Preparation method and application of nitrogen-doped highly graphitized carbon materials

Abstract

The present invention discloses a preparation method and application of a nitrogen-doped highly graphitized coconut shell activated carbon material, wherein the nitrogen content in the material is 2-3 at.%, the pore size distribution is 2-5 nm, and the specific surface area is 1526 m 2 / g. Using coconut shell activated carbon, bamboo charcoal, or softwood charcoal as a carbon source and 2,6-diaminopyridine as a nitrogen source, the mixed precursor is pyrolyzed via a hard template method. Transient Joule heating is then used to prepare nitrogen-doped natural biomass carbon materials with greater defects, higher graphitization, and high catalytic performance. NaCl and ZnCl2 serve as hard templates to increase the material's specific surface area and pore content, promoting graphitization. Transient Joule heating and high-temperature annealing further enhance the carbon material's graphitization, forming a N-type configuration with high electrochemical performance. The prepared nitrogen-doped carbon materials can be used to efficiently catalyze oxygen reduction reactions and are suitable for use in metal-air batteries.

Description

Technical field:

[0001] The invention relates to a nitrogen-doped highly graphitized coconut shell carbon material, a preparation method thereof, and electrocatalytic applications thereof. Background technology:

[0002] Huge energy consumption has triggered an energy crisis based on fossil fuels, leading to growing interest in renewable clean energy storage and conversion systems. Among various energy conversion devices, zinc-air batteries have attracted much attention due to their safety, high energy density, and commercial feasibility. However, there are many challenges in developing effective electrocatalysts for high-performance zinc-air batteries. Biomass carbon-based materials have the advantages of wide availability, low cost, and controllable structure, and have become a hot topic of research today. At the same time, biomass carbon materials obtained by high-temperature pyrolysis of biomass materials have advantages such as high porosity, large specific surface area, good chemical stability, and environmental friendliness. Therefore, they are considered as potential alternatives to metal-based catalysts in the field of electrocatalysis, which can effectively reduce the use of precious metals. Therefore, it is of great significance to study biomass carbon-based materials as electrocatalytic oxygen reduction catalysts and apply them to zinc-air batteries.

[0003] Topological or edge defects in carbon materials, such as pentagonal and heptagonal carbon defects, can accelerate charge transfer during the reaction and modify electronic effects, thereby providing catalytically active sites for the electrocatalytic oxygen reduction reaction. Introducing more defect structures into the carbon substrate will alter the local electron redistribution within the carbon material, leading to changes in its internal geometry and electronic structure, thereby increasing the number of active sites within the material itself and optimizing its electrocatalytic performance. Therefore, introducing and regulating defects in carbon materials is an important research direction for the preparation of electrocatalytic oxygen reduction catalysts.

[0004] Converting non-metallic heteroatom doping sites into carbon defects is an effective strategy for constructing advanced metal-free carbon-based electrocatalysts for oxygen reduction reaction. However, precisely controlling the configuration conversion to achieve highly active oxygen reduction catalysts remains a huge challenge. The addition of heteroatoms to the carbon skeleton can make inert carbon electrocatalytically active for oxygen reduction reaction by significantly disrupting its charge distribution balance and inducing charge delocalization. Based on the heteroatom doping activation strategy, a variety of heteroelement doped carbon materials have been prepared, including N, B, F, S and P, and have shown significant activity for electrocatalytic oxygen reduction reaction. However, non-metallic heteroatom doped carbon materials often have the problem of low porosity, resulting in a small specific surface area, few exposed active sites, difficult charge transfer, and ultimately poor catalytic activity. Summary of the invention:

