Utilization of CO2 activated litchi seed biochar for the fabrication of supercapacitor electrodes

Biochar prepared from litchi seeds was investigated for the fabrication of supercapacitor electrodes. The specific capacitance of 190 F g−1 at 1 A g−1 current density was achieved in symmetric supercapacitor fabricated using biochar obtained at 700 °C. Upon activation using CO2, the capacitance was significantly enhanced, reaching up to 493 F g−1. Moreover, the charge-discharge cyclic stability of the activated biochar supercapacitor was well maintained with capacitance retention above 90% after 10,000 charge-discharge cycles in 1 M H2SO4 electrolyte. The energy and power density of the aqueous symmetric supercapacitor prepared using activated biochar were 24.6 Wh kg−1 and 0.6 kW kg−1, respectively. Physicochemical analysis of activated biochar using BET, XRD, Raman, TEM, and XPS revealed a high surface area, hierarchical porous structure, and heteroatom rich functionalities responsible for its excellent charge storage behaviour.