A method for preparing a boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material

Abstract

The present application belongs to the field of development of fuel cell cathode materials, and relates to a preparation method of a boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material prepared by modifying a white bark powder as a carbon source precursor with bayberry tannin. The hydrolysis product of the white bark powder is gelatin with rich active groups, and the gelatin molecular structure is rich in active groups such as amino groups and hydroxyl groups, and can efficiently complex various metal ions, so that the white bark powder can be used as an anchor for various nano-metal active ingredients to prepare an electrocatalyst carrier with high catalytic activity and long service life. In the present application, the gelatin, which is the hydrolysis product of the white bark powder, is used as a base material, and is compounded with boron and chromium modified by bayberry tannin to prepare a high-performance low-cost bayberry tannin modified boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material through pyrolysis.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane fuel cell catalyst technology, specifically a method for preparing a boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material based on white bark powder as a carbon source precursor and modified with bayberry tannin. Background Technology

[0002] Fossil fuel reserves are dwindling, and their extensive use severely pollutes the environment. Therefore, developing clean, inexpensive, and sustainable energy conversion and storage systems is a major research focus. Fuel cells directly convert the energy released from the reaction of fuel and oxygen into electrical energy through chemical reactions, without being limited by the Carnot cycle, thus achieving highly efficient energy conversion. The ORR reaction at the fuel cell cathode is a crucial factor determining the overall performance of the cell. Although platinum-based catalysts exhibit excellent catalytic performance in the ORR reaction, their high cost and susceptibility to corrosion and deactivation limit their commercial application in fuel cells. Furthermore, Pt / C catalysts are prone to degradation under harsh environments such as high potentials and strong acids, leading to decreased electrocatalyst activity and stability, which in turn affects the overall performance and lifespan of the fuel cell. Therefore, researchers are actively seeking alternative platinum-based materials, such as non-precious metal catalysts, single-atom catalysts, and alloy catalysts, to address the problems associated with platinum-based materials and obtain more stable and efficient fuel cell catalysts.

[0003] Single-atom catalysts (SACs) hold great potential in the field of ORR electrocatalysts due to their fine MNC structure (M = iron, cobalt, nickel, etc.). The SAC structure effectively reduces the coordination number of the metal center, avoiding the binding effect of multiple metal atoms, and improving the contact rate between reactants and metal ions, thereby enhancing catalytic activity. Simultaneously, SACs achieve high atom utilization and provide high catalytic activity and selectivity. Transition metal-nitrogen-carbon-based materials, supported by carbon-based materials, can be processed to obtain excellent mesoporous structures with advantages such as large specific surface area and strong resistance to methanol. Furthermore, nitrogen doping can improve the overall electrical conductivity of the material. Therefore, transition metal-nitrogen-carbon-based materials have strong potential in fuel cell cathode catalysts. To further improve the catalytic activity of carbon-based electrocatalysts, it is often necessary to artificially introduce heteroatoms such as N, F, B, S, and P. Among these, N and B co-doping can simultaneously utilize the positive charge polarization of N and the negative charge polarization of B, producing a synergistic effect when forming an NCB structure, significantly improving the catalytic activity of active carbon sites. However, co-doped systems are complex, and it is even more difficult to synthesize carbon materials with a certain doping configuration in a specific direction.

[0004] Using gelatin derived from the hydrolysis of white husk powder as a biomass precursor, and boron and chromium elements chelated with myricetin as the main carbon source for the graphitic phase, a fuel cell cathode material with dual chromium-boron active sites and co-doped with non-metals was prepared. On the one hand, the effective coordination and chelation of boron with myricetin provides abundant active sites for the catalytic reaction; on the other hand, the aromatic ring structure of myricetin can further increase the graphitic phase content of the synthesized metal-carbon based material during pyrolysis, thus potentially yielding a higher-performance ORR catalyst.

