Preparation method and application of a pyrrole nitrogen-doped carbon material

Abstract

The present invention discloses a preparation method and application of a pyrrole-nitrogen-doped carbon material. The method includes using a natural clay material as a template, mixing raw materials with a salt catalyst to form a homogeneous solution, and then adopting a combination of hydrothermal treatment, freeze-drying and high-temperature heat treatment to form a preliminary product. Subsequently, the template material is removed by acid solution 1 and acid solution 2, and after centrifugal washing and drying, the pyrrole-nitrogen-doped carbon material is obtained. The present invention realizes the preparation of the pyrrole-nitrogen-doped carbon material by combining hydrothermal treatment, freeze-drying and high-temperature heat treatment. At the same time, the two-step method can effectively remove the clay template, ensuring the complete structure of the pyrrole-nitrogen-doped carbon material. A remarkable feature of the present invention is that the template material used is a natural clay material, which helps to form pyridine nitrogen, and the content of pyrrole nitrogen can be 59-84%. The obtained pyrrole-nitrogen-doped carbon material exhibits high catalytic activity in the oxygen reduction reaction. The materials of the present invention all use non-precious metal elements, reducing the use cost, facilitating the large-scale production of the catalyst, and providing a prerequisite for its wide use.

Description

Technical Field

[0001] The present invention relates to the field of manufacturing non-metal oxygen reduction catalysts, and particularly to a preparation method and application of a pyrrole nitrogen-doped carbon material. Background Art

[0002] In the field of fuel cells, excellent oxygen reduction (ORR) catalysts have always received extensive attention. Currently, classified by materials, ORR catalysts can be divided into two categories: noble metal catalysts and non-metal catalysts.

[0003] Platinum (Pt), as the core material of ORR noble metal catalysts, has become the preferred material for ORR catalysts due to its high performance and high stability. However, the high cost of Pt leads to a significant increase in the usage cost. To reduce the cost, researchers in various countries have developed Pt-based ORR catalysts. When other inexpensive noble metals or non-noble metals are introduced to form alloys with Pt, by optimizing the electronic structure of Pt, the goals of reducing cost and improving the activity of ORR catalytic reactions can be achieved. In addition, to fully exert the catalytic ability of Pt and improve the utilization rate of Pt, researchers have supported Pt nanoparticles on some conductive carriers, such as graphene, carbon black, carbon nanotubes, etc. Through the anchoring effect of the carrier, the dispersion of Pt nanoparticles has been greatly improved, the problem of nanoparticle accumulation during long cycles has been alleviated, and the stability of the catalyst has been effectively improved.

[0004] In recent years, to reduce the cost of catalysts, non-metal-based materials have become a research hotspot for ORR catalysts. Among them, carbon-based materials have been the most widely studied, mainly because carbon-based materials have good electrical conductivity, simple preparation methods, and low prices. However, compared with common noble metal catalysts, the charge distribution of carbon materials is uniform, resulting in poor adsorption / desorption ability between carbon materials and reactants, which severely limits the improvement of catalytic performance. Heteroatom doping is an effective way to regulate the surface charge characteristics of carbon materials. By incorporating heteroatoms, the redistribution of charges in the carbon skeleton can be caused, and then the adsorption / desorption ability with surface species can be optimized. Among many doped atoms, nitrogen (N) atoms have become the most studied and widely used heteroatoms due to their similar atomic radius to carbon and low doping difficulty. The doping forms of N in carbon materials are mainly divided into three forms: pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen.

[0005] Through the regulation of nitrogen atoms, the charge density and spin density of carbon-based materials can be changed, the electron transfer in the catalytic process can be accelerated, the adsorption ability of oxygen molecules on the catalyst surface can be effectively regulated, thereby improving the catalytic activity, which also provides a theoretical model for in-depth study of the ORR reaction mechanism. It is found that N-doped carbon can effectively regulate sp as an ORR catalytic active site. 2The charge density and spin distribution on carbon promote the adsorption of oxygen molecules and the cleavage of the O-O bond. In addition, it can also alleviate the aggregation and accumulation of active sites of the catalyst during long-term cycling, improving the catalytic stability. Compared with the six-membered ring structures of pyridine nitrogen and graphitic nitrogen, pyrrole nitrogen has a five-membered ring structure, and its unique structure endows it with unique catalytic properties. However, in the actual doping preparation process, due to the limitation of the surface characteristics of carbon materials, the contents of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen are relatively small, especially the pyrrole nitrogen with a five-membered ring is even less, making it difficult to exert its catalytic properties. Therefore, how to increase the content of pyrrole nitrogen has become a research hotspot for ORR catalytic activity.

