Nitrogen doped and hierarchically porous carbons derived from chitosan hydrogel via rapid microwave carbonization for high-performance supercapacitors

Abstract We have demonstrated a rapid and facile approach for preparing nitrogen doped and hierarchically porous carbons (NHPCs) using renewable chitosan as precursor via microwave carbonization in only 10 min. In microwave carbonization, ZnCl 2 impregnated in chitosan hydrogel serves as microwave absorber, chemical activation agent and porogen. The porous textures of NHPCs can be modulated by altering the concentration of ZnCl 2 in chitosan hydrogel. The optimal NHPC possesses a high nitrogen content of 9.4 wt% along with high specific surface area of 1170 m 2  g −1 , pore volume of 1.32 cm 3  g −1 and mesopore ratio of 78%. Electrochemical performance suggests that a high specific capacitance of 435 F g −1 is achieved at 0.2 A g −1 in three-electrode system with 6 M KOH as electrolyte. The as-assembled symmetrical supercapacitor exhibits a high energy density of 9.4 Wh kg −1 at the power density of 50 W kg −1 and remarkable retention ratio of 79.8% at a high power density of 2500 W kg −1 in 6 M KOH. Moreover, the supercapacitor displays a long cycle life with the capacitance retention of nearly 100% over 10000 cycles. Conversion of chitosan hydrogel to NHPCs via rapid microwave carbonization represents a promising route for preparing carbon materials for high-performance supercapacitors.