[0005] The present invention discloses a nitrogen-doped highly graphitized coconut shell activated carbon material (NC D) preparation method and application, the nitrogen content in the material is 2-3at.%, the pore size distribution is 2-5nm, and the specific surface area is 1526m 2 / g. Using coconut shell activated carbon, bamboo charcoal or softwood charcoal as a carbon source and 2,6-diaminopyridine as a nitrogen source, the mixed precursor is pyrolyzed via a hard template method, and then transient Joule heating is used to prepare nitrogen-doped carbon materials with greater defects and higher graphitization. Coconut shell activated carbon, bamboo charcoal or softwood charcoal, NaCl, ZnCl2 and 2,6-diaminopyridine are dispersed in deionized water, and the mixture is heated, stirred and the water evaporated to prepare the precursor. The precursor is pyrolyzed using a tube furnace annealing process, and the remaining metal salts in the pyrolyzed material are washed with dilute sulfuric acid multiple times. The graphitization and defect level of the material are then enhanced using transient Joule heating, resulting in a natural biomass carbon catalyst with high catalytic performance. NaCl and ZnCl2 act as hard templates to increase the specific surface area and pore content of the material, promoting graphitization; transient Joule heating and high-temperature annealing further enhance the graphitization of the carbon material, forming an N configuration with high electrochemical performance. The prepared nitrogen-doped carbon material can be used to efficiently catalyze oxygen reduction reactions and be used in metal-air batteries.

[0006] The purpose of the present invention is to provide a NC D Preparation method. A two-step method is used for preparation, using secondary annealing, using a tube furnace and instantaneous Joule heating technology to achieve the preparation effect. The present invention provides a secondary annealing process to NC D For the four-electron oxygen reduction reaction (4e - ORR) catalyst. First, coconut shell activated carbon, bamboo charcoal or softwood charcoal, 2,6-diaminopyridine, NaCl and ZnCl2 are dispersed in deionized water, and magnetic stirring and drying are carried out under heating conditions to obtain a uniformly mixed precursor. The dried precursor is then subjected to the first tube furnace high-temperature annealing in a N2 protective atmosphere. During the tube furnace high-temperature annealing process, on the one hand, the molten NaCl is inserted into the carbon layer and produces a stress effect, which promotes the formation of carbon defects. On the other hand, Zn acts as a template and sublimates during the heating process, removing and rebuilding the configuration of carbon atoms, which contributes to the formation of carbon defects and the doping of nitrogen atoms. The material annealed in the tube furnace is ultrasonically washed multiple times with dilute sulfuric acid to completely wash away the remaining metal salts, and then washed with deionized water to neutrality. Subsequently, a transient Joule heating device is used for a second transient high-temperature annealing treatment. During the transient Joule heat high-temperature annealing, the graphitization degree of the carbon material is further enhanced, forming an N configuration with high electrochemical performance, and obtaining a nitrogen-doped highly graphitized coconut shell activated carbon material. This material has a good effect on 4e - The ORR process is highly active and has been applied to metal-air batteries, showing long-term stability.

[0007] The technical solution of the present invention is: a nitrogen-doped highly graphitized coconut shell activated carbon material NC DThe N content in the material reaches 2-3 at.%, the pore size distribution is 2-5 nm, and the specific surface area is 1526 m 2 / g, using coconut shell activated carbon, bamboo charcoal or softwood charcoal as carbon source, 2,6-diaminopyridine as nitrogen source, NaCl and ZnCl2 as hard templates, the mixed precursor was annealed at high temperature in a tube furnace, and then transient Joule heating was used to prepare NC with larger defects and higher graphitization. D Under the conditions of instantaneous Joule heat high temperature annealing, the graphitization degree of the carbon material is further enhanced, forming an N configuration with high electrochemical performance.