[0006] Clay is generally formed after the weathering of silicate minerals on the earth's surface. It is a type of layered silicate, and the lamellae are composed of silicon-oxygen tetrahedrons and aluminum-oxygen octahedrons. At the same time, clay is also an important mineral raw material, widely distributed in rocks and soils around the world, and can be used to manufacture ceramic products, refractory materials, building materials, etc. Based on the characteristics of silicon-oxygen tetrahedrons in clay, it can rapidly adsorb carbon sources, especially nitrogen-containing carbon sources. Through the strong electron adsorption characteristics of nitrogen atoms, it can greatly enhance the adsorption and growth of N-doped carbon and promote the formation of pyrrole nitrogen. Summary of the Invention

[0007] In order to overcome the problem of low content of pyrrole nitrogen in the existing ORR catalysts, the present invention uses clay as a template and effectively promotes the formation of pyrrole nitrogen through its inherent silicon-oxygen tetrahedrons. At the same time, a method combining hydrothermal treatment, freeze-drying, and high-temperature heat treatment is adopted to realize the preparation of a carbon material doped with a high content of pyrrole nitrogen. This material can effectively promote the adsorption of oxygen molecules and the cleavage of the O-O bond in ORR, showing high catalytic activity.

[0008] The purpose of the present invention is to provide a preparation method of a pyrrole nitrogen-doped carbon material, and the preparation method includes the following steps:

[0009] (1) Homogeneous solution mixing: Using a clay material as a template material and any one of cellulose, urea, and melamine as a raw material, dissolving the raw material and a salt catalyst in water to form a homogeneous solution, and then mixing it with the template material to obtain a uniformly dispersed liquid;

[0010] (2) Hydrothermal reaction: Placing the dispersion liquid in step (1) into a hydrothermal reaction kettle in a homogeneous reactor, heating for a certain time, and naturally cooling to room temperature to obtain a reaction solution;

[0011] (3) Centrifugal washing: Centrifuging the reaction solution in step (2), washing the centrifuged product, and drying to obtain a solid powder material;

[0012] (4) Freeze-drying: Freeze-drying the solid powder material in step (3) to obtain a dry solid powder;

[0013] (5) High-temperature heat treatment: The dried solid powder from step (4) is subjected to high-temperature heat treatment to obtain a product sample;

[0014] (6) Template removal: The product sample from step (5) is successively placed in acid solution 1 and acid solution 2 to obtain a pyrrole-nitrogen-doped carbon sample;

[0015] (7) Centrifugation and washing: The pyrrole-nitrogen-doped carbon sample from step (6) is centrifuged, washed, and dried to obtain a pyrrole-nitrogen-doped carbon material.

[0016] Preferably, in step (1), the clay material is one of kaolin, montmorillonite, and attapulgite, and the concentration of the clay material in the homogeneous dispersion is 20 - 50 mg / mL. The salt catalyst is one of iron salts, cobalt salts, manganese salts, and nickel salts.

[0017] Preferably, in step (2), the heating temperature is 120 - 220 °C and the heating time is 6 - 24 h.

[0018] Preferably, in step (3), the drying temperature is 50 - 80 °C.

[0019] Preferably, in step (4), the freeze-drying temperature is < -10 °C and the vacuum degree is < 10 Pa.

[0020] Preferably, in step (5), the heat treatment temperature is 500 - 800 °C, the time is 1 - 6 h, and the heat treatment atmosphere is one of nitrogen, argon, and hydrogen / argon mixed gas.

[0021] Preferably, in step (6), acid solution 1 is sulfuric acid with a concentration of 0.5 - 3.0 mol / L, the reaction time is 5 - 24 h, the reaction temperature is 25 - 60 °C, acid solution 2 is hydrofluoric acid with a mass fraction of 10 - 50%, the reaction time is 0.5 - 2.0 h, and the reaction temperature is 25 - 40 °C.

