A preparation method of a bimetallic phosphide / nitrogen-carbon electrocatalyst based on active site protection and three-dimensional mass transfer channel design

Abstract

The application relates to a bimetallic phosphide / nitrogen-carbon electrocatalyst based on active site protection and three-dimensional mass transfer channel design and a preparation method thereof. The preparation process of the catalyst comprises the following steps: firstly, mixing 2-methyl imidazole aqueous solution and cobalt and zinc-containing nitrate aqueous solution, stirring, washing and drying to obtain a Co-ZIF-8 precursor. Then, the precursor is secondarily modified by using phytic acid as a phosphorus source and iron ions. Finally, the CoFeP-NC electrocatalyst is prepared through a high-temperature chemical vapor deposition reaction under the assistance of dicyandiamide. The preparation process has the advantages of environmental protection, convenience and low cost. The obtained CoFeP-NC catalyst exhibits excellent bifunctional electrocatalytic activity (oxygen reduction and oxygen evolution reaction) and stability, and the potential difference (△E) between the oxygen evolution and oxygen reduction reactions is as low as 0.70 V. The zinc-air battery assembled based on the catalyst shows high peak power density and excellent cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic material synthesis and new energy conversion device technology, specifically relating to a non-precious metal bifunctional catalyst for the cathode of a rechargeable zinc-air battery and its preparation method. Background Technology

[0002] The increasing demand for portable electronic devices and large-scale energy storage continues to drive the development of efficient, safe, and low-cost electrochemical energy storage and conversion systems. Zinc-air batteries, with their high theoretical energy density (1086 Wh / kg), are particularly promising. -1 Zinc-air batteries are considered one of the most promising next-generation energy technologies due to their abundant and safe raw material reserves and environmental friendliness. However, their commercialization faces severe challenges. A key bottleneck lies in the extremely slow kinetics of the oxygen reduction and oxygen evolution reactions at the air cathode, leading to low energy efficiency. Furthermore, zinc-air batteries suffer from oxidation and corrosion of the cathode carbon material during long-term operation, accelerating the loss of active sites and the separation of active materials. While current mainstream noble metal-based materials (platinum-carbon + ruthenium dioxide) exhibit high activity for ORR or OER in noble metal catalysts, they are limited by inherent defects such as high cost, scarce resources, and insufficient long-term stability. This has spurred the research and development of non-noble metal materials.

[0003] In recent years, transition metal derivatives (especially nitrides, carbides, sulfides, and phosphides) have attracted widespread attention as a promising class of electrocatalysts due to their excellent catalytic performance and low cost. Among them, transition metal phosphides (TMPs) are particularly favored for their unique physicochemical properties and good stability. The introduction of non-metallic phosphorus can not only modulate the electronic structure of transition metals but also induce polymerization effects by changing the d-electron density, thereby generating more reaction sites. (Journal of Colloid and Interface Science, 653 (2024) 1246-1255.) Given the inherent performance limitations and lack of active sites of single transition metal phosphides, the design and synthesis of multi-metal phosphides can significantly improve catalytic activity by utilizing synergistic effects. Furthermore, the development of high-performance catalysts for zinc-air batteries requires attention not only to their intrinsic activity but also to ensuring efficient mass transfer between oxygen and electrolyte.

[0004] ZIF-8 is a common metal-organic framework (MOF) material, showing broad application prospects in many fields as a multifunctional support or sacrificial template. Notably, ZIF-8-derived carbon materials typically possess large surface areas, abundant pore structures, high nitrogen content, and good electrical conductivity, providing a convenient route for synthesizing high-performance ORR and OER electrocatalysts. Similarly, ZIF-8-derived carbon materials can serve as ideal supports for TMPs. However, due to the relatively low content of surface active groups in ZIF-8-derived carbon materials, they often struggle to effectively capture external metal ions, potentially leading to particle agglomeration during high-temperature calcination. Furthermore, while ZIF-8-derived carbon materials exhibit porous structures, most are microporous. Studies have shown that mass transfer between active sites is faster in mesoporous carbon materials than in microporous materials. Therefore, reasonable surface modification of ZIF-8 to enhance its affinity for external metal ions, while simultaneously introducing sufficient mesopores into the material, is an effective strategy to address these issues. Summary of the Invention

