Preparation And Performance Of Biomass-based Porous Carbon Materials

Supercapacitors,a kind of energy storage devices,have attracted extensive attentions.The most core component of supercapacitors is electrode material,and carbon materials are employed as supercapacitor electrodes due to their superior performances.However,their commercial use is not widespread due to the limitations imposed by complicated production processes and high cost of most carbon materials.Biomass-based porous carbon materials have been regarded as efficient supercapacitor electrodes,because of their simple synthesis processes,low equipment requirements and low cost.In this thesis,low cost and eco-friendly porous bio-carbons were fabricated from konjaku flour and watermelon rind via pyrolysis-activation processes.Moreover,porous bio-carbon derived from watermelon rind was successfully employed to support polyaniline(PANI)particles to obtain bio-carbon/PANI composite.And their electrochemical performances have been studied systematically as supercapacitor electrode materials.The details are as follows:(1)Low cost and eco-friendly porous biocarbons were fabricated from konjaku flour via pre-carbonization and KOH activation processes.The porous biocarbon ACK-5,which was obtained with a precarbonized carbon/KOH mass ratio of 1:5,possessed a specific surface area of 1403.3 m2 g-1.When ACK-5 was employed as a supercapacitor electrode,a high specific capacitance of 216 F g-1 was achieved at a current density of 1 A g-1 in 6 M KOH electrolyte,and an excellent cycling stability with capacitance retention remaining 93.7%after 5000 cycles was demonstrated.Moreover,when p-phenylenediamine(PPD)as a redox electrolyte was added to the 6 M KOH electrolyte,the ACK-5 sample acquired a supramaximal specific capacitance of 609 F g-1,and a high energy density of ACK-5//ACK-5 symmetrical cells reached up to 9.2 Wh kg-1 at a power density of 0.25 kW kg-1.(2)Self-nitrogen-doped bio-carbon was prepared via an easy one-step pyrolysis-activation process from watermelon rind.Porous bio-carbon ACW-2,which was obtained with a watermelon/KOH mass ratio of 1:2,exhibited a large specific surface area of 1303.3 m2 g-1,and was decorated with abundant nitrogen/oxygen-containing functional groups.When ACW-2 was used as a supercapacitor electrode,a superb specific capacitance of 260 F g-1 was achieved at a current density of 1 A g-1 in 6 M KOH electrolyte.ACW-2 also exhibited an ultrahigh cycling stability,and its retention rate was maintained at 93.8%even after 5000 cycles.Furthermore,ACw-2 acquired a supramaximal specific capacitance(852 F g-1)and a high energy density(12.9 Wh kg-1)when PPD was added into the 6 M KOH electrolyte.(3)A high performance bio-carbon/PANI composite was prepared by an in-situ polymerization of aniline monomers on the ACw-2 biomass-based porous carbon.The composite obtained with an ACw-2/aniline mass ratio of 20:80 was named ACPA-2.Polyaniline nanofiber arrays grew on the ACw-2 surface due to electrostatic interaction and van der Waals forces between ACw-2 and PANI.When ACPA-2 was used as a supercapacitor electrode,a specific capacitance of 520 F g-1 was achieved at a current density of 1 A g-1 and a high cycling stability with retention rate of 85.3%even after 2000 cycles.Furthermore,an asymmetric supercapacitor using ACPA-2 as a positive electrode assembled with ACw-2 negative electrode acquired a high cell voltage of 1.8 V and a high energy density of 21.2 Wh kg-1.Therefore,ACK-5,ACw-2 and ACPA-2 are all suggested to be excellent candidates for electrochemical supercapacitors.