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

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, ZnCl2 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 ZnCl2 in chitosan hydrogel. The optimal NHPC possesses a high nitrogen content of 9.4 wt% along with high specific surface area of 1170 m2 g−1, pore volume of 1.32 cm3 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.