Sustainable Green Route for Activated Carbon Synthesis from Biomass Waste for High-Performance Supercapacitors

Supercapacitors are high-power energy storage devices due to their charge storage capability and long cyclic stability. These devices rely on highly porous materials for electrodes providing a substantial surface area per mass, such as highly porous carbon. Developing high-performance porous carbon from biomass wastes such as waste-activated sludge and spent coffee is a sustainable way to reduce adverse environmental effects, contributing toward a carbon circular economy. In this study, hierarchically porous carbon with a high surface area of 1198 ± 60 m² g^-1 was synthesized through a green route. Sodium acetate was utilized as an environmentally friendly electrolyte. The long-term stability test at a high current density was conducted, providing valuable insights into the viability of sodium acetate as a robust electrolyte in supercapacitor application. The supercapacitor demonstrated an excellent cycle stability of 98.4% after 20,000 cycles at a current density of 10 A g^-1 in sodium acetate. Further assessment revealed dominant fast surface kinetics. Moreover, a maximum energy density of 15.9 Wh kg^-1 at 0.2 A g^-1 was achieved. By utilizing highly porous carbon in conjunction with a water-based binder, a substantial improvement of 76% in capacity with respect to a nonaqueous-based binder was demonstrated.