[0005] The surface of white skin powder contains abundant functional groups. Its hydrolysis product, gelatin, is a natural polymer material with good conductivity, rich in various polar functional groups such as amino and hydroxyl groups, and abundant heteroatoms. It possesses a natural hierarchical fibrous structure and can serve as an organic ligand for metal catalysts to construct one-dimensional carbon-based electrocatalysts with a certain hierarchical porous structure, achieving natural nitrogen doping. Therefore, this study synthesizes gelatin obtained from the hydrolysis of white skin powder with boron and chromium elements chelated with myricetin in a certain proportion, and then prepares a high-performance, low-cost boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material via pyrolysis. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material based on white bark powder as a carbon source precursor and modified with bayberry tannin, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution, with specific steps as follows:

[0008] Step 1: Weigh a certain amount of white bark powder, prepare a certain amount of sodium hydroxide and sodium chloride solution and mix them together. Dissolve the white bark powder in the mixed solution, then stir it on a magnetic stirrer to form a gelatin solution. After filtering to precipitate the impurities, neutralize it with acid to a pH between 6 and 8, freeze it in a refrigerator, and then put it in a freeze dryer to dry for 24 hours to obtain solid gelatin.

[0009] Step 2: Weigh a certain amount of bayberry tannin and chromium nitrate, dissolve them in deionized water, and after ultrasonic treatment, perform magnetic stirring to obtain a chromium metal polyphenol network precursor solution.

[0010] Step 3: Weigh a certain amount of boric acid and dissolve it in deionized water, stir to form a uniform boric acid solution, and pour the gelatin obtained in Step 1 into the boric acid solution to obtain a mixed solution;

[0011] Step 4: Pour the chromium metal polyphenol network precursor solution from Step 2 into the mixed solution from Step 3, place it on a magnetic stirrer and stir thoroughly until all the water evaporates;

[0012] Step 5: Filter the product from Step 4, wash it 2-3 times with deionized water and anhydrous ethanol, and dry the product in an oven to obtain the C@CrB-BT-N precursor.

[0013] Step 6: Place the C@CrB-BT-N precursor in a tube furnace under a nitrogen atmosphere for high-temperature pyrolysis, and then allow it to cool naturally to room temperature;

[0014] Step 7: Place the calcined sample in boiling water for reflux, then wash and dry the sample to obtain the fuel cell cathode material.

[0015] As a preferred embodiment, the amounts of white bark powder and mixed solution used in step one are 1g and 50ml, respectively. The mixed solution is prepared by mixing 0.1mol / L sodium hydroxide and 2mol / L sodium chloride solutions in a volume ratio of 3:2. The magnetic stirrer is set at a temperature of 60℃, a speed of 700rpm, and a time of 7h. The freezer is frozen for 12h, and the freeze dryer is set at a temperature of -78℃ for 24h.

[0016] As a preferred option, in step three, the concentration of the boric acid solution is 1.5 mol / L.

[0017] As a preferred option, in step four, the temperature of the magnetic stirrer is 80℃ and the stirring time is 24 h.

[0018] As a preferred option, in step five, the drying temperature in the oven is 60℃ and the drying time is 18 hours.

[0019] As a preferred option, in step six, the specific operation of high-temperature pyrolysis is as follows: under a pure nitrogen atmosphere, the temperature is increased to 400℃ at a heating rate of 5℃ / min and stabilized for 30 min, then increased to 800℃ at a heating rate of 5℃ / min and held for 2 h, and finally cooled to room temperature with the furnace.

[0020] As a preferred option, in step seven, the reflux time in boiling water is 2 hours.

[0021] Compared with commercial Pt / C electrode materials, the boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material modified with myrica tannins in this invention has the following advantages:

[0022] 1. This invention employs a simple and convenient synthesis method, which is economical, efficient, green and environmentally friendly. The synthesis steps are simple to operate, the reaction conditions are mild and easy to control, and the preparation cost is low. The oxygen reduction catalyst prepared not only exhibits high potential and good limiting current, but also has excellent stability.

