Preparation method and application of lignite-derived porous carbon with double active sites

Abstract

The invention belongs to the technical field of preparation of supercapacitor energy storage electrode materials, and particularly discloses a preparation method and application of lignite-derived porous carbon with double active sites, and the method comprises the following steps: constructing a theoretical model; the method comprises the following steps: mixing oxygen-enriched low-order lignite serving as a carbon precursor and a self-oxygen doping agent and stacked carbon nitride serving as a nitrogen doping agent by a grinding or ball-milling method to obtain a mixed pyrolysis precursor; placing the mixed pyrolysis precursor in a tubular furnace or a muffle furnace filled with an inert atmosphere, and carrying out constant-temperature pyrolysis at 700 DEG C to obtain a pyrolysis product; and washing and purifying the pyrolysis product to obtain the brown coal derived porous carbon with pyrrole type nitrogen vacancy and oxygen-doped double active sites. According to the preparation method and application of the lignite-derived porous carbon with the double active sites, the carbon material doped with vacancy defects is prepared from the perspective of vacancy defect doping, and the prepared lignite-derived porous carbon material has excellent capacitance characteristics as a supercapacitor electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of supercapacitor energy storage electrode materials, and specifically relates to a preparation method and application of lignite-derived porous carbon with dual active sites. Background Art

[0002] In the prior art, porous carbon is the most widely used electrode material in supercapacitors due to its adjustable pore structure, good conductivity, high specific surface area, and chemical / thermal stability. However, the energy and power density of most reported electric double-layer capacitors are still unsatisfactory, which limits their practical applications. Therefore, the rational design of high-performance electrode materials is crucial for the development of advanced supercapacitors.

[0003] At present, the improvement of supercapacitor capacitance characteristics is mainly based on large specific surface area and pore structure regulation to improve double-layer capacitance and then improve the total capacitance performance. However, the space for improving the capacitance performance of supercapacitors based on double-layer capacitance is limited, which further restricts the development of supercapacitors. Pseudocapacitance, as another energy storage mechanism of supercapacitors, can further improve the capacitance space of supercapacitors on the basis of double-layer capacitance. Usually for carbon materials, pseudocapacitance characteristics are mainly improved by doping with inorganic elements such as nitrogen, oxygen, phosphorus, and sulfur. However, current research mainly focuses on improving the capacitance performance of porous carbon materials in terms of doping element types, doping amounts, doping functional group species, and multi-element doping. The vacancy defects formed by doping and the synergistic effect between vacancy defects and other doping elements have not been deeply studied.

[0004] Therefore, the art needs to develop a method for preparing and applying lignite-derived porous carbon with dual active sites, which can effectively solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a lignite-derived porous carbon with dual active sites and its application. The method prepares a carbon material doped with vacancy defects from the perspective of doping vacancy defects. The prepared lignite-derived porous carbon material has excellent capacitance characteristics as a supercapacitor electrode material.

[0006] To achieve the above object, the present invention provides a method for preparing a lignite-derived porous carbon with dual active sites, comprising the following steps: Step S1, constructing a theoretical model of nitrogen vacancy defects and oxygen doping dual active sites; Step S2, according to the theoretical model, oxygen-rich low-rank lignite is selected as a carbon precursor and a self-oxygen dopant, and stacked carbon nitride is used as a nitrogen dopant, and the oxygen-rich low-rank lignite, carbon nitride and potassium carbonate stripping agent are mixed by solid phase grinding or ball milling to obtain a mixed pyrolysis precursor; Among them, the mass ratio of oxygen-enriched low-rank lignite, carbon nitride, and potassium carbonate stripping agent added is 1:1:0.1~2; Step S3, placing the mixed pyrolysis precursor in a tube furnace or a muffle furnace with an inert atmosphere, and pyrolyzing at 700° C. for 1-3 hours to obtain a pyrolysis product; Step S4: purify the obtained pyrolysis product by washing with water to obtain lignite-derived porous carbon having pyrrole-type nitrogen vacancies and oxygen-doped dual active sites.