[0008] Preparation of the nitrogen-doped highly graphitized coconut shell activated carbon material NC D The method comprises the following steps: the carbon source is coconut shell activated carbon, bamboo charcoal or softwood charcoal, the nitrogen source is 2,6-diaminopyridine, the defect hard template is NaCl and ZnCl2, the mixed precursor is subjected to high-temperature annealing in a tubular furnace, and then a nitrogen-doped carbon material with a greater degree of defects and higher graphitization is prepared by transient Joule heating. Under the conditions of transient Joule heating and high-temperature annealing, the graphitization degree of the carbon material is further enhanced to form an N configuration with high electrochemical performance. The specific steps are as follows:

[0009] Step 1: Prepare the precursor: Coconut shell activated carbon, bamboo charcoal or softwood charcoal, 2,6-diaminopyridine, NaCl and ZnCl2 are dispersed in deionized water to form a mixed solution. The carbon source, nitrogen source and defect template are evenly mixed by heating and stirring in a water bath for a long time. The mixed solution is heated and stirred in a water bath and the water is evaporated. The evaporated solid is thoroughly dried, and then the large solid pieces are ground into fine powder to obtain the precursor.

[0010] Step 2: Preparation of NC D : Under the protection of non-reactive gas, the above precursor is subjected to high-temperature annealing in a tube furnace, followed by acid washing to remove metal salts in the material, washing with water until neutral, filtering and vacuum drying. The dried tube furnace high-temperature annealed material is subjected to secondary high-temperature annealing by an instantaneous Joule heating device to prepare NC D .

[0011] The mass ratio of the carbon source: nitrogen source: NaCl: ZnCl2 used is 1:1:5:0.5.

[0012] In step 1, the water bath temperature is 100° C., the stirring condition is 450 rpm, and the stirring time is 12-16 h.

[0013] In step 1, the drying temperature is 80°C and the drying time is 10h-12h.

[0014] The first annealing process in step 2 uses a tube furnace and the non-reactive gas is N2.

[0015] In the first annealing process in step 2, the heating rate is 5°C / min, the annealing temperature is 1000°C, and the annealing time is 2h.

[0016] In step 2, the acid washing is to use 0.5M dilute sulfuric acid to ultrasonically wash multiple times to remove excess metal salts and then wash with deionized water until neutral, and then filter using a 0.45 micron filter membrane.

[0017] In step 2, the secondary high-temperature annealing process uses an instantaneous Joule heating device, and the non-reactive gas is Ar. In the instantaneous Joule heating annealing process, the current is 20A, the heating rate is 800°C / s, the annealing temperature is 700°C-800°C, and the annealing time is 1s.

[0018] The NC D Applications in electrocatalytic oxygen reduction reaction and metal-air batteries.

[0019] Beneficial effects:

[0020] 1. The preparation method of the present invention is simple, the N content in the material is 2-3at.%, the pore size distribution is 2-5nm, and the specific surface area is 1526m 2 / g, while taking into account the heteroatom structure of the material, the inherent excellent electrochemical conductivity of carbon nanomaterials is maintained, making it have an excellent catalytic effect in electrocatalytic oxygen reduction reaction.

[0021] 2. A two-step preparation method is used to produce a nitrogen-doped highly graphitized coconut shell activated carbon structure, which is simple and efficient. The present invention uses coconut shell activated carbon, bamboo charcoal or softwood charcoal as a carbon source and 2,6-diaminopyridine as a nitrogen source. The mixed precursor is pyrolyzed by a hard template method, and then a nitrogen-doped carbon material with a greater degree of defects and higher graphitization is prepared by instantaneous Joule heating. Coconut shell activated carbon, bamboo charcoal or softwood charcoal, NaCl, ZnCl2 and 2,6-diaminopyridine are dispersed in deionized water, the mixed solution is heated and stirred, and the water is evaporated. The obtained precursor is annealed in a tubular furnace to pyrolyze the precursor, and acid washed multiple times to remove the remaining metal salts in the pyrolyzed material. The instantaneous Joule heating process is then used to enhance the graphitization degree and defect degree of the material to prepare a natural biomass carbon catalyst with high catalytic performance. NaCl and ZnCl2 act as hard templates to increase the material's specific surface area and pore content, promoting graphitization. High-temperature annealing using transient Joule heating further enhances the carbon material's graphitization, forming a nitrogen-doped carbon structure with high electrochemical performance. The resulting nitrogen-doped carbon material can be used to efficiently catalyze oxygen reduction reactions and be used in metal-air batteries.

