Nitrogen and phosphorus doped ZIF-67 fuel cell catalyst and preparation method thereof

Abstract

The invention provides a nitrogen and phosphorus doped ZIF-67 fuel cell catalyst and a preparation method thereof, and relates to the technical field of fuel cells, the nitrogen and phosphorus doped ZIF-67 fuel cell catalyst comprises a nitrogen and phosphorus doped ZIF-67 derived carbon carrier and platinum nanoparticles loaded on the carrier; the mass fraction of nitrogen doping in the carrier is 0.5%-2.0%, the mass fraction of phosphorus doping in the carrier is 1.5%-0.5%, and the loading capacity of the platinum nanoparticles is 5%-20%. According to the nitrogen and phosphorus doped ZIF-67 fuel cell catalyst and the preparation method thereof, rich active sites are formed on the surface and in the carrier through a unique step-by-step nitrogen and phosphorus doped structure, the active sites and loaded platinum nanoparticles generate a synergistic catalytic effect, the activation energy of an oxygen reduction reaction is remarkably reduced, and the reaction rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a nitrogen-phosphorus doped ZIF-67 fuel cell catalyst and a preparation method thereof. Background Art

[0002] In the cathode reaction of fuel cells, the slow kinetics of the oxygen reduction reaction (ORR) is a key factor limiting battery efficiency. Platinum (Pt)-based catalysts are currently the most effective ORR catalysts, but they face three core problems: low platinum utilization: traditional carbon supports (such as Vulcan XC-72) lack active sites on the surface, which causes Pt nanoparticles to easily agglomerate (average particle size > 5nm), and only less than 20% of Pt atoms participate in the catalytic reaction; poor support stability: in acidic or alkaline environments, carbon supports are prone to corrosion, causing Pt particles to fall off, resulting in rapid degradation of catalyst performance; insufficient synergistic effect: the electronic interaction between a single doped support and Pt is weak, making it difficult to achieve efficient synergistic catalysis of active sites.

[0003] Metal-organic framework (MOF)-derived carbon materials have become a research hotspot due to their high specific surface area and adjustable pore structure. ZIF-67, as a cobalt-based MOF, forms a nitrogen-doped carbon skeleton (Co-N / C) after carbonization, which has certain ORR intrinsic activity. However, its electronic structure regulation ability of single nitrogen doping is limited, and the introduction of phosphorus elements is mostly uniform co-doping, lacking a gradient distribution design, resulting in the need to improve the dispersion of Pt particles and the stability of the carrier. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst and a preparation method thereof. By step-by-step doping, a ZIF-67-derived carbon support with a multi-level pore structure is constructed, and a controlled reduction technology is combined to achieve ultra-dispersed loading of Pt nanoparticles, thereby improving the dispersibility of Pt particles and the stability of the support.

[0005] The technical solution adopted in the present invention is: A nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst, wherein the nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst comprises a nitrogen-phosphorus-doped ZIF-67-derived carbon support and platinum nanoparticles supported on the support; the nitrogen doping mass fraction of the support is 0.5%-2.0%, the phosphorus doping mass fraction is 1.5%-0.5%, and the loading amount of the platinum nanoparticles is 5%-20%.

[0006] Preferably, the nitrogen and phosphorus doped ZIF-67 fuel cell catalyst, wherein the nitrogen and phosphorus doped ZIF-67 derived carbon support has a hierarchical pore structure, including micropores, mesopores and macropores, wherein the mesopores account for 30%-50%, and the nitrogen and phosphorus doped ZIF-67 derived carbon support has a specific surface area of ​​≥1400 m 2 / g.