[0007] Preferably, step S1 specifically comprises: Step S11, using different nitrogen functional group species and oxygen doping species as designed active sites, and constructing a nitrogen-oxygen co-doping theoretical model of nitrogen vacancies generated by different nitrogen species with an ideal single-layer graphene structure; Step S12, optimizing the nitrogen-oxygen co-doping theoretical model of nitrogen vacancies generated by different nitrogen species based on density functional theory and using VASP calculation; Step S13, calculating the adsorption energy of alkaline electrolyte potassium ions of the optimized model to obtain a theoretical model of dual active sites of pyrrole nitrogen-type nitrogen vacancies and oxygen doping with optimal adsorption energy.

[0008] Preferably, in step S11, the types of nitrogen species include but are not limited to pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen.

[0009] Preferably, in step S2, the oxygen content of the oxygen-enriched low-rank lignite is greater than 15%.

[0010] Preferably, in step S4, the nitrogen vacancy is a nitrogen vacancy formed by pyrrole nitrogen.

[0011] Preferably, in step S4, the nitrogen and oxygen contents of the lignite-derived porous carbon having pyrrole-type nitrogen vacancies and oxygen-doped dual active sites are both greater than 10%, and the three-electrode test specific capacitance performance is greater than 300 F g -1 .

[0012] A method for preparing lignite-derived porous carbon with dual active sites, and application of the prepared lignite-derived porous carbon with dual active sites of pyrrole-type nitrogen vacancies and oxygen doping in supercapacitor electrode materials.

[0013] The present invention adopts the above-mentioned preparation method and application of lignite-derived porous carbon with dual active sites, and the beneficial effects are as follows: (1) The present invention utilizes the oxygen-rich properties of low-rank lignite as a precursor of porous carbon materials, which can effectively solve the problem of providing low-cost precursors for the synthesis of supercapacitor carbon electrode materials, and provides a new solution for the high value-added utilization of low-rank lignite, thereby achieving higher value-added utilization of lignite; (2) The preparation method of the present invention is simple, and the pyrolysis stripping temperature is only 700°C. The prepared highly nitrogen-oxygen co-doped lignite-derived porous carbon material having nitrogen vacancies and oxygen doping dual active sites, the defects and vacancies in the highly nitrogen-oxygen co-doped lignite-derived porous carbon structure can improve the interaction with mobile ions and promote electrochemical reactions by enhancing charge separation and transfer kinetics, thereby the carbon material has excellent capacitive properties; (3) The present invention provides a new idea for designing and constructing vacancy defects and doping dual sites for structural synergy in carbon materials for supercapacitors; the structural design of pyrrolic nitrogen-type nitrogen vacancy and oxygen doping dual sites provides a new path for defective materials to show unique capacitance advantages in energy storage applications in porous carbon electrode materials for supercapacitors.

[0014] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a graph showing the nitrogen vacancy test results of a paramagnetic resonance spectrometer of a preparation method of a lignite-derived porous carbon with dual active sites of the present invention and application example 1 and comparative examples 1 and 2; Figure 2 It is a graph of element contents quantitatively calculated by XPS test for the preparation method of lignite-derived porous carbon with dual active sites of the present invention and application example 1 and comparative example 1 and comparative example 2; Figure 3 A preparation method of a lignite-derived porous carbon with dual active sites according to the present invention and application example 1 and comparative example 1 and comparative example 2 are N / C molar ratio diagrams quantitatively calculated based on XPS test; Figure 4 The O / C molar ratio diagram of the preparation method of the lignite-derived porous carbon with dual active sites of the present invention and application example 1 and comparative example 1 and comparative example 2 quantitatively calculated based on XPS test; Figure 5 This is a comparison chart of specific capacitance values ​​at different current densities obtained by GCD testing of a method for preparing a lignite-derived porous carbon with dual active sites of the present invention and application example 1 and comparative example 1 and comparative example 2. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0017] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0018] Example 1 A method for preparing a lignite-derived porous carbon with dual active sites comprises the following steps: Step S1, constructing a theoretical model of nitrogen vacancy defects and oxygen doping dual active sites.

[0019] Step S11, using nitrogen functional group species of pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen and ether oxygen type oxygen functional group doping species as design active sites respectively, and constructing a double-site nitrogen-oxygen co-doping model with vacancy defects and doping of nitrogen vacancies generated by single nitrogen species and ether oxygen type oxygen functional group doping species using a single-layer graphene structure.

[0020] Step S12: Based on the density functional theory (DFT), VASP calculation is used to optimize the constructed dual-site nitrogen and oxygen co-doping model.