[0022] Preferably, in step (7), the drying temperature is 50 - 80 °C.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The present invention discovers for the first time that when natural clay materials are used as templates, they can promote the formation of pyrrole-nitrogen-doped carbon materials and achieve an improvement in oxygen reduction performance.

[0025] (2) The clay templates used in the present invention all have a silicon-oxygen structure, which helps the formation of nitrogen-doped carbon materials and also helps the formation of pyridine nitrogen.

[0026] (3) The present invention uses natural clay materials as templates and prepares pyrrole-nitrogen-doped carbon materials by combining hydrothermal treatment, freeze-drying, and high-temperature heat treatment. This material is used in the oxygen reduction reaction and exhibits high catalytic activity.

[0027] (4) The present invention combines hydrothermal treatment, freeze-drying, and high-temperature heat treatment to achieve the preparation of pyrrole-nitrogen-doped carbon materials. At the same time, two acid solutions are used separately and the natural clay template is removed step by step, which can ensure the structural integrity of the pyrrole-nitrogen-doped carbon materials while removing the template.

[0028] (5) The present invention discovers the unique silicon-oxygen bonds on the surface of clay materials, which enables the pyrrole nitrogen content in the nitrogen-doped carbon materials to reach as high as 59%-84%.

[0029] (6) The natural clay materials used in the present invention are relatively abundant in reserves around the world and in China, which provides a new direction for broadening the application fields of natural clay materials.

[0030] (7) The raw materials selected in the present invention are one of cellulose, urea, and melamine. The raw material prices are low, which helps to reduce the catalyst cost.

[0031] (8) The salt catalysts selected in the present invention are all sulfates. Adding iron, cobalt, and nickel metal elements can reduce the reaction temperature, increase the reaction rate, and play a role in energy conservation and time saving for the preparation reaction.

[0032] (9) All elements in the material preparation of the present invention are non-precious metal elements, which can effectively reduce the catalyst cost, contribute to the large-scale production of the catalyst, and provide a prerequisite for its wide use.

[0033] (10) The dried solid powder is heat-treated at a high temperature of 500-800 °C, which can improve the graphitization degree of the material, contribute to the transmission of electrons, and provide a favorable guarantee for its application in the field of electrocatalysis. Description of the Drawings

[0034] Figure 1 It is the TEM image of montmorillonite / pyrrole-nitrogen-doped carbon materials.

[0035] Figure 2 It is the TEM image of pyrrole-nitrogen-doped carbon materials.

[0036] Figure 3 It is the Raman image of pyrrole-nitrogen-doped carbon materials.

[0037] Figure 4 It is the peak splitting image of N1s in pyrrole-nitrogen-doped carbon materials.

[0038] Figure 5ORR performance comparison chart of montmorillonite, montmorillonite / pyrrole nitrogen-doped carbon, and pyrrole nitrogen-doped carbon materials.

[0039] Figure 6 Peak separation diagram of N1s in kaolin / pyrrole nitrogen-doped carbon material. Detailed implementation methods

[0040] Example 1: Preparation of montmorillonite / pyrrole nitrogen-doped carbon material

[0041] Completed according to the following process:

[0042] (1) Homogeneous solution mixing: Cellulose and cobalt sulfate are dispersed in deionized water at a mass ratio of 1:1, ultrasonicated until a homogeneous solution is formed, and then a certain mass of clay material montmorillonite is added to form a uniform dispersion. At this time, the concentration of montmorillonite in the dispersion is 25 mg / mL.

[0043] (2) Hydrothermal reaction: The homogeneous dispersion in step (1) is placed in a hydrothermal reaction kettle in a 50 mL homogeneous reactor, heated to 200 °C, kept at a constant temperature for 24 h, and naturally cooled to room temperature to obtain a reaction solution.

[0044] (3) Centrifugation and washing: The reaction solution in step (2) is centrifuged, the centrifuged product is washed, and then dried at 80 °C for 8 h to obtain a solid powder material.

[0045] (4) Freeze-drying: The solid powder material prepared in step (3) is placed in a freeze-dryer and dried at a temperature of -45 °C and a vacuum of <10 Pa to obtain a dried solid powder.

