Metal single atom dispersed nitrogen-doped spherical mesoporous carbon material and preparation method thereof

Abstract

The invention relates to the technical field of carbon material preparation, and discloses a dispersed metal monatomic nitrogen-doped spherical mesoporous carbon material and a preparation method thereof, and the preparation method comprises the following steps: introducing a vinyl-containing metal precursor in a prepolymer stage, and grafting a metal center to a polymer skeleton in situ through chemical bonding; then preparing phenolic resin balls by using the amphiphilic block copolymer as a soft template and combining an emulsification curing process; and finally, carbonizing the resin balls, and introducing water vapor with a specific proportion for activation to construct mesoporous and microporous graded channels. According to the invention, agglomeration of metal atoms at a high temperature is effectively inhibited through in-situ chemical bonding, and high-dispersion loading of single atoms is realized; meanwhile, the soft template and water vapor activation have a synergistic effect, so that the material is endowed with a high specific surface area and a developed hierarchical pore structure. When the obtained material is used as a supercapacitor electrode, high specific capacitance, excellent rate capability and good cycling stability are shown.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon material preparation, in particular to a nitrogen-doped spherical mesoporous carbon material with dispersed metal monatomic atoms and a preparation method thereof. BACKGROUND

[0002] Mesoporous carbon materials have application potential in the fields of energy storage and conversion, catalysis and adsorption due to their structural characteristics. In terms of material morphology, compared with non-spherical materials, spherical carbon materials have higher packing density and structural stability, which is conducive to accommodating more active substances in limited space and ensuring the performance of the materials in long-term use. Phenolic resin is a commonly used precursor for preparing such carbon materials due to its high carbon residue rate and good thermal stability. In the synthesis process of phenolic resin, the alkaline condition is more controllable than the acidic condition in the polymerization process, which is conducive to forming a precursor with uniform structure, and the pore structure of the material obtained by subsequent carbonization is also more developed.

[0003] At present, in order to further improve the performance of carbon materials, pore regulation and functional modification are usually performed, but in the aspect of pore structure construction, the existing technology often uses a hard template method such as silica to prepare a porous structure. This method is complicated, and strong alkali or strong acid etching is needed to remove the template, which not only increases the production cost and environmental load, but also pollutes the pore due to the residual template, affecting the purity and performance of the material.

[0004] In terms of introducing metal active sites, a direct impregnation method is commonly used, that is, the formed carbon material is soaked in a metal salt solution. However, this method is difficult to control the dispersion of metal, and the metal particles are easy to migrate and agglomerate in subsequent heat treatment, forming larger particles, which not only reduces the utilization rate of active sites, but also blocks the pores of the material, affecting the mass transfer.

[0005] For nitrogen element doping, some technologies use ammonia atmosphere calcination and other methods after the formation of carbon materials. This post-processing method often leads to uneven distribution of nitrogen elements on the substrate, and the thermodynamic stability of the immobilized nitrogen species is poor, affecting the uniformity and long-term performance of the overall electrochemical performance of the material. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a nitrogen-doped spherical mesoporous carbon material with dispersed metal monatomic atoms and a preparation method thereof, which solves the problem that the prior art is difficult to simultaneously achieve high dispersion of metal atoms, uniform doping of nitrogen elements and effective construction of hierarchical pore structure when preparing metal monatomic atom-doped carbon materials, thereby resulting in insufficient electrochemical performance of the material.

[0007] To solve the above problems, the present application provides the following technical solutions: In a first aspect, the present application provides a nitrogen-doped spherical mesoporous carbon material dispersing metal monatomic atoms, which is made of raw materials comprising the following weight parts: phenol 45-55 parts; amino phenol 9-13 parts; aqueous solution of formaldehyde with a mass concentration of 37% 100-120 parts; vinyl-containing metallocene precursor 0.4-0.6 parts; triblock copolymer pore-forming agent 6-8 parts; hexamethylenetetramine 4.5-8.0 parts.

[0008] By adopting the above technical solution, the present application uses phenol and amino phenol with a specific ratio as carbon source and nitrogen source, introduces vinyl-containing metallocene precursor, and cooperates with block copolymer pore-forming agent to realize the high dispersion of metal monatomic atoms in the nitrogen-doped carbon skeleton. The action mechanism is as follows: Double-source copolymerization introduces coordination sites: phenol and amino phenol undergo polycondensation reaction under the action of formaldehyde, and amino phenol introduces nitrogen atoms into the polymer skeleton. These nitrogen atoms act as Lewis bases to provide electrons for metal atoms to form stable metal-nitrogen coordination structures.

