Preparation method and application of high content nitrogen-doped porous carbon material

Abstract

The application relates to a preparation method and application of high-content nitrogen-doped porous carbon material. Tri-sodium citrate dihydrate and melamine are uniformly mixed and ground, the obtained solid mixture is placed in a tube furnace, and gradient heating is carried out under an inert gas atmosphere, the solid mixture is first heated from room temperature to 350-400 DEG C at a low speed, is kept for 1-5 hours, and is then rapidly heated to 600-800 DEG C for pyrolysis and carbonization, a high-nitrogen-content carbonized product is obtained, the carbonized product is washed by a hydrochloric acid solution, vacuum filtration and drying are carried out, and the high-content nitrogen-doped porous carbon material is prepared. The raw material is rich in source, cheap and easy to obtain, green and environment-friendly, the process is simple, the operation is convenient, and the high-content nitrogen-doped porous carbon material is easy to produce in large scale. The nitrogen-doped amount of the prepared high-content nitrogen-doped porous carbon material is as high as 11-14 at%, is obviously higher than that (5.81 at%) of a nitrogen-doped material prepared by direct carbonization, the specific surface area is large, the pore diameter is composed of micropores and mesopores, and the high-content nitrogen-doped porous carbon material is suitable for being used as an electrode material of a super capacitor.

Description

Technical Field

[0001] This invention belongs to the field of porous carbon nanomaterial preparation technology, specifically relating to a method for preparing and applying a high-nitrogen-doped porous carbon material. Background Technology

[0002] Porous carbon materials, due to their tunable pore size distribution, high specific surface area, and excellent chemical stability, have broad application prospects in energy storage, photo / electrocatalysis, and biomedicine. Generally, the preparation methods for porous carbon are mainly divided into activation methods and template methods. Activation methods typically require potassium hydroxide or phosphoric acid as activators, which suffer from difficulties in controlling the pore structure and severe corrosion of equipment. Template methods use surfactants as soft films or silica as hard films to prepare porous carbon materials. This method can usually produce porous carbon materials with controllable morphology, but the complex preparation process limits its large-scale production and application.

[0003] In addition, to improve the performance and applications of porous carbon materials, heteroatoms (nitrogen, sulfur, phosphorus, boron) are usually doped into the surface or structure of porous carbon. This can increase the defect sites of the porous carbon structure, improve its surface hydrophilicity, improve the electron transport speed of the material, and thus increase its electrochemical activity.

[0004] Invention patent CN 106564868B discloses a method for preparing nitrogen-doped porous carbon materials. This method involves mixing an anhydrous ethanol solution of poly(4-vinylpyridine) (P4VP) with an iron salt solution to form a coordination precursor, followed by carbonization and washing to obtain nitrogen-doped carbon materials. However, the nitrogen doping content is only 2.7–9.9 wt%. Invention patent CN 103922306B discloses a method for preparing and applying high-content nitrogen-doped porous carbon materials. This method uses biomass as a carbon source, and obtains high-content (6–13%) nitrogen-doped carbon materials through carbonization and high-temperature ammoniation treatment. However, the resulting porous carbon has only micropores (0.6–2.0 nm), and the small pore size is not conducive to rapid electron transport when used as an electrode material in supercapacitors. Therefore, how to simply and effectively prepare high-content nitrogen-doped porous carbon materials remains a challenge. Summary of the Invention

[0005] This invention provides a method for preparing high-nitrogen-doped porous carbon materials and their applications. It solves the problems of low nitrogen content, small pore size, narrow pore size distribution, and low electrochemical performance in nitrogen-doped carbon materials prepared by existing technologies. The method offers advantages such as abundant and inexpensive raw material sources, environmental friendliness, simple process, convenient operation, and ease of large-scale production. The prepared high-nitrogen-doped porous carbon materials have a nitrogen doping content as high as 11–14 at%, a large specific surface area, and pores consisting of micropores and mesopores, making them suitable as electrode materials for supercapacitors.

[0006] This invention is specifically achieved through the following technical solution: a method for preparing high-nitrogen-doped porous carbon materials according to this invention includes the following steps:

[0007] (1) Mix trisodium citrate dihydrate and melamine in a certain mass ratio and grind them evenly to obtain a solid mixture;

[0008] (2) The solid mixture from step (1) is placed in a tube furnace and heat-treated by gradient heating under an inert gas atmosphere. First, the temperature is raised slowly from room temperature to 350-400°C and kept at this temperature for 1-5 hours for melting and compounding. Then, the temperature is rapidly raised to 600-800°C and pyrolyzed and carbonized at this temperature to obtain carbonized products with high nitrogen content.

