Graphitized carbon supported platinum nanoparticles, method for preparing the same, and use thereof
By introducing carbon and sulfur onto a graphitized carbon support to form carbon envelopes and platinum-sulfur bonds, the corrosion problem of platinum-carbon catalysts at the cathode of proton exchange membrane fuel cells was solved, resulting in improved catalytic activity and durability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- UNIV OF SCI & TECH OF CHINA
- Filing Date
- 2023-02-13
- Publication Date
- 2026-07-03
AI Technical Summary
The platinum-carbon catalyst at the cathode of existing proton exchange membrane fuel cells is prone to corrosion during start-up and shutdown, leading to catalyst layer collapse and loss of platinum nanoparticles, which affects catalytic activity and durability.
Platinum nanoparticles are supported on graphitized carbon. By introducing carbon and sulfur onto the graphitized carbon support and platinum nanoparticles, carbon encapsulation and platinum-sulfur bonds are formed, ensuring uniform dispersion and stability of the platinum nanoparticles and avoiding sintering.
It improves the electrochemical active area and catalytic activity, enhances corrosion resistance, and significantly outperforms the cycle durability of commercial Pt/C catalysts.
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Figure CN116111123B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of fuel cell catalysts, specifically to a graphitized carbon-supported platinum nanoparticle, its preparation method, and its application. Background Technology
[0002] Proton exchange membrane fuel cells (PEMFCs), as electrochemical energy conversion devices that directly convert the chemical energy of hydrogen and oxygen into electrical energy, possess advantages such as high energy conversion efficiency, environmental friendliness, and zero emissions, and are considered one of the preferred clean and efficient power generation technologies for the future. In recent years, fuel cells have made remarkable progress, but still face many challenges, particularly the durability of the platinum-carbon cathode catalyst, which is considered a key obstacle to the large-scale commercial application of fuel cells. Among these challenges, the corrosion behavior of the carbon support under start-up and shutdown conditions is often a significant factor leading to the durability problem of platinum-carbon catalysts. This is because carbon corrosion causes severe collapse of the catalyst layer, resulting in large-scale ripening and dissolution of platinum nanoparticles, ultimately leading to a sharp decline in catalyst activity.
[0003] To address this challenge, researchers have studied various carbon materials, such as carbon nanotubes, carbon fibers, porous carbon, and carbon black, as catalyst supports. Studies have revealed that certain structural properties of carbon materials, such as the degree of graphitization, morphology, and surface area, significantly influence the activity and durability of catalysts. Highly graphitized carbon produced through high-temperature treatment is considered to have outstanding effects in reducing resistivity and enhancing carbon corrosion resistance. However, most graphitization methods damage the porosity and specific surface area of carbon, while also weakening the interaction between the carbon support and platinum nanoparticles. This makes it difficult for platinum nanoparticles to be uniformly dispersed on the carbon support, ultimately resulting in a lower electrochemically active surface area for the platinum particles in the catalyst. This reduction in electrochemically active surface area leads to a significant decrease in atom utilization and a substantial increase in local oxygen transport resistance in the catalyst layer, resulting in additional mass transfer problems. Therefore, it is urgent to find a suitable support for loading platinum nanoparticles that can effectively improve the corrosion resistance of the support while also possessing good catalytic activity. Summary of the Invention
[0004] In view of this, the purpose of this invention is to provide graphitized carbon-supported platinum nanoparticles, their preparation method, and their applications. The graphitized carbon-supported platinum nanoparticles can be used as cathode catalysts in proton exchange membrane fuel cells, exhibiting superior catalytic performance and start-stop cycle durability compared to commercially available Pt / C catalysts.
[0005] To achieve this objective, the present invention adopts the following technical solution:
[0006] In a first aspect, the present invention provides graphitized carbon-supported platinum nanoparticles, comprising a graphitized carbon support; platinum nanoparticles supported on the graphitized carbon support; and carbon and sulfur independently supported on the graphitized carbon support or the platinum nanoparticles.
[0007] Preferably, the carbon and sulfur are simultaneously loaded on a graphitized carbon support and platinum nanoparticles.
