battery based on NP / Fe-NC reaches 804.5 mAh·g. -1 The Pt / C-based zinc-air battery has a capacity of only 754.5 mAh·g. -1 This result demonstrates that, at the same current density, NP / Fe-NC can utilize the zinc anode more effectively and achieve efficient energy storage.

[0050] To further investigate the cycling stability of the NP / Fe-NC catalyst, a composite catalyst was prepared from NP / Fe-NC and commercial RuO2 at a mass ratio of 1:1 and used as a catalytic electrode. The air electrode assembled with the composite catalyst was tested at a current density of 5 mA·cm⁻¹. -2The zinc-air battery can cycle stably for 1300 hours, while Pt / C+RuO2 can only maintain a cycle life of about 220 hours. In the initial 3 hours, the charge-discharge voltage difference of this zinc-air battery continuously increases until it stabilizes at 0.723V after 5 hours, with a round-trip efficiency as high as 62.19%. After 1300 hours of cycling, the voltage difference only increased by 0.187V, and the cycle efficiency remained above 50%.

[0051] Furthermore, at 10 mA·cm -2 A zinc-air battery assembled with NP / Fe-N-C+RuO2 was subjected to cycle charge-discharge tests at a high current density. The results are as follows: Figure 20 As shown, where, Figure 20 In this context, 'a' is 5 mA·cm. -2 The results of the cyclic charge-discharge test, among which, Figure 20 In this context, 'a' is 10 mA·cm. -2 Results of cyclic charge-discharge tests; by Figure 20 It can be seen that the NP / Fe-N-C+RuO2-based zinc-air battery can cycle stably for 380 hours, while the Pt / C+RuO2-based zinc-air battery has a lifespan of less than 100 hours. Specifically, in the first 3.5 hours, the charge-discharge voltage difference of the NP / Fe-N-C+RuO2-based ZABs increases with the number of cycles, and then enters a stable operating state. Around 5 hours, the charge-discharge voltage difference and round-trip efficiency stabilize at 0.827V and 58.25%, respectively. Even after 100 hours of cycling, the voltage difference only increases slightly to 0.875V, while the Pt / C+RuO2-based zinc-air battery has significantly deactivated (voltage difference greater than 1.6V). Thereafter, thanks to the stable electrochemical activity of the NP / Fe-N-C+RuO2 catalyst, the round-trip efficiency remains at 57.18% and 55.4% at the 200 and 300 hour test points, respectively. Even after 380 hours, the voltage difference of the zinc-air battery increased to 0.906V, and the round-trip efficiency remained at 54.39%. The zinc-air battery assembled with the composite catalyst exhibited a cycle stability of up to 380 hours, mainly due to the effective reduction of voltage polarization in the oxygen reduction process during discharge by the NP / Fe-NC catalyst component, as well as the synergistic effect of the ORR / OER active species. This result provides an important reference for the design and research of dual-center composite bifunctional electrocatalysts.

[0052] To further investigate the stability of the catalyst, 10 mA·cm -2 The zinc-air battery was disassembled after being cycled for 380 hours at a current density, and the catalyst layer of the air electrode was analyzed by SEM. Figure 21As shown, the catalyst layer is mainly composed of aggregates of catalyst and carbon black, resulting in large carbon black particles. The figure reveals that the morphology of the NP / Fe-NC nanoparticles has changed somewhat due to prolonged cycling, but they still largely maintain a dodecahedral morphology without significant structural collapse or agglomeration. Furthermore, a small number of nanotubes can still be found in the catalyst layer, indicating that the flexible carbon nanotubes appropriately mitigate the volume changes of the catalyst during cycling, thereby further enhancing the structural stability of the catalyst layer.

[0053] In summary, the NP / Fe-NC prepared by this invention retains a typical granular dodecahedral morphology and carries an appropriate amount of carbon nanotubes, thus exhibiting an extremely high specific surface area (817.02 m²). 2 ·g -1 The hierarchical porous structure of the carbon matrix increases the contact area between the oxygen, catalyst, and electrolyte three-phase interfaces, shortens the diffusion paths of oxygen-containing reactants and products, and exposes more active sites. The incorporation of additional nitrogen atoms into the carbon matrix induces uneven surface charge distribution and improves oxygen adsorption, while simultaneously making adjacent carbon atoms positively charged and increasing the degree of graphitization. The introduction of phosphorus (P) increases topological defects in the carbon framework, leading to charge delocalization and further improving conductivity.

[0054] After determining the optimal doping ratio and pyrolysis temperature, the synthesized NP / Fe-NC exhibits a porous structure, effectively adapting to volumetric strain during the ORR process, thereby improving the ORR activity and stability of NP / Fe-NC. Benefiting from these advantages, NP / Fe-NC exhibits the most positive onset potential in 0.1 MKOH. E on =1.051V), half-wave potential (0.884V) and high dynamic current density ( J k =25.1mA·cm -2 Meanwhile, NP / Fe-NC exhibits excellent selectivity for the four-electron reaction pathway and a high electrochemically active surface area (…). C dl =25.5mF·cm -2 It exhibits excellent stability. Even after 5000 CV cycles, the half-wave potential of the NP / Fe-NC catalyst only decreased by 10 mV, and there was no significant change in morphology.

[0055] Compared to commercial Pt / C, the NP / Fe-NC assembled zinc-air battery exhibits a high open-circuit voltage (1.49V) and a high power density (166.4mW·cm⁻¹). -2 260.8 mA·cm -2It boasts excellent rate performance, long-term stability (>157 hours), and a large discharge specific capacity (804.5 mAh·g). -1 Even at 20mA·cm -2 At high current densities, NP / Fe-NC maintains a voltage plateau of 1.243V and can discharge stably for approximately 68 hours. A dual-center composite bifunctional catalyst formed by physically mixing NP / Fe-NC and RuO2 is applied to a rechargeable zinc-air battery, achieving high current densities at 5 mA·cm⁻¹. -2 Capable of achieving a cycle time of up to 1300 hours; 10 mA·cm -2 It has a lifespan of 380 hours.