[0009] In-situ chemical bonding of vinyl groups: the vinyl-containing metallocene precursor uses its vinyl functional group to participate in the polymerization process of phenolic resin. The metal precursor is combined into the polymer macromolecular chain through covalent bond, which limits the migration of metal atoms in the high-temperature carbonization process, thereby inhibiting the agglomeration of metal atoms and ensuring that the metal exists in the form of monatomic atoms in the final product.

[0010] Mesoporous spherical structure regulation: the triblock copolymer acts as a soft template to guide the precursor to assemble into an ordered mesoporous structure, and the hexamethylenetetramine acts as a curing agent and supplements the nitrogen source to ensure the curing and shaping of the spherical structure, thereby obtaining a spherical mesoporous structure with a large specific surface area.

[0011] Preferably, the amino phenol is selected from one of p-aminophenol and m-aminophenol; and the vinyl-containing metallocene precursor is selected from one of vinyl ferrocene and vinyl cobaltocene.

[0012] By adopting the above technical solution, the isomer structure of amino phenol is used to adjust the polymerization reaction rate and crosslinking degree; and the thermal stability of the metallocene derivative is used to decompose and release metal atoms at high temperature and be captured by the surrounding nitrogen atoms.

[0013] Preferably, the triblock copolymer pore-forming agent is polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer; and the raw materials further comprise a dispersing agent, which is an aqueous polyvinyl alcohol solution with a mass concentration of 1%-3%.

[0014] By adopting the technical scheme, the polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer forms micelles through self-assembly to generate mesoporous channels in the interior of the polymer; the polyvinyl alcohol adjusts the oil-water interfacial tension to control the droplet size, so that the product has a uniform spherical morphology.

[0015] Preferably, the mass ratio of phenol to aminophenol in the raw material is 5:(1-1.2); and the mass ratio of the triblock copolymer pore-forming agent to phenol is 1:(7-9).

[0016] By adopting the technical scheme, the cross-linking density and nitrogen content of the polymer can be adjusted by controlling the ratio of phenol to aminophenol, so as to avoid structural collapse caused by excessively high nitrogen content; and the ratio of the pore-forming agent is controlled to balance the porosity and mechanical strength.

[0017] Preferably, the carbon material has a spherical morphology, and the metal monatomic is dispersed in the nitrogen-doped carbon skeleton through in-situ grafting.

[0018] In a second aspect, the present application provides a preparation method of a nitrogen-doped spherical mesoporous carbon material dispersing metal monatomic, comprising the following steps: S1, dissolving phenol and aminophenol in an alkaline aqueous solution to obtain a phenolic amine solution; S2, adding a formaldehyde aqueous solution to the solution obtained in step S1, and performing a prepolymerization reaction at a high temperature to obtain a prepolymer; S3, reducing the temperature of the prepolymer, adding an alcohol solution in which a metallocene precursor containing a vinyl group is dissolved, and stirring to make the metal precursor and the prepolymer perform a grafting reaction; S4, adding a triblock copolymer pore-forming agent and a dispersant solution to the reactant obtained in step S3, stirring to emulsify, then adding hexamethylenetetramine, and solidifying at a high temperature, so as to obtain a phenolic resin ball after post-treatment; S5, performing multi-stage heat treatment on the phenolic resin ball: first, performing an oxidation treatment in an air atmosphere; then, switching to an inert atmosphere to perform a carbonization treatment; and then, introducing water vapor under the protection of an inert atmosphere to perform an activation treatment, and obtaining the carbon material after cooling.

[0019] By adopting the technical scheme, the preparation method controls the polymerization, emulsification and heat treatment processes step by step to regulate the microstructure and chemical composition of the material. The synergistic mechanism of each step is as follows: Prepolymerization and grafting stage: first, a phenolic formaldehyde prepolymer containing a methylol group is generated under alkaline conditions. Then, the temperature is reduced and a metallocene precursor containing a vinyl group is introduced, so that the active sites in the prepolymer react with the vinyl group to chemically bond the metal center to the polymer chain.

[0020] Emulsification and solidification stage: under the action of dispersant, the pre-polymer grafted with metal is dispersed into micron-sized droplets, and the block copolymer is assembled to form a mesoporous template inside the droplets. Hexamethylenetetramine decomposes to release ammonia and formaldehyde, promoting the crosslinking and curing of the resin.

