Preparation Of Carbon Nanomaterials Based On Technical Lignin And Their Application In Supercapacitors

With the constant consumption of petroleum resource and the increasingly serious global environmental crisis,the development of sustainable resources becomes the inevitable choice.Among these resources,lignin has attracted wide attention in the preparation of carbon materials because it is abundant,renewable,aromatic,and has high carbon content.However,porous carbon materials from lignin are dominated by microporous ones and the preparation of mesoporous ones are complex and expensive.In addition,lignin-based carbon nanofibers are research hotspot for the past decade,but the control of morphology and how to improve their electrochemical performance in a simple and efficient way are still in short of research.To cope with these problems,some works has been done in this thesis.Generally,carbon materials based on lignin from conventional hydrothermal carbonization are·microporous dominated and contain few mesoporous structure,which limit their applications.Complemental to hydrothermal carbonization,a solvent-thermal carbonization method based on deep eutectic solvent was adopted to prepare carbon nano-spheres in this thesis.It was found that lignin went through similar chemical changes to the hydrothermal carbonization,including degradation,alkylation,and condensation.After subsequent high-temperature activation,the carbon nano-sphere material with the specific surface area of 3126.3 m2/g and the mesopore volume of 1.789 cm3/g was obtained.The size and morphology of lignin-based electrospinning nanofibers was efficiently tuned by simply adding surfactants into the alkali lignin-polyvinyl alcohol solutions.It was found that the viscosity,rheology behavior,surface tension,and conductivity of the solution was affected by surfactants of different kinds and contents.Furthermore,the kenetic model among the solution components was built as well.Smooth nanofibers with the minimized diameters of 137 nm were produced by incorporating surfactant of appropriate kind and content(e.g.1%sodium lauryl sulfate).This contributed to the decrease of surface tension and the enhance of tangle of the polymers in solution.Based on the last research section,the electrochemical performance of lignin-based carbon nanofibers was improved using the nitrogen doping by infiltration in urea solution.The nitrogen doping significantly enhanced the electrochemical performance as electrodes for supercapacitors.Specifically,the gravimetric capacitance was 166.0 F/g at a current density of 0.5 A/g,which was increased by 84.3%as compared to the undoped ones.The energy density and power density were 5.76 Wh/kg and 250 W/kg,respectively.