A sustainable and novel physical activation method for synthesizing Activated Carbon from coconut shell for supercapacitor electrodes

The present study describes a low-cost and sustainable method for synthesizing activated carbon (AC) from coconut shell biowaste. The synthesis consisted of two steps: carbonization followed by physical activation via water quenching. Coconut shells were first carbonized, and the resulting carbon powder was rapidly quenched in an enclosed mild-steel box, yielding hierarchically porous AC. The innovative quenching significantly influenced the material's structural and electrochemical properties. The optimized sample (QAC-1) delivered a high specific capacitance of 595 Fg -1 at 1 Ag -1 , an energy density of 82.6 Whkg -1 , and a power density of 52.6 Wkg -1 , evaluated in a three-electrode configuration using 4 M KOH electrolyte. The symmetric coin cell exhibited a specific capacitance of 148 Fg -1 , an energy density of 20.7 Whkg -1 , and a power density of 13.1 Wkg -1 , confirming its practical potential for energy storage applications. The results demonstrate the water-quenching activation route as a sustainable and efficient alternative to conventional chemical activation for developing AC electrodes for high-performance supercapacitors.