[0007] A method for preparing a nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst comprises the following steps: Step S1. Cobalt nitrate and 2-methylimidazole are dissolved in N,N-dimethylformamide and mixed, followed by microwave-assisted reaction, followed by centrifugation, washing, and drying to obtain ZIF-67 nanocrystals; Step S2. Dispersing ZIF-67 nanocrystals and melamine in an ethanol solution and subjecting the mixture to a reflux reaction to partially embed the melamine into the pores, followed by centrifugation, washing, and drying to obtain preliminary nitrogen-doped ZIF-67. Step S3. Preliminary nitrogen-doped ZIF-67, urea, and ammonium dihydrogen phosphate are dispersed in an aqueous solution and stirred for reaction, followed by centrifugation, washing, and drying to obtain a nitrogen-phosphorus-doped ZIF-67 precursor; Step S4. Carbonizing the NP-ZIF-67 precursor under an argon atmosphere to obtain a cobalt-containing NG-ZIF-67 precursor. The carbonized cobalt-containing NG-ZIF-67 precursor is then placed in an acid solution and stirred to dissolve the cobalt ions in the acid solution. The mixture is then centrifuged, washed, and dried to obtain the NG-ZIF-67 support from which the metallic cobalt has been removed. Step S5. Dissolving the NG-ZIF-67 support and a platinum precursor in a solvent at a Pt loading of 5% to 20% and dispersing the mixture to obtain a mixed solution. Then, adding a NaBH4 aqueous solution dropwise to the mixed solution, stirring the mixture after the addition is complete, and finally centrifuging and washing to obtain a Pt-loaded semi-finished product. Step S6: annealing the Pt-loaded semi-finished product to obtain a nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst.

[0008] Preferably, in the method for preparing the nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst, the molar ratio of cobalt nitrate to 2-methylimidazole in step S1 is 1:4-1:8, the mixing temperature is 30-50°C, and the mixing time is 1-2 hours; the microwave-assisted reaction temperature is 120-140°C, and the reaction time is 3-6 hours.

[0009] Preferably, in the method for preparing the nitrogen-phosphorus doped ZIF-67 fuel cell catalyst, the washing solvent in step S1 is methanol, the washing times are 3-5 times, the drying temperature is 60-80° C., and the drying time is 12-24 h.

[0010] Preferably, in the method for preparing the nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst, the mass ratio of ZIF-67 nanocrystals to melamine in step S2 is 1:0.05-1:0.2, the concentration of the ethanol solution is 70-90 vol%, the reflux reaction temperature is 50-70°C, the reflux time is 4-8 h, the washing solvent is ethanol, the number of washing times is 2-3 times, the drying temperature is 60-80°C, and the drying time is 12-24 h.

[0011] Preferably, the method for preparing the nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst, wherein the mass ratio of the preliminary nitrogen-doped ZIF-67, urea, and ammonium dihydrogen phosphate in step S3 is 1:0.1-0.3:0.05-0.2, the stirring reaction temperature is 80-100°C, the time is 6-12 h, the washing solvent is deionized water, the number of washing times is 3-5 times, the drying temperature is 60-80°C, and the drying time is 12-24 h.

[0012] Preferably, in the method for preparing the nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst, the carbonization temperature in step S4 is 700-900°C, the heating rate is 5-10°C / min, and the carbonization time is 2-4 h; the stirring reaction temperature is 60-80°C, the stirring time is 6-12 h, the drying temperature is 60-80°C, and the drying time is 12-24 h.

[0013] Preferably, in the method for preparing the nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst, the solvent in step S5 is ethanol and water in a volume ratio of 2:1-4:1, the dispersion time is 20-40 min, the molar ratio of NaBH4 and Pt is 2-5:1, the stirring temperature is 25-50°C, and the stirring time is 2-4 h.

[0014] Preferably, in the method for preparing the nitrogen and phosphorus doped ZIF-67 fuel cell catalyst, the annealing treatment in step S6 is performed in a 5% H2 / Ar mixed gas atmosphere, the annealing temperature is 250-350°C, and the annealing time is 1-3h.