[0023] 2. The prepared carbon-based oxygen reduction fuel cell cathode material based on boron-chromium-nitrogen co-doped material modified with myricetin of bayberry has an initial potential of 1.088V, a half-wave potential of 0.666V, and a limiting current density of 6.05mA / cm². -2 Slightly higher than commercial platinum-carbon catalysts, and with better electrocatalytic stability than commercial Pt / C catalysts, this cathode material outperforms commercial platinum-carbon electrode materials in terms of overall performance. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the C@CrB-BT-N nanocomposite material;

[0025] Figure 2 The images show the XRD patterns of C@CrB-BT-N nanocomposites at different calcination temperatures (scanning range: 5°-80°, step size: 0.02°, scan rate: 1.5° / min).

[0026] Figure 3 This is the XPS analysis diagram of the C@CrB-BT-N nanocomposite material;

[0027] Figure 4 This is a cyclic voltammetric characteristic curve of the C@CrB-BT-N cathode material (test voltage scan range: -0.9-0.1 V, scan speed: 50 mV / s);

[0028] Figure 5 This is a linear cyclic voltammogram of C@CrB-BT-N in O2-saturated 0.1 M KOH with different composite ratios of boron and metallic chromium (scan range: -0.9–0.1 V, scan rate: 10 mV / s);

[0029] Figure 6 The linear cyclic voltammograms of boron and metallic chromium at different temperatures in 0.1 M KOH saturated with O2 at a molar ratio of 1:1 are shown (scan range: -0.9–0.1 V, scan rate: 10 mV / s).

[0030] Figure 7 Linear cyclic voltammograms of C@CrB-BT-N cathode materials under different rotation speeds (400, 625, 900, 1225, 1600, 2025, 2500 rpm) (scanning speed: 10 mV / s);

[0031] Figure 8 This is a methanol tolerance test chart of C@CrB-BT-N cathode material and commercial Pt / C (20 wt% Pt) catalyst, measured by constant voltage chronoamperometry.

[0032] Figure 9This is a stability test chart of C@CrB-BT-N cathode material and commercial Pt / C (20 wt% Pt) catalyst, measured by constant voltage chronoamperometry. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available. Example

[0035] This embodiment demonstrates a method for preparing a boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material C@CrB-BT-N.

[0036] Weigh 1g of white bark powder and dissolve it in 60ml of a mixed solution of sodium hydroxide and sodium chloride. The mixed solution is prepared by mixing 30ml of 0.1mol / L sodium hydroxide solution and 20ml of 2mol / L sodium chloride solution. Stir the solution on a magnetic stirrer at 60℃ for 7 hours to form a gelatin solution. After filtering to precipitate impurities, neutralize the solution with acid to a pH between 6 and 8. Finally, freeze the solution for 12 hours and then freeze-dry it for 24 hours to obtain solid gelatin.

[0037] Weigh 1g of bayberry tannin and 0.06mol of Cr(NO3)3·9(H2O), dissolve them in 30ml of deionized water, sonicate for 1h, and then stir magnetically for 2h to obtain a tannin-constructed metal polyphenol network precursor solution.

[0038] Weigh 0.3 mol of boric acid and dissolve it in 200 ml of deionized water at 80 °C. Stir to form a homogeneous boric acid solution. Pour 2 g of the gelatin prepared in step (1) into the boric acid solution.

[0039] The metal polyphenol precursor solution in step two is poured into the mixed solution in step (3), and then placed on a magnetic stirrer at 80°C for thorough stirring to evaporate all the water.

[0040] The product from step four was washed 2 to 3 times with deionized water and anhydrous ethanol, filtered, and dried in a 60°C oven for 18 hours to obtain C@CrB-BT-N.

[0041] The dried precursor product was evenly spread in a ceramic boat. Under a pure nitrogen atmosphere, the temperature was increased to 400℃ at a heating rate of 5℃ / min and stabilized for 30 min. Then, the temperature was increased to 800℃ at a heating rate of 5℃ / min and held for 2 h. Finally, the furnace was cooled to room temperature to obtain the fuel cell cathode material.

[0042] The calcined sample was refluxed in boiling water for 2 hours, and then washed and dried to obtain the fuel cell cathode material.