[0022] 3. The average selectivity of the nitrogen-doped highly graphitized coconut shell activated carbon material for electrocatalysis of O2 to produce H2O2 is only 1%-6%, and the electron transfer number is calculated to be around 3.88, which has a very high 4e -The selectivity and catalytic activity (expressed by the size of the disk current in the rotating disk test) are 4.35-5.88 mA, and the half-wave potential E 1 / 2 By changing the precursor carbon source, nitrogen-doped highly graphitized carbon structures of different biomass carbon materials were prepared to change their electrocatalytic oxygen reduction effects. When bamboo charcoal was used as the carbon source, the half-wave potential E 1 / 2 is 0.868 V. When softwood charcoal is used as the carbon source, the half-wave potential E 1 / 2 The material exhibits excellent electrocatalytic oxygen reduction performance, with a current density of 0.846 V. The material also exhibits excellent methanol resistance and long-term catalytic stability. In a current-time (it) test, the current density of the prepared material decayed to 93.5% within 11 hours, surpassing the 89.5% of commercial Pt / C materials. Description of the drawings:

[0023] Figure 1 NC D High-resolution transmission electron microscopy (HR-TEM) of the material. According to the data analysis in the figure, NC D It shows a typical biomass-based amorphous carbon material structure, containing abundant pores and short-range ordered lattice lines.

[0024] Figure 2 The Raman spectra data of the material are shown in Figure 2. According to the analysis of the figure, the material is not as good as the pure carbon material control sample (pure C) and the defect template control sample (pure C D ) and the control sample (NC) with the introduction of a single heteroatom, NC D The D-band / G-band intensity ratio of the material is significantly reduced, indicating that the defect template and heteroatom doping work synergistically during the secondary annealing process to enhance the graphitization degree of the material.

[0025] Figure 3 The BET specific surface area data of the material is shown in the figure. The figure shows the pure carbon material control sample pure C, pure C D , single heteroatom introduced control sample (NC) and one-step tube furnace annealing control sample (NC D '), according to the data analysis in the figure, the material has a large specific surface area and forms a rich porous structure.

[0026] Figure 4 The following plots the material's pore diameter and volume data. The figure shows the distribution of pores in the 0-2nm, 2-50nm, and >50nm ranges. Analysis of the data in the figure indicates that the material has a rich microporous and mesoporous structure.

[0027] Figure 5This is the X-ray photoelectron spectroscopy (XPS) spectrum data of the material. The figure shows the chemical environment and bonding configuration of the nitrogen atom.

[0028] Figure 6 The LSV electrochemical data of the material are shown in the figure. D 、pure C、pure C D ,NC,NC D ' and the commercial Pt / C control sample's disk current intensity, according to the data analysis in the figure, NC D The material exhibited the highest half-wave potential (0.884 V) and the largest limiting current density (5.88 mA cm -2 ), with extremely high electrocatalytic four-electron oxygen reduction reaction (4e - ORR) catalytic activity.

[0029] Figure 7 The LSV electrochemical data for different carbon sources are plotted. The figure shows the disk current intensity for coconut shell activated carbon, bamboo charcoal, and cork charcoal as carbon sources. All materials exhibit excellent electrocatalytic oxygen reduction performance.

[0030] Figure 8 The figure shows the long-term stability data of the material. The figure shows the current change of the material tested using a rotating ring disk electrode over a period of 11 hours. According to the data analysis in the figure, NC D The disk current of the material maintains good stability within 11 hours, which is better than the commercial Pt / C control sample.