[0021] Multi-stage heat treatment stage: Oxidation treatment: low-temperature oxidation further crosslinks and cyclizes the polymer spheres, improving thermal stability.

[0022] Carbonization treatment: at high temperature, the organic skeleton is converted into a carbon skeleton, the metal precursor decomposes, and the metal atoms are unable to migrate long distances due to chemical bond constraints, and are captured by the surrounding nitrogen atoms.

[0023] Steam activation: steam reacts with amorphous carbon to etch new microporous defects on the carbon skeleton, increasing the specific surface area and exposing the internal metal-nitrogen active sites.

[0024] Preferably, in step S1, the alkaline aqueous solution is a sodium hydroxide aqueous solution, and the pH value of the system is adjusted to 8.5-10.0; in step S2, the temperature of the pre-polymerization reaction is 75-85℃, and the reaction time is 1.5-2.5 hours.

[0025] By adopting the above technical solution, the weak alkaline environment is conducive to controlling the polycondensation rate of phenolic resin, forming a pre-polymer with appropriate viscosity, and facilitating subsequent emulsification and dispersion.

[0026] Preferably, in step S3, the temperature of the pre-polymer is reduced to 55-65℃; the vinyl-containing metallocene precursor is pre-dissolved in anhydrous ethanol; and the stirring grafting time is 20-40 minutes.

[0027] By adopting the above technical solution, the temperature reduction treatment reduces the reactivity of the pre-polymer, preventing local intense reactions when the metal precursor is added; and the ethanol solvent assists in the uniform dispersion and penetration of the metal precursor into the pre-polymer molecular chains.

[0028] Preferably, in step S5, the specific process parameters of the multi-stage heat treatment are: Oxidation treatment: heat to 380-400℃ at a heating rate of 1-3℃ / min, and hold for 0.5-1.5 hours; Carbonization treatment: heat to 800-850℃ at a heating rate of 1-3℃ / min, and hold for 1.5-3.5 hours; Activation treatment: heat to 800-825℃ at a heating rate of 3-5℃ / min, control the mass ratio of steam to carbonized material to be (3-27):1, and activate for 0.5-1.5 hours.

[0029] By adopting the technical scheme, the skeleton structure is reserved by controlling the oxidation temperature at 380-400 DEG C; the expansion effect and carbon yield are balanced by controlling the ratio of water vapor to carbonized material and the activation time, and the structure collapse caused by excessive activation is prevented.

[0030] Preferably, in the step S4, the stirring and emulsifying speed is 450-550 rpm, and the emulsifying time is 15-25 minutes; the temperature for the temperature raising and solidifying is 85-95 DEG C, and the solidifying time is 2-4 hours.

[0031] By adopting the technical scheme, the uniformity of the liquid drop particle size is ensured by controlling the shearing rate and the emulsifying time; and the resin ball is completely crosslinked by controlling the solidifying temperature and time, so that the resin ball has the mechanical strength to resist high temperature treatment.

[0032] The application provides a nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms and a preparation method. 1. In the application, a metal precursor containing a vinyl group is selected to participate in the polycondensation reaction of phenolic resin, and a metal complex is anchored in a polymer skeleton in situ by a covalent bond. The chemical bond effectively limits the thermal migration of metal atoms during high-temperature carbonization, prevents the agglomeration of metal particles, and realizes the high dispersion of metal single atoms in the carbon base, thereby effectively improving the utilization rate of active sites and the cycle stability of the material.

[0033] 2. In the application, a process combining a soft template guide and steam activation is adopted to construct a developed hierarchical pore structure. Mesoporous channels formed by pyrolysis of an amphiphilic block copolymer effectively shorten the transmission path of electrolyte ions, and controlled steam etching produces abundant micropores in the carbon wall and increases the specific surface area. The synergistic structure of mesopores and micropores provides sufficient charge storage sites and meets the demand for rapid ion transmission under high current density.