[0009] (3) The carbonization product of step (2) is washed with hydrochloric acid solution, vacuum filtered with microporous membrane, and washed with deionized water until the filtrate is neutral. Then it is dried to obtain a high-nitrogen-doped porous carbon material.

[0010] Furthermore, in step (1), the mass ratio of trisodium citrate dihydrate to melamine is 1:1 to 4:1.

[0011] In step (2), the low-speed heating rate is 0.2-2℃ / min, the inert gas flow rate is 0.5-2.0L / min, the rapid heating rate is 5-20℃ / min, the inert gas flow rate is 0.5-2.0L / min, and the pyrolysis carbonization time is 0.5-4h.

[0012] Furthermore, the concentration of the hydrochloric acid solution is 1.0–3.0 mol / L; the inert gas is nitrogen or argon.

[0013] The percentage of nitrogen-doped porous carbon atoms in the high-nitrogen-content materials prepared by the above method can reach 11-14 at, and the specific surface area is 1000-1400 m². 2 / g, with a pore size of 0.5–10.0 nm.

[0014] The high-nitrogen-doped porous carbon material prepared by the above method can be used as an electrode material for supercapacitors, with a specific capacitance of 218-290 F / g. After 10,000 cycles at a current density of 2 A / g, its specific capacitance retention rate is over 99.0%.

[0015] Compared with the prior art, the present invention has significant advantages and beneficial effects. Through the above technical solution, the present invention can achieve considerable technical progress and practicality, and has broad application value. It has at least the following advantages:

[0016] (1) In this invention, environmentally friendly trisodium citrate dihydrate and melamine raw materials are ground and mixed evenly in different mass ratios. Then, in an inert atmosphere, taking advantage of the similar melting point of trisodium citrate dihydrate (300℃) and melamine (354℃), a gradient heating method is adopted. First, the temperature is raised at a low speed to melt and composite. The ammonia gas generated by the decomposition of melamine replaces the -ONa group, -NH2 and -OH group in the molten trisodium citrate and undergoes a dehydration condensation reaction. Then, the ammonia gas generated at high temperature is used as the nitrogen source, and the sodium salt generated by the decomposition of trisodium citrate dihydrate is used as the template and pore-forming agent. CN bonds are formed in situ during the carbonization process to obtain a high-nitrogen-doped porous carbon material.

[0017] (2) The nitrogen doping content of the prepared nitrogen-doped porous carbon material is as high as 11-14 at%, significantly higher than that of carbon materials prepared by direct carbonization (5.81 at%), thus solving the problem of low nitrogen doping content in porous carbon materials. Furthermore, it has a large specific surface area, reaching 1000-1400 m². 2 With a pore size of 0.5–10 nm, composed of micropores and mesopores, it possesses more defects and active sites, promoting electrolyte penetration and wettability, and shortening ion diffusion distance, making it particularly suitable as an electrode material for supercapacitors. When used as an electrode material for supercapacitors, its specific capacitance is 218–290 F / g, and after 10,000 cycles at a current density of 2 A / g, its specific capacitance retention is above 99.0%, thus exhibiting excellent reversible charge-discharge capacity and cycle stability.

[0018] (3) The present invention has the advantages of abundant and inexpensive raw material sources, green and environmentally friendly, continuous melting, carbonization and nitrogen doping processes, simple process, convenient operation and easy to scale up production. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation process of the high-nitrogen-doped porous carbon material in Example 1.

[0020] Figure 2 This is a scanning electron microscope (SEM) image of the high-nitrogen-doped porous carbon material prepared in Example 1.

[0021] Figure 3 The nitrogen adsorption-desorption curve is shown for the high-nitrogen-doped porous carbon material prepared in Example 1.

[0022] Figure 4 The image shows the pore size distribution of the high-nitrogen-doped porous carbon material prepared in Example 1.

[0023] Figure 5 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the high-nitrogen-doped porous carbon material prepared in Example 1.

[0024] Figure 6 The graph shows a comparison of the cyclic voltammetry (CV) curves of the high nitrogen-doped porous carbon materials prepared in Examples 1-4 and the carbon material obtained in Comparative Example 5 at a scan rate of 10 mV / s.

[0025] Figure 7 The graph shows a comparison of the galvanostatic charge-discharge (GCD) curves of the high-nitrogen-doped porous carbon materials prepared in Examples 1-4 and the carbon material obtained in Comparative Example 5 at a current density of 1 A / g.