[0031] Figure 9 The charge and discharge cycle data of the material applied to metal-air batteries. The constant current charge and discharge test was performed at 5 mA cm -2 The charge and discharge time of each cycle was 10 min. After 1200 hours, NC D The cell overpotential of the catalyst assembly also showed no obvious change, indicating excellent catalytic stability during continuous ORR and OER cycles. Specific implementation method:

[0032] The present invention provides an NC D The preparation method adopts a two-step method, uses secondary annealing, uses a tube furnace and instantaneous Joule heating technology to achieve the preparation effect. The present invention provides a secondary annealing process to NC D For the four-electron oxygen reduction reaction (4e -ORR) catalyst. First, coconut shell activated carbon, bamboo charcoal or softwood charcoal, 2,6-diaminopyridine, NaCl and ZnCl2 are dispersed in deionized water, and magnetic stirring and drying are carried out under heating conditions to obtain a uniformly mixed precursor. The dried precursor is then subjected to the first tube furnace high-temperature annealing in a N2 protective atmosphere. During the tube furnace high-temperature annealing process, on the one hand, the molten NaCl is inserted into the carbon layer and produces a stress effect, which promotes the formation of carbon defects. On the other hand, Zn acts as a template and sublimates during the heating process, removing and rebuilding the configuration of carbon atoms, which contributes to the formation of carbon defects and the doping of nitrogen atoms. The material annealed in the tube furnace is ultrasonically washed multiple times with dilute sulfuric acid to completely wash away the remaining metal salts, and then washed with deionized water to neutrality. Subsequently, a transient Joule heating device is used for a second transient high-temperature annealing treatment. During the transient Joule heat high-temperature annealing, the graphitization degree of the carbon material is further enhanced, forming an N configuration with high electrochemical performance, and obtaining a nitrogen-doped highly graphitized coconut shell activated carbon material. This material has a good effect on 4e - The ORR process is highly active and has been applied to metal-air batteries, showing long-term stability.

[0033] Using coconut shell activated carbon, bamboo charcoal or softwood charcoal as carbon source and 2,6-diaminopyridine as nitrogen source, the mixed precursor was pyrolyzed by hard template method, and then nitrogen-doped carbon materials (NCs) with larger defects and higher graphitization were prepared by transient Joule heating. D ). Coconut shell activated carbon, bamboo charcoal or softwood charcoal, NaCl, ZnCl2 and 2,6-diaminopyridine are dispersed in deionized water, the mixture is heated and stirred, and the water is evaporated to obtain a precursor. The precursor is pyrolyzed using a tube furnace annealing process, and the remaining metal salts in the pyrolyzed material are acid-washed multiple times with dilute sulfuric acid. Then, the material is graphitized and the degree of defects is enhanced using transient Joule heating technology to prepare a natural biomass carbon catalyst with high catalytic performance. NaCl and ZnCl2 act as hard templates to increase the specific surface area and pore content of the material and promote graphitization; transient Joule heating high-temperature annealing further enhances the graphitization degree of the carbon material, forming an N configuration with high electrochemical performance. The prepared nitrogen-doped carbon material can be used to efficiently catalyze oxygen reduction reactions and is used in metal-air batteries. The carbon source used in the material is coconut shell activated carbon, bamboo charcoal or softwood charcoal, the nitrogen source is 2,6-diaminopyridine, and the defect templates are NaCl and ZnCl2, with the ratio used being 1:1:5:0.5.

[0034] The heating and stirring temperature is 100° C., the stirring condition is 450 rpm, and the stirring time is 12 h to 16 h.

[0035] The drying temperature is 80° C. and the drying time is 10-12 hours.

[0036] The first annealing process uses a tubular furnace and the non-reactive gas is N2.

[0037] The tubular furnace annealing process has a heating rate of 5°C / min, an annealing temperature of 1000°C, and an annealing time of 2h.

[0038] The washing and filtration process uses 0.5M dilute sulfuric acid and a 0.45um filtration membrane.

[0039] The second annealing process uses an instantaneous Joule heating device, and the non-reactive gas is Ar.