[0015] Advantages of the present invention: (1) The present invention adopts a unique two-step doping method to construct an active site network. In step S2, preliminary nitrogen doping is performed by refluxing melamine in an 80 vol% ethanol solution at 60°C for 6 h, so that the melamine is partially embedded in the ZIF-67 pores to form a basic nitrogen-doped skeleton. In step S3, urea and ammonium dihydrogen phosphate are further stirred in an oil bath at 90°C for 10 h to achieve secondary nitrogen and phosphorus co-doping. This step-by-step strategy can accurately control the doping amount and distribution of nitrogen (0.5%-2.0%) and phosphorus (0.5%-1.5%), forming a "defect-heteroatom" active site cluster on the surface and inside the carrier. (2) The phosphorus-doped ZIF-67 fuel cell catalyst of the present invention, from the perspective of reaction mechanism, after nitrogen and phosphorus atoms replace carbon atoms in the carbon skeleton, the local electron cloud density is changed, so that an electron-rich area is formed on the surface of the carrier; when platinum nanoparticles are loaded, a strong electronic coupling effect is generated between the carrier and platinum, and the d-band center of platinum is shifted, which optimizes the adsorption and desorption ability of O2 and reaction intermediates. The synergistic effect between the carrier and platinum significantly reduces the activation energy of the oxygen reduction reaction and improves the reaction rate. (3) The phosphorus-doped ZIF-67 fuel cell catalyst of the present invention has a hierarchical pore structure with transport and stabilization functions. In step S4, a hierarchical pore structure containing micropores, mesopores (accounting for 30%-50%) and macropores is successfully constructed by carbonization in an argon atmosphere at 800°C and etching cobalt ions with hydrochloric acid. This structural design improves catalyst performance in two aspects: Mass transfer optimization: Macropores (>50nm) serve as "high-speed channels" for reactants and products, mesopores (2-50nm) assist uniform diffusion, and micropores (<2nm) provide a high specific surface area for active site loading. The three work synergistically to significantly reduce mass transfer resistance, allowing O2 and electrolyte to quickly reach the active centers. Stable structure: The three-dimensional network of hierarchical channels creates a spatial confinement effect on platinum nanoparticles. During the ORR process, the stress generated by lattice changes in platinum particles can be effectively buffered by the channels, inhibiting particle agglomeration and shedding. The platinum particles of the catalyst are evenly dispersed in the channels, with a particle size of approximately 2-3 nm. In addition, nitrogen and phosphorus doping further enhances the chemical stability of the carrier, improves its corrosion resistance, and extends the service life of the catalyst. (4) The phosphorus-doped ZIF-67 fuel cell catalyst of the present invention has a platinum loading optimization and cost reduction mechanism. Based on the excellent performance of the hierarchical pore carrier, the present invention achieves a significant reduction in platinum loading. In step S5, the platinum loading is controlled within 5%-20% by accurately calculating the amount of platinum salt and ultrasonic dispersion process. Within this loading range, the high specific surface area (≥1400m² / g) and rich pore structure of the carrier ensure that the platinum nanoparticles are evenly dispersed, avoiding particle stacking and active site burial due to excessive loading. Specifically, the defect sites and heteroatoms formed by nitrogen and phosphorus doping can "anchor" the platinum particles on the inner wall of the pore through coordination (such as the coordination of the lone pair electrons of N and P with platinum), thereby improving the dispersion of platinum. Under the same loading, the catalytic efficiency of the unit mass of platinum of the catalyst of the present invention is higher. When achieving similar ORR performance, the platinum dosage of the catalyst of the present invention can be reduced by more than 50%, significantly reducing the cost and providing economic feasibility for the commercialization of fuel cells. (5) The phosphorus-doped ZIF-67 fuel cell catalyst of the present invention adopts a number of green technologies in the preparation process. In terms of solvent system, water / ethanol is used to replace traditional organic solvents (such as N,N-dimethylformamide), which not only reduces the emission of volatile organic compounds, but also the ethanol aqueous solution can be recycled and reused, which is in line with the principles of green chemistry. In terms of synthesis process, microwave-assisted synthesis technology is introduced in step S1, which shortens the synthesis time of ZIF-67 nanocrystals from several hours of conventional heating to 4 hours, and the reaction temperature is controlled at 130°C, which significantly reduces energy consumption. Microwave radiation has the characteristics of rapid heating and selective molecular excitation, which makes the reactant molecules vibrate at high frequency, achieving uniform heating and rapid reaction. This technology not only improves the synthesis efficiency, but also promotes the uniform growth of ZIF-67 nanocrystals, laying the foundation for the subsequent formation of hierarchical channels. In addition, the preparation process does not generate toxic by-products, reduces the post-processing cost, is both environmentally friendly and economical, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is a flow chart of a method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to the present invention.

