Nitrogen-doped graphitized carbon material and preparation method therefor

Abstract

The present application relates to the technical field of fuel cells, and discloses a nitrogen-doped graphitized carbon material and a preparation method therefor. The preparation method comprises the following steps: sequentially adding graphitized carbon, pyrrole, concentrated hydrochloric acid, and a non-noble metal ion compound to water, uniformly mixing these materials, finally adding an ammonium persulfate solution to prepare polypyrrole-coated graphitized carbon, and carrying out a high-temperature annealing treatment and cleaning to prepare the nitrogen-doped graphitized carbon material. The nitrogen-doped graphitized carbon material prepared by means of the preparation method for a nitrogen-doped graphitized carbon material of the present application comprises a coating layer and a substrate, wherein the coating layer covers the surface of the substrate, the coating layer is epitaxially grown graphitized nitrogen-doped carbon, and the substrate is graphitized carbon. The substrate and the coating layer of the nitrogen-doped graphitized carbon material of the present application both have a relatively high graphitization degree, thereby improving the stability of the carbon material.

Description

A nitrogen-doped graphitized carbon material and preparation method thereof Technical Field

[0001] The present application relates to the field of fuel cell technology, and mainly to a nitrogen-doped graphitized carbon material and a preparation method thereof. Background Art

[0002] The use of sustainable energy can effectively alleviate the environmental pollution and greenhouse gas challenges currently facing humanity. Hydrogen, with an energy density three times greater than that of petroleum, is considered a key technology for the future energy revolution. As the most promising application of hydrogen energy, hydrogen-oxygen fuel cells can effectively convert hydrogen into electricity. They offer advantages such as high energy conversion efficiency, zero emissions, and a noise-free environment. They are expected to be widely used in devices such as automobiles, power plants, portable devices, and aerospace vehicles.

[0003] Fuel cells use hydrogen and oxygen in the air as energy sources, and can convert the chemical energy of hydrogen into electrical energy. However, the cathode oxygen reduction reaction (ORR) process in current fuel cells is relatively slow, and a catalyst is required to reduce the reaction overpotential. The most commonly used ORR catalyst is the platinum-carbon catalyst. Compared with other types of catalysts, platinum-carbon catalysts have higher catalytic activity and better stability. However, the durability of commercial platinum-carbon catalysts is still the main factor restricting their long-term use in fuel cells. Due to the poor stability of carbon materials, carbon supports made of carbon materials will be corroded during the catalytic process, especially under high voltage, causing the platinum nanoparticles loaded thereon to fall off, and the activity energy will be greatly attenuated, resulting in poor durability of the platinum-carbon catalyst. Therefore, stable carbon materials are the key to ensuring the high stability of the catalyst.

[0004] One of the important means to improve the stability of carbon materials is to graphitize the carbon materials. The ordered graphitized structure can effectively resist the corrosion of carbon materials in acidic environments. At present, graphitized carbon has begun to be used in commercial catalysts, such as Tanaka Takashi catalyst. Compared with other commercial catalysts, this type of catalyst has lower activity, but shows better stability. The ordered structure of graphitized carbon will lead to a reduction in surface defect sites, thereby reducing the anchoring effect of platinum or platinum-based alloys, and the low specific surface area makes it easy for surface particles to agglomerate, reducing catalytic performance. Therefore, it is particularly important to modify the surface of graphitized carbon, but generally, substances that modify the surface of graphitized carbon, such as nitrogen-doped carbon materials, are prone to corrosion and decomposition in acidic environments due to their low degree of graphitization, resulting in the shedding of metal nanomaterials and poor stability.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a nitrogen-doped graphitized carbon material and a preparation method thereof, aiming to solve the problem that the stability of the existing graphitized carbon needs to be improved.

