Preparation And Electrochemical Performance Research Of Chitosan Derived Porous Carbon As Negative Material For Supercapacitor

As one of the new energy storage devices,it has the characteristics of high power density(10 kWkg^-1),long cycle life（>100000 cycles）and superior rate performance,and it has been widely used in industry,transportation and military.As the most commonly used electrode material for supercapacitors,carbon materials have many advantages,such as controllable specific surface area and pore structure,wide source,environment-friendly and low cost,etc.Various new types of carbon materials are constantly being developed and gradually become a hot spot in the field of electrode materials.However,the development of carbon materials is limited by their lower energy density.The studies have shown that the doping of heteroatoms（nitrogen,oxygen,phosphorus,sulfur,boron,etc.）can effectively improve the energy density of carbon materials.The purpose of this study is to use a wide range of sources,low price,environmentally friendly and renewable biomass chitosan as a carbon precursor,through the activation of NH₄Cl and KOH to prepare three-dimensional（3D）hierarchical porous carbon materials with good pore size distribution,and the electrochemical performance of it was studied.The main research contents are as follows:（1）Firstly,the chitosan was degraded by the hydrogen peroxide oxidation method to obtain degraded chitosan.Then the degraded chitosan was activated by the NH₄Cl activation method.When the mass ratio of NH₄Cl/degraded chitosan is 4 and the activation temperature is 900℃,the obtained HPC-900 has good pore size distribution and electrochemical performance.The specific surface area can reach 662.54 m² g^-1,the pore volume is 0.29 cm³ g^-1,and the average pore diameter is 1.69 nm.In the three electrode system,using 6 M KOH as electrolyte,it is found that the specific capacitance can reach297.35 F g^-1 when the current density is 0.5 A g^-1.When the current density is 5 A g^-1,the capacitance retention reaches 100%after 10000 cycles.（2）The degraded chitosan in the previous step was used as a carbon source.First,the degraded chitosan hydrogel was synthesized by the cross-linking density method.Then KOH was used to activate the carbonization product of the hydrogel,and the pore structure of the material was further regulated by controlling the carbonization temperature,the activation temperature and the amount of activator.The prepared DCHPC-3 has the best pore size distribution and electrochemical performance.In the three electrode system with6 M KOH as electrolyte,the specific capacitance of DCHPC-3 can reach 506 F g^-1(Current density is 0.3 A g^-1).The energy density of the symmetrical capacitor（DCHPC-3//DCHPC-3）can reach 40.62 Wh kg^-1(Power density is 800 W kg^-1).After10000 cycles of charge and discharge,the specific capacitance retention rate is 100%.