[0046] (5) High-temperature heat treatment: The dried solid powder in step (4) is subjected to high-temperature heat treatment. Under a nitrogen atmosphere, it is heated to 700 °C at a rate of 5 °C / min and kept at a constant temperature for 2 h to obtain a product sample.

[0047] (6) Removal of template: The product sample in step (5) is first placed in 1.0 mol / L sulfuric acid solution and reacted at 40 °C for 7 h. After washing with deionized water, it is then placed in 40% hydrofluoric acid and reacted at 25 °C for 2 h to remove the template and obtain a pyrrole nitrogen-doped carbon sample.

[0048] (7) Centrifugation and washing: The pyrrole nitrogen-doped carbon sample in step (6) is centrifuged at 8000 rpm, and the pyrrole nitrogen-doped carbon sample is centrifuged and washed 3 times with deionized water, and dried at 60 °C for 12 h to obtain a pyrrole nitrogen-doped carbon material.

[0049] Example 2: Preparation of attapulgite / pyrrole nitrogen-doped carbon material

[0050] It is completed according to the following process:

[0051] (1) Homogeneous solution mixing: Cellulose and ammonium ferrous sulfate are dispersed in deionized water at a mass ratio of 1:1, and ultrasonicated until a homogeneous solution is formed. Then, a certain mass of clay material attapulgite is added to form a homogeneous dispersion. At this time, the concentration of attapulgite in the dispersion is 25 mg / mL.

[0052] (2) Hydrothermal reaction: The homogeneous dispersion obtained in step (1) is placed in a hydrothermal reaction kettle in a 50 mL homogeneous reactor, heated to 200 °C, kept at a constant temperature for 24 h, and naturally cooled to room temperature to obtain a reaction solution.

[0053] (3) Centrifugation and washing: The reaction solution in step (2) is centrifuged, the centrifuged product is washed, and then dried at 80 °C for 8 h to obtain a solid powder material.

[0054] (4) Freeze-drying: The solid powder material prepared in step (3) is placed in a freeze-dryer and dried at a temperature of -45 °C and a vacuum degree <10 Pa to obtain a dried solid powder.

[0055] (5) High-temperature heat treatment: The dried solid powder in step (4) is subjected to high-temperature heat treatment. Under a nitrogen atmosphere, it is heated to 700 °C at a rate of 5 °C / min and kept at a constant temperature for 2 h to obtain a product sample.

[0056] (6) Template removal: The product sample in step (5) is first placed in 1.0 mol / L sulfuric acid solution and reacted at 40 °C for 7 h. After washing with deionized water, it is then placed in 40% hydrofluoric acid and reacted at 25 °C for 2 h to remove the template and obtain a pyrrole-nitrogen-doped carbon sample.

[0057] (7) Centrifugation and washing: The pyrrole-nitrogen-doped carbon sample in step (6) is centrifuged at 8000 rpm, and the pyrrole-nitrogen-doped carbon sample is centrifuged and washed 3 times with deionized water, and dried at 60 °C for 12 h to obtain a pyrrole-nitrogen-doped carbon material.

[0058] Example 3: Preparation of montmorillonite / pyrrole-nitrogen-doped carbon material

[0059] It is completed according to the following process:

[0060] (1) Homogeneous solution mixing: Melamine and ammonium ferrous sulfate are dispersed in deionized water at a mass ratio of 1:1, and ultrasonicated until a homogeneous solution is formed. Then, a certain mass of clay material montmorillonite is added to form a homogeneous dispersion. At this time, the concentration of montmorillonite in the dispersion is 25 mg / mL.

[0061] (2) Hydrothermal reaction: Place the homogeneous dispersion obtained in step (1) into a hydrothermal reaction kettle in a 50 mL homogeneous reactor, heat it to 200 °C, maintain the temperature for 24 h, and naturally cool it to room temperature to obtain a reaction solution.

[0062] (3) Centrifugation and washing: Centrifuge the reaction solution in step (2), wash the centrifuged product, and then dry it at 80 °C for 8 h to obtain a solid powder material.

[0063] (4) Freeze-drying: Place the solid powder material prepared in step (3) into a freeze-dryer and dry it at a temperature of -45 °C and a vacuum degree < 10 Pa to obtain a dried solid powder.