[0017] FIG2 is a nitrogen adsorption curve of the NG-ZIF-67-derived carbon support of Example 1 of the present invention.

[0018] FIG3 is a TEM image of the NG-ZIF-67-derived carbon support of Example 1 of the present invention.

[0019] FIG4 is a CV cyclic voltammetry curve diagram of the catalysts prepared in Examples 1-3 of the present invention and Comparative Example 1.

[0020] FIG5 is a diagram showing the ORR polarization curves of the catalysts prepared in Examples 1-3 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific embodiments.

[0022] Example 1 A nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst comprises a nitrogen-phosphorus-doped ZIF-67-derived carbon support and platinum nanoparticles loaded on the support; the nitrogen doping mass fraction in the support is 2.0%, the phosphorus doping mass fraction is 0.5%, and the loading amount of the platinum nanoparticles is 5%; the nitrogen-phosphorus-doped ZIF-67-derived carbon support has a hierarchical pore structure including micropores, mesopores, and macropores, wherein the mesopores account for 35%; the nitrogen-phosphorus-doped ZIF-67-derived carbon support has a specific surface area of ​​1432 m 2 / g.

[0023] The preparation method of the fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 of this embodiment comprises the following steps: Step S1. Synthesis of ZIF-67 Nanocrystals: 0.01 mol of cobalt nitrate and 0.04 mol of 2-methylimidazole were dissolved in 50 mL of N,N-dimethylformamide and mixed. The solution was transferred to a three-necked flask and stirred in an oil bath at 40°C at 200 r / min for 1.5 h. The solution was then transferred to a microwave reactor and microwave-assisted reacted at 130°C for 4 h. After the reaction, the product was centrifuged at 4000 r / min for 10 min to obtain a purple precipitate. The precipitate was washed three times with methanol, centrifuged again after each wash, and dried at 70°C for 18 h to obtain ZIF-67 nanocrystals. Step S2. Preliminary nitrogen doping: 1 g of ZIF-67 nanocrystals and 0.1 g of melamine were dispersed in an 80 vol% ethanol solution. The solution was transferred to a round-bottom flask with a condenser and refluxed in a 60°C water bath at 300 r / min with magnetic stirring for 6 h to partially embed the melamine into the pores. After the reaction, the solution was centrifuged at 3500 r / min for 8 min. The precipitate was washed twice with ethanol and dried in a vacuum drying oven at 70°C for 12 h to obtain preliminary nitrogen-doped ZIF-67. Step S3. Secondary nitrogen and phosphorus doping: 1 g of preliminarily nitrogen-doped ZIF-67 was dispersed with 0.2 g of urea and 0.1 g of ammonium dihydrogen phosphate in an aqueous solution. The mixture was stirred in an oil bath at 90°C at 250 r / min for 10 h. The mixture was then centrifuged at 4500 r / min for 12 min and washed five times with deionized water. The washed precipitate was dried in a vacuum oven at 70°C for 24 h to obtain a nitrogen and phosphorus-doped ZIF-67 precursor. Step S4. Preparation of nitrogen-phosphorus-doped derivative carbon support: The NP-ZIF-67 precursor was carbonized under an argon atmosphere to obtain a cobalt-containing NG-ZIF-67 precursor. The carbonization temperature was 800°C, the heating rate was 5°C / min, and the carbonization time was 2-3 h. The carbonized cobalt-containing NG-ZIF-67 precursor was then placed in 1M dilute hydrochloric acid and stirred to dissolve the cobalt ions in the acid solution. The stirring reaction temperature was 65°C and the stirring time was 9 h. The product was then centrifuged and washed with deionized water until neutral. The product was dried at 70°C for 20 h to obtain the NG-ZIF-67 support with the metal cobalt removed. The specific surface area of ​​the support was 1445 m 2 / g; Step S5. Controllable loading of platinum nanoparticles: 0.95 g of NG-ZIF-67 support and 0.133 g of H2PtCl6•6H2O were dissolved in 60 mL of ethanol and water in a volume ratio of 3:1, with a Pt loading of 5%. The solution was placed in an ultrasonic cleaner and ultrasonically dispersed at a power of 100 W for 30 min to obtain a mixed solution to fully wet the pores of the support. The above solution was transferred to a three-necked flask and stirred in a 30°C water bath at a stirring speed of 200 r / min. Then, 10 mL of 0.1 M NaBH4 aqueous solution was added dropwise to the mixed solution. The molar ratio of NaBH4 to Pt was 2:1, and the dropping rate was controlled at 1 drop / s. After the addition, the reaction was stirred at 30°C for 3 h, centrifuged at 4000 r / min for 10 min, and the precipitate was washed with deionized water until no Cl was detected using silver nitrate reagent. - Until a platinum-loaded semi-finished product is obtained; Step S6. The Pt-loaded semi-finished product was placed in a tube furnace and annealed in a 5% H2 / Ar mixed gas atmosphere at a temperature of 300°C for 2 h. After annealing, the product was naturally cooled to room temperature to obtain a 5% Pt / NG-ZIF-67 catalyst.

