Preparation And Application Of Multi-stage Self-doped Biomass Carbon In Supercapacitors

As reserves of traditional fossil energy seriously deplete and the global warming situation becomes more severe,there is an urgent need for the development and utilization of sustainable energy.Supercapacitors have attracted increasing attention recently because of their high power density,good cycling performance and environmental friendliness.Carbon materials are widely used in supercapacitor electrode materials because of their good electrical conductivities,high specific surface areas,adjustable pore structures and excellent chemical stabilities.Recently,biomass-derived porous carbon has been increasingly applied to the electrodes of supercapacitors.Compared to conventional carbon material,the biomass are abundant,renewable,environmentally friendly and has a lower cost.In this paper,biomass-derived porous carbon was prepared by KOH activation method using dictyophora and azolla as carbon source with delicate multi-level structure,and the effects of KOH activation conditions on the structure and properties of the obtained carbon materials were investigated.The main research contents of this paper are as follows:We prepared a novel dictyophora-derived hierarchical porous carbon(DHPC)by simple carbonization and direct activation.The resulting carbon has a large specific surface area(2254 m2 g-1),abundant heteroatom doping and a three-dimensionally interconnected multi-level pore structure.This structure contains a natural honeycomb-like porous structure with micropores and mesopores on the carbon walls.In a three-electrode test system,the DHPC-2 electrode exhibits a high specific capacitance of 357 F g-1 at 0.5 A g-1,a considerable rate performance of 279 F g-1 even at 30 A g-1(78%retention)and a stable cycling performance with 94%retention after 5000 cycles at 5Ag-1.Furthermore,the DHPC-2 based symmetric supercapacitor device delivers an excellent energy density of 43.7 Wh kg-1 at 0.1 A g-1,and power density of 18 kW kg-1 at 10 A g-1.Therefore,this dictyophora-based electrode material is promising for the preparation of environmentally friendly and high-performing energy storage devices.In addition,we prepared azolla-derived biomass porous carbon(APC)using the same simple carbonization and activation method.Through BET characterization analysis,the surface of the material was etched out of the nanopores by KOH,forming a large specific surface area and a hierarchical porous structure.XPS results show that the material contains doping of hetero atoms such as N,O,which can improve the electrochemical performance of the material.In the electrochemical test,the specific capacitance of the APC-800 electrode in the three-electrode system is 346.3 F g-1(0.5 A g-1),when the current density increased to 30 A g-1,the specific capacitance can be retained by 78.3%.After 5000 charge-discharge cycles at 5 A g-1,the loss of specific capacitance was maintained at 5%,showing good cycle stability.The symmetric supercapacitor made by APC-800 exhibits an energy density of 38.9 Wh kg-1(0.1 A g-1)and a power density of 8.7 kW kg-1(5 A g-1),showing excellent electrochemical performance.