[0008] Preferably, the loading amount of the platinum nanoparticles on the graphitized carbon support is 20–40 wt%.
[0009] Preferably, the average particle size of the platinum nanoparticles is 3–5 nm.
[0010] Secondly, the present invention provides a method for preparing graphitized carbon-supported platinum nanoparticles, comprising the following steps:
[0011] (1) Mix sulfur / carbon-containing material dispersion, platinum salt dispersion and graphitized carbon to obtain a suspension;
[0012] (2) After removing the solvent from the suspension, it is calcined in a reducing atmosphere to obtain the graphitized carbon-supported platinum nanoparticles.
[0013] Preferably, the sulfur / carbon-containing dispersion is obtained by mixing the sulfur / carbon-containing substance and a first solvent.
[0014] Preferably, the platinum salt dispersion is obtained by mixing a platinum salt and a second solvent.
[0015] Preferably, the sulfur- or carbon-containing substance is selected from propanethiol.
[0016] Preferably, the first solvent is selected from cyclohexane and / or n-hexane.
[0017] Preferably, the platinum salt is selected from one or more of H2PtCl6·6H2O, potassium chloroplatinate, or platinum acetylacetonate.
[0018] Preferably, the second solvent is selected from any one or more of ethanol, methanol, or isopropanol.
[0019] Preferably, the graphitized carbon is obtained by treating carbon materials at 2000–3000°C for 1.5–3 hours.
[0020] Preferably, the carbon material is selected from carbon black.
[0021] Preferably, the ratio of the sulfur / carbon-containing substance, platinum salt and graphitized carbon is (4-8) mmol:(0.8-1.6) mmol:(400-800) mg.
[0022] Preferably, step (1) specifically involves mixing the sulfur / carbon-containing material dispersion and the platinum salt dispersion for 10-30 minutes, and then mixing the resulting mixed solution with graphitized carbon for 20-30 hours to obtain a suspension.
[0023] Preferably, the calcination specifically involves heating to 300-600°C at a rate of 2-30°C / min and maintaining the temperature for 2-10 hours.
[0024] Thirdly, the present invention provides a cathode catalyst for a proton exchange membrane fuel cell, comprising graphitized carbon-supported platinum nanoparticles as described in the above technical solutions.
[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0026] This invention provides graphitized carbon-supported platinum nanoparticles. Using graphitized carbon as a support, platinum nanoparticles are loaded onto the graphitized carbon support and / or platinum nanoparticles during the preparation process. A sulfur / carbon source is added to introduce carbon and sulfur into the graphitized carbon support and / or platinum nanoparticles. Carbon atoms form carbon envelopes on the surface of the platinum nanoparticles, ensuring uniform dispersion and a small size (3-5 nm) of the platinum nanoparticles, preventing sintering and agglomeration. Sulfur atoms can coordinate with platinum, allowing the platinum nanoparticles to primarily combine with the graphitized carbon support through platinum-sulfur bonds. This overcomes the low loading rate of platinum nanoparticles on the graphitized carbon support, resulting in graphitized carbon-supported platinum nanoparticles with a high electrochemical active surface area, ensuring both corrosion resistance and good catalytic activity. These graphitized carbon-supported platinum nanoparticles can be used as cathode catalysts in proton exchange membrane fuel cells. Studies have shown that they exhibit excellent catalytic performance and significantly better start-stop cycle durability than commercially available Pt / C catalysts. Attached Figure Description
[0027] Figure 1 X-ray diffraction pattern of graphitized carbon-supported platinum nanoparticles prepared in Example 1;
[0028] Figure 2 SEM image of the graphitized carbon-supported platinum nanoparticles prepared in Example 1;
[0029] Figure 3 The image shows a comparison of the cyclic voltammetry curves of the graphitized carbon-supported platinum nanoparticles prepared in Example 1 as a cathode catalyst for PEMFCs, both initially and after 5000 cycles of high-potential support stability.
[0030] Figure 4 The figure shows a comparison of the hydrogen-air polarization curves of the graphitized carbon-supported platinum nanoparticles prepared in Example 1 as cathode catalysts for PEMFCs, both initially and after different cycles, to demonstrate the stability of the high-potential support.
