Modification of a rice husk-based activated carbon by thermal treatment and its effect on its electrochemical performance as a supercapacitor electrode

A hierarchically porous rice husk-based activated carbon, which had been prepared by a combined method (carbonization, NaOH-leaching and KOH activation), has a high specific capacitance and power density as a supercapacitor electrode in aqueous or organic electrolytes. It was subjected to a simple thermal treatment at 800℃ for 1 h to modify its microstructure and electrochemical performance. Results indicate that its original hierarchical pore structure is retained and the number of oxygen-containing functional groups is reduced after this modification. Mesopores developed and the volume ratio of mesopores to total pores increased from 25.62 to 33.62%. The modified activated carbon showed a higher specific capacitance of 147 F g^-1 than the unmodified one (116 F g^-1) at a current density of 0.5 A g^-1. The voltage of the modified activated carbon was 84.5% of its initial value after self-discharge for 24 h, which is higher than that (75.2%) of the unmodified one. The capacitance retention of the modified carbon was 92% while that of the unmodified one was 85% after 10 000 galvanostatic charge/discharge cycles at 1 A g^-1, indicating the better cycling stability of the former.