[0043] The C@CrB-BT-N material obtained in this embodiment was subjected to phase identification and microstructure and structural characterization: the phase of the prepared material was identified using XPS analyzer, powder X-ray diffractometer and X-ray photoelectron spectroscopy, and the microstructure and structure of the obtained material were characterized using scanning electron microscope.

[0044] Figure 1 This is a scanning electron microscope (SEM) image of the C@CrB-BT-N nanocomposite material. As can be seen from the image, this catalyst, which supports a metal polyphenol network composed of myricetin and chromium nitrate on B / N co-doped carbon nanosheets formed by the pyrolysis of gelatin and boric acid, possesses a porous structure. Furthermore, its sheet-like structure imparts higher toughness and makes it less prone to breakage. The abundant microporous structure of the catalyst allows for better exposure of catalytic active sites, resulting in improved ORR catalytic performance.

[0045] Figure 2 The XRD patterns of C@CrB-BT-N nanocomposite materials at different calcination temperatures (700℃, 800℃, 900℃) are shown in the figure. As can be seen from the figure, the obtained sample has high purity with no obvious impurities. The sharp diffraction peaks indicate good crystallinity of the synthesized material. The material exhibits six distinct diffraction peaks at 2θ = 27.769°, 30.591°, 39.855°, 54.581°, 57.257°, ​​and 66.337°, corresponding to the (310), (232), (420), (442), (620), and (711) crystal planes of B2O3 (PDF#06-0297).

[0046] Figure 3This is the XPS spectrum of the C@CrB-BT-N nanocomposite material. The figure further confirms the surface elemental composition of the material. (a) is the XPS full spectrum analysis of the material, confirming the presence of five elements: C, N, O, B, and Cr on the surface. The C1S spectrum shows three main peaks, corresponding to two sharp peaks of C–Cr (283.027 eV) and sp2 C–C (284.8 eV), and a small sharp peak of C–O (287.48 eV). The C1S absorption peaks indicate that the composite material has a graphitized carbon matrix with good electrical conductivity. The O1S spectrum shows the presence of oxygen-containing functional groups CO (532.20 eV) and COC (531.06 eV). This is consistent with the XRD analysis results. In the high-resolution N1S spectrum (… Figure 3-1 d) It can be seen that it is formed by fitting four distinct peaks, indicating the presence of four forms of N: pyridine N (397.92 eV), quaternary N (400.73 eV), pyridine-N-oxide (404.82 eV), and nitrate (409.39 eV). From the high-resolution B1s spectrum ( Figure 3-1 e) It can be seen that there are two different signals with dissociation binding energies of 191.65 eV and 192.52 eV, which correspond to B-C2O / BN and B-CO2, respectively. From the elemental spectrum of Cr 2p, it can be found that it is also formed by fitting four obvious peaks. The peaks at 586.09 eV and 576.32 eV correspond to Cr 2p1 / 2 and Cr 2p3 / 2 of hexavalent chromium, respectively, while the other two peaks correspond to trivalent chromium. Example

[0047] This embodiment demonstrates the electrochemical performance study of a method for preparing a boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material C@CrB-BT-N.

[0048] This invention uses a carbon rod as the counter electrode, a saturated silver chloride electrode (Ag / AgCl) as the reference electrode, and a glassy carbon electrode as the working electrode.

[0049] The electrode pretreatment in the testing process of this invention involves adding α-Al2O3 electrode polishing powder and a small amount of deionized water to a nylon polishing cloth base, grinding the rotating disc electrode back and forth in a figure-eight pattern for 10 minutes, then cleaning the residual powder on the electrode with deionized water, and finally air-drying it to complete the treatment.

[0050] The cathode material of this invention was prepared by weighing 4 mg of catalyst and dispersing it in a 1 mL centrifuge tube, adding 235 μL of deionized water, 735 μL of isopropanol, and 15 μL of 5 wt% Nafion solution, and then sonicating at room temperature for 50 minutes to obtain catalyst ink. Then, 28 μL of the ink was gradually added dropwise to the surface of a glassy carbon electrode (catalyst loading 0.25 mg / cm³). -2 After air drying, the electrocatalytic performance was tested.