[0031] Figure 5X-ray diffraction pattern of graphitized carbon-supported platinum nanoparticles prepared in Comparative Example 1;
[0032] Figure 6 SEM image of the graphitized carbon-supported platinum nanoparticles prepared in Example 1;
[0033] Figure 7 for Figure 7 The figure shows a comparison of the hydrogen-air polarization curves of the initial performance of graphitized carbon-supported platinum nanoparticles as cathode catalysts obtained in Example 1 and Comparative Example 1.
[0034] Figure 8 Hydrogen-air polarization curves for the initial and 1000-cycle high-potential support stability of commercial Pt / C as a cathode catalyst for PEMFCs. Detailed Implementation
[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0036] To address the problem that existing platinum-carbon cathode catalysts in proton exchange membrane fuel cells cannot simultaneously achieve high catalytic activity and durability, this invention provides graphitized carbon-supported platinum nanoparticles, comprising a graphitized carbon support; platinum nanoparticles supported on the graphitized carbon support; and carbon and sulfur independently supported on the graphitized carbon support or the platinum nanoparticles. In some embodiments of this invention, the carbon and sulfur are preferably simultaneously supported on the graphitized carbon support and the platinum nanoparticles. In this invention, the graphitized carbon support is obtained by high-temperature treatment of a carbon material, wherein the carbon material is selected from carbon black, and the carbon black is a commercially available product, generally one or more of KJ600, BP2000, or KJ300. Characterization of the graphitized carbon-supported platinum nanoparticles using X-ray diffraction and scanning electron microscopy revealed that the platinum nanoparticles are small in size and uniformly dispersed, with an average particle size of 3–5 nm. According to the research of this invention, a low loading of platinum nanoparticles on a graphitized carbon support will result in excessively small Pt particle size, while a high loading will result in excessively large Pt particle size. Therefore, in theory, the loading of platinum nanoparticles on a graphitized carbon support is preferably 20 to 40 wt%.
[0037] This invention introduces carbon and sulfur onto a graphitized carbon support and / or platinum nanoparticles. Carbon atoms form carbon envelopes on the surface of the platinum nanoparticles, ensuring uniform dispersion and small size of the platinum nanoparticles and preventing sintering and agglomeration. Sulfur atoms coordinate with platinum, allowing the platinum nanoparticles to primarily combine with the graphitized carbon support through platinum-sulfur bonds (with a small amount combining through platinum-oxygen bonds). This overcomes the low loading rate of platinum nanoparticles on the graphitized carbon support, resulting in graphitized carbon-supported platinum nanoparticles with a high electrochemical active area, ensuring both corrosion resistance and good catalytic activity.
[0038] In some embodiments of the present invention, the graphitized carbon-supported platinum nanoparticles are prepared by the following method:
[0039] (1) Mix sulfur / carbon-containing material dispersion, platinum salt dispersion and graphitized carbon to obtain a suspension;
[0040] (2) After removing the solvent from the suspension, it is calcined in a reducing atmosphere to obtain the graphitized carbon-supported platinum nanoparticles.
[0041] According to this invention, a sulfur-containing / carbon-based dispersion, a platinum salt dispersion, and graphitized carbon are first mixed to obtain a suspension. The sulfur-containing / carbon-based dispersion is obtained by mixing the sulfur-containing / carbon-based substance with a first solvent, wherein the sulfur-containing / carbon-based substance is selected from propane mercaptan, and the first solvent is selected from cyclohexane and / or n-hexane. The platinum salt dispersion is obtained by mixing a platinum salt with a second solvent, wherein the platinum salt is any one or more selected from H₂PtCl₆·6H₂O, potassium chloroplatinate, or platinum acetylacetonate, and the second solvent is any one or more selected from ethanol, methanol, or isopropanol. The graphitized carbon is obtained by treating a carbon material at 2000–3000°C for 1.5–3 hours, wherein the carbon material is selected from carbon black, and the specific selection is as described in the above technical solution, and will not be repeated here. In some embodiments of this invention, the ratio of the sulfur-containing / carbon-based substance, platinum salt, and graphitized carbon is (4–8) mmol:1 mmol:(350–650) mg. In some embodiments of the present invention, it is preferable to mix the sulfur / nitrogen-containing substance dispersion and the platinum salt dispersion in the above proportions for 10-30 minutes, so that platinum and sulfur automatically coordinate to form a platinum-sulfur interaction. Then, the resulting mixed solution is mixed with graphitized carbon for 20-30 hours to obtain a suspension. The mixing can be carried out at room temperature.