[0040] The Joule heat annealing process has a current of 20A, a heating rate of 800°C / min, an annealing temperature of 700°C-800°C, and an annealing time of 1s.

[0041] The NC D The material is used in electrocatalytic oxygen reduction reaction.

[0042] The material has a catalytic application in the electrocatalytic oxygen reduction reaction, and the electron transfer number is calculated to be 3.88, which has a high electrocatalytic four-electron oxygen reduction reaction (4e - ORR) selectivity, catalytic activity (expressed by the size of the disk current in the rotating disk test) is 4.35-5.88 mA, and the half-wave potential E 1 / 2 It is 0.884V.

[0043] Example 1: Nitrogen-doped highly graphitized coconut shell activated carbon material NC D

[0044] Disperse 1g coconut shell activated carbon, 1g 2,6-diaminopyridine, 5g NaCl and 0.5g ZnCl2 in 150ml deionized water, heat and stir at 450rpm and 100℃ to mix evenly, and evaporate the deionized water. The mixed precursor is dried in an oven at 80℃, and the dried powder is heated at 1000℃ in a tube furnace in a protective atmosphere of N2 gas for 2h with a heating rate of 5℃ / min. After cooling to room temperature, it is pickled with 0.5M dilute sulfuric acid to remove metal salts, washed with deionized water to neutrality, and then treated with instantaneous Joule heating technology. The treatment conditions are current 20A, heating rate 800℃ / s, heating time 1s, and argon atmosphere to prepare NC. D The catalytic activity (expressed as the current in the rotating disk test) was 5.88 mA / cm 2 , half-wave potential E 1 / 2 It is 0.884V.

[0045] Example 2: Bamboo charcoal instead of coconut shell activated carbon NC D Material

[0046] Disperse 1g of bamboo charcoal, 1g of 2,6-diaminopyridine, 5g of NaCl and 0.5g of ZnCl2 in 150ml of deionized water, heat and stir at 450rpm and 100℃ to mix evenly, and evaporate the deionized water. The mixed precursor is dried in an oven at 80℃, and the dried powder is heated at 1000℃ in a tube furnace in a protective atmosphere of N2 gas for 2h with a heating rate of 5℃ / min. After cooling to room temperature, it is pickled with 0.5M dilute sulfuric acid to remove metal salts, and then washed with deionized water to neutrality, and then treated with instantaneous Joule heating technology. The treatment conditions are current 20A, heating rate 800℃ / s, heating time 1s, and argon atmosphere to prepare NC with bamboo charcoal as the carbon base. D The catalytic activity (expressed as the current in the rotating disk test) was 5.60 mA / cm 2 , half-wave potential E 1 / 2 It is 0.868V.

[0047] Example 3: NC with softwood charcoal instead of coconut shell activated carbon D Material

[0048] Disperse 1g of soft charcoal, 1g of 2,6-diaminopyridine, 5g of NaCl and 0.5g of ZnCl2 in 150ml of deionized water, heat and stir at 450rpm and 100℃ to mix evenly, and evaporate the deionized water. The mixed precursor is dried in an oven at 80℃, and the dried powder is heated at 1000℃ in a tube furnace in a protective atmosphere of N2 gas for 2h with a heating rate of 5℃ / min. After cooling to room temperature, it is pickled with 0.5M dilute sulfuric acid to remove metal salts, and then washed with deionized water to neutrality, and then treated with instantaneous Joule heating technology. The treatment conditions are current 20A, heating rate 800℃ / s, heating time 1s, and argon atmosphere to prepare NC with soft charcoal as the carbon base. D The catalytic activity (expressed as the current in the rotating disk test) was 5.80 mA / cm 2 , half-wave potential E 1 / 2 It is 0.846V.