[0064] (5) High-temperature heat treatment: Perform high-temperature heat treatment on the dried solid powder in step (4). Under a nitrogen atmosphere, heat it to 700 °C at a rate of 5 °C / min and maintain the temperature for 2 h to obtain a product sample.

[0065] (6) Template removal: Place the product sample in step (5) into 1.0 mol / L sulfuric acid solution and react at 40 °C for 7 h. After washing with deionized water, then place it into 40% hydrofluoric acid by mass fraction and react at 25 °C for 2 h to remove the template and obtain a pyrrole nitrogen-doped carbon sample.

[0066] (7) Centrifugation and washing: Centrifuge the pyrrole nitrogen-doped carbon sample in step (6) at 8000 rpm, wash the pyrrole nitrogen-doped carbon sample 3 times with deionized water by centrifugation, and dry it at 60 °C for 12 h to obtain a pyrrole nitrogen-doped carbon material.

[0067] Example 4: Preparation of kaolin / pyrrole nitrogen-doped carbon material

[0068] Complete according to the following process:

[0069] (1) Homogeneous solution mixing: Disperse urea and manganese sulfate in deionized water at a mass ratio of 1:1, ultrasonicate until a homogeneous solution is formed, and then add a certain mass of clay material kaolin to form a homogeneous dispersion. At this time, the concentration of kaolin in the dispersion is 50 mg / mL.

[0070] (2) Hydrothermal reaction: Place the homogeneous dispersion obtained in step (1) into a hydrothermal reaction kettle in a 50 mL homogeneous reactor, heat it to 220 °C, maintain the temperature for 6 h, and naturally cool it to room temperature to obtain a reaction solution.

[0071] (3) Centrifugation and washing:: Centrifuge the reaction solution in step (2), wash the centrifuged product, and then dry it under drying conditions at 50 °C for 12 h to obtain a solid powder material.

[0072] (4) Freeze-drying: Place the solid powder material prepared in step (3) in a freeze-dryer and dry it at a temperature of -45°C and a vacuum of <10 Pa to obtain dry solid powder.

[0073] (5) High-temperature heat treatment: Perform high-temperature heat treatment on the dry solid powder in step (4). Under an argon atmosphere, heat it at a rate of 5°C / min to 800°C and keep it at a constant temperature for 1 h to obtain a product sample.

[0074] (6) Template removal: First, place the product sample in step (5) in 3.0 mol / L sulfuric acid solution and react at 60°C for 5 h. After washing with deionized water, then place it in 10% hydrofluoric acid and react at 25°C for 1 h to remove the template and obtain a pyrrole-nitrogen-doped carbon sample.

[0075] (7) Centrifugation and washing: Centrifuge the pyrrole-nitrogen-doped carbon sample in step (6) at 8000 rpm and wash the pyrrole-nitrogen-doped carbon sample 3 times with deionized water. Dry it at a temperature of 80°C for 6 h to obtain the pyrrole-nitrogen-doped carbon material.

[0076] Example 5: Preparation of kaolin / pyrrole-nitrogen-doped carbon material

[0077] Complete according to the following process:

[0078] (1) Homogeneous solution mixing: Disperse melamine and nickel sulfate in deionized water at a mass ratio of 1:1.5 and ultrasonicate until a homogeneous solution is formed. Then add a certain mass of clay material kaolin to form a uniform dispersion. At this time, the concentration of kaolin in the dispersion is 20 mg / mL.

[0079] (2) Hydrothermal reaction: Place the uniform dispersion in step (1) in a hydrothermal reaction kettle in a 50 mL homogeneous reactor, heat it to 120°C, keep it at a constant temperature for 12 h, and cool it naturally to room temperature to obtain a reaction solution.

[0080] (3) Centrifugation and washing: Centrifuge the reaction solution in step (2), wash the centrifuged product, and then dry it at 60°C for 8 h to obtain a solid powder material.

[0081] (4) Freeze-drying: Place the solid powder material prepared in step (3) in a freeze-dryer and dry it at a temperature of -20°C and a vacuum of <10 Pa to obtain dry solid powder.

