Fabrication Of Biomass-derived Porous Carbon With Hierarchical Structure For Supercapacitors

The energy problem has been a concern all over the world,people are paying more attention to this problem with the development of the global economy.World development and economic globalization or modernization cannot maintain without the fossil energy such as oil,natural gas,and coal.In pursuit of the speed of industrialization all over the world,the energy consumption is greatly accelerated.According to some reports,Global will face a problem of serious lack of fossil energy in the middle of 21 st century.The global energy crisis will be increasingly prominent.In addition,the use of fossil fuels has led to serious environmental problems.The energy crisis and environmental problems pose a threat to the survival and development of human beings directly.Therefore,sustainable development of clean energy and research for advanced energy storage technology has become a very urgent problem.The emergence of supercapacitor provides a possibility for the sustainable development.Supercapacitor is a unique energy storage device,not only can provide the energy density of several orders of magnitude larger than conventional capacitors but exhibit higher power density than batteries as well as good cycle performance.The electrode material plays a crucial role for supercapacitor.Herein,three kinds of biomass materials are selected as the precursor to prepare porous carbon materials with different morphology and structures by different synthesis methods,and the electrochemical performance of as-prepared porous carbon materials were studied as electrode materials for supercapacitor.1.A nitrogen-doped foam-like 3D carbon plate is prepared by carbonizing a selected biomass precursor of pomelo peel.The carbon plate is composed of interwoven connected carbon tubes and shows a unique 3D interpenetrating macroporous network with binary-channel structure.Owing to the proper pore structures,short ion-diffusion paths,high conductivity,and high structure stability,the carbon plate exhibits excellent electrochemical performance as an electrode for supercapacitors directly.A high specific capacitance of up to 338 Fg-1 at 1 Ag-1,good rate capability with a capacitance retention of 59% at 20 Ag-1,and high cycling stability with only 4% capacitance loss after 5000 cycles at 20 Ag-1 can be achieved in 6M KOH electrolyte in a three electrode system.Furthermore,a symmetric supercapacitor fabricated by using the carbon plates delivers an energy density of 11.05 Whkg-1 at a power density of 250 Wkg-1,and an outstanding cycling stability with only 2.4% capacitance decay over 5000 cycles at 5 Ag-1 in 6M KOH electrolyte.These very attractive electrochemical properties indicate that the carbon plate derived from pomelo peel is a promising electrode material for supercapacitors.2.N-doped hierarchical porous carbon(NHPC)was obtained from waste boat-fruited sterculia seed by hydrothermal carbonization and KOH activation. The influence factors including the ratio of activation agent to precursor, activation temperature,heteroatom-doping were discussed.The results show that the NHPC-800-1 activated at 800 oC with the ratio of activation agent to precursor being 1 as an electrode in an electrical double layer capacitor(EDLC)exhibited the best electrochemical performance in 6 M KOH electrolyte.It delivered the specific capacitance up to 337 Fg-1 at a current density of 1 Ag-1,and still retained a capacitance of 181.5 Fg-1 at the high current density of 50 Ag-1.This material also shows excellent capacitance retention of 98.8 % after 5000 cycles at a current density of 20 Ag-1.In addition,a symmetric supercapacitor fabricated by NHPC-800-1 released an energy density of 8.05 Whkg-1 at a power density of 10 k Wkg-1 and a high cycling stability with capacitance retention of 98.5 % over 10000 cycles at 20 Ag-1 in 6?M KOH electrolyte.The superior performance of NHPC-800-1 could be attributed to these advantages of hierarchical porous structure,narrow micropore size distribution and rational micro/mesopore ratio,as well as the doping of N atom.These very attractive electrochemical properties indicate that the NHPC-800-1 derived from boat-fruited sterculia is a promising electrode material for supercapacitors.3.Osmanthus-derived honeycomb porous carbon was obtained by hydrothermal carbonization and the further activation with KOH.The obtained porous carbon at the ratio of activator to biochar being 2:1,exhibited the best electrochemical performance in 6 M KOH electrolyte.It delivered the specific capacitance up to 262 Fg-1 at a current density of 1 Ag-1.In addition,the specific capacitance of the a symmetric supercapacitor fabricated by honeycomb porous reduced from 70 Fg-1 to 60.2 Fg-1 with current density increased from 1 Ag-1 to 20 Ag-1,which imply excellent rate capability with capacitance retention of 85.7%.High cycling stability with only 1.6 % capacitance loss were observed after 10000 cycles at 20 Ag-1.