[0026] Figure 8 The graph shows the stability of the high nitrogen-doped porous carbon material prepared in Example 1 after 10,000 cycles at a current density of 2 A / g. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] 3g of trisodium citrate dihydrate and 3g of melamine were ground and mixed evenly in a mortar. The mixture was then placed in a tube furnace, and after evacuation, it was treated under a nitrogen atmosphere with a gas flow rate of 0.5 L / min using a gradient heating method. First, the temperature was slowly increased from room temperature to 400℃ at a rate of 1℃ / min, and maintained at 400℃ for melting and composite for 2 hours. Then, the temperature was increased to 600℃ at a rate of 5℃ / min, and pyrolysis and carbonization were carried out at 600℃ for 2 hours to obtain a carbonized product with high nitrogen content. The carbonized product was washed with 1.0 mol / L hydrochloric acid solution with stirring, vacuum filtered using a microporous membrane, and washed with deionized water until the filtrate was neutral. Finally, it was dried in a vacuum drying oven at 60℃ for 12 hours to obtain a high-nitrogen-doped porous carbon material.

[0030] Weigh out 80 mg of the prepared high-nitrogen-doped porous carbon material, 10 mg of the binder polytetrafluoroethylene (PTFE), and 10 mg of the conductive agent acetylene black. Mix the three together, add a small amount of anhydrous ethanol to wet the mixture, and stir until it becomes an approximately mud-like slurry. Then, use a glass rod to take a small amount of the slurry and evenly coat it onto a known mass of nickel foam surface (1×1 cm in size). 2 After drying at 60℃ for 12 hours in a vacuum drying oven, the material is then held at 2MPa for 1 minute on a hydraulic press and weighed. The mass of the active material coated on the nickel foam is calculated using the differential method, typically controlled at 2-3 mg / cm³.2 .

[0031] Using the prepared electrode as the working electrode, the Ag / AgCl electrode as the reference electrode, and the Pt sheet electrode as the counter electrode, a 6 mol / L potassium hydroxide solution as the electrolyte, the electrochemical performance of the electrode materials was tested on an electrochemical workstation using a three-electrode system. Cyclic voltammetry (CV) was performed in the voltage range of -1.0 V to 0.0 V (vs. Ag / AgCl) with a scan rate of 5–200 mV / s; galvanostatic charge-discharge (GCD) was performed in the voltage range of -1.0 V to 0.0 V (vs. Ag / AgCl) with current densities of 0.5 A / g, 1.0 A / g, 2.0 A / g, 5 A / g, and 10 A / g; and cycle stability testing was performed at a current density of 2 A / g for 10,000 cycles. Tests and calculations show that the prepared electrode material has a specific capacitance of 290 F / g at a current density of 1 A / g, and retains 99.1% of its specific capacitance after 10,000 cycles at 2 A / g.

[0032] Figure 1 This is a schematic diagram of the preparation process of the high-nitrogen-doped porous carbon material prepared in this embodiment. At the melting temperature, ammonia gas generated from the decomposition of melamine replaces the -ONa groups in the molten trisodium citrate. The -NH2 and -OH groups undergo a dehydration condensation reaction. Using ammonia gas generated at high temperature as the nitrogen source, and sodium salt generated from the decomposition of trisodium citrate dihydrate as the template and pore-forming agent, CN bonds are formed in situ during the carbonization process to obtain a high-nitrogen-doped porous carbon material.

[0033] Figure 2 This is a scanning electron microscope (SEM) image of the high-nitrogen-doped porous carbon material prepared in Example 1, which shows that the porous carbon material has a uniform structure.

[0034] Figure 3 The nitrogen adsorption-desorption curve is shown for the high-nitrogen-doped porous carbon material prepared in Example 1. This curve is a type IV isotherm with a hysteresis loop, indicating that the material exhibits microporous and mesoporous characteristics, with a specific surface area of ​​1400 m². 2 / g.

[0035] Figure 4 The figure shows the pore size distribution curve of the high-nitrogen-doped porous carbon material prepared in Example 1. As can be seen from the figure, the pore size distribution of this material is between 0.5 and 10.0 nm.

[0036] Figure 5 This is the X-ray photoelectron spectroscopy (XPS) spectrum of the high-nitrogen-doped porous carbon material prepared in Example 1. A strong N atom valence band can be seen at the binding energy of 400 eV. Spectral analysis indicates that the percentage of doped N atoms is 13.94 at%.