[0042] After obtaining the suspension, the solvent is removed, and then calcined in a reducing atmosphere to obtain the graphitized carbon-supported platinum nanoparticles. In some embodiments of the present invention, it is preferable to evaporate the solvent by rotary evaporation after obtaining the suspension, followed by drying and calcination in a reducing atmosphere. The drying process can be carried out using conventional techniques well known to those skilled in the art. In some embodiments of the present invention, it is preferable to place the dried product in a tube furnace, and under an atmosphere of 5% hydrogen and 95% argon, heat the tube furnace to 300-600°C at a rate of 2-30°C / min, maintain the temperature for 2-10 hours, and allow it to cool naturally to room temperature. The tube furnace is then kept at atmospheric pressure to obtain the graphitized carbon-supported platinum nanoparticles.
[0043] This invention involves mixing a sulfur / carbon-containing dispersion, a platinum salt dispersion, and graphitized carbon, removing the solvent, and then calcining the mixture. This introduces carbon and sulfur into platinum nanoparticles supported on the graphitized carbon. Carbon atoms form carbon capsules on the surface of the platinum nanoparticles, ensuring uniform dispersion and small size. Sulfur atoms coordinate with platinum, allowing the platinum nanoparticles to be composited with the graphitized carbon support primarily through platinum-sulfur bonds, resulting in uniform dispersion on the graphitized carbon support surface. The preparation method provided by this invention is simple, convenient, and easy to implement, facilitating industrialization.
[0044] The graphitized carbon-supported platinum nanoparticles provided by this invention can be used as cathode catalysts in proton exchange membrane fuel cells. Studies have shown that they exhibit superior operational stability compared to commercial Pt / C catalysts, with a current density of 1.5 A cm⁻¹ after initial loading and after 5000 cycles of high-potential support accelerated stress testing. -2 The voltage dropped by only 10mV, and its catalytic activity was excellent.
[0045] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention can all be purchased commercially or prepared using conventional techniques well-known to those skilled in the art.
[0046] Example 1
[0047] This embodiment provides graphitized carbon-supported platinum nanoparticles, the preparation method of which is as follows:
[0048] (1) Disperse 30 μL of propanethiol in 25 mL of cyclohexane solution, then add 34 mg of H2PtCl6·6H2O solution dissolved in 5 mL of ethanol. Stir at room temperature for 30 min, then add 30 mg of highly graphitized carbon and continue stirring at room temperature for 24 h. Remove the solvent by rotary evaporator to obtain precursor powder.
[0049] The highly graphitized carbon was obtained by treating KJ600 carbon black at 3000℃ for 2 hours;
[0050] (2) After the precursor powder is dried in an oven, it is transferred to a quartz crucible and placed in a tube furnace. Under an atmosphere of 5% hydrogen and 95% argon, the tube furnace is heated to 300°C at 5°C / min and kept for 2 hours. It is then naturally cooled to room temperature. The tube furnace is kept at atmospheric pressure to obtain graphitized carbon-supported platinum nanoparticles.
[0051] According to the formula: w(Pt)=m(Pt) / (m(Pt)+m(graphitized carbon support)), theoretically, the loading of platinum nanoparticles on the graphitized carbon support in this embodiment is 30wt%. The accurate Pt content in the prepared catalyst was determined to be 31.9wt% using inductively coupled plasma atomic emission spectrometry (ICP-AES).
[0052] X-ray diffraction tests were performed on the obtained graphitized carbon-supported platinum nanoparticles, and the results are as follows: Figure 1 As shown, the diffraction peaks of the corresponding Pt nanoparticles have a large full width at half maximum (FWHM), indicating that the size of the platinum nanoparticles is small.