[0021] Step S13, calculating the adsorption energy of alkaline electrolyte potassium ions of the optimized model, and obtaining a theoretical model of dual active sites of pyrrole nitrogen type nitrogen vacancies and oxygen doping with the best adsorption energy.

[0022] Step S2: According to the theoretical model, 200-mesh lignite powder with an oxygen content of 24.62% is mixed with stacked carbon nitride and potassium carbonate in a mass ratio of 1:1:1 by solid phase ball milling for 1 hour to obtain a mixed pyrolysis precursor.

[0023] Step S3: placing the mixed pyrolysis precursor in a nitrogen atmosphere 2 In a tubular furnace with an atmosphere, the starting temperature was 30 °C and the temperature was increased to 700 °C at a heating rate of 5 ° / min, and the pyrolysis was carried out at 700 °C for 3 h to obtain a pyrolysis product.

[0024] Step S4, purifying the obtained pyrolysis product by washing with water to obtain a highly nitrogen-oxygen co-doped lignite-derived porous carbon material having pyrrole-type nitrogen vacancies and oxygen-doped dual active sites.

[0025] Comparative Example 1 The 200-mesh lignite powder with an oxygen content of 24.62% was placed in a nitrogen 2 In a tubular furnace with an atmosphere, the temperature was increased to 700°C at a heating rate of 5°C / min, and pyrolysis was carried out at 700°C for 3 hours to obtain pyrolysis products. The pyrolysis products were washed and purified to obtain highly oxygen-doped lignite-derived porous carbon materials.

[0026] Comparative Example 2 The stacked carbon nitride prepared by pyrolysis of melamine at 550℃ and 200-mesh lignite powder containing 24.62% oxygen was mixed by ball milling and placed in a nitrogen atmosphere. 2The mixture was placed in a tubular furnace with an atmosphere and heated to 700°C at a heating rate of 5°C / min, and pyrolyzed at 700°C for 3 h to obtain pyrolysis products. The pyrolysis products were purified by washing to obtain highly nitrogen and oxygen co-doped lignite-derived porous carbon materials.

[0027] 1. The lignite-derived porous carbon materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are applied to supercapacitor electrode materials, specifically comprising the following steps: (1) The obtained lignite-derived porous carbon material is used as an active material, mixed with a conductive agent carbon black and a binder polyvinylidene fluoride in a mass ratio of 8:1:1, and nitrogen methyl pyrrolidone is added to prepare a mixed slurry, which is then coated on a carbon sheet and vacuum dried to prepare an electrode.

[0028] (2) In a 6 M potassium hydroxide aqueous electrolyte system, a mercury-mercury oxide electrode was selected as the reference electrode, a platinum electrode was used as the counter electrode, and the prepared electrode material was used as the working electrode. The capacitance performance of the material was calculated by constant current charge and discharge (GCD) test on a Chenhua CHI760E electrochemical workstation. The voltage range was -1 to 0 V and the current density was 0.5 to 20 A·g -1 .

[0029] 2. The lignite-derived porous carbon materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 were applied to supercapacitor electrode materials and the electrochemical performance was tested.

[0030] like Figure 1 As shown, compared with Comparative Examples 1 and 2, the brown-derived porous carbon material prepared in Example 1 has obvious nitrogen vacancies at g=2.003.

[0031] like Figure 2 As shown, the N content is 13.23% and the O content is 11.08%, indicating that the lignite-derived porous carbon material prepared in Example 1 is doped with a high nitrogen and oxygen content.

[0032] like Figure 3 As shown, compared with comparative example 1, the N / C ratio of Example 1 increases, indicating that carbon nitride introduces high nitrogen content doping, and compared with comparative example 2, the N / C ratio decreases, indicating that the addition of potassium carbonate forms nitrogen vacancy defects with the aid of high-temperature stripping.

[0033] like Figure 4 As shown, compared with Comparative Examples 1 and 2, the O / C ratio of Example 1 increases continuously, confirming the high oxygen content doping.

[0034] like Figure 5 As shown, the material prepared in Example 1 has the largest specific capacitance value, and the current density is 0.5A g -1 When the maximum specific capacitance is 332F g -1Compared with Comparative Examples 1 and 2, the highly nitrogen-oxygen co-doped lignite-derived porous carbon material having nitrogen vacancies and oxygen doping dual active sites prepared in Example 1 shows excellent capacitive properties.