[0024] Example 2 The difference between Example 2 and Example 1 is: Step S5. According to the Pt loading of 10%, 0.9 g of NG-ZIF-67 carrier and 0.265 g of H2PtCl6•6H2O were dissolved in 60 mL of ethanol and water with a volume ratio of 3:1. The solution was placed in an ultrasonic cleaner and ultrasonically dispersed at a power of 100 W for 30 min to obtain a mixed solution so that the pores of the carrier were fully infiltrated. The above solution was transferred to a three-necked flask and stirred in a water bath at 30°C at a stirring speed of 200 r / min. Then, 15 mL of 0.1 M NaBH4 aqueous solution was added dropwise to the mixed solution. The molar ratio of NaBH4 to Pt was 3:1, and the dropping speed was controlled at 1 drop / second. After the addition was completed, the reaction was stirred at 30°C for 3 h, centrifuged at a speed of 4000 r / min for 10 min, and the precipitate was washed with deionized water until no Cl was detected using a silver nitrate reagent. - Until now, a platinum-loaded semi-finished product has been obtained.

[0025] Step S6. The Pt-loaded semi-finished product was placed in a tube furnace and annealed in a 5% H2 / Ar mixed gas atmosphere at a temperature of 300°C for 2 h. After annealing, the product was naturally cooled to room temperature to obtain a 10% Pt / NG-ZIF-67 catalyst.

[0026] Example 3 The difference between Example 3 and Example 1 is: Step S5. According to the Pt loading of 15%, 0.85 g of NG-ZIF-67 support and 0.398 g of H2PtCl6•6H2O were dissolved in 60 mL of ethanol and water with a volume ratio of 3:1. The solution was placed in an ultrasonic cleaner and ultrasonically dispersed at a power of 120 W for 30 min to obtain a mixed solution so that the pores of the support were fully infiltrated. The above solution was transferred to a three-necked flask and stirred in a water bath at 40°C at a stirring speed of 200 r / min. Then, 20 mL of 0.1 M NaBH4 aqueous solution was added dropwise to the mixed solution. The molar ratio of NaBH4 to Pt was 4:1, and the dropping speed was controlled at 1 drop / second. After the addition was completed, the reaction was stirred at 40°C for 3 h, centrifuged at a speed of 4000 r / min for 10 min, and the precipitate was washed with deionized water until no Cl was detected using a silver nitrate reagent. - Until a platinum-loaded semi-finished product is obtained; Step S6. The Pt-loaded semi-finished product was placed in a tube furnace and annealed in a 5% H2 / Ar mixed gas atmosphere at a temperature of 320°C for 2 h. After annealing, the product was naturally cooled to room temperature to obtain a 15% Pt / NG-ZIF-67 catalyst.