[0034] 3. In the application, amino phenol is used as a carbon-nitrogen double source in combination with metal single atom sites to effectively improve the electrochemical performance of the carbon material. Uniform doping of nitrogen atoms improves the wettability and conductivity of the material surface, and metal, nitrogen, carbon active sites and nitrogen-containing functional groups provide additional pseudo-capacitance through redox reaction, so that the obtained material has high specific capacitance and excellent rate retention rate in supercapacitor applications. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The nitrogen adsorption and desorption curve of the mesoporous carbon material prepared for Example 1 of the application is shown in the figure; Figure 2 The pore size distribution graph of the mesoporous carbon material prepared for Example 1 of the application is shown in the figure; Figure 3Nitrogen adsorption-desorption curve of the mesoporous carbon material prepared for Example 2 of the present application; Figure 4 Pore size distribution graph of the mesoporous carbon material prepared for Example 2 of the present application; Figure 5 Nitrogen adsorption-desorption curve of the mesoporous carbon material prepared for Example 3 of the present application; Figure 6 Pore size distribution graph of the mesoporous carbon material prepared for Example 3 of the present application; Figure 7 Nitrogen adsorption-desorption curve of the mesoporous carbon material prepared for Example 4 of the present application; Figure 8 Pore size distribution graph of the mesoporous carbon material prepared for Example 4 of the present application; Figure 9 Constant current charge-discharge curve of the mesoporous carbon material prepared for Example 1 of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described below in conjunction with the examples, comparative examples and test examples of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0037] Examples 1-5: Example 1

[0038] The present embodiment provides a nitrogen-doped spherical mesoporous carbon material dispersing metal monatomic atoms and a preparation method, comprising the following steps: S1, 50g of phenol and 10g of p-aminophenol were dissolved in 21mL of 10% by mass sodium hydroxide aqueous solution, and stirred at 60℃ for 30min until the solid was completely dissolved; S2, 108mL of 37% by mass formaldehyde aqueous solution was slowly added to the solution obtained in step S1, and after the addition was completed, the temperature was raised to 80℃ and reacted for 2 hours to obtain a brown-red viscous prepolymer; S3, the prepolymer obtained in step S2 was cooled to 60℃, and a solution prepared by dissolving 0.5g of vinyl ferrocene in 5mL of anhydrous ethanol was added, and stirred at a speed of 300rpm for 30min to make the metal precursor fully react; S4, 6.25 g of pore-forming agent F127 and 500 mL of 1% polyvinyl alcohol aqueous solution were added to the reaction obtained in step S3, the stirring speed was adjusted to 550 rpm, after 20 minutes of stirring and emulsification, 7.5 g of hexamethylenetetramine was added, and the temperature was increased to 90°C for 3 hours of curing, after the reaction was completed, the product was filtered, washed with deionized water and ethanol, and dried in a vacuum drying oven to obtain phenolic resin spheres; S5, the phenolic resin spheres obtained in step S4 were placed in a tube furnace, and the temperature was increased to 400°C at a rate of 2°C / min under air atmosphere for 1 hour of oxidation; then the atmosphere was switched to nitrogen, and the temperature was increased to 800°C at a rate of 2°C / min for 2 hours of carbonization; then water vapor was introduced, the mass ratio of water vapor to carbonized material was controlled to be 14:1, the temperature was increased to 825°C at a rate of 4°C / min under nitrogen protection, and the temperature was maintained for 1 hour of activation at this temperature, and then the temperature was naturally cooled to room temperature to obtain the metal atom-enriched nitrogen-doped spherical mesoporous carbon material. Example 2

[0039] The present embodiment provides a metal atom-dispersed nitrogen-doped spherical mesoporous carbon material and a preparation method, which is different from example 1 in that part of the raw material ratio and carbonization and activation process parameters are adjusted to verify the applicability of the process range, including the following steps: S1, 50 g of phenol and 12 g of p-aminophenol (mass ratio about 5:1.2) were dissolved in 21 mL of 10% sodium hydroxide aqueous solution (pH value controlled at 10.0), and stirred at 60°C for 30 min until the solid was completely dissolved; S2, 108 mL of 37% formaldehyde aqueous solution was slowly added to the solution obtained in step S1, and the temperature was increased to 80°C for 2 hours of reaction to obtain a prepolymer; S3, the prepolymer obtained in step S2 was cooled to 60°C, and a solution prepared by dissolving 0.5 g of vinyl ferrocene in 5 mL of anhydrous ethanol was added, and stirred at a speed of 300 rpm for 30 minutes; S4, 6.25 g of pore-forming agent F127 (pore-forming agent to phenol mass ratio about 1:9) and 500 mL of 3% polyvinyl alcohol aqueous solution were added to the reaction obtained in step S3, the stirring speed was adjusted to 550 rpm, after 20 minutes of stirring and emulsification, 7.5 g of hexamethylenetetramine (about 15% of the solid content of the resin) was added, and the temperature was increased to 90°C for 3 hours of curing, the product was filtered, washed and vacuum dried to obtain phenolic resin spheres; S5, the phenolic resin balls obtained in step S4 are placed in a tube furnace, and heated to 400℃ at a heating rate of 2℃ / min under an air atmosphere for 1 hour of oxidation; then switched to a nitrogen atmosphere, and heated to 800℃ at a heating rate of 2℃ / min for 2 hours of carbonization; then water vapor is introduced, the mass ratio of water vapor to carbonized material is controlled to be 22:1, heated to 825℃ at a heating rate of 4℃ / min under a nitrogen atmosphere, and activated at this temperature for 1.0 hour, and then naturally cooled to room temperature to obtain the nitrogen-doped spherical mesoporous carbon material rich in metal single atoms. Example 3

