Study On Preparation And Capacitive Performance Of N/S Co-Doped Hierarchical Porous Carbon Materials From Biomass

Carbon materials have great advantages in the application of electrode materials in supercapacitors due to their large surface area,good electrical conductivity and adjustable porosity.The pore structures（porosity and pore size distribution）of carbon materials and the surface properties of carbon materials have an important influence on its electrochemical performance.The capacitive properties of the electrode can be further improved by introducing heteroatoms artificially.This work chooses biomasses as carbon sources to prepare hierarchical porous carbon materials with heteroatoms doped through adding heteroatoms.The feasibility of replacing the traditional harmful KOH and ZnCl₂ with more environmentally friendly NaCl,Li Cl and Ca Cl₂ as biomass activators and the effect of different carbonization temperatures on the pore structure,heteroatom doping amount and electrochemical properties of the prepared carbon materials are explored.（1）The material NHC-NaCl prepared with NaCl as the activator has a higher specific surface area(988.6 m²g^-1),2D sheet-like hierarchical porous structure,appropriate N doping amount（6.15 at.%）and the maximum specific capacitance value reaches 285 F g^-1 in 6 M KOH solution.The prepared flexible symmetrical supercapacitor NHC-NaCl//NHC-NaCl also shows a high specific capacitance of 172F g^-1 at a current density of 0.2 A g^-1 and a relatively high specific energy of 19.4 Wh kg^-1 at a power density of 90 W kg^-1.（2）The materials show three-dimensional honeycomb structures when they were carbonized at different temperature.Among them,S-NHP-800 has highest specific surface area(2310.9 m² g^-1)and exhibits an excellent capacitive performance(428 F g^-1 at 0.2 A g^-1).In addition,S-NHP-800 shows a high capacitive retention rate（over 93%）at a current density of 10 A g^-1 after 10,000 cycles.This indicates that the electrode material S-NHP-800 is a kind of excellent materials for supercapacitor.The assembled S-NHP-800//S-NHP-800 symmetrical supercapacitor was tested in 1 mol L^-1 Na₂SO₄solution.And the results indicate that the specific capacitance can reach 260 F g^-1 at a current density of 0.2 A g^-1 and the energy density can reach 9.7 Wh kg^-1at a power density of 19.8 W kg^-1.