[0051] All electrocatalytic performance tests described in this invention were conducted in a 0.1 M KOH (pH=13.62) electrolyte. The measured potentials can be converted to a potential relative to a reversible hydrogen electrode (RHE) using the following formula:

[0052] All potential values ​​involved in this invention are relative to the potential of a reversible hydrogen electrode.

[0053] The cathode material described in this invention requires CV activation for 3 cycles before electrochemical testing.

[0054] The cathode materials described in this invention are all tested at room temperature to prevent large temperature variations from affecting the performance of the cathode materials.

[0055] The Nafion added during the preparation of the cathode material described in this invention is produced by Aldrich Sigma and has a concentration of 5%.

[0056] Use a pipette to drop 7 μL of the catalyst onto the working electrode. Allow it to air dry naturally, then repeat this step 3 times. Next, slowly immerse the working electrode into an oxygen-saturated 0.1 M KOH electrolyte. During this step, prevent air bubbles from forming on the working electrode. Throughout the test, oxygen should be continuously introduced into the electrolyte to ensure oxygen saturation.

[0057] Cyclic voltammetry and linear cyclic voltammetry tests were performed on the cathode material obtained in this embodiment. Cyclic voltammetry experiments were conducted using an electrochemical workstation manufactured by Pine Corporation (USA). The test voltage scan range was -0.9–0.1 V, and the scan rate was 50 mV / s. During the test, the material was activated for 3 cycles at a current density of 50 mV / s before the cyclic voltammetry test. Similarly, linear cyclic voltammetry tests were performed using a Pine electrochemical workstation, with a test voltage scan range of -0.9–0.1 V and a scan rate of 50 mV / s. Rotation speed measurements were used to obtain the current density of the catalyst material at different rotation speeds, and the number of transferred electrons could be determined using the KL equation. The test current density was 10 mV / s, and the rotation speeds were 400, 625, 900, 1225, 1600, and 2025 rpm. Stability and methanol tolerance are also important indicators of catalyst performance. This test was also performed on an electrochemical workstation. The stability test voltage was -0.189 V and the test duration was 20,000 s. The methanol tolerance test voltage was -0.189 V and the test duration was 1,000 s. 2 M methanol solution was added dropwise at 300 s.

[0058] Figure 4 The figure shows the cyclic voltammetric characteristics of the C@CrB-BT-N cathode material (test voltage scan range: -0.9-0.1 V, scan rate: 50 mV / s). In an O2-saturated electrolyte, a cathode oxygen reduction peak is present at 0.71 V, indicating that a catalytic oxygen reduction reaction has occurred. The response to oxygen shows that C@CrB-BT-N has significant oxygen reduction catalytic activity in alkaline solution.

[0059] Figure 5 These are linear cyclic voltammograms of C@CrB-BT-N cathode material at different temperatures (test voltage range: -0.9-0.1 V, scan rate: 10 mV / s). The C@CrB-BT-N catalyst exhibits the best performance when calcined at 800℃.

[0060] Figure 6 This is a linear cyclic voltammogram (scan range -0.9–0.1 V, scan rate 10 mV / s) in O2-saturated 0.1 M KOH with different ratios of chromium and boron. The molar ratios of boron to chromium are 0:1, 0.05:1, 0.1:1, 0.2:1, and 0.5:1. The figure shows that at a heat treatment temperature of 800 °C, the oxygen reduction (ORR) performance of the nanocomposite material is optimal when the molar ratio of boron to chromium is 0.2:1, with the limiting current density increasing from 2.89 mA cm⁻¹. 2 Increased to 6.05 mA cm 2 .

[0061] Figure 7 The linear cyclic voltammograms of the C@CrB-BT-N cathode material under different rotation speeds (400, 625, 900, 1225, 1600, 2025, 2500 rpm) (scanning speed: 10 mV / s) show that the limiting diffusion current density of the catalyst gradually increases with the increase of rotation speed. This is because the faster the rotation speed, the faster the diffusion rate of oxygen, indicating that the oxygen reduction catalytic process is controlled by mass transfer and conforms to first-order kinetics.