[0037] Example 2

[0038] 3g of trisodium citrate dihydrate and 1g of melamine were ground and mixed evenly in a mortar. The mixture was then placed in a tube furnace, evacuated, and treated under an argon atmosphere at a gas flow rate of 1L / min using a gradient heating method. First, the temperature was slowly increased from room temperature to 380℃ at a rate of 2℃ / min, and maintained at 380℃ for melting and composite for 3 hours. Then, the temperature was increased to 600℃ at a rate of 10℃ / min, and pyrolysis and carbonization were carried out at 600℃ for 3 hours to obtain a carbonized product with high nitrogen content. The carbonized product was washed with 2.0mol / L hydrochloric acid solution, stirred, and then vacuum filtered using a microporous membrane. After washing with deionized water until the filtrate was neutral, it was dried in a vacuum drying oven at 60℃ for 12 hours to obtain a high-nitrogen-doped porous carbon material.

[0039] Tests and analyses showed that the specific surface area of ​​this high-nitrogen-doped porous carbon material is 1020 m². 2 / g, with a pore size distribution between 0.5 and 10.0 nm, and a doping percentage of 12.75 at%.

[0040] Using the same electrode preparation and testing methods as in Example 1, the specific capacitance of the electrode material was calculated to be 240 F / g at a current density of 1 A / g, and the specific capacitance retention rate was 99.2% after 10,000 cycles at 2 A / g.

[0041] Example 3

[0042] 4 g of trisodium citrate dihydrate and 1 g of melamine were ground and mixed evenly in a mortar. The mixture was then placed in a tube furnace, evacuated, and treated under a nitrogen atmosphere at a gas flow rate of 0.5 L / min using a gradient heating method. First, the temperature was slowly increased from room temperature to 360°C at a rate of 1°C / min, and maintained at 360°C for 1 hour of melting and composite. Then, the temperature was increased to 800°C at a rate of 10°C / min, and pyrolyzed at 800°C for 2 hours to obtain a carbonized product with high nitrogen content. The carbonized product was washed with 1.0 mol / L hydrochloric acid solution, stirred, and vacuum filtered through a microporous membrane. After washing with deionized water until the filtrate was neutral, it was dried in a vacuum drying oven at 80°C for 10 hours to obtain a high-nitrogen-doped porous carbon material.

[0043] Tests and analyses showed that the specific surface area of ​​this high-nitrogen-doped porous carbon material is 1300 m². 2 / g, with a pore size distribution between 0.5 and 10.0 nm, and a doping percentage of 12.87 at%.

[0044] Using the same electrode preparation and testing methods as in Example 1, the specific capacitance of the electrode material was calculated to be 218 F / g at a current density of 1 A / g, and the specific capacitance retention rate was 99.1% after 10,000 cycles at 2 A / g.

[0045] Example 4

[0046] After grinding and mixing 3g of trisodium citrate dihydrate and 2g of melamine in a mortar until homogeneous,

[0047] The mixture was placed in a tube furnace, evacuated, and then treated under a nitrogen atmosphere at a gas flow rate of 1 L / min using a gradient heating method. First, the temperature was slowly increased from room temperature to 400℃ at a rate of 0.5℃ / min, maintained at 400℃ for melting and compounding for 4 hours, and then increased to 600℃ at a rate of 5℃ / min. After pyrolysis and carbonization at 600℃ for 1 hour, a high-nitrogen-content carbonized product was obtained. The carbonized product was washed with 2.0 mol / L hydrochloric acid solution with stirring, vacuum filtered using a microporous membrane, and washed with deionized water until the filtrate was neutral. Finally, it was dried in a vacuum drying oven at 60℃ for 12 hours to obtain a high-nitrogen-doped porous carbon material.

[0048] Tests and analyses showed that the specific surface area of ​​this high-nitrogen-doped porous carbon material is 1160 m². 2 / g, with a pore size distribution between 0.5 and 10.0 nm, and a doping percentage of 12.93 at%.

[0049] Using the same electrode preparation and testing methods as in Example 1, the specific capacitance of the electrode material was calculated to be 280 F / g at a current density of 1 A / g, and the specific capacitance retention rate was 99.0% after 10,000 cycles at 2 A / g.

[0050] Comparative Example 5

[0051] 3g of trisodium citrate dihydrate and 3g of melamine were ground and mixed evenly in a mortar. The mixture was then placed in a tube furnace, evacuated, and heated directly to 600℃ at a rate of 5℃ / min under an argon atmosphere with a gas flow rate of 1L / min. After pyrolysis and carbonization at 600℃ for 3 hours, nitrogen-doped carbonized products were obtained. The carbonized products were washed with 1.0mol / L hydrochloric acid solution with stirring, filtered under vacuum using a microporous membrane, and washed with deionized water until the filtrate was neutral. The filtrate was then dried in a vacuum drying oven at 60℃ for 12 hours to obtain nitrogen-doped porous carbon materials.

