KMnO4-assisted synthesis of hierarchical porous carbon with ultrahigh capacitance for supercapacitor

Porous carbon obtained by the conventional method (KOH/ZnCl2 chemical activation after carbonization) is faced with long ion diffusion distance, large ion diffusion resistance, which resulting in unsatisfactory electrochemical properties. Herein, we report a facile method to synthesize oxygen rich hierarchical porous carbon (OHPC) using corn stalks as carbon precursor and KMnO4 act as activator. Due to the high specific surface area, hierarchical porous framework and abundant oxygen functional groups, the optimized OHPC-600 displays a large specific capacitance of 464.7 F g(-1) at 0.5 A g(-1) and still maintains a large specific capacitance of 253.3 F g(-1) even at 50 A g(-1), suggesting superior rate property. More interestingly, the as-assembled symmetric supercapacitor shows a large energy density of 21.0 W h kg(-1) and good cycle stability (the retention rate is 89.8% after 10,000 cycles) in 1 M Na2SO4 aqueous electrolyte. This work provides an excellent renewable candidate and a practicable route design strategy for conversion of biowaste into excellent performance electrode material.