[0040] The present embodiment provides a nitrogen-doped spherical mesoporous carbon material dispersing metal single atoms and a preparation method, which comprises the following steps: S1, 50g of phenol and 10g of m-aminophenol (mass ratio of 5:1) are dissolved in 21mL of 10% sodium hydroxide aqueous solution, and stirred at 60℃ for 30min until the solid is completely dissolved; S2, 108mL of 37% formaldehyde aqueous solution is slowly added to the solution obtained in step S1, and then heated to 80℃ for 2 hours of reaction to obtain a prepolymer; S3, the prepolymer obtained in step S2 is cooled to 60℃, and a solution prepared by dissolving 0.5g of vinyl ferrocene in 5mL of anhydrous ethanol is added, and stirred at a speed of 300rpm for 30min; S4, 6.25g of pore-forming agent F127 and 500mL of 1% polyvinyl alcohol aqueous solution are added to the reactant obtained in step S3, the stirring speed is adjusted to 550rpm, and after 20min of stirring and emulsification, 7.5g of hexamethylenetetramine is added, heated to 90℃ for 3 hours of solidification, and then the product is filtered, washed and vacuum dried to obtain phenolic resin balls; S5, the phenolic resin balls obtained in step S4 are placed in a tube furnace, and heated to 400℃ at a heating rate of 2℃ / min under an air atmosphere for 1 hour of oxidation; then switched to a nitrogen atmosphere, and heated to 800℃ at a heating rate of 2℃ / min for 2 hours of carbonization; then water vapor is introduced, the mass ratio of water vapor to carbonized material is controlled to be 27:1, heated to 825℃ at a heating rate of 4℃ / min under a nitrogen atmosphere, and activated at this temperature for 1 hour, and then naturally cooled to room temperature to obtain the nitrogen-doped spherical mesoporous carbon material rich in metal single atoms. Example 4

[0041] The present embodiment provides a nitrogen-doped spherical mesoporous carbon material dispersing metal single atoms and a preparation method, which is different from example 1 in that vinyl ferrocene is used as a metal precursor, and the water vapor activation temperature is adjusted to verify the feasibility of different metal single atom loading and activation conditions, which comprises the following steps: S1, 50 g of phenol and 10 g of p-aminophenol (mass ratio of 5:1) were dissolved in 21 mL of 10% by mass sodium hydroxide aqueous solution, and stirred at 60°C for 30 min until the solids were completely dissolved; S2, 108 mL of 37% by mass formaldehyde aqueous solution was slowly added dropwise to the solution obtained in step S1, and after the addition was completed, the temperature was raised to 80°C and reacted for 2 hours to obtain a prepolymer; S3, the prepolymer obtained in step S2 was cooled to 60°C, and a solution prepared by dissolving 0.5 g of vinyl ferrocene in 5 mL of anhydrous ethanol was added, and stirred at a speed of 300 rpm for 30 min to perform in-situ grafting using double bonds; S4, 6.25 g of pore-forming agent F127 and 500 mL of 1% by mass polyvinyl alcohol aqueous solution were added to the reactant obtained in step S3, the stirring speed was adjusted to 550 rpm, and after stirring and emulsifying for 20 min, 7.5 g of hexamethylenetetramine was added, the temperature was raised to 90°C and solidified for 3 hours, and the product was filtered, washed and vacuum dried to obtain a phenolic resin sphere; S5, the phenolic resin sphere obtained in step S4 was placed in a tube furnace, and heated to 400°C at a heating rate of 2°C / min under an air atmosphere for 1 hour; then switched to a nitrogen atmosphere, heated to 800°C at a heating rate of 2°C / min for 2 hours; then water vapor was introduced, the mass ratio of water vapor to carbonized material was controlled to be 27:1, heated to 810°C at a heating rate of 4°C / min under nitrogen protection, and activated at this temperature for 1 hour, and then naturally cooled to room temperature to obtain the nitrogen-doped spherical mesoporous carbon material rich in metal single atoms. Example 5

