Rice husk derived capacitive carbon prepared by one-step molten salt carbonization for supercapacitors

Abstract

High-performance carbonaceous electrode materials for supercapacitor were prepared via a simple molten salt carbonization of rice husk in molten eutectic Na2CO3-K2CO3 at 850 °C. Carbon material with carbonization time of 12 h exhibits an ideal capacitive property, benefitting from the synergistic effect of hierarchically porous structure with high SSA and mesopore/micropore ratio, oxygen doping and excellent electrical conductivity. In a three-electrode system, it exhibits specific capacitance of 117.0–163.1 F g−1 at current density of 20–0.2 A g−1 with rate performance of 72 % capacitance retention, energy (power) density of 22.6 Wh kg−1 (99.9 W kg−1) at 0.2 A g−1 and power (energy) density of 9.5 kW kg−1 (14.5 Wh kg−1) at 20 A g−1. When the carbon material was assembled into a symmetrical supercapacitor, it exhibits specific capacitance of 103.4–148.3 F g−1 at current density of 20–0.2 A g−1 with rate performance of 70 % capacitance retention, energy (power) density of 5.1 Wh kg−1 (49.9 W kg−1) at 0.2 A g−1 and power (energy) density of 4.3 kW kg−1 (2.7 Wh kg−1) at 20 A g−1, as well as excellent cyclic stability with 85 % capacitance retention and the coulombic efficiency close to 100 % after 6000 charge-discharge cycles at 1 A g−1. The dependence of hierarchically porous structure on capacitive performance is also discussed.