[0053] The surface morphology of the obtained graphitized carbon-supported platinum nanoparticles was characterized using scanning electron microscopy, and the results are as follows: Figure 2 As shown, the size of the Pt nanoparticles is around 3-5 nm and they are uniformly distributed.
[0054] Electrochemical tests of PEMFCs were performed on the graphitized carbon-supported platinum nanoparticles obtained in Example 1. The experimental steps are as follows:
[0055] (1) 30 mg of the graphitized carbon supported platinum nanoparticles were dispersed in 6.6 mL of water, 8.4 mL of isopropanol and 50 μL of 25% Nafion solution, and sonicated for 2 h to obtain the catalyst ink.
[0056] (2) The ink is sprayed onto a 5cm surface using an ultrasonic spraying device. 2 It is used as a cathode catalyst on the heat-insulating film; the Pt loading is 0.1 mg Pt / cm³. 2 ;
[0057] (3) Commercial Pt / C catalyst ink was sprayed onto a 5cm layer using an ultrasonic spraying device. 2 On the heat-insulating film, as an anode catalyst, the Pt loading is 0.05 mg Pt / cm³. 2 .
[0058] Electrochemical active area measurements were conducted at 40℃, with an anode of 200 sccm H2 and a cathode of 5 sccm N2. The CV range was 0.03V–0.6V (vs RHE), and the scan rate was 150 mV s. -1 .
[0059] High-potential carrier accelerated stress testing was performed using a triangular wave cycle (1.0–1.5 V, 100 kPa). abs H2 / N2, 80℃, 100% RH, 200 / 75 sccm (H2 / N2), scan rate 500 mV / s -1 The number of scans is 5000.
[0060] The hydrogen-air fuel cell test was conducted in a single cell using a commercial fuel cell test system, with the cell operating at 80°C and a pressure of 150 kPa. abs H2 / air, anode / cathode gas flow rates were 0.5 and 2.0 L / min, respectively. -1 .
[0061] Test results are as follows Figure 3 and Figure 4 As shown, Figure 3 The cyclic voltammetry (CV) curves of graphitized carbon-supported platinum nanoparticles as cathode catalysts are shown in the initial and cyclic voltammetry (CV) curves after 5000 cycles of high-potential support accelerated stress testing. The results show that the CV changes little before and after cycling, and only slightly decreases in the Hupd region of 0.03V to 0.6V (vs RHE), indicating that the electrochemical active area of platinum only decreased slightly, suggesting that graphitized carbon-supported platinum nanoparticles have good stability.
[0062] Figure 4 The hydrogen-air polarization curves for graphitized carbon-supported platinum nanoparticles as cathode catalysts are shown in the initial and after 5000 cycles of high-potential support accelerated stress testing. The results show that at a current density of 1.5 A cm⁻¹, the polarization is achieved before and after cycling. -2 The voltage drop was only 10 mV, indicating that graphitized carbon-supported platinum nanoparticles have excellent stability and catalytic activity.
[0063] Comparative Example 1
[0064] This comparative example provides graphitized carbon-supported platinum nanoparticles, the preparation method of which is as follows:
[0065] (1) Mix 30mg of highly graphitized carbon, 34mg of H2PtCl6·6H2O and 30mL of water, impregnate and stir the liquid, remove the solvent by rotary evaporator, and obtain a uniformly mixed precursor powder.
[0066] The highly graphitized carbon was obtained by treating carbon black at 3000°C for 2 hours;
[0067] (2) After the precursor powder is dried in an oven, it is transferred to a quartz crucible and placed in a tube furnace. Under an atmosphere of 5% hydrogen and 95% argon, the tube furnace is heated to 300°C at 5°C / min and kept for 2 hours. It is then naturally cooled to room temperature. The tube furnace is kept at atmospheric pressure to obtain highly graphitized carbon-loaded non-uniformly dispersed Pt nanoparticles.
[0068] X-ray diffraction tests were performed on the obtained graphitized carbon-supported platinum nanoparticles, and the results are as follows: Figure 5 As shown, the diffraction peaks of the corresponding Pt nanoparticles have a narrow half-width at half-maximum (FWHM), indicating that the platinum nanoparticles are relatively large.