[0082] (5) High-temperature heat treatment: Perform high-temperature heat treatment on the dried solid powder in step (4). Under a hydrogen / argon atmosphere, heat it at a rate of 5°C / min to 500°C and keep it at a constant temperature for 6 h to obtain a product sample.

[0083] (6) Template removal: The product sample in step (5) is first placed in an acid solution of 0.5 mol / L sulfuric acid and reacted at 25 °C for 24 h. After washing with deionized water, it is then placed in hydrofluoric acid with a mass fraction of 50% and reacted at 40 °C for 0.5 h to remove the template, obtaining a pyrrole nitrogen-doped carbon sample.

[0084] (7) Centrifugation and washing: The pyrrole nitrogen-doped carbon sample in step (6) is centrifuged at 8000 rpm, and the pyrrole nitrogen-doped carbon sample is centrifuged and washed with deionized water three times, and dried at 50 °C for 12 h to obtain the pyrrole nitrogen-doped carbon material.

[0085] Comparative Example 1: Preparation of montmorillonite / pyridine nitrogen-doped carbon material

[0086] It is completed according to the following process:

[0087] (1) Homogeneous solution mixing: Cellulose and ammonium ferrous sulfate are dispersed in deionized water at a mass ratio of 1:2, and ultrasonicated until a homogeneous solution is formed. Then a certain mass of clay material montmorillonite is added to form a uniform dispersion. At this time, the concentration of montmorillonite in the dispersion is 25 mg / mL.

[0088] (2) Hydrothermal reaction: The homogeneous dispersion in step (1) is placed in a hydrothermal reaction kettle in a 50 mL homogeneous reactor, heated to 200 °C, kept at a constant temperature for 24 h, and naturally cooled to room temperature to obtain a reaction solution.

[0089] (3) Centrifugation and washing: The reaction solution in step (2) is centrifuged, the centrifuged product is washed, and then dried at 60 °C for 12 h to obtain a solid powder material.

[0090] (4) Freeze drying: The solid powder material prepared in step (3) is placed in a freeze dryer and dried at a temperature of -45 °C and a vacuum degree of <10 Pa to obtain a dried solid powder.

[0091] (5) High-temperature heat treatment: The dried solid powder in step (4) is subjected to high-temperature heat treatment. In a nitrogen atmosphere, it is heated to 700 °C at a rate of 5 °C / min and kept at a constant temperature for 2 h to obtain a product sample.

[0092] (6) Template removal: The product sample in step (5) is first placed in an acid solution of 1.0 mol / L sulfuric acid and reacted at 40 °C for 7 h. After washing with deionized water, it is then placed in hydrofluoric acid with a mass fraction of 40% and reacted at 25 °C for 2 h to completely remove the template, obtaining a pyrrole nitrogen-doped carbon sample.

[0093] (7) Centrifugal washing: Centrifuge the pyrrole nitrogen-doped carbon sample in step (6) at 8000 rpm, and centrifuge and wash the pyrrole nitrogen-doped carbon sample with deionized water three times, and dry it at 60 °C for 12 h to obtain the pyrrole nitrogen-doped carbon material.

[0094] The TEM image of montmorillonite / pyrrole nitrogen-doped carbon is shown as Figure 1 follows. It can be seen from the figure that the prepared material has a two-dimensional structure and a relatively flat surface. The two-dimensional structure mainly comes from the morphology of montmorillonite. After removing montmorillonite, the pyrrole nitrogen-doped carbon material can still maintain the two-dimensional structure ( Figure 1 ), which indicates that the two-step acid treatment does not change the morphology of the pyrrole nitrogen-doped carbon material. After removing montmorillonite, the pyrrole nitrogen-doped carbon material can still maintain the two-dimensional structure (as shown in Figure 2 ), which indicates that the two-step acid treatment does not change the morphology of the pyrrole nitrogen-doped carbon material. The Raman image of the pyrrole nitrogen-doped carbon material is shown as Figure 3 follows. It can be seen from the figure that obvious D peak and G peak appear at 1340 cm -1 and 1580 cm -1 respectively. Given that the G peak value is higher than the D peak value, it can be inferred that the material has a high degree of graphitization, which is of great significance for electron transport.