[0049] Comparative Example 1: Pure carbon material without nitrogen source and defect template

[0050] Disperse 1g of coconut shell activated carbon in 150ml of deionized water, heat and stir at 450rpm and 100℃ to mix evenly, and evaporate the deionized water. The mixed precursor is dried in an oven at 80℃, and the dried powder is heated at 1000℃ in a tube furnace in a protective atmosphere of N2 gas for 2h with a heating rate of 5℃ / min. After cooling to room temperature, it is pickled with 0.5M dilute sulfuric acid to remove metal salts, then washed with deionized water until neutral, and then treated with instantaneous Joule heating technology. The treatment conditions are current 20A, heating rate 800℃ / s, heating time 1s, and argon atmosphere to prepare pure carbon material. The catalytic activity (expressed by the size of the disk current in the rotating disk test) is 4.35mA / cm 2 , half-wave potential E 1 / 2 is 0.712V.

[0051] Comparative Example 2: Pure C, a material with defective template without nitrogen source added D

[0052] 1g coconut shell activated carbon, 5g NaCl and 0.5g ZnCl2 were dispersed in 150ml deionized water, heated at 450rpm and 100℃ for uniform mixing, and the deionized water was evaporated. The mixed precursor was dried in an oven at 80℃, and the dried powder was heated in a tube furnace at 1000℃ for 2h in a protective atmosphere of N2 gas with a heating rate of 5℃ / min. After cooling to room temperature, it was pickled with 0.5M dilute sulfuric acid to remove metal salts, then washed with deionized water until neutral, and then treated with instantaneous Joule heating technology. The treatment conditions were current 20A, heating rate 800℃ / s, heating time 1s, and argon atmosphere to prepare pure C material with defect template effect without adding nitrogen source. D The catalytic activity (expressed as the current in the rotating disk test) was 4.56 mA / cm 2 , half-wave potential E 1 / 2 It is 0.748V.

[0053] Comparative Example 3: NC material with single heteroatom introduction without adding defect template

[0054] Disperse 1g coconut shell activated carbon and 1g 2,6-diaminopyridine in 150ml deionized water, heat and stir at 450rpm and 100℃ to mix evenly, and evaporate the deionized water. The mixed precursor is dried in an oven at 80℃, and the dried powder is heated at 1000℃ in a tube furnace in a protective atmosphere of N2 gas for 2h with a heating rate of 5℃ / min. After cooling to room temperature, it is pickled with 0.5M dilute sulfuric acid to remove metal salts, then washed with deionized water until neutral, and then treated with instantaneous Joule heating technology. The treatment conditions are current 20A, heating rate 800℃ / s, heating time 1s, and argon atmosphere to prepare a single heteroatom introduced NC material without adding a defect template. The catalytic activity (expressed by the size of the disk current in the rotating disk test) is 5.16mA / cm 2 , half-wave potential E 1 / 2 is 0.85V.

[0055] Comparative Example 4: Material NC without secondary instantaneous Joule heating treatment D '

[0056] 1g coconut shell activated carbon, 1g 2,6-diaminopyridine, 5g NaCl, and 0.5g ZnCl2 were dispersed in 150ml deionized water and heated at 100°C at 450rpm with stirring to mix thoroughly. The deionized water was evaporated. The mixed precursor was dried in an 80°C oven. The dried powder was heated in a tube furnace at 1000°C for 2h under a protective atmosphere of N2 gas at a heating rate of 5°C / min. After cooling to room temperature, it was acid-washed with 0.5M dilute sulfuric acid to remove metal salts and washed with deionized water until neutral. NC was prepared. D The catalytic activity (expressed as the current in the rotating disk test) was 4.46 mA / cm 2 , half-wave potential E 1 / 2 It is 0.886V.