Claims

1. A method for preparing a nitrogen-phosphorus co-doped Fe-NC catalyst, characterized in that, The specific steps are as follows: S1: Dissolve Zn(NO3)2·6H2O in methanol to obtain solution A, and dissolve 2-methylimidazole in methanol to obtain solution B; S2: After mixing solutions A and B, add phthalocyanine iron and stir the reaction at room temperature for 24 hours. Centrifuge the product and wash and dry it with methanol to obtain ZnFe-ZIF powder. S3: Dissolve ZnFe-ZIF powder in methanol to obtain solution C; dissolve melamine in methanol and then add triphenylphosphine to obtain solution D; S4: Add solution D to solution C and stir rapidly for 12 h. Wash the resulting precipitate with methanol and dry to obtain NP / ZnFe-ZIF. Incubate NP / ZnFe-ZIF under Ar atmosphere at 5 °C·min. -1 The temperature was increased to 950℃ and held for 2 hours. After natural cooling to room temperature, the target product, nitrogen-phosphorus co-doped Fe-NC catalyst, was obtained.

2. The method for preparing the nitrogen-phosphorus co-doped Fe-NC catalyst according to claim 1, characterized in that, In step S1, the ratio of Zn(NO3)2·6H2O to 2-methylimidazole is 2.5g:6.568g; and when preparing solution A, the ratio of Zn(NO3)2·6H2O to methanol is 2.5g:80mL; when preparing solution B, the ratio of 2-methylimidazole to methanol is 6.568g:80mL.

3. The method for preparing the nitrogen-phosphorus co-doped Fe-NC catalyst according to claim 2, characterized in that, In step S2, the ratio of iron phthalocyanine to Zn(NO3)2·6H2O is 100mg:2.5g.

4. The method for preparing the nitrogen-phosphorus co-doped Fe-NC catalyst according to claim 1, characterized in that, In step S3, when preparing solution C, the ratio of ZnFe-ZIF powder to methanol is 300mg:100mL; when preparing solution D, the ratio of melamine to methanol is 100mg:50mL, and the ratio of ZnFe-ZIF powder, melamine and triphenylphosphine is 300mg:100mg:90~110mg.

5. A nitrogen-phosphorus co-doped Fe-NC catalyst prepared by any one of the preparation methods according to claims 1 to 4, characterized in that, The nitrogen-phosphorus co-doped Fe-NC catalyst has a granular dodecahedral morphology, carrying carbon nanotubes, and possesses a high specific surface area and a hierarchical porous structure. This increases the contact area between the three phase interfaces of oxygen, catalyst, and electrolyte, shortens the diffusion path of oxygen-containing reactants and products, and exposes more active sites.

6. The application of the nitrogen-phosphorus co-doped Fe-NC catalyst according to claim 5 in the preparation of zinc-air batteries, characterized in that, The preparation method of zinc-air batteries adopts the following steps: A1: Nitrogen-phosphorus co-doped Fe-NC catalyst, acetylene black, water, isopropanol and 5% Nafion solution were added sequentially to the reactor vessel; ultrasonic treatment was then performed to obtain a uniform suspension. A2: Add the suspension droplets onto the current collector and dry under vacuum; A3: Press the gas diffusion layer, the dry catalyst-containing current collector prepared in A2, and the diaphragm together to obtain an air cathode; A4: A zinc-air battery was prepared by using a polished zinc sheet as the air anode and a mixed solution of KOH and Zn(Ac)2 as the electrolyte.

7. The application according to claim 6, characterized in that, In step A1, the ratio of nitrogen-phosphorus co-doped Fe-NC catalyst, acetylene black, water, isopropanol, and 5% Nafion solution is 5 mg: 2 mg: 600 μL: 360 μL: 40 μL.

8. The application according to claim 7, characterized in that, In step A2, the current collector is nickel foam, and the loading of the suspension on the nickel foam is 1 mg·cm³. -2 .

9. The application according to claim 8, characterized in that, In step A4, the concentration of KOH in the electrolyte is 6 mol·L⁻¹. -1 The concentration of Zn(Ac)₂ in the electrolyte is 0.2 mol·L⁻¹. -1 .

10. The application of the nitrogen-phosphorus co-doped Fe-NC catalyst according to claim 5 in the preparation of zinc-air batteries, characterized in that, The preparation method of zinc-air batteries adopts the following steps: B1: Nitrogen-phosphorus co-doped Fe-NC catalyst, RuO2 catalyst, acetylene black, water, isopropanol, and 5% Nafion solution were added sequentially to the reactor vessel; a homogeneous suspension was obtained by ultrasonic treatment; the ratio of the volume of nitrogen-phosphorus co-doped Fe-NC catalyst, RuO2 catalyst, acetylene black, water, isopropanol, and 5% Nafion solution was 5 mg: 5 mg: 2 mg: 600 μL: 360 μL: 40 μL; B2: Add the suspension droplets onto the current collector and dry under vacuum; B3: Press the gas diffusion layer, the dry catalyst-containing current collector prepared in B2, and the diaphragm together to obtain an air cathode; B4: A zinc-air battery was prepared by using a polished zinc sheet as the air anode and a mixed solution of KOH and Zn(Ac)₂ as the electrolyte. The concentration of KOH in the electrolyte was 6 mol·L⁻¹. -1 ; The concentration of Zn(Ac)₂ in the electrolyte is 0.2 mol·L⁻¹. -1 .

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