A high-performance carbon derived from corn stover via microwave and slow pyrolysis for supercapacitors

•Corn stover biochar is cheap and firstly reported as activated carbon source for producing supercapacitors.•Corn stover biochar from slow pyrolysis progressively treated by KOH presents suitable pore size and shape distributions for supercapacitors.•High specific capacitance of 245.9 F g−1 was obtained by progressively activation of slow pyrolysis carbon.

Microwave and slow pyrolysis were conducted for converting corn stover to biochar. Chemical agents of sodium hydroxide and potassium hydroxide were used to progressively produce activated carbon. The pore structures and surface area of the samples were characterized by nitrogen adsorption/desorption at 77 K. The results demonstrated that higher specific surface areas of activated carbons were obtained by microwave pyrolysis combined with potassium hydroxide activation. However, electrochemical measurements showed that the slow pyrolysis biochar treated with 0.05 mol g−1 (potassium hydroxide/biochar) presented the best electrochemical properties. For this sample the specific capacitance was 245.9 F g−1 at a current density of 0.1 A g−1, and it can maintain a specific capacitance of 211.6 F g−1 even at the high current density of 1.0 A g−1.