[0035] The contents of various functional groups obtained by XPS spectrum peak fitting of N 1s and O1s of all materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown in Table 1.

[0036] Table 1 Content of various functional groups ;

[0037] As can be seen from Table 1, by comparing Comparative Example 1 with Comparative Example 2, it is found that the contents of various nitrogen species and oxygen species are significantly increased, indicating that the introduction of carbon nitride leads to high nitrogen and oxygen content doping; by comparing Example 1 with Comparative Example 2, it is found that the pyrrole nitrogen content is significantly reduced, and various types of oxygen doping continue to increase, confirming the coordinated doping of nitrogen vacancy defects and oxygen of the mainly pyrrole nitrogen type.

[0038] Comprehensive analysis confirmed the successful preparation of the dual-site nitrogen vacancy and oxygen doping and high nitrogen and oxygen co-doped lignite-derived porous carbon material in Example 1.

[0039] Therefore, the present invention adopts the above-mentioned method for preparing and applying the dual-active site lignite-derived porous carbon. The method prepares a carbon material doped with vacancy defects from the perspective of doping vacancy defects. The prepared lignite-derived porous carbon material has excellent capacitance characteristics as a supercapacitor electrode material.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a lignite-derived porous carbon with dual active sites, characterized in that: The following steps are involved: Step S1, constructing a theoretical model of nitrogen vacancy defects and oxygen doping dual active sites; Step S2, according to the theoretical model, oxygen-rich low-rank lignite is selected as a carbon precursor and a self-oxygen dopant, and stacked carbon nitride is used as a nitrogen dopant, and the oxygen-rich low-rank lignite, carbon nitride and potassium carbonate stripping agent are mixed by solid phase grinding or ball milling to obtain a mixed pyrolysis precursor; Among them, the mass ratio of oxygen-enriched low-rank lignite, carbon nitride, and potassium carbonate stripping agent added is 1:1:0.1~2; Step S3, placing the mixed pyrolysis precursor in a tube furnace or a muffle furnace with an inert atmosphere, and pyrolyzing at 700° C. for 1-3 hours to obtain a pyrolysis product; Step S4: purify the obtained pyrolysis product by washing with water to obtain lignite-derived porous carbon having pyrrole-type nitrogen vacancies and oxygen-doped dual active sites.

2. The method for preparing a dual-active-site lignite-derived porous carbon according to claim 1, characterized in that: Step S1 specifically comprises: Step S11, using different nitrogen functional group species and oxygen doping species as designed active sites, and constructing a nitrogen-oxygen co-doping theoretical model of nitrogen vacancies generated by different nitrogen species with an ideal single-layer graphene structure; Step S12, optimizing the nitrogen-oxygen co-doping theoretical model of nitrogen vacancies generated by different nitrogen species based on density functional theory and using VASP calculation; Step S13, calculating the adsorption energy of alkaline electrolyte potassium ions of the optimized model to obtain a theoretical model of dual active sites of pyrrole nitrogen-type nitrogen vacancies and oxygen doping with optimal adsorption energy.

3. The method for preparing a dual-active-site lignite-derived porous carbon according to claim 2, characterized in that: In step S11 , the types of nitrogen species include but are not limited to pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen.

4. The method for preparing a dual-active-site lignite-derived porous carbon according to claim 1, characterized in that: In step S2, the oxygen content of the oxygen-enriched low-rank lignite is greater than 15%.

5. The method for preparing a dual-active-site lignite-derived porous carbon according to claim 1, characterized in that: In step S4, the nitrogen vacancy is a nitrogen vacancy formed by pyrrolic nitrogen.

6. The method for preparing a dual-active-site lignite-derived porous carbon according to claim 1, characterized in that: In step S4, the nitrogen and oxygen contents of the lignite-derived porous carbon with pyrrole-type nitrogen vacancies and oxygen-doped dual active sites are both greater than 10%, and the three-electrode test specific capacitance performance is greater than 300 F g -1 .

7. An application of lignite-derived porous carbon having dual active sites of pyrrole-type nitrogen vacancies and oxygen doping prepared by the method for preparing lignite-derived porous carbon having dual active sites as described in any one of claims 1 to 6 in supercapacitor electrode materials.

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