[0057] A variety of comparative examples were designed and prepared to compare the effects of nitrogen source and NaCl / ZnCl2 defect template, including pure C without nitrogen source and defect template, pure C without nitrogen source, and D Comparative example, NC without defect template, and NC without secondary transient Joule heat treatment D 'Comparative Example. By comparison, NC D Due to the treatment of metal Zn and transient Joule heat, the crystallinity of carbon is enhanced, and its high-resolution transmission electron microscopy image also shows the typical biomass-based amorphous carbon material structure, which contains abundant pores and short-range ordered lattice lines. Compared with the comparative example, NC D According to Raman characterization data, NC DThe D-band / G-band intensity ratio of the material is significantly reduced, indicating that the defect template and heteroatom doping work synergistically during the secondary annealing process to enhance the graphitization degree of the material. From the BET specific surface area data, it can be seen that the addition of nitrogen precursors and metal salts leads to the collapse of the porous structure. The reconstruction of carbon rings is a normal phenomenon after two annealing treatments in the tubular and Joule furnace. Therefore, NC D The specific surface area of ​​NC is significantly reduced. D showed the highest electrocatalytic 4e - The oxygen reduction catalytic activity, the highest half-wave potential (0.884 V), and the highest limiting current density (5.88 mA cm -2 ).

Claims

1. A nitrogen-doped highly graphitized carbon material NC for electrocatalytic oxygen reduction reaction and metal-air batteries D Preparation method of carbon material NC D The nitrogen content in the nanostructured carbon nanotubes reaches 2-3 at.%, with a pore size distribution of 2-5 nm and a specific surface area of ​​1526 m 2 / g, the preparation method uses coconut shell activated carbon, bamboo charcoal or soft wood charcoal as a carbon source, 2,6-diaminopyridine as a nitrogen source, NaCl and ZnCl2 as a hard template, and performs a high-temperature annealing treatment on the mixed precursor in a tube furnace. Then, transient Joule heating is used to prepare NC with a larger defect level and higher graphitization. D , under the condition of instantaneous Joule heat high temperature annealing, further enhance the graphitization degree of the carbon material to form an N configuration with high electrochemical performance; the specific steps of the preparation method are: Step 1: Prepare a precursor: Coconut shell activated carbon, bamboo charcoal or softwood charcoal, 2,6-diaminopyridine, NaCl and ZnCl2 are dispersed in deionized water to form a mixed solution. The carbon source, nitrogen source and hard template are evenly mixed by long-term water bath heating and stirring. The mixed solution is heated and stirred in a water bath and the water is evaporated. The evaporated solid is thoroughly dried, and then the large solid is ground into a fine powder, which is the precursor; the water bath temperature is 100°C, the stirring condition is 450 rpm, and the stirring time is 12-16 hours; Step 2: Preparation of NC D : Under the protection of non-reactive gas, the above precursor is subjected to high-temperature annealing in a tube furnace, followed by acid washing to remove metal salts in the material, washing with water until neutral, filtering and vacuum drying, and the dried tube furnace high-temperature annealed material is subjected to secondary high-temperature annealing through an instantaneous Joule heating device to prepare NC D ; The secondary high-temperature annealing process uses an instantaneous Joule heating device, and the non-reactive gas is Ar; the current in the instantaneous Joule heating annealing process is: 20A, the heating rate is: 800℃ / s, the annealing temperature is 700℃-800℃, and the annealing time is: 1s; the high-temperature annealing process in a tubular furnace, the heating rate is: 5℃ / min, the annealing temperature is 1000℃, and the annealing time is: 2h.

2. The preparation method according to claim 1, wherein The mass ratio of the carbon source: nitrogen source: NaCl: ZnCl2 used is 1:1:5:0.

5.

3. The preparation method according to claim 1, wherein In step 1, the drying temperature is 80°C and the drying time is 10h-12h.

4. The preparation method according to claim 1, wherein The non-reactive gas in step 2 is N2.

5. The preparation method according to claim 1, wherein In step 2, the acid washing is performed by using 0.5 M dilute sulfuric acid to ultrasonically wash the excess metal salts multiple times and washing with deionized water until neutral, and then filtering with a 0.45 μm filter membrane.

6. NC obtained by the preparation method according to claim 1 D Applications in electrocatalytic oxygen reduction reaction and metal-air batteries.

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