Study Of Self-doped Micro-mesoporous Carbon Electrode Derived From Biomass For High Performance Supercapacitor

Doping and surface modification of porous carbon materials derived from biomass are part of the research hotspots that promote high performance and low cost of electrode materials for supercapacitors,owing to advantage of tunable unique structure of renewable biomass.In this thesis,porous carbon materials with excellent electrochemical properties were synthesized from biomass.The structure-activity relationship between porous carbon structure and its electrochemical performance was optimized.The intrinsic relationship between material structure and preparation process was also explored.The research focuses mainly on the following aspects:Improvement of pore structure and surface properties of porous carbon by quenching biomass carbon in liquid nitrogen and investigation.Use of nitrogen-rich spirulina extract as nitrogen doping reagent to regulate the mesoporous structure of biomass castor shell carbon and to improve the electrochemical performance of porous carbon.Novel methods are used for synthesis and modification of the porous carbon electrode materials.For example,poly-condensate amino acids from biomass sources by hydrothermal were carbonized at high temperature to synthesize binder-free electrodes for supercapacitors.The main results are as follows:1.Castor shell carbon activated with KOH at high temperature of 800? was quenched by liquid nitrogen for improving pore size distribution.The obtained porous carbon showed a suitable micro-mesoporous structure with a larger specific surface area,which could be attributed to the Van der Waals force between carbon atoms and the elastic force between carbon sheets.The microporous carbon prepared by liquid nitrogen quenching has a specific surface area of 1618 m2g-1 compared with a 1334 m2g-1 for that without liquid nitrogen treatment.Further,electrochemical measurements showed that the samples quenched by liquid nitrogen had a specific capacitance of up to 73.6 Fg-1 and an energy density of 6.8 Wh kg-1 compared with the samples without liquid nitrogen quenching,which has only 47.5 Fg-1 and 4.2 Wh kg-1 energy density at 1 A g-1.2.Nitrogen-rich spirulina extract impregnated castor shell was used to effectively regulate and modify the surface morphology of biomass carbon by KOH activation and high-temperature calcination.The prepared porous carbon exhibits nitrogen-rich micro-mesoporous carbon with unique interconnected network structure and higher specific surface area(1527 m2g-1)after the high temperature treatment for supercapacitor electrode.The nitrogen-rich organic functional groups derived from extract of spirulina improve interaction of KOH and castor shells responsible for formation of unique interconnected micro-mesoporous structure.The as-prepared nitrogen doped micro-mesoporous carbon contributes to enhance charge transfer,and to decrease mass transfer resistance of supercapacitor electrode.A good electrochemical performance with high specific capacitance of 333 F g-1 at 1 Ag-1 was obtained.The charge/discharge cycling behavior shows only loss of 0.3%of total capacity after 10,000 cycles at 10 Ag-1.The two-electrode configuration of assembled CSSK material displayed a remarkable energy density of 10 Wh kg-1 at a power density of 600 W kg-1 and good cycling behavior(after 10000 cycles 91.7%retention of specific capacitance).Thus,strategy of the extract mediated synthesis is facile and effective to improve the performance of porous carbon for promising candidates as low cost electrode materials for supercapacitors.3.Amino acid-based binder-free electrodes were synthesized by facile hydrothermal and carbonization method.The hydrogen bond structure,network on the surface created from the functional groups effectively promoted the adhesive and contact of active structural material.The results include characteristic crinkled,channel and loops morphology as observed is apparently the nature of required ionic pore sizes for supercapacitors with high wettability surface and nitrogen doped surface,which induces pseudo-adsorption and promotes total specific capacitance.Two-electrode system was assembled in 6 M aqueous KOH electrolyte.The material demonstrated excellent conductive contact between deposited carbon and graphite sheet substrate.Its high specific capacitance(109 F g-1 at 0.25 A g-1)resulted in simultaneously improved energy and power densities at the tune of 15 Wh kg-1 and 125 W kg-1,respectively.