[0027] Comparative Example 1 10% Pt / C catalyst (commercial XC-72 support) Comparative Example 1 is to directly load 10% Pt on the XC-72 carrier using the same method as Example 2.

[0028] The catalysts prepared in Examples 1 to 3 and Comparative Example 1 were subjected to performance tests.

[0029] Electrochemical performance test: In 0.1M HClO4 electrolyte, the oxygen reduction reaction (ORR) performance of the catalyst was tested using a rotating disk electrode (RDE) technique. The test results are shown in Table 1. NG-ZIF-67 as a Pt carrier can significantly improve the ORR catalytic performance, and the performance shows a linear optimization trend with the increase of Pt loading. Compared with the commercial Pt / C in Comparative Example 1, it performs better in activity and Pt utilization efficiency, and is expected to become a candidate carrier for high-efficiency electrochemical catalysts. In Examples 1-3, with the coordinated regulation of nitrogen and phosphorus doping amounts, the half-wave potential of the catalyst gradually increases, indicating that the starting potential of the ORR reaction is more positive and the catalytic activity is enhanced. This synergistic effect of the carrier and platinum significantly reduces the activation energy of the oxygen reduction reaction and increases the reaction rate. 10% Pt / NG-ZIF-67 in Table 1 The mass activity of the catalyst (0.103A / mgPt) is higher than that of commercial 10%Pt / C (0.086A / mgPt), indicating that under the same loading amount, the catalytic efficiency of the unit mass of platinum in the catalyst of the present invention is higher; when achieving similar ORR performance, the amount of platinum used in the catalyst of the present invention can be reduced by more than 50%, significantly reducing the cost and providing economic feasibility for the commercialization of fuel cells.

[0030] Table 1 Catalyst type Half-wave potential (V) Mass activity (A / mgPt) <![CDATA[Electrochemical active area (m 2 / g)]]> 5% Pt / NG-ZIF-67 0.925 0.085 66.756 10% Pt / NG-ZIF-67 0.927 0.103 71.415 15% Pt / NG-ZIF-67 0.929 0.146 76.610 10% Pt / C (XC-72) 0.924 0.086 62.175 Figure 2 is a nitrogen adsorption curve of the NG-ZIF-67 derived carbon support of the present invention, and the curve shows typical hierarchical pore structure characteristics; Figure 3 is a TEM image of the NG-ZIF-67 derived carbon support of the present invention. The TEM image shows that the platinum particles of the catalyst of the present invention are uniformly dispersed in the pores, with a particle size of about 2-3 nm; Figure 4 is a CV cyclic voltammetry curve of the catalysts prepared in Examples 1-3 of the present invention and Comparative Example 1, and the electrochemical active areas of Examples 1-3 are all higher than those of the Comparative Example; Figure 5 is an ORR polarization curve of the catalysts prepared in Examples 1-3 of the present invention and Comparative Example 1, and the mass activity of 10% Pt / NG-ZIF-67 is higher than that of commercial 10% Pt / C, indicating that under the same loading amount, the catalytic efficiency of the catalyst of the present invention per unit mass of platinum is higher.

[0031] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A nitrogen and phosphorus doped ZIF-67 fuel cell catalyst, characterized in that: The fuel cell catalyst of nitrogen-phosphorus-doped ZIF-67 includes a nitrogen-phosphorus-doped ZIF-67-derived carbon support and platinum nanoparticles supported on the support; the mass fraction of nitrogen doping in the support is 0.5%-2.0%, the mass fraction of phosphorus doping is 1.5%-0.5%, and the loading amount of the platinum nanoparticles is 5%-20%.

2. The nitrogen and phosphorus doped ZIF-67 fuel cell catalyst according to claim 1, characterized in that: The nitrogen and phosphorus doped ZIF-67 derived carbon support has a hierarchical pore structure, including micropores, mesopores and macropores, of which the mesopores account for 30%-50%. The specific surface area of ​​the nitrogen and phosphorus doped ZIF-67 derived carbon support is ≥1400 m 2 / g.

