Synthesis of Physically Activated Carbons from Vitellaria paradoxa Shells for Supercapacitor Electrode Applications

This study investigates the processing of shea nut shells (SNSs), an abundant agricultural waste, into porous activated carbon for supercapacitor electrodes through a two-stage thermal treatment involving pyrolysis and physical activation with CO2 and steam. The aim was to develop sustainable, high-performance electrode materials while addressing waste management. Carbonization followed by activation yielded 16.5% (CO2) and 11.3% (steam) activation yields, with total yields of 4.3% and 2.9%, respectively. CO2 activation produced carbon (AC_CO2) with a specific surface area (SBET) of 1528 m2 g−1 and a total pore volume of 0.72 cm3 g−1, a graphitization degree (ID/IG = 1.0), and low charge transfer resistance (9.05 Ω), delivering a specific capacitance of 47.5 F g−1 at 0.5 A g−1, an energy density of 9.5 Wh kg−1 at 299 W kg−1, and a fast discharge time of 2.10 s, ideal for power-intensive applications. Steam activation yielded carbon (AC_H2O) with a higher specific surface area (1842 m2 g−1) and pore volume (1.57 cm3 g−1), achieving a superior specific capacitance of 102.2 F g−1 at 0.5 A g−1 and a power density of 204 W kg−1 at 9.2 Wh kg−1, suited for energy storage. AC_CO2 also exhibited exceptional cyclic stability (90% retention after 10,000 cycles). These findings demonstrate SNS-derived activated carbon as a versatile, eco-friendly material, with CO2 activation optimizing power delivery and steam activation enhancing energy capacity, offering tailored solutions for supercapacitor applications and sustainable waste utilization.