[0052] Tests and analyses showed that the specific surface area of ​​this nitrogen-doped porous carbon material is 520 m². 2 / g, with pore size distribution between 0.5 and 2.0 nm, and the percentage of N atoms doped is only 5.81 at%.

[0053] Using the same electrode preparation and testing methods as in Example 1, the specific capacitance of the electrode material was calculated to be 180 F / g at a current density of 1 A / g, and the specific capacitance retention rate was 99.5% at 2 A / g after 10,000 cycles.

[0054] Figure 6 The figure shows a comparison of the cyclic voltammetry (CV) curves of the high-nitrogen-doped porous carbon materials prepared in Examples 1-4 and the carbon material prepared in Comparative Example 5 at a scan rate of 10 mV / s. As can be seen from the figure, the curves of Examples 1-4 show a pair of weak redox peaks at -0.2V / -0.4V, indicating that nitrogen doping generates pseudocapacitance. No redox peaks were observed in the curve of Comparative Example 5, possibly due to its lower nitrogen content.

[0055] Figure 7 The graph shows a comparison of the galvanostatic charge-discharge (GCD) curves of the high-nitrogen-doped porous carbon materials prepared in Examples 1-4 and the carbon material prepared in Comparative Example 5 at a current density of 1 A / g. As can be seen from the graph, all curves are approximately symmetrical triangles. Clearly, the area enclosed by the curves of Examples 1-4 is larger than that enclosed by the curve of Comparative Example 5. Using the formula Cg = (I × Δt) / (ΔV × m), the specific capacitances of Examples 1-4 at 1 A / g are 290 F / g, 240 F / g, 218 F / g, and 280 F / g, respectively, which are significantly higher than the 180 F / g of Comparative Example 5. This indicates that high nitrogen atom doping can improve the specific capacitance of porous carbon materials.

[0056] Figure 8 The graph shows the cycle stability test results of the high nitrogen-doped porous carbon material prepared in Example 1 after 10,000 cycles at a current density of 2 A / g. As can be seen from the graph, the specific capacitance retention remains stable at 99.2% after 10,000 cycles.

[0057] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a high content nitrogen-doped porous carbon material, characterized in that The method comprises the following steps: (1) mixing trisodium citrate dihydrate and melamine according to a mass ratio of 1:1-4:1, grinding uniformly to obtain a solid mixture; (2) placing the solid mixture of step (1) in a tube furnace, and performing heat treatment in an inert gas atmosphere by using a gradient heating method, first heating from room temperature to 350-400 DEG C at a rate of 0.2-2 DEG C / min, keeping melting and compounding at the temperature for 1-5 h, then heating to 600-800 DEG C at a rate of 5-20 DEG C / min, and pyrolyzing and carbonizing at the temperature for 0.5-4 h to obtain a carbonized product with high nitrogen content; (3) The carbonized product of step (2) is washed with a hydrochloric acid solution, vacuum filtered using a microporous filter membrane, and washed with deionized water until the filtrate is neutral, and dried to obtain a high-content nitrogen-doped porous carbon material. The specific surface area of the obtained high-content nitrogen-doped porous carbon material is 1000-1400 m 2 / g, the pore size is 0.5-10.0 nm, and the percentage of doped nitrogen atoms is 11-14 at %.

2. The method for preparing high content nitrogen-doped porous carbon material according to claim 1, characterized in that in step (2), the flow rate of the inert gas is 0.5-2.0 L / min.

3. The method for preparing high-nitrogen-doped porous carbon materials according to claim 1, characterized in that... in step (3), the concentration of the hydrochloric acid solution is 1.0-3.0 mol / L.

4. The method for preparing high content nitrogen-doped porous carbon material according to any one of claims 1-3, characterized in that the inert gas is nitrogen or argon.

5. The high-content nitrogen-doped porous carbon material obtained by the preparation method according to any one of claims 1-3.

6. Application of the high-content nitrogen-doped porous carbon material obtained by the preparation method according to any one of claims 1-3 to supercapacitor electrode materials.

7. Use according to claim 6, characterized in that When the high-content nitrogen-doped porous carbon material is used as a supercapacitor electrode material, the specific capacitance thereof is 218-290 F / g, and the specific capacity retention rate thereof is 99.0% or more after 10,000 cycles at a current density of 2 A / g.

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