[0007] The technical solution of this application is as follows:

[0008] A method for preparing a nitrogen-doped graphitized carbon material, comprising the following steps:

[0009] Graphitized carbon, pyrrole, concentrated hydrochloric acid, and a non-noble metal ion compound are sequentially added to water and mixed evenly, and finally an ammonium persulfate solution is added to prepare polypyrrole-coated graphitized carbon. The polypyrrole-coated graphitized carbon is then annealed at a high temperature and washed to prepare the nitrogen-doped graphitized carbon material.

[0010] The present invention discloses a method for preparing a nitrogen-doped graphitized carbon material. The prepared nitrogen-doped graphitized carbon material comprises a coating layer and a substrate. The coating layer is coated on the surface of the substrate, and the coating layer is epitaxially grown graphitized nitrogen-doped carbon, while the substrate is graphitized carbon. The substrate and coating layer of the nitrogen-doped graphitized carbon material of the present invention both have a high degree of graphitization, thereby improving the stability of the carbon material.

[0011] The method for preparing the nitrogen-doped graphitized carbon material, wherein, during the high-temperature annealing treatment, the temperature is 700-2000° C. and the treatment time is 0.5-6 hours.

[0012] In the present application, a nitrogen-doped carbon coating layer with a high degree of graphitization can be formed by adding non-noble metal ions to promote epitaxial growth and performing a high-temperature annealing treatment at 700-2000°C.

[0013] The method for preparing the nitrogen-doped graphitized carbon material, wherein, for every 10 mL-10 L of the water, 100 mg-1 kg of the graphitized carbon, 0.5 mL-1 L of the pyrrole, and 0.1 g-500 g of the non-noble metal ion compound are added.

[0014] The method for preparing the nitrogen-doped graphitized carbon material, wherein, for every 10 mL-10 L of the water, 1 mL-1 L of the concentrated hydrochloric acid and 10 mL-10 L of the ammonium persulfate solution with a concentration of 0.1-5 M are added.

[0015] The method for preparing the nitrogen-doped graphitized carbon material, wherein the non-noble metal ion compound is one or more of a chloride, acetate, nitrate, or oxide containing a non-noble metal ion, or a non-aqueous or hydrated compound;

[0016] The non-noble metal ions include one of cobalt ions, iron ions, nickel ions, manganese ions, zinc ions, and molybdenum ions.

[0017] The method for preparing the nitrogen-doped graphitized carbon material, wherein the preparation process of the graphitized carbon comprises the following steps:

[0018] The carbon material is heated at 1400-2500° C. for 1 hour under argon protection to obtain the graphitized carbon.

[0019] The method for preparing the nitrogen-doped graphitized carbon material further comprises the following steps before the high-temperature annealing treatment:

[0020] Stir at room temperature for 1 h, heat to 90°C, and evaporate to dryness with stirring.

[0021] The method for preparing the nitrogen-doped graphitized carbon material, wherein the cleaning process is to wash with a 0.5M sulfuric acid solution and then wash with water three times.

[0022] The method for preparing the nitrogen-doped graphitized carbon material, after the cleaning, further comprises the following steps:

[0023] Carry out drying treatment;

[0024] During the drying process, the temperature range is 50-100°C.

[0025] A nitrogen-doped graphitized carbon material is prepared using the above-mentioned method for preparing a nitrogen-doped graphitized carbon material. The nitrogen-doped graphitized carbon material comprises a coating layer and a substrate, wherein the coating layer is coated on the surface of the substrate, the coating layer is epitaxially grown graphitized nitrogen-doped carbon, and the substrate is graphitized carbon.

[0026] Beneficial Effects: The method for preparing the nitrogen-doped graphitized carbon material of the present application enables epitaxial growth of the graphitized nitrogen-doped carbon coating layer on the graphitized carbon substrate. The graphitized nitrogen-doped carbon grown based on the graphitized structure of the graphitized carbon substrate. The nitrogen-doped graphitized carbon material of the present application has a high degree of graphitization in both the substrate and the coating layer, thereby improving the stability of the carbon material. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a TEM image of the nitrogen-doped graphitized carbon material prepared in Example 1 of the present application.

[0028] FIG2 is a TEM image of the nitrogen-doped graphitized carbon material prepared in Example 2 of the present application.

