The Study Of N-doped Biochar And Porous Carbon Electrode Materials Derived From Biomass

Supercapacitors(SCs)display a broad application prospects in energy storage because of its high power density,excellent cycle performance,fast charge and discharge rate.Carbon materials are one of the most important electrode materials for supercapacitors.With the rapid depletion of non-renewable resources,carbon electrode materials derived from biomass have been prepared due to the abundant natural source and low cost.Lignin is a irregular polymer containing a large amount of benzene ring in its molecular structure,which became ideal carbon source of carbon materials in view of abundant source and low cost.Sodium lignosulfonate is a water-soluble lignin derivative,mainly come from the byproduct of the paper production process.At present,the conversion of lignin or its derivatives into porous carbon electrode material using chemical activation has become a hot research,while the specific capacitance of the obtained lignin-based porous carbon electrode material is usually low.Therefore,it can obtained additional pseudocapacitance by heteroatom doping,which provides new possibilities for further improving total capacitance of lignin-based porous carbon electrode material.Although lignin-based nitrogen-doped porous carbon can achieve a relatively high specific gravimetric capacitance,the volumetric capacitance will suffer from seriously reduction attributed to its low density,moreover,the chemical activation process involves in more energy and time consumption.Generally,biochar can achive possess high density and yield by direct low-temperature pyrolysis biomass.But,it can not be directly used as the electrode material for SCs because of its low specific surface area and poor electrical conductivity.Therefore,it may achieve high specific gravimetric and volumetric capacitances by simultaneously introducing the conductive agent and heteroatoms.The main research contents are as follows:(1)Biochar is a charcoal-like material produced by the thermal decomposition of biomass or its derivatives at relatively low temperature.However,biochar is rarely used for energy storage due to its poor conductivity and low specific surface area.But,in this work,graphene oxide(GO)is acted as the precursor of graphene with high conductivity.Sodium ligninsulfonate(Lig)is used as biochar source.The p-phenylenediamine(PPD)is used as nitrogen source.The nitrogen-doped biochar-based electrode material(NB-GLP)with high content of nitrogen(14.3 at.%),high yield(69.5 wt.%)and high density(1.98 g cm-3)was synthesized by GO,Lig and PPD via one-step low temperature pyrolysis(400 ?).The synthetic NB-GLP exhibited high gravimetric capacitances of 480 F g-1I,high volumetric capacitances of 950 F cm-3 at 1 A g-1,and good cycle stability at 10 A g-1(96.6%of its initial capacitance after 2000 charge-discharge cycles)in three electrode system.Especially,after assembling the NB-GLP electrodes into a symmetric supercapacitor,it simultaneously possessed high gravimetric and volumetric energy density of 13.4 Wh kg-1(at the power density of 248 W kg-1)and 26.5 Wh L-1(at the power density of 491 W L-1)in 1 M H2SO4 electrolyte,respectively.Moreover,it displayed higher gravimetric and volumetric energy density of 21.6 Wh kg-1(at the power density of 450 W kg-1)and 42.8 Wh L-1(at the power density of 891 W L-1)in 1 M Na2S04 electrolyte,respectively.This work opens up a useful way for the nitrogen-doped biochar-based materials used as electrode materials for energy storage(2)Nitrogen-doped porous carbon was prepared by low temperature pretreatment and chemical activation process using sodium lignosulfonate as carbon source and o-phenylenediamine as nitrogen source.The structures were characterized by XPS and XRD.The specific surface area and pore size distribution were analyzed by nitrogen desorption/adsorption apparatus.The influence of reaction parameters on electrochemical performance is further studied,including carbonization temperature and different mass ratio of raw materials.It showed optimal electrochemical performance when the mass ratio of sodium lignosulfonate to o-phenylenediamine was 5:3 and the carbonization temperature was 750 ?.The specific capacitance of NPC-750 is 226 F g-1 and 178 F g-1 at 1 and 20 A g-1,respectively,showing a high rate performance(78.8%).Moreover,it showed good cycle stability at 10 A g-1(98.8%of its initial capacitance after 1000 charge-discharge cycles).(3)Nitrogen-doped porous carbon with excellent electrochemical performance was also prepared by hydrothermal polymerization and chemical activation process using sodium lignosulfonate as carbon source and hexamethylene diamine as nitrogen source and crosslinking agent.The influence of reaction parameters on electrochemical performance is further studied,including carbonization temperature and different mass ratio of raw materials.NPC1:1-3-800 shows a high specific capacitance of 440 F g-1 in 6 M KOH electrolyte at 0.5 A g-1.Moreover,it showed good cycle stability at 20 A g-1(98.6%of its initial capacitance after 1000 charge-discharge cycles).The obtained NPC1:-3-800 also shows the specific capacitance of 331(at 1 A g-1)and 266 F g-1(at 20 A g-1)in 1 M H2SO4 electrolyte,showing high rate performance(80.4%).