Hierarchical Biocarbons with Controlled Micropores and Mesopores Derived from Kapok Fruit Peels for High-Performance Supercapacitor Electrodes

Abstract

Hierarchical microporous and mesoporous biocarbons derived from kapok fruit peels were prepared by a two-step method. First, a carbon precursor was prepared from the kapok fruit peels by precarbonization at lower temperature, and then it was activated at a higher temperature with KOH as an activation agent. Micropores and mesopores of the biocarbons were controlled by adjusting the mass ratio of KOH to the carbon precursor. Especially, the biocarbon AC4 that was prepared with a KOH/carbon precursor mass ratio of 4:1 possesses a sheet structure with hierarchical pores, a high specific surface area of 1257.6 m2/g, and a pore volume of 1.05 cm3/g. The AC4 biocarbon exhibits a maximum specific capacitance of 332.3 F/g at a current density of 1 A/g, and it still remains a specific capacitance as high as 180 F/g with increasing the current density up to 50 A/g. The AC4 electrode material also possesses an excellent life span after 10 000 cycles. On the basis of these obtained results, the relationship between the electrochemical performance and the structure of the biocarbon was discussed.