[0029] FIG3 is a TEM image of the nitrogen-doped graphitized carbon material prepared in Example 3 of the present application.

[0030] FIG4 is a TEM image of the nitrogen-doped graphitized carbon material prepared in Example 4 of the present application.

[0031] FIG5 is a TEM image of the nitrogen-doped graphitized carbon material prepared in Comparative Example 1 of the present application.

[0032] FIG6 is a TEM image of the nitrogen-doped graphitized carbon material prepared in Comparative Example 1 of the present application.

[0033] FIG7 is an XPS N1s spectrum of the nitrogen-doped graphitized carbon material prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0034] This application provides a nitrogen-doped graphitized carbon material and a preparation method thereof. To make the purpose, technical solution, and effects of this application clearer and more explicit, this application is further described in detail below. It should be understood that the specific embodiments described herein are merely for the purpose of explaining this application and are not intended to limit this application.

[0035] Existing common carbon materials have a low degree of graphitization, making them less stable as carriers in fuel cell catalysts. The lack of defect sites on the surface of graphitized carbon impairs anchoring with metal catalysts, which can easily lead to metal dissolution and redeposition during the catalytic process. Furthermore, graphitized carbon has a low specific surface area and poor ability to disperse metal catalysts, which can easily lead to the agglomeration of metal nanomaterials during catalyst preparation. However, materials that typically modify the surface of graphitized carbon, such as nitrogen-doped carbon materials, are susceptible to corrosion and decomposition in acidic environments due to their low degree of graphitization, causing the metal nanomaterials to fall off and exhibit poor stability.

[0036] The present application provides a method for preparing a nitrogen-doped graphitized carbon material, comprising the following steps:

[0037] Graphitized carbon, pyrrole, concentrated hydrochloric acid, and a non-precious metal ion compound are sequentially added to water and mixed evenly, and finally an ammonium persulfate solution is added to prepare polypyrrole-coated graphitized carbon. After high-temperature annealing and washing, a nitrogen-doped graphitized carbon material is prepared. The nitrogen-doped graphitized carbon material is epitaxially grown graphitized nitrogen-doped carbon-coated graphitized carbon.

[0038] The preparation method of the nitrogen-doped graphitized carbon material of the present application, the prepared nitrogen-doped graphitized carbon material includes a coating layer and a substrate, the coating layer is coated on the surface of the substrate, the coating layer is epitaxially grown graphitized nitrogen-doped carbon, and the substrate is graphitized carbon. The preparation method of the nitrogen-doped graphitized carbon material of the present application can make the coating layer graphitized nitrogen-doped carbon epitaxially grow on the substrate graphitized carbon, and the coating layer graphitized nitrogen-doped carbon is grown based on the graphitized structure of the substrate graphitized carbon. The substrate and coating layer of the nitrogen-doped graphitized carbon material of the present application have a high degree of graphitization as a whole, which can inhibit the corrosion of the carbon material during the operation of the fuel cell. The preparation method of the nitrogen-doped graphitized carbon material of the present application is simple to operate, has fewer processes, good repeatability, low cost, and is conducive to mass production.

[0039] In the present application, graphitized carbon is obtained by graphitizing an existing carbon material. The existing carbon material can be carbon powder or amorphous carbon, and can be a commercially available carbon material such as Ketjen Black 600, Ketjen Black 300, Bp2000, Vulcan XC72, Toray carbon, etc.

[0040] Furthermore, the graphitization treatment specifically includes the following steps:

[0041] The carbon material is heated at 1400-2500° C. for 1 hour under argon protection to obtain graphitized carbon.

[0042] The prepared graphitized carbon has a certain graphitized structure and a high specific surface area. Furthermore, the non-precious metal ions include one of cobalt ions, iron ions, nickel ions, manganese ions, zinc ions, molybdenum ions, etc., and the non-precious metal ion compound can be one or more of non-aqueous or hydrated chlorides, acetates, nitrates, oxides, etc. containing non-precious metal ions. The addition of metal ions will cause the nitrogen-doped carbon layer on the surface to grow epitaxially according to the crystal form of the underlying graphitized carbon, so that the entire carbon material has a high degree of graphitization from the inside out, thereby improving the stability of the carbon material.