[0095] By deconvoluting the N 1s peak of the pyrrole nitrogen-doped carbon material (as shown in Figure 4 ), three obvious characteristic peaks of nitrogen appear at 398.6 eV, 400.8 eV, and 402.4 eV respectively, which correspond to pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen respectively. At the same time, the pyrrole nitrogen content is as high as 84%. Figure 5 The ORR performance comparison chart of montmorillonite, montmorillonite / pyrrole nitrogen-doped carbon, and pyrrole nitrogen-doped carbon materials is shown. It can be seen that when the current density is 0.2 mA cm -2 respectively, compared with montmorillonite and montmorillonite / pyrrole nitrogen-doped carbon samples, the onset potential of the ORR of the pyrrole nitrogen-doped carbon material is positively shifted by 120 mV and 100 mV respectively, and the half-wave potential of the pyrrole nitrogen-doped carbon material is 0.61 V, which indicates that the pyrrole nitrogen-doped carbon material has good ORR catalytic activity.

[0096] In addition, by deconvoluting the N 1s peak of the kaolin / pyrrole nitrogen-doped carbon material (as shown in Figure 6 ), three obvious characteristic peaks of nitrogen appear at 398.6 eV, 400.8 eV, and 402.4 eV respectively, which correspond to pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen respectively. At the same time, the pyrrole nitrogen content reaches 59%.

[0097] The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those of ordinary skill in the art to understand the content of the present invention and implement it accordingly. It should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the essence of the content of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a pyrrole nitrogen-doped carbon material, characterized in that, it comprises the following steps: (1) Homogeneous solution mixing: Using a clay material as a template material, and using any one of cellulose, urea, and melamine as a raw material, dissolving the raw material and a salt catalyst in water to form a homogeneous solution, and then mixing with the template material to obtain a uniformly dispersed liquid. The clay material is one of kaolin, montmorillonite, and attapulgite; (2) Hydrothermal reaction: Placing the dispersed liquid of step (1) in a hydrothermal reaction kettle in a homogeneous reactor, heating for a certain time, and naturally cooling to room temperature to obtain a reaction solution; (3) Centrifugal washing: Centrifuging the reaction solution of step (2), washing the centrifuged product, and drying to obtain a solid powder material; (4) Freeze-drying: Subjecting the solid powder material of step (3) to freeze-drying to obtain a dried solid powder; (5) High-temperature heat treatment: Subjecting the dried solid powder of step (4) to high-temperature heat treatment to obtain a product sample; (6) Removing the template: Placing the product sample of step (5) in acid solution 1 and acid solution 2 successively to obtain a pyrrole nitrogen-doped carbon sample. Acid solution 1 is sulfuric acid with a concentration of 0.5 - 3.0 mol / L, the reaction time is 5 - 24 h, the reaction temperature is 25 - 60 °C, acid solution 2 is hydrofluoric acid with a mass fraction of 10 - 50%, the reaction time is 0.5 - 2.0 h, and the reaction temperature is 25 - 40 °C; (7) Centrifugal washing: Centrifuging, washing, and drying the pyrrole nitrogen-doped carbon sample of step (6) to obtain a pyrrole nitrogen-doped carbon material.

2. The method according to claim 1, characterized in that, in step (1), the concentration of the clay material in the uniformly dispersed liquid is 20 - 50 mg / mL, and the salt catalyst is one of iron salts, cobalt salts, manganese salts, and nickel salts.

3. The method according to claim 1, characterized in that, in step (2), the heating temperature is 120 - 220 °C, and the heating time is 6 - 24 h.

4. The method according to claim 1, characterized in that, in step (3), the drying temperature is 50 - 80 °C.

5. The method according to claim 1, characterized in that, in step (4), the freeze-drying temperature is < -10 °C, and the vacuum degree is < 10 Pa.

6. The method according to claim 1, characterized in that, in step (5), the heat treatment temperature is 500 - 800 °C, the heat treatment time is 1 - 6 h, and the heat treatment atmosphere is one of nitrogen, argon, and hydrogen / argon mixed gas.

7. The method according to claim 1, characterized in that, in step (7), the drying temperature is 50 - 80 °C.

8. Use of the pyrrole nitrogen-doped carbon material prepared by the preparation method according to any one of claims 1 - 7 as an oxygen reduction catalyst.

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