Preparation Of Nitrogen-doped Carbon By Carbonization Of Triazole-based Ionic Liquid And Its Properties

Since the "Twelfth Five-Year Plan",the development of new,green and efficient energy storage devices to utilize the renewable energy more rationally has become a research hotspot for scientists under the new situation.Supercapacitors have gradually been widely concerned because of their advantages such as fast charge and discharge characteristics and good cycle stability.Carbon material,as one of the most widely used electrode materials,is limited by the mechanism of electrostatic energy storage,and its energy density and specific capacitance are limited,which affects its further application.It can be doped with heteroatoms(N,O etc.)to further improve the electrochemical performance of the material.In this paper,triazole-based ionic liquids were designed and synthesized independently,and used as the precursor to the synthesis high-performance nitrogen-doped carbon for the first time.Carbonization was carried out by one-step pyrolysis method,hydrothermal method and template method,respectively.The effects of different carbonization methods and carbonization conditions on the physical structure and electrochemical properties of nitrogen-doped carbon were studied.The details are as follows:(1)N-methylimidazole,N-methylmorpholine and pyridine were selected as cationic ligands,and triazole was used as anionic ligand to synthesize three kinds of triazole-based ionic liquids with high nitrogen content([Bmm]tr:33.80 wt%;[Bmmo]tr:24.76 wt%;[Bpy]tr:27.43 wt%).One-step pyrolysis method was used to carbonize the ionic liquids,and the high-temperature carbonization products were characterized and analyzed,and the pyrolysis process of ILs was investigated in detail.It was found that after pyrolysed at 1000?,ILs were converted into nitrogen-doped carbon materials with high nitrogen content(6.18 wt%-7.80 wt%),the residual masses rates were 9.49%,2.64%,and 13.97%,respectively,and the products have high degree of graphitization.The pyrolysis of ILs are composed of two stages,namely,low temperature(decomposition temperature of ILs-500?)heterocyclic ring-opening decomposition,cross-linking polymerization occurs between fragments formed in situ,and continuous polycondensation between layers at high temperature(500?-1000?).The carbonized products are transformed into a graphitized state.It shows that the introduction of triazole group with high N content can promote the deposition of carbon.After carbonization,considerable amount of N is doped into the main body of carbon to produce nitrogen-doped carbon materials with good oxidation stability(2)Using[Bmim]tr as the nitrogen/carbon source,a series of porous nitrogen/oxygen co-doped carbon materials were prepared by hydrothermal synthesis.The study found that the carbonization temperature and the concentration of[Bmim]tr aqueous solution are two major factors that affect the physical structure and electrochemical performance of the products.As the carbonization temperature(700?-1000?)increases,the nitrogen and oxygen contents in the sample gradually decreased,and the specific surface area and pore volume reached the optimal state at 900?;As the concentration of the IL solution increases,the Ostwald ripening of the particles in the solution gradually becames obvious,causing the specific surface area and pore volume of the samples to increase and then decrease after carbonization.Taking the solution of IL critical micelle concentration(22 wt%)as the precursor and carbonization at 900? for 2 h,the sample htCN.22-900 has the highest specific surface area(327.32 m2·g-1)and high nitrogen doping amount(6.96 wt%)and the relatively high specific capacitance(155 F·g-1).(3)Using[Bmim]tr as the nitrogen/carbon source and MCM-41 molecular sieve as the porous template,porous nitrogen-doped carbon material with rich pore structure was prepared by the template method.The study found that[Bmim]tr is an ideal precursor for template carbonization,and the carbonized product can obtain the topology of the molecular sieve template;Carbonization temperature is an important factor affecting the physical properties and electrochemical performance of CNIL/MCM-T samples.After carbonization at 900?,the CNIL/MCM-900 sample has the largest specific surface area(784.78 m2·g-1)and a relatively high N-doping amount(9.63 wt%).The specific capacitance measured in the three/two electrode system is 307 F·g-1 and 235 F·g-1(at 0.1 A·g-1),and the sample has high energy density and cycle stability.In the two-electrode system,the energy density is 22.08 W-h·kg-1(when the power density is 500 W·kg-1),and after 2000 times of charge and discharge cycles,the capacitance retention rate still exceeds 75%.This paper provides a theoretical reference for the carbonization process of triazole-based ionic liquids,provides a new idea for the selection of IL-based carbonization precursors,and demonstrates the huge application potential of tri azole-based ionic liquids in the preparation of high-performance N-doped carbon-based supercapacitor electrode materials.