[0043] Furthermore, during the high temperature annealing treatment, the temperature is 700-2000°C and the treatment time is 0.5-6h. In the present application, by adding non-noble metal ions to promote epitaxial growth and performing high temperature annealing treatment at 700-2000°C, a nitrogen-doped carbon coating layer with a high degree of graphitization can be formed.

[0044] During the high temperature annealing process, it is preferably carried out under the protection of an inert gas, such as argon (Ar).

[0045] Furthermore, the dosage ratio range between pyrrole, ammonium persulfate, graphitized carbon, non-precious metal ion compound, and concentrated hydrochloric acid is 100mg-1kg graphitized carbon, 0.5mL-1L pyrrole, 0.1g-500g non-precious metal ion compound, 1mL-1L concentrated hydrochloric acid, and 10mL-10L 0.1-5M ammonium persulfate solution can be added to every 10mL-10L of water. The above dosage range is basically the minimum to maximum amount of each raw material. Within this range, as the amount of raw materials increases, the amount of nitrogen-doped surface porous carbon material synthesized will also increase accordingly. Among them, the concentration of concentrated hydrochloric acid should be 36% to 38%. Concentrated hydrochloric acid purchased is used directly without dilution.

[0046] Furthermore, before the high temperature annealing treatment is performed, the following steps are included:

[0047] Stir at room temperature for 1 h, heat to 90°C, and evaporate to dryness with stirring.

[0048] Furthermore, the cleaning process can be performed by washing with a 0.5M sulfuric acid solution and then washing with water three times. After washing, a drying process can be performed. Furthermore, the temperature range of the drying process is 50-100°C.

[0049] Furthermore, the graphitized carbon, pyrrole, concentrated hydrochloric acid, and non-precious metal ion compound are sequentially added to water and mixed uniformly, and finally the ammonium persulfate solution is added. Specifically, the graphitized carbon and pyrrole are sequentially added to water, mixed uniformly, concentrated hydrochloric acid is added to adjust the pH value and the non-precious metal ion compound, and finally the ammonium persulfate solution is added. The mixing method can be ultrasonic dispersion or stirring.

[0050] The present application also provides a nitrogen-doped graphitized carbon material, which is prepared using the above-mentioned method for preparing nitrogen-doped graphitized carbon material. The nitrogen-doped graphitized carbon material includes a coating layer and a substrate, wherein the coating layer is coated on the surface of the substrate, the coating layer is epitaxially grown graphitized nitrogen-doped carbon, and the substrate is graphitized carbon. The nitrogen-doped graphitized carbon material has the following advantages:

[0051] (1) The graphitized carbon substrate itself is difficult to interact with the metal catalyst due to its graphitized carbon structure. However, the graphitized nitrogen-doped carbon coating on the substrate surface can interact with the metal catalyst, inhibiting the aggregation and shedding of metal nanomaterials during metal loading and oxygen reduction.

[0052] (2) The introduction of graphitized nitrogen-doped carbon on the graphitized carbon surface provides a higher specific surface area, which is conducive to the loading and dispersion of surface metal catalysts;

[0053] (3) The addition of metal ions will cause the nitrogen-doped carbon layer on the surface to grow epitaxially according to the graphitized crystal form of the underlying graphitized carbon, so that the entire carbon material has a high degree of graphitization from the inside to the outside, thereby improving the stability of the carbon material.

[0054] The present application is further described below through specific examples.

[0055] The graphitized carbon powders in Examples 1-4 were all prepared by the following method:

[0056] Ketjen Black 600 carbon powder was heated at 1800°C for 1 hour under argon protection to obtain graphitized carbon powder.

