Green synthesis of high-performance supercapacitor electrode materials from agricultural corncob waste by mild potassium hydroxide soaking and a one-step carbonization

Porous carbons derived from waste biomass are distinguished active materials for developing high performance, low-cost and environmental-friendly electrochemical double layer supercapacitors. However, efficient control over the microstructure of biomass activated carbons to achieve high capacitor performance still remains a challenge. Herein, agricultural waste biomass corncobs that were simply chopped were demonstrated to be effectively activated via facile KOH solution soaking at room temperature prior to a one-step carbonization process. The electrode material showed a high capacity of 394.9 F g(-1), at a current density of 1 A g(-1) in a three-electrode system in a 6 M KOH aqueous electrolyte solution. Corncobs, carbonized at 750 degrees C, were further assembled into coin-type symmetrical devices, and displayed a high energy density of 8.9 W h kg(-1), achieving outstanding cycling stability (99 % life time retention after 10,000 cycles). Through this green and energy-efficient process, the natural hierarchical nature of the corncob was fully utilized and partly preserved, and the obtained porous carbon has high degree of graphitization and effective specific surface area with improved electrochemical performance. These porous carbons are expected to become ideal active materials for high-performance supercapacitors. The mild KOH soaking coupled with the one-step carbonization method developed herein is considered as a facile way to up-scale production of functional carbon materials from waste biomass.