[0062] Figure 8 The methanol tolerance of the optimal sample C@CrB-BT-N and the commercial 20% Pt / C catalyst was determined using IT technology by adding 2 mL of methanol to 0.1 M KOH electrolyte at 300 s and running at 1600 rpm. The graph shows that the limiting current density of C@CrB-BT-N only changed slightly, while the Pt / C catalyst exhibited a significant change in current density due to methanol oxidation. After running for another 700 s, the current density of C@CrB-BT-N remained stable, while the retention rate of Pt / C decreased to below 50%. This indicates that C@CrB-BT-N is superior to Pt / C in terms of methanol tolerance.

[0063] Figure 9 The C@Cr0.2B-BT-800℃ and Pt / C catalysts were tested using the chronoamperometry method. After 20,000 s of testing, the initial current density of the Pt / C catalyst decreased significantly by about 23%, while that of the C@Cr0.2B-BT-800℃ catalyst decreased by 19%. This indicates that the stability of this cathode material is superior to that of commercial Pt / C catalysts.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material, characterized in that: Includes the following steps: Step 1: Weigh a certain amount of white bark powder, prepare a certain amount of sodium hydroxide and sodium chloride solution and mix them together. Dissolve the white bark powder in the mixed solution, then stir it on a magnetic stirrer to form a gelatin solution. After filtering to precipitate the impurities, neutralize it with acid to a pH between 6 and 8, freeze it in a refrigerator, and then put it in a freeze dryer to dry for 24 hours to obtain solid gelatin. Step 2: Weigh a certain amount of bayberry tannin and chromium nitrate, dissolve them in deionized water, and after ultrasonic treatment, perform magnetic stirring to obtain a chromium metal polyphenol network precursor solution. Step 3: Weigh a certain amount of boric acid and dissolve it in deionized water, stir to form a uniform boric acid solution, and pour the gelatin prepared in Step 1 into the boric acid solution. Step 4: Pour the chromium metal polyphenol network precursor solution from Step 2 into the mixed solution from Step 3, place it on a magnetic stirrer and stir thoroughly until all the water evaporates; Step 5: Filter the product from Step 4, wash it 2-3 times with deionized water and anhydrous ethanol, and dry the product in an oven to obtain the C@CrB-BT-N precursor. Step 6: Place the C@CrB-BT-N precursor in a tube furnace under a nitrogen atmosphere for high-temperature pyrolysis, and then allow it to cool naturally to room temperature; Step 7: Place the calcined sample in boiling water for reflux, then wash and dry the sample to obtain the fuel cell cathode material.

2. The preparation method according to claim 1, characterized in that: In step one, the amounts of white powder and mixed solution used are 1g and 50ml, respectively. The mixed solution is prepared by mixing 0.1mol / L sodium hydroxide and 2mol / L sodium chloride solutions in a volume ratio of 3:

2. The magnetic stirrer is set at 60℃, 700rpm, and 7h for the time. The freezer is frozen for 12h for the time. The freeze dryer is set at -78℃ for the time of 24h.

3. The preparation method according to claim 1, characterized in that: In step three, the concentration of the boric acid solution is 1.5 mol / L.

4. The preparation method according to claim 1, characterized in that: In step four, the temperature of the magnetic stirrer is 80°C, and the stirring time is 24 hours.

5. The preparation method according to claim 1, characterized in that: In step five, the drying temperature in the oven is 60°C and the drying time is 18 hours.

6. The preparation method according to claim 1, characterized in that: In step six, the specific operation of high-temperature pyrolysis is as follows: under a pure nitrogen atmosphere, the temperature is increased to 400℃ at a heating rate of 5℃ / min and stabilized for 30 min, then increased to 800℃ at a heating rate of 5℃ / min and held for 2 h, and finally cooled to room temperature with the furnace.

7. The preparation method according to claim 1, characterized in that: The reflux time is 2 hours.

8. A boron-chromium-nitrogen co-doped carbon-based oxygen reduction fuel cell cathode material prepared according to any one of claims 1-7.

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