[0042] This embodiment provides a nitrogen-doped spherical mesoporous carbon material dispersed with metal single atoms and a preparation method, which is different from example 1 in that a lower pore-forming agent ratio, different oxidation and carbonization temperatures, and a lower water vapor activation ratio are used, comprising the following steps: S1, a sodium hydroxide aqueous solution with a pH value of 8.5 was prepared, and 50 g of phenol and 10 g of p-aminophenol (mass ratio of 5:1) were added, and stirred at 60°C until the solids were completely dissolved; S2, 108 mL of 37% by mass formaldehyde aqueous solution was slowly added dropwise to the solution obtained in step S1, and after the addition was completed, the temperature was raised to 80°C and reacted for 2 hours to obtain a prepolymer; S3, the prepolymer obtained in step S2 was cooled to 60°C, and a solution prepared by dissolving 0.5 g of vinyl ferrocene in 5 mL of anhydrous ethanol was added, and stirred at a speed of 300 rpm for 30 min; S4, 7.14 g of pore-forming agent F127 (mass ratio of pore-forming agent to phenol is about 1:7) and 500 mL of 1% polyvinyl alcohol aqueous solution were added to the reactant obtained in step S3, the stirring speed was adjusted to 450 rpm, after 20 minutes of stirring and emulsification, 5.0 g of hexamethylenetetramine (about 10% of the solid content of the resin) was added, the temperature was raised to 90°C and cured for 3 hours, and the product was filtered, washed and vacuum dried to obtain phenolic resin spheres; S5, the phenolic resin spheres obtained in step S4 were placed in a tube furnace, and the temperature was raised to 380°C at a rate of 2°C / min under air atmosphere for 1 hour; then the atmosphere was switched to nitrogen, and the temperature was raised to 850°C at a rate of 2°C / min for 3 hours; then water vapor was introduced, the mass ratio of water vapor to carbonized material was controlled to be 3:1, the temperature was raised to 800°C at a rate of 4°C / min under nitrogen protection, and the activation was carried out at this temperature for 0.5 hours, and then the temperature was naturally cooled to room temperature to obtain the metal atom-rich nitrogen-doped spherical mesoporous carbon material.

[0043] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the difference is that in step S3, the vinyl ferrocene is replaced by an equal amount of ferrocene without vinyl functional groups to verify the effect of in-situ bonding of vinyl groups on the dispersion of metal atoms and the conductivity of the material, and the rest are the same.

[0044] Comparative Example 2: Compared with Example 1, the difference is that in step S1, instead of adding p-aminophenol, an equal amount of phenol is added (i.e. the total amount of phenol is 60 g) to verify the contribution of p-aminophenol as an endogenous nitrogen source to the specific capacitance and cycle stability of the material, and the rest are the same.

[0045] Comparative Example 3: Compared with Example 1, the difference is that in step S4, no pore-forming agent F127 is added to verify the importance of soft template agent in forming mesoporous structure and improving rate performance, and the rest are the same.

[0046] Comparative Example 4: Compared with Example 1, the difference is that in step S1, the aqueous sodium hydroxide solution is replaced by an aqueous hydrochloric acid solution and the pH value is adjusted to 2.0, i.e. the polymerization reaction is carried out under acidic conditions, to verify the advantages of alkaline catalytic system in regulating the spherical morphology and pore structure, and the rest are the same.

[0047] Test Examples 1-2: Test Example 1: physicochemical property and microstructure characterization Experimental steps: The carbon materials prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to physical and chemical property characterization. Field emission scanning electron microscopy was used to observe the surface morphology and particle size of the samples; transmission electron microscopy and high-angle annular dark field scanning transmission electron microscopy were used to observe the internal pore structure and metal element distribution state of the materials; X-ray diffractometry was used to analyze the crystal structure and graphitization degree; laser Raman spectroscopy was used to characterize the degree of carbon structural defects, and the intensity ratio of the D peak (about 1350 cm -1 ) and the G peak (about 1580 cm -1 ) was recorded. Nitrogen adsorption-desorption testing was performed at 77 K using a full-automatic specific surface area and pore size analyzer, the specific surface area was calculated based on the Brunauer-Emmett-Teller equation, the pore size distribution and mesopore volume were calculated based on the Barrett-Joyner-Halenda model, and the micropore volume was calculated using the t-plot method.