[0005] To address the aforementioned issues, this invention relates to a bimetallic phosphide / nitrogen-carbon electrocatalyst designed based on active site protection and a three-dimensional mass transfer channel, and its preparation method. By precisely controlling the synthesis process, a three-dimensional leaf-like nanostructure is constructed, significantly promoting mass transfer. The generated phosphides (CoFeP, Co2P) effectively regulate the local coordination environment of the iron and cobalt active sites, enhancing catalytic activity. Furthermore, the carbon matrix not only provides a highly conductive network but also effectively coats and anchors the phosphide active centers, effectively inhibiting the dissolution, migration, and aggregation of active components, thereby significantly improving the catalyst's structural stability and long-term operational durability. This provides a new approach to improving the catalytic activity and stability of zinc-air cathode catalysts and offers a material basis for practical applications.

[0006] The preparation process of this catalyst includes: First, a 2-methylimidazole aqueous solution is mixed with a cobalt and zinc nitrate aqueous solution, and after stirring, washing, and drying, a Co-ZIF-8 precursor is obtained. Subsequently, the precursor is further modified using phytic acid as a phosphorus source and iron ions. Finally, the CoFeP-NC electrocatalyst is prepared by high-temperature chemical vapor deposition reaction assisted by dicyandiamide.

[0007] The specific steps of its preparation method are as follows:

[0008] A method for preparing a bimetallic phosphide / nitrogen-carbon electrocatalyst based on active site protection and three-dimensional mass transfer channel design includes the following steps: Step 1: Mix and stir the aqueous solutions of zinc nitrate hexahydrate and cobalt nitrate hexahydrate with the aqueous solution of 2-methylimidazole. The precipitate obtained by centrifugation is washed with methanol and dried under vacuum to obtain the Co-ZIF-8 precursor. Step 2: Disperse the Co-ZIF-8 precursor in an aqueous solution containing phytic acid and ferrous sulfate, and obtain the CoFeP-ZIF-8 precursor by stirring, centrifugation, washing, and vacuum drying. Step 3: Place CoFeP-ZIF-8 and dicyandiamide in the middle and upstream of a tube furnace, respectively, and perform high-temperature chemical vapor deposition under N2 atmosphere. After carbonization, the CoFeP-NC catalyst is obtained.

[0009] Preferably, the precipitate obtained by centrifugation in step 1 is washed with methanol 2-3 times and then vacuum dried for 10-12 hours.

[0010] Preferably, in step 1, the mass ratio of zinc nitrate hexahydrate, cobalt nitrate hexahydrate, and 2-methylimidazole is 1:(0.06-0.12):(2.1-2.3).

[0011] Preferably, in step 1, the mass ratio of zinc nitrate hexahydrate, cobalt nitrate hexahydrate, and 2-methylimidazole is 1:0.0811:2.2048.

[0012] Preferably, in step 2, the molar ratio of phytic acid to total metal ions is 1:(1.5-2.5), preferably 1:2, and the mass ratio of zinc nitrate to ferrous nitrate is 1:(0.1-0.2). Preferably, it is 1:0.103.

[0013] Preferably, in step 2, the molar ratio of phytic acid to total metal ions is 1:2, and the mass ratio of zinc nitrate to ferrous nitrate is 1:0.103.

[0014] Preferably, the heating rate of the tubular furnace in step 3 is 5. o C min -1 The vapor deposition reaction temperature is 900°C. o C, the heat preservation time is 2 hours.

[0015] The method described above for preparing the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC is used to apply the CoFeP-NC catalyst to zinc-air batteries.

[0016] Preferably, a self-made dual-electrode system is used to test the performance of the rechargeable zinc-air battery.