[0069] The surface morphology of the obtained graphitized carbon-supported platinum nanoparticles was characterized using scanning electron microscopy, and the results are as follows: Figure 6 As shown, the size of the Pt nanoparticles is around 4–10 nm, and their distribution is uneven.
[0070] Electrochemical tests were performed on the graphitized carbon-supported platinum nanoparticles obtained in Comparative Example 1, according to the method in Example 1. Figure 7 The figure shows a comparison of the hydrogen-air polarization curves of the initial performance of graphitized carbon-supported platinum nanoparticles as cathode catalysts obtained in Example 1 and Comparative Example 1. It can be seen that compared with the graphitized carbon-supported platinum nanoparticles prepared by the impregnation method in Comparative Example 1, the graphitized carbon-supported platinum nanoparticles obtained by introducing carbon and sulfur in Example 1 have better catalytic activity.
[0071] Figure 8 The hydrogen-air polarization curves for the initial and 1000-cycle high-potential support accelerated stress tests of Pt / C as a commercial cathode catalyst show that its cycle stability is poor, far lower than that of the graphitized carbon-supported platinum nanoparticles provided in this application.
[0072] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A graphitized carbon-supported platinum nanoparticle cathode catalyst for proton exchange membrane fuel cells, characterized in that, It includes a graphitized carbon support; platinum nanoparticles loaded on the graphitized carbon support; and carbon and sulfur loaded on the graphitized carbon support and the platinum nanoparticles. The graphitized carbon-supported platinum nanoparticles were prepared according to the following method: (1) Mix sulfur / carbon-containing material dispersion, platinum salt dispersion and graphitized carbon to obtain a suspension; (2) After removing the solvent from the suspension, it is calcined in a reducing atmosphere to obtain the graphitized carbon-supported platinum nanoparticles; The sulfur- or carbon-containing substance is selected from propanethiol; The carbon forms a carbon envelope on the surface of the platinum nanoparticles; the sulfur is coordinated with platinum through platinum-sulfur bonds.
2. The graphitized carbon-supported platinum nanoparticle cathode catalyst according to claim 1, characterized in that, The platinum nanoparticles are loaded at a rate of 20-40 wt% on the graphitized carbon support.
3. The graphitized carbon-supported platinum nanoparticle cathode catalyst according to claim 1, characterized in that, The average particle size of the platinum nanoparticles is 3~5 nm.
4. A method for preparing a graphitized carbon-supported platinum nanoparticle cathode catalyst as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Mix sulfur / carbon-containing material dispersion, platinum salt dispersion and graphitized carbon to obtain a suspension; (2) After removing the solvent from the suspension, it is calcined in a reducing atmosphere to obtain the graphitized carbon-supported platinum nanoparticles.
5. The preparation method according to claim 4, characterized in that, The sulfur-containing / carbon-containing material dispersion is obtained by mixing the sulfur-containing / carbon-containing material with a first solvent; The platinum salt dispersion is obtained by mixing a platinum salt and a second solvent.
6. The preparation method according to claim 5, characterized in that, The sulfur- or carbon-containing substance is selected from propanethiol; The first solvent is selected from cyclohexane and / or n-hexane; The platinum salt is selected from any one or more of H2PtCl6·6H2O, potassium chloroplatinate, or platinum acetylacetonate. The second solvent is selected from any one or more of ethanol, methanol, or isopropanol.
7. The preparation method according to claim 4, characterized in that, The graphitized carbon is obtained by treating carbon materials at 2000~3000℃ for 1.5~3 h; The carbon material is selected from carbon black; The ratio of the sulfur / carbon-containing substance, platinum salt and graphitized carbon is (4~8) mmol:(0.8~1.6) mmol:(400~800) mg.
8. The preparation method according to claim 4, characterized in that, Step (1) specifically involves mixing the sulfur / carbon-containing dispersion and the platinum salt dispersion for 10-30 min, and then mixing the resulting mixed solution with graphitized carbon for 20-30 h to obtain a suspension. The calcination process specifically involves heating to 300-600 ℃ at a rate of 2-30 ℃ / min and holding for 2-10 h.