[0048] The test results of various physical parameters are shown in the following table:

[0049] Conclusion analysis: Referring to the attached Figures 1-8 , according to the data in Table 1 and the electron microscopy results, the water vapor activation conditions have a significant effect on the pore parameters of the materials. In Examples 1 to 2, as the amount of water vapor increases, the specific surface area increases from 1931.4 m 2 / g to 2145.7 m 2 / g, and the average pore size increases, indicating that increasing the amount of water vapor promotes pore expansion and the generation of new micropores. In Example 3, the total pore volume further increases to 1.31 cm 3 / g, and the average pore size increases to 2.38 nm, but the specific surface area decreases to 2088.3 m 2 / g. This indicates that high-concentration water vapor etching is stronger, resulting in the ablation and merging of some micropore walls into mesopores, reducing the number of micropores. Comparing Example 3 with Example 4, the specific surface area and average pore size of Example 4 are lower than those of Example 3 after reducing the activation temperature, indicating that reducing the temperature inhibits the water vapor activation reaction rate and prevents excessive pore widening.

[0050] Comparing Comparative Example 1 with Comparative Example 3, the specific surface area of Comparative Example 3 is only 856.4 m 2 / g, mesopore ratio 12.4%, confirming that the micelles formed by F127 in the aqueous phase play a key role in the formation of mesoporous channels. In terms of morphology, Example 1 is a uniform sphere, while Comparative Example 4 is an irregular block, indicating that an alkaline environment is conducive to the formation of a spherical hydroxymethyl precursor in the PVA dispersion, and an acidic condition tends to linear polycondensation. In terms of structural defects, the ID / IG value of Example 1 is 1.02, higher than 0.92 of Comparative Example 1, indicating that the introduction of metal centers through vinyl copolymerization bonding has better dispersity than physical mixing, and induces more defect sites in the carbon base.

[0051] Test Example 2: Electrochemical energy storage performance test Experimental steps: The prepared carbon material was tested for electrochemical performance under a three-electrode system. The working electrode preparation process was as follows: the carbon material to be tested, acetylene black and polytetrafluoroethylene emulsion (solid content 60%) were mixed in a mass ratio of 8:1:1, and ethanol was added for dispersion to prepare a slurry, which was coated on a 1 cm x 1 cm nickel foam current collector (coating amount 3-5 mg), and then vacuum dried at 80°C for 12 hours and pressed into a sheet at 10 MPa. The electrochemical workstation (CHI660E) was used for testing, with the prepared nickel foam electrode as the working electrode, platinum as the counter electrode, Hg / HgO electrode as the reference electrode, and 6 mol / L potassium hydroxide aqueous solution as the electrolyte. Constant current charge and discharge tests were carried out at a current density of 1 A / g to 20 A / g in a voltage window of -1.0 V to 0 V, and the mass specific capacitance was calculated according to the discharge time; continuous charge and discharge cycles were carried out at a current density of 5 A / g, and the capacitance retention rate was recorded.

[0052] The test electrochemical performance data are shown in the following table:

[0053] Conclusion analysis: Referring to the Figure 9 Table 2 shows that the specific capacitances of Examples 1 to 4 at a current density of 1 A / g are all more than 340 F / g. Among them, the specific capacitance of Example 2 is the highest, reaching 368.1 F / g, which is better than 342.5 F / g of Example 1, because the highest specific surface area is obtained at an activation ratio of 1:22, increasing the adsorption sites of electrolyte ions. Although Example 3 has the largest pore volume, the rate retention rate is comparable to that of Example 2, but the specific capacitance and cycle stability are slightly lower, indicating that excessive activation can reduce the bulk density or local conductivity of the material. The specific capacitance and cycle stability of Example 4 increase to a level close to that of Example 1 after reducing the activation temperature, indicating that reducing the temperature under a higher water vapor flow helps to balance the pore structure and skeleton stability.