[0017] More preferably, the prepared catalyst ink is uniformly coated on hydrophobic carbon paper (effective area 1 cm²). 2 The cathode is used as an air cathode, and the loading is controlled at 2 mg cm⁻¹. -2A polished zinc plate was used as the anode, and the electrolyte was a mixed solution of 6 M KOH and 0.2 M Zn(Ac)₂. A gas diffusion layer was set on the air cathode side to prevent leakage. A noble metal catalyst (Pt / C:RuO₂ = 1:1) was used as a control electrode. The discharge polarization curves were measured using a CHI760E electrochemical workstation, and the results were obtained using a LANDCT2001A system at 5 mA cm⁻¹. -2 Cyclic stability tests were conducted under constant current.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The CoFeP-NC electrocatalyst of this invention possesses a unique three-dimensional porous foliate carbon structure, which not only provides abundant pore channels but also effectively promotes mass transfer efficiency during the reaction process. The uniformly dispersed metal phosphides (CoFeP, Co2P) in the catalyst optimize the local coordination environment of the iron and cobalt active centers, thereby significantly enhancing the intrinsic catalytic activity of the material. Furthermore, the nitrogen-doped carbon matrix uniformly coats the phosphide active sites, enhancing overall conductivity while further improving the catalyst's structural stability and long-term cycling tolerance. A CoFeP bimetallic phosphide / nitrogen-carbon composite material with a unique three-dimensional foliate hierarchical porous structure is prepared through a synergistic process of phytic acid-assisted coordination-etching and vapor deposition nitrogen doping. This specific structure enables it to exhibit excellent mass transfer efficiency in GDE. The generated CoFeP / Co2P phosphide phase synergistically regulates the electronic structure of the active sites, enhancing intrinsic catalytic activity. The stable multilayered carbon matrix coats and protects the phosphide active centers, significantly improving the catalyst's structural stability and long-term cycling durability. The resulting CoFeP-NC composite material exhibits excellent catalytic performance, with a half-wave potential of 0.86 V (vs. RHE), an overpotential of 280 mV, and a low potential difference of 0.70 V, while also demonstrating excellent tolerance. Zinc-air batteries assembled based on this catalyst exhibit a high power density (204 mW / cm²). 2 ) and high stability (>5000 h).

[0019] The preparation of the CoFeP-NC electrocatalyst involved in this invention has the advantages of low cost, simple and controllable process, and high reproducibility. Attached Figure Description

[0020] Figure 1 These are the XRD patterns of the products prepared in Examples 4 and 1.

[0021] Figure 2 This is an SEM image of the product prepared in Example 4.

[0022] Figure 3This is a TEM image (100 nm) of the oxygen electrocatalyst prepared in Example 5.

[0023] Figure 4 The image shows a TEM image (200 nm) of the oxygen electrocatalyst prepared in Example 4.

[0024] Figure 5 This is a high-resolution transmission electron microscope (HRTEM) image of a region of the oxygen electrocatalyst prepared in Example 4.

[0025] Figure 6 This is a high-resolution transmission electron microscope (HRTEM) image of a region of the oxygen electrocatalyst prepared in Example 4.

[0026] Figure 7 The BET pore size distribution diagrams are for the oxygen electrocatalysts prepared in Examples 4 and 5.

[0027] Figure 8 The image shows the GDE diagrams of the oxygen electrocatalysts prepared in Examples 4 and 1.

[0028] Figure 9 The graphs show the ORR polarization curves of the products prepared in Examples 1-4.

[0029] Figure 10 These are OER performance graphs of the products prepared in Examples 1-4.

[0030] Figure 11 The graphs show the ORR stability test performance of the oxygen electrocatalysts in Examples 1-4.

[0031] Figure 12 The graph shows the OER stability test performance of the oxygen electrocatalysts in Examples 2-4.

[0032] Figure 13 The LSV curves of the oxygen electrocatalysts in Examples 1-4 and Pt / C+RuO2 are shown.

[0033] Figure 14 The polarization curves and corresponding power density curves are shown for the liquid zinc-air battery assembled based on the oxygen electrocatalyst prepared in Example 4 and the Pt / C+RuO2 catalyst.