3. A method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67, characterized in that: The following steps are involved: Step S1. Cobalt nitrate and 2-methylimidazole are dissolved in N,N-dimethylformamide and mixed, followed by microwave-assisted reaction, followed by centrifugation, washing, and drying to obtain ZIF-67 nanocrystals; Step S2. Dispersing ZIF-67 nanocrystals and melamine in an ethanol solution and subjecting the mixture to a reflux reaction to partially embed the melamine into the pores, followed by centrifugation, washing, and drying to obtain preliminary nitrogen-doped ZIF-67. Step S3. Preliminary nitrogen-doped ZIF-67, urea, and ammonium dihydrogen phosphate are dispersed in an aqueous solution and stirred for reaction, followed by centrifugation, washing, and drying to obtain a nitrogen-phosphorus-doped ZIF-67 precursor; Step S4. Carbonizing the NP-ZIF-67 precursor under an argon atmosphere to obtain a cobalt-containing NG-ZIF-67 precursor. The carbonized cobalt-containing NG-ZIF-67 precursor is then placed in an acid solution and stirred to dissolve the cobalt ions in the acid solution. The mixture is then centrifuged, washed, and dried to obtain the NG-ZIF-67 support from which the metallic cobalt has been removed. Step S5. Dissolving the NG-ZIF-67 support and a platinum precursor in a solvent at a Pt loading of 5% to 20% and dispersing the mixture to obtain a mixed solution. Then, adding a NaBH4 aqueous solution dropwise to the mixed solution, stirring the mixture after the addition is complete, and finally centrifuging and washing to obtain a Pt-loaded semi-finished product. Step S6: annealing the Pt-loaded semi-finished product to obtain a nitrogen-phosphorus-doped ZIF-67 fuel cell catalyst.

4. The method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to claim 3, characterized in that: In step S1, the molar ratio of cobalt nitrate to 2-methylimidazole is 1:4-1:8, the mixing temperature is 30-50° C., and the time is 1-2 h; the microwave-assisted reaction temperature is 120-140° C., and the reaction time is 3-6 h.

5. The method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to claim 3, characterized in that: In step S1, the washing solvent is methanol, the washing times are 3-5 times, the drying temperature is 60-80° C., and the drying time is 12-24 hours.

6. The method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to claim 3, characterized in that: In step S2, the mass ratio of ZIF-67 nanocrystals to melamine is 1:0.05-1:0.2, the concentration of the ethanol solution is 70-90 vol%, the reflux reaction temperature is 50-70°C, the reflux time is 4-8 h, the washing solvent is ethanol, the number of washes is 2-3 times, the drying temperature is 60-80°C, and the drying time is 12-24 h.

7. The method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to claim 3, characterized in that: In step S3, the mass ratio of the preliminary nitrogen-doped ZIF-67, urea, and ammonium dihydrogen phosphate is 1:0.1-0.3:0.05-0.2, the stirring reaction temperature is 80-100°C, the time is 6-12 h, the washing solvent is deionized water, the washing number is 3-5 times, the drying temperature is 60-80°C, and the drying time is 12-24 h.

8. The method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to claim 3, characterized in that: In step S4, the carbonization temperature is 700-900°C, the heating rate is 5-10°C / min, and the carbonization time is 2-4 h; the stirring reaction temperature is 60-80°C, the stirring time is 6-12 h, the drying temperature is 60-80°C, and the drying time is 12-24 h.

9. The method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to claim 3, characterized in that: In step S5, the solvent is ethanol and water in a volume ratio of 2:1-4:1, the dispersion time is 20-40 min, the molar ratio of NaBH4 to Pt is 2-5:1, the stirring temperature is 25-50°C, and the stirring time is 2-4 h.

10. The method for preparing a fuel cell catalyst of nitrogen and phosphorus doped ZIF-67 according to claim 3, characterized in that: The annealing treatment in step S6 is performed in a 5% H2 / Ar mixed gas atmosphere, with an annealing temperature of 250-350°C and an annealing time of 1-3 h.

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