Increasing surface area via Urea-KOH activation for enhanced supercapacitor electrodes

• Synergistic KOH + urea activation enhances electrochemical performance. • Urea addition increases the surface area with hierarchical micro- and mesopores. • The best sample achieves 329 F g-1 at 0.5 A g-1 in three-electrode configuration. • The symmetric supercapacitor retains 105% of its initial capacitance (50.7 F g-1). This study presents the synthesis and characterization of activated carbons derived from corn husks, using KOH as an activating agent and urea as synergistic contributor to the enhancement of the specific surface area. The chemical impregnation method, followed by pyrolysis, was used to improve surface contact with the electrolyte. Physicochemical characterizations, including SEM, XPS, TEM, XRD, Raman, and BET, confirmed increased surface area and disorder after urea incorporation. The CHKU2 sample, impregnated with KOH and urea (1:2:2 ratio of carbon:KOH:urea), showed