[0054] In terms of rate performance, the capacitance retention of Example 1 at 20 A / g is 75.5%, higher than that of Comparative Example 3 without F127, which confirms that mesoporous structure shortens the ion diffusion path and improves the utilization of active surface at large current. In terms of cycle stability, Example 1 is better than Comparative Example 1. In Example 1, vinyl ferrocene is grafted in situ by covalent bond, and after carbonization, the metal atoms are stably anchored in the carbon lattice; in Comparative Example 1, ferrocene is physically adsorbed, and during the cycle process, it is easy to cause aggregation or fall off, resulting in capacity attenuation. In addition, the specific capacitance of Comparative Example 2 is 215.3 F / g, lower than that of Example 1, which confirms that nitrogen doping improves the surface wettability of the material and provides a pseudo-capacitance contribution.

Claims

1. A nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms, characterized in that, The carbon material is made from raw materials comprising the following parts by weight: 45-55 parts of phenol; 9-13 parts of aminophenol; 100-120 parts of a 37% formaldehyde aqueous solution; 0.4-0.6 parts of a vinyl-containing metallocene precursor; 6-8 parts of triblock copolymer pore-forming agent; 4.5-8.0 parts of hexamethylenetetramine.

2. The nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 1, characterized in that, The aminophenol is selected from one of p-aminophenol and m-aminophenol; the vinyl-containing metallocene precursor is selected from one of vinyl ferrocene and vinyl cobalt cadmium.

3. The nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 1, characterized in that, The pore-forming agent of the triblock copolymer is a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer; the raw materials also include a dispersant, which is a polyvinyl alcohol aqueous solution with a mass concentration of 1%-3%.

4. The nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 1, characterized in that, The mass ratio of phenol to aminophenol in the raw materials is 5:(1-1.2); the mass ratio of the triblock copolymer pore-forming agent to phenol is 1:(7-9).

5. The nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 1, characterized in that, The carbon material has a spherical morphology, and the metal single atoms are dispersed in the nitrogen-doped carbon framework through in-situ grafting.

6. A method for preparing a nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Phenol and aminophenol are dissolved in an alkaline aqueous solution to obtain a phenolamine solution; S2. Add formaldehyde aqueous solution dropwise to the solution obtained in step S1, and heat to carry out prepolymerization reaction to obtain prepolymer; S3. Lower the temperature of the prepolymer, add an alcohol solution containing a vinyl metallocene precursor, and stir to allow the metal precursor and prepolymer to undergo a grafting reaction. S4. Add the triblock copolymer pore-forming agent and dispersant solution to the reactants obtained in step S3, stir and emulsify, add hexamethylenetetramine, heat and cure, and the product is post-treated to obtain phenolic resin balls. S5. Perform multi-stage heat treatment on the phenolic resin balls: first, perform oxidation treatment in an air atmosphere; then switch to an inert atmosphere for carbonization treatment; then, pass water vapor through the balls under inert atmosphere protection for activation treatment, and obtain the carbon material after cooling.

7. The method for preparing a nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 6, characterized in that, In step S1, the alkaline aqueous solution is a sodium hydroxide aqueous solution, and the pH value of the system is adjusted to 8.5-10.0; in step S2, the temperature of the prepolymerization reaction is 75-85℃, and the reaction time is 1.5-2.5 hours.

8. The method for preparing a nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 6, characterized in that, In step S3, the prepolymer temperature is reduced to 55-65°C; the vinyl-containing metallocene precursor is pre-dissolved in anhydrous ethanol; and the stirring grafting time is 20-40 minutes.

9. The method for preparing a nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 6, characterized in that, In step S5, the specific process parameters for the multi-stage heat treatment are as follows: Oxidation treatment: Heat to 380-400℃ at a heating rate of 1-3℃ / min, and hold for 0.5-1.5 hours; Carbonization treatment: Heat to 800-850℃ at a heating rate of 1-3℃ / min, and hold for 1.5-3.5 hours; Activation treatment: Heat to 800-825℃ at a heating rate of 3-5℃ / min, control the mass ratio of water vapor to carbonized material to be (3-27):1, and the activation time is 0.5-1.5 hours.

10. The method for preparing a nitrogen-doped spherical mesoporous carbon material with dispersed metal single atoms according to claim 6, characterized in that, In step S4, the stirring and emulsification speed is 450-550 rpm, and the emulsification time is 15-25 minutes; the heating and curing temperature is 85-95℃, and the curing time is 2-4 hours.

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