[0057] Example 1:

[0058] In water, 1 gram of graphitized carbon powder, 2 mL of pyrrole, 10 mL of concentrated hydrochloric acid, and 3.34 g of cobalt chloride hexahydrate were added in sequence, stirred evenly, and then 40 mL of 0.5 M ammonium persulfate solution was added. The mixture was stirred at room temperature for 1 hour, and then heated to 90 ° C and stirred to evaporate the water. The mixture was treated at a high temperature of 800 ° C for 2 hours under argon protection. The obtained sample was washed with 0.5 M sulfuric acid solution and then washed three times with water. After drying at 60 ° C, a nitrogen-doped graphitized carbon material was obtained, in which the mass ratio of the coating layer graphitized nitrogen-doped carbon to the base graphitized carbon was approximately 1:1.

[0059] Example 2:

[0060] In an aqueous solution, 1 gram of graphitized carbon powder, 1 mL of pyrrole, 10 mL of concentrated hydrochloric acid, and 2.2 g of ferric chloride hexahydrate were added in sequence, stirred evenly, and then 40 mL of 0.5 M ammonium persulfate solution was added. The mixture was stirred at room temperature for 1 hour, and then heated to 90 ° C and stirred to evaporate the water. The mixture was treated at a high temperature of 900 ° C for 2 hours under argon protection. The obtained sample was washed with 0.5 M sulfuric acid solution and then washed three times with water. After drying at 60 ° C, a nitrogen-doped graphitized carbon material was obtained, in which the mass ratio of the coating layer graphitized nitrogen-doped carbon to the base graphitized carbon was approximately 1:2.

[0061] Example 3:

[0062] In an aqueous solution, 2 grams of graphitized carbon powder, 1 mL of pyrrole, 10 mL of concentrated hydrochloric acid, and 4.44 g of zinc nitrate were added in sequence, stirred evenly, and then 40 mL of 0.5 M ammonium persulfate solution was added. The mixture was stirred at room temperature for 1 hour, and then heated to 90 ° C and stirred to evaporate the water. The mixture was treated at a high temperature of 1200 ° C for 2 hours under argon protection. The obtained sample was washed with 0.5 M sulfuric acid solution and then washed three times with water. After drying at 60 ° C, a nitrogen-doped graphitized carbon material was obtained, in which the mass ratio of the graphitized nitrogen-doped carbon coating layer to the graphitized carbon substrate was approximately 1:4.

[0063] Example 4:

[0064] 20 grams of graphitized carbon powder, 10 mL of pyrrole, 100 mL of concentrated hydrochloric acid, and 95 g of manganese acetate were added to an aqueous solution in sequence. After stirring evenly, 400 mL of 0.5 M ammonium persulfate solution was added, stirred at room temperature for 1 hour, and then heated to 90 ° C and stirred to evaporate the water. The mixture was treated at a high temperature of 800 ° C for 2 hours under argon protection. The obtained sample was washed with 0.5 M sulfuric acid solution and then washed three times with water. After drying at 60 ° C, a nitrogen-doped graphitized carbon material was obtained, in which the mass ratio of the coating layer graphitized nitrogen-doped carbon to the base graphitized carbon was approximately 1:4.

[0065] Comparative Example 1

[0066] The preparation method is the same as that of Example 1, except that cobalt chloride hexahydrate is not added.

[0067] TEM images of the nitrogen-doped graphitized carbon materials prepared in Examples 1-4 and Comparative Example 1 are shown in Figures 1-6, wherein Figures 1-4 are TEM images of the nitrogen-doped graphitized carbon materials prepared in Examples 1-4, respectively, and Figures 5-6 are TEM images of the nitrogen-doped graphitized carbon materials prepared in Comparative Example 1. As can be seen from Figures 1-4, the graphitized nitrogen-doped carbon of the outer coating layer grows on the graphitized carbon substrate in an epitaxial growth manner, indicating that after the addition of metal ions to assist in the formation of nitrogen-doped carbon, the coating layer grows epitaxially on the graphitized carbon substrate, so that the nitrogen-doped carbon of the coating layer has an obvious graphitized structure, so that the entire material has a high degree of graphitization, and the material stability is improved; as can be seen from Figures 5-6, the nitrogen-doped graphitized carbon material synthesized in the absence of metal ions has no obvious continuous layered graphitized structure.

