Effect of removing silica in rice husk for the preparation of activated carbon for supercapacitor applications

Abstract

Renewable biomass-derived activated carbons have attracted attentions for supercapacitor applications. Rice husk is a kind of abundant biomass, which has been studied for the preparation of hierarchical activated carbons. Rice husk is rich in silica. Silica in rice husk affects the formation of pore structure in the KOH activation process, which further affects the electrochemical performance of the resultant activated carbon for supercapacitors. In this paper, the effects of silica in rice husk on the activation process were investigated. When the silica in rice husk is not removed, KOH preferentially reacts with silica to produce silicate, which hinders the formation and enlargement of mesopores; the obtained activated carbon exhibits high microporous ratio, high specific area (up to 3263m2/g), high specific capacitance (315F/g at 0.5A/g), but poor rate capability (51.7% capacitance retention with increasing the current density from 0.5A/g to 20A/g). When the silica in rice husk is removed, the pores produced by the removal of silica are etched to mesopores in activation process; the obtained activated carbon exhibits high mesoporous ratio, relative high specific surface area of 2804m2/g and relative high capacitance of 278F/g at 0.5A/g with excellent rate capability (76.6% capacitance retention with increasing the current density from 0.5A/g to 20A/g).