Preparation Of Humic Acid-based Porous Carbon Materials For Supercapacitors

With the advantages of large capacity,high power density and long cycle life,super capacitors have become the focus of attention in the energy field in recent years.One of the most important factors affecting the performance of supercapacitors is the electrode material.Humic acid is a kind of biomass material which widely exists in peat and lignite,which has a high carbon content.At the same time,it can be processed by its unique physicochemical properties to prepare electrode materials that meet the requirements of super capacitors.In this paper,lignite from Yunnan Qujing was raw material and humic acid was extracted from the lignite by nitric acid oxidation method as carbon source precursor.Different types of carbon materials were prepared by carbonization before activation.The effects of activation temperature and alkali-carbon ratio on the surface functional groups,microcrystalline structure,pore structure and electrochemical properties of the materials were discussed.The materials were characterized by Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,X-ray diffraction,scanning electron microscopy,transmission electron microscopy and N₂ absorption and desorption.The electrochemical properties of carbon electrodes were tested by cyclic voltammetry,constant current charge-discharge test,AC impedance test and cycle life test.The main results are as follows:（1）NHA was directly carbonized at 500 ^oC,and the activated samples all had a hierarchical pore structure,with a maximum specific surface area of 1859.17 m²×g^-1.The HC1-700 was prepared when the ratio of alkali to carbon was 1:1 and the activation temperature was 700 ^oC.And when the current density of the three-electrode system in 6 M KOH solution was 0.5 A×g^-1,the specific capacitance of HC1-700 was336.25 F×g^-1.When the current density is 10 A×g^-1,the specific capacitance reached276.24 F×g^-1,which showed excellent capacitance retention.（2）The carbon material with carbong aerogel structure was successfully prepared by solvent replacement and atmospheric drying with NHA.The carbon aerogel was formed by the accumulation of 40-150 nm nano-carbon spheres,and the activated material had a certain mesoporous structure,and the maximum specific surface area was 1220.06 m²×g^-1.The CA₂prepared under the conditions of activation temperature of 600 ^oC and alkali-carbon ratio of 2:1 in the three-electrode system had a specific capacitance of 312.89 F×g^-1 when the current density was 0.5 A×g^-1.When the current density was 50 A×g^-1,the specific capacitance of CA₂ was 233.67 F×g^-1.Besides,CA₂was prepared as a button type capacitor with a capacitance retention of 95.6%for 5000cycles.（3）NHA and F127 were mechanically stirred and mixed at room temperature,and then poured on a petri dish to dry to realize water phase self-assembly.Then the humic acid-based mesoporous carbon material CF₀,with a specific surface area of 462.79m²×g^-1 was prepared after carbonization at 500 ^oC.The developed mesoporous structure laid the foundation for its high magnification performance.The specific surface area of CF₃ was 2101.58 m²×g^-1.The specific capacitance of CF₃ in the three-electrode system was 397.14 F×g^-1 when the current density was 0.5 A×g^-1,and the specific capacitance was274.18 F×g^-1 when the current density was 50 A×g^-1.Finally,it was prepared as a button-type capacitor with a capacity retention of 96.4%after 5000 cycles,which showedits excellent electrochemical performance.There were 55 figures,and 19 tables and 97 references in this paper.