Synergistic KOH–Urea Activation of Spent Coffee Grounds Into Hierarchically Porous Carbons for High‐Performance Supercapacitors

ABSTRACT Activated carbon derived from spent coffee grounds is synthesized by chemical activation with a defined KOH concentration and varying urea concentration. The effects of urea concentration on porosity development, electrical conductivity, and charge storage performance are systematically evaluated using SEM, Raman, XRD, BET, TEM, and electrochemical characterization methods. The sample activated with a 1:2:1 of carbon:KOH:urea ratio (ACKU1) exhibits the highest specific surface area ( S BET = 2805 m 2 g −1 ) and the most favorable pore structure, combining micro‐ and mesoporosity, whereas the sample without urea, 1:2 of carbon:KOH ratio, shows a much smaller specific surface area ( S BET = 1357 m 2 g −1 ). The electrochemical characterization of ACKU1 in the three‐electrode configuration reveals that it exhibits the highest specific capacitance ( C g = 270 F g −1 at 5 mV s −1 and C g = 293 F g −1 at 0.5 A g −1 ). Furthermore, the ACKU1 symmetric supercapacitor exhibits a C g cell of 54.2 F g −1 at 0.5 A g −1 , retaining 95% of its capacitance after 10,000 charge‐discharge cycles at 4 A g −1 , with energy and power densities of 7.5 Wh kg −1 and 58 kW kg −1 , respectively. These results highlight the synergistic effect of KOH and urea in producing high‐performance, sustainable carbon materials from biomass residues for energy storage applications.