[0068] Figure 7 is the XPS N1s spectrum of the nitrogen-doped graphitized carbon material prepared in Example 2. The spectrum shows the appearance of nitrogen in the nitrogen-doped graphitized carbon material and the coordination of nitrogen on the surface of the coating layer. It mainly appears in the form of graphitized nitrogen and pyridinic nitrogen, and unstable pyrrolic nitrogen does not appear, indicating that nitrogen appears in a relatively stable form on the surface of the coating layer, which also shows that the nitrogen-doped graphitized carbon material has high stability.

[0069] The specific surface area and pore capacity of the raw material graphitized carbon powder and the nitrogen-doped graphitized carbon material prepared in Examples 1-3 were tested, and the results are shown in Table 1. As can be seen from Table 1, compared with the graphitized carbon powder, the specific surface area and pore capacity of the nitrogen-doped graphitized carbon material prepared in Examples 1-3 are significantly increased. The graphitized nitrogen-doped carbon on the surface can provide a higher specific surface area for the nitrogen-doped graphitized carbon material, which is beneficial to the loading of metal particles. Moreover, the preparation method provided in the present application uses a relatively simple preparation method (one-pot cooking), can be mass-produced, and is conducive to industrial application.

[0070] Table 1

[0071] It should be understood that the application of this application is not limited to the above examples. For ordinary technicians in this field, they can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of this application.

Claims

1. A preparation method of a nitrogen-doped graphitized carbon material, characterized in that, It includes the following steps: Graphitized carbon, pyrrole, concentrated hydrochloric acid, and non-noble metal ion compounds are successively added to water and mixed evenly. Finally, an ammonium persulfate solution is added to prepare graphitized carbon coated with polypyrrole. After high-temperature annealing treatment and washing, the nitrogen-doped graphitized carbon material is obtained.

2. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, wherein During the high-temperature annealing treatment, the temperature is 700 - 2000 °C, and the treatment time is 0.5 - 6 h.

3. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, wherein, For every 10 mL - 10 L of the water, 100 mg - 1 kg of the graphitized carbon, 0.5 mL - 1 L of the pyrrole, and 0.1 g - 500 g of the non-noble metal ion compound are added.

4. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, characterized in that For every 10 mL - 10 L of the water, 1 mL - 1 L of the concentrated hydrochloric acid and 10 mL - 10 L of an ammonium persulfate solution with a concentration of 0.1 - 5 M are added.

5. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, characterized in that, The non-noble metal ion compound is one or more of non-aqueous or hydrates of chlorides, acetates, nitrates, and oxides containing non-noble metal ions. The non-noble metal ions include one of cobalt ions, iron ions, nickel ions, manganese ions, zinc ions, and molybdenum ions.

6. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, characterized in that, The preparation process of the graphitized carbon includes the following steps: The carbon material is kept at 1400 - 2500 °C for 1 hour under argon protection to obtain the graphitized carbon.

7. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, characterized in that, Before the high-temperature annealing treatment, it also includes the following steps: Stir at room temperature for 1 h, heat to 90 °C, and stir to evaporate the water.

8. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, characterized in that, The washing process is to wash with a 0.5 M sulfuric acid solution and then wash three times with water.

9. The preparation method of the nitrogen-doped graphitized carbon material according to claim 1, characterized in that, After the washing, it also includes the following steps: Perform a drying treatment; During the drying treatment, the temperature range is 50 - 100 °C.

10. A nitrogen-doped graphitized carbon material, characterized in that, Prepared by using the preparation method of the nitrogen-doped graphitized carbon material according to any one of claims 1 - 9, the nitrogen-doped graphitized carbon material includes a coating layer and a substrate. The coating layer covers the surface of the substrate. The coating layer is epitaxially grown graphitized nitrogen-doped carbon, and the substrate is graphitized carbon.

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