[0034] Figure 15 The diagram shows the charge-discharge cycle stability of a liquid zinc-air battery assembled based on the oxygen electrocatalyst prepared in Example 4 and the Pt / C+RuO2 catalyst (5 mA / cm). 2 ). Detailed Implementation

[0035] Example 1 (1) Synthesis of Co-NC 7.88 g of 2-methylimidazole was dissolved and dispersed in 100 mL of deionized water (solution A), and 3.75 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate were dissolved and dispersed in 50 mL of deionized water (solution B). After solutions A and B were fully dissolved, solution B was injected into solution A and mixed evenly and stirred for 2 h. The precipitate was collected, washed 2-3 times with methanol, and dried in an oven at 60-70℃. The resulting purple powder was named (Co-ZIF-8). The dicyandiamide and Co-ZIF-8 precursor were placed in the upstream and midstream of a tube furnace, respectively, by centrifugation. The temperature was increased to 900℃ at a rate of 5℃ / min under N2 atmosphere, and pyrolyzed for 2 h to obtain Co-NC.

[0036] Example 2 (1) Synthesis of CoP-NC 7.88 g of 2-methylimidazole was dissolved and dispersed in 100 mL of deionized water (solution A), and 3.75 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate were dissolved and dispersed in 50 mL of deionized water (solution B). After solutions A and B were fully dissolved, solution B was added to solution A and mixed thoroughly. The mixture was stirred for 2 h, and the precipitate was collected, washed 2-3 times with methanol, and dried in an oven at 60-70℃ to obtain the Co-ZIF-8 precursor. Subsequently, the Co-ZIF-8 precursor was dissolved and dispersed in 50 mL of aqueous solution containing 100 μL of phytic acid. After stirring, centrifugation, washing, and drying, the CoP-ZIF-8 precursor was obtained. CoP-ZIF-8 and dicyandiamide were then placed in the middle and upstream sections of a tubular furnace, respectively, and heated to 900℃ at a rate of 5℃ / min under a N2 atmosphere. High-temperature chemical vapor phase pyrolysis was performed for 2 h to obtain the target product CoP-NC.

[0037] Example 3 (1) Synthesis of CoFe-NC 7.88 g of 2-methylimidazole was dissolved and dispersed in 100 mL of deionized water (solution A), and 3.75 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate were dissolved and dispersed in 50 mL of deionized water (solution B). After solutions A and B were fully dissolved, solution B was added to solution A and mixed thoroughly. The mixture was stirred for 2 h, and the precipitate was collected, washed 2-3 times with methanol, and dried in an oven at 60-70℃ to obtain the Co-ZIF-8 precursor. Subsequently, the Co-ZIF-8 precursor was dissolved and dispersed in 50 mL of aqueous solution containing 0.03 g of ferrous sulfate. After stirring, centrifugation, washing, and drying, the CoFe-ZIF-8 precursor was obtained. CoFe-ZIF-8 and dicyandiamide were then placed in the middle and upstream sections of a tubular furnace, respectively, and heated to 900℃ at a rate of 5℃ / min under a N2 atmosphere. High-temperature chemical vapor phase pyrolysis was performed for 2 h to obtain the target product CoFe-NC.

[0038] Example 4 (1) Synthesis of CoFeP-NC 7.88 g of 2-methylimidazole was dissolved and dispersed in 100 mL of deionized water (solution A), and 3.75 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate were dissolved and dispersed in 50 mL of deionized water (solution B). After solutions A and B were fully dissolved, solution B was added to solution A and mixed thoroughly. The mixture was stirred for 2 h, and the precipitate was collected, washed 2-3 times with methanol, and dried in an oven at 60-70℃ to obtain the Co-ZIF-8 precursor. Subsequently, the Co-ZIF-8 precursor was dissolved and dispersed in 50 mL of aqueous solution containing 100 μL of phytic acid and 0.03 g of ferrous sulfate. After stirring, centrifugation, washing, and drying, the CoFeP-ZIF-8 precursor was obtained. CoFe-ZIF-8 and dicyandiamide were then placed in the middle and upstream of a certain amount of tubular furnace, respectively, and heated to 900 °C at a heating rate of 5 °C / min under N2 atmosphere. High-temperature chemical vapor phase pyrolysis was then performed for 2 h to obtain the target product CoFeP-NC.

[0039] Example 5 Based on Example 4, an auxiliary agent, tea saponin, was introduced and added to the preparation of the Co-ZIF-8 precursor, while other experimental conditions remained unchanged. 7.88 g of 2-methylimidazole and 0.1-0.5 g of tea saponin were dissolved and dispersed in 100 mL of deionized water (solution A), and 3.75 g of zinc nitrate hexahydrate and 0.29 g of cobalt nitrate hexahydrate were dissolved and dispersed in 50 mL of deionized water (solution B). After solutions A and B were fully dissolved, solution B was injected into solution A, mixed thoroughly, and stirred for 2 h. The precipitate was collected, washed 2-3 times with methanol, and dried in an oven at 60-70℃ to obtain the precursor. The precursor was then dissolved and dispersed in 50 mL of an aqueous solution containing 100 μL of phytic acid and 0.03 g of ferrous sulfate. After stirring, centrifugation, washing, and drying, the sample and dicyandiamide were placed in the middle and upstream of a certain amount of tubular furnace, respectively. The temperature was increased to 900 °C at a rate of 5 °C / min under N2 atmosphere, and the high-temperature chemical vapor phase pyrolysis was carried out for 2 h to obtain the target product.

[0040] Table 1

[0041] Table 1 shows that tea saponin in Example 5 effectively improved the specific surface area and pore structure of the material; the specific surface area increased from 723.29 m² / g. - ¹Increased significantly to 925.12 m² g - ¹ indicates that the tea soap agent, acting as a foaming agent during synthesis, formed a more developed porous structure. Pore size distribution data further confirms that there are more mesopores with pore sizes of 3.5-5 nm, and the average pore size ranges from 0.78 cm³ / g. - ¹Increased to 0.89 cm³ g - ¹ This means that the material not only achieves a higher exposed area of ​​active sites, but more importantly, it constructs a more optimized three-dimensional mass transfer channel, which is conducive to the rapid diffusion of reactants and products. Secondly, tea saponin significantly enhances the material's loading and anchoring ability for active metals. The changes in metal content (Atomic %) in XPS: cobalt (Co) content increased from 1.68% to 3.57%, and iron (Fe) content increased even more from 0.52% to 2.52%. This phenomenon is attributed to the abundant hydroxyl and other functional groups in the tea saponin molecule structure, which can form stronger coordination with metal ions, thereby more efficiently and uniformly capturing and fixing metal ions in the precursor stage of synthesis, inhibiting their high-temperature migration and aggregation.

[0042] The prepared bifunctional oxygen electrocatalyst was subjected to X-ray diffraction analysis, scanning electron microscopy analysis, ORR and OER performance and stability tests, discharge polarization performance tests of liquid zinc-air batteries, and charge-discharge cycle stability tests of liquid zinc-air batteries. The results are as follows: Figures 1-14 As shown.

[0043] XRD test results show that: Figure 1 As shown, the x-axis represents the diffraction angle (2θ), and the y-axis represents the relative diffraction intensity. For Example 4, the diffraction peaks originate from the (002) crystal plane of C and the (112), (211), (020), and (302) crystal planes of the CoFeP alloy phase (PDF #97-062-2955). The diffraction peaks are all relatively sharp, and the baselines are relatively clean and smooth, indicating that the crystallinity of the samples is good. The diffraction peaks of Example 1 originate from the (111), (200), and (220) crystal planes of Co metal (PDF #01-071-4651). For the material morphology analysis in this embodiment, the obtained images are as follows: Figure 2-6 As shown, where Figure 2 The image shows the SEM morphology of the CoFeP-NC material. The CoFeP-NC catalyst exhibits a layered, porous, wrinkled, leaf-like morphology. Nanoparticles are unevenly distributed on the surface of the leaf layers, partially embedded in the carbon matrix, displaying a rich porous structure. The key role of introducing phytic acid is as both a phosphorus source and an etchant, leading to the formation of a novel structure. Figure 3 The transmission spectrum of the catalyst in Example 5 shows that it is a porous material, presumably due to the co-foaming effect of phytic acid and tea saponin. Figure 4 This is a transmission electron microscope (TEM) image of the CoFeP-NC catalyst, showing numerous nanoparticles dispersed and embedded within a nitrogen-doped carbon matrix. Figure 5-6 High-resolution transmission electron microscopy (HRTEM) images of the CoFeP-NC catalyst show that the carbon layer on the surface of a single particle acts like an armor, inhibiting the dissolution and shedding of active components and thus enhancing durability. The HRTEM images also reveal distinct lattice striations on the surface, with interplanar spacings of 2.22 Å and 4.32 Å, corresponding to the (112) and (111) crystal planes of the CoFeP nanoparticles, and interplanar spacings of 3.45 Å and 4.97 Å, corresponding to the (001) and (100) crystal planes of the Co2P nanoparticles. The synergistic effect of these active sites enhances the catalyst's activity.

[0044] BET testing was performed on it, and the pore size distribution curve was obtained. Figure 7 The results show that the size of the mesopores is mainly concentrated in the range of 3.5-5.0 nm. The rich distribution of mesopores in the CoFeP-NC sample is more conducive to the permeation and diffusion of electrolytes and reactant gases, thereby increasing the catalytic reaction rate, fully exposing the active sites of the catalyst, and improving the performance of the catalyst.

[0045] To reveal the effect of sample pore size on mass transfer performance, the polarization curves of Co-NC and CoFeP-NC were also measured using GDE, as shown in ( Figure 8As shown, CoFeP-NC with a larger pore size can achieve up to 800 mA cm⁻¹ at a positive potential of 0.71 V. The current density of CoFeP-NC is 2, while Co-NC requires a positive potential of 0.51 V, which confirms that CoFeP-NC has a fast mass transfer efficiency.

[0046] The ORR performance of the prepared CoFeP-NC electrocatalysts in O2-saturated 0.1M KOH solution was tested, and the results are as follows: Figure 9 As shown, CoFeP-NC exhibits a large limiting current density (J). L The efficiency is 5.15 mA / cm⁻², and the half-slope potential is 0.86 V, which is better than Co-NC (J). L =4.79 mA / cm2 and 0.85 V) and CoP (J L =4.98 mA / cm2 and 0.835 V), slightly lower than CoFeP-NC (J L =5.03 mA / cm2 and 0.87 V) simultaneously with Pt / C (J L =5.21 mA / cm2 and 0.87 V) are comparable. This indicates that CoFeP-NC exhibits high ORR activity, and the introduction of Fe promotes oxygen reduction. The OER performance of the prepared electrocatalyst was tested in 1 MKOH solution, and the results are as follows. Figure 10 As shown, at a current density of 10 mA / cm², the overpotential of CoFeP-NC is 280 mV, lower than that of CoFe-NC (318 mV), CoP-NC (329 mV), and Co-NC (368 mV), and significantly lower than that of commercial RuO2 (330 mV). This indicates that further introduction of P to form a CoFeP alloy greatly improves the OER catalytic performance. In addition, the in-situ introduction of CoFeP nanoparticles into the nitrogen-doped carbon matrix can significantly improve the oxygen evolution reaction activity. Figure 13 The results show that the bifunctional activity (ΔE=0.70 V) of the CoFeP-NC composite material is significantly better than that of Examples 1, 2, and 3.

[0047] ORR stability tests were performed on the electrocatalysts of Examples 1-4, such as... Figure 11 As shown, it can be observed that after a stability test of 7200 s, the current density of the catalyst can still be maintained at 96.28% of the initial current, which is higher than the current retention rate of Examples 1-4, indicating that the ORR performance of the catalyst has good stability.

[0048] The OER stability of the electrocatalysts in Examples 2-4 was tested, such as... Figure 12As shown, it can be observed that the voltage of CoFeP-NC only decreased by 9 mV after 350 h, indicating that the catalyst has good tolerance.

[0049] Figure 14 The example shows the assembly of a liquid zinc-air battery in Example 4, using a polished zinc plate as the anode, and a solution containing 0.2 M Zn(OAc)2. A liquid zinc-air battery was assembled using 6 M KOH (2H₂O) as the electrolyte and CoFeP-NC electrocatalyst as the air cathode. Performance testing revealed a maximum power density of 204 mW / cm². 2 It significantly outperforms the peak power density of zinc-air batteries assembled based on commercial Pt / C+RuO2.

[0050] Long-cycle stability tests were conducted on CoFeP-NC-based liquid zinc-air batteries, and the results are as follows: Figure 15 As shown, the assembled liquid zinc-air battery operated stably for 5600 hours, indicating that the zinc-air battery assembled with the CoFeP-NC electrocatalyst prepared in this invention has ultra-long cycle stability and has the potential to replace Pt / C+RuO2 in practice.

Claims

1. A method for preparing a bimetallic phosphide / nitrogen-carbon electrocatalyst based on active site protection and three-dimensional mass transfer channel design, characterized in that, Includes the following steps: Step 1: Mix and stir the aqueous solutions of zinc nitrate hexahydrate and cobalt nitrate hexahydrate with the aqueous solution of 2-methylimidazole. The precipitate obtained by centrifugation is washed with methanol and dried under vacuum to obtain the Co-ZIF-8 precursor. Step 2: Disperse the Co-ZIF-8 precursor in an aqueous solution containing phytic acid and ferrous sulfate, and obtain the CoFeP-ZIF-8 precursor by stirring, centrifugation, washing, and vacuum drying. Step 3: Place CoFeP-ZIF-8 and dicyandiamide in the middle and upstream of a tube furnace, respectively, and perform high-temperature chemical vapor deposition under N2 atmosphere. After carbonization, the CoFeP-NC catalyst is obtained.

2. The method for preparing the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC according to claim 1, characterized in that, The precipitate obtained by centrifugation in step 1 is washed with methanol 2-3 times and then vacuum dried for 10-12 hours.

3. The method for preparing the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC according to claim 1, characterized in that, In step 1, the mass ratio of zinc nitrate hexahydrate, cobalt nitrate hexahydrate, and 2-methylimidazole is 1:(0.06-0.12):(2.1-2.3).

4. The method for preparing the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC according to claim 1, characterized in that, In step 1, the mass ratio of zinc nitrate hexahydrate, cobalt nitrate hexahydrate, and 2-methylimidazole is 1:0.0811:2.2048.

5. The method for preparing the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC according to claim 1, characterized in that, In step 2, the molar ratio of phytic acid to total metal ions is 1:(1.5-2.5); the mass ratio of zinc nitrate to ferrous nitrate is 1:(0.1-0.2).

6. The method for preparing the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC according to claim 5, characterized in that, In step 2, the molar ratio of phytic acid to total metal ions is 1:2, and the mass ratio of zinc nitrate to ferrous nitrate is 1:0.

103.

7. The method for preparing the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC according to claim 1, characterized in that, The heating rate of the tubular furnace in step 3 is 5. o C min -1 The vapor deposition reaction temperature is 900°C. o C, the heat preservation time is 2 hours.

8. The catalyst CoFeP-NC obtained by the preparation method of the bimetallic phosphide nitrogen-doped carbon high-efficiency and stable bifunctional electrocatalyst CoFeP-NC according to any one of claims 1-7 is applied to zinc-air batteries.

9. The application according to claim 8, characterized in that: The performance of a rechargeable zinc-air battery was tested using a dual-electrode system.

10. The application according to claim 9, characterized in that: The specific procedure for testing the performance of a rechargeable zinc-air battery using a dual-electrode system is as follows: the prepared catalyst ink is uniformly coated onto hydrophobic carbon paper to serve as the air cathode, with the loading controlled at 2 mg cm⁻¹. -2 A polished zinc plate was used as the anode, and the electrolyte was a mixed solution of 6 M KOH and 0.2 M Zn(Ac)2. A gas diffusion layer was set on the air cathode side to prevent leakage. A noble metal catalyst (Pt / C:RuO2=1:1) was used as a control electrode. The discharge polarization curve was tested using a CHI760E electrochemical workstation, and the results were obtained using a LAND CT2001A system at 5 mA cm⁻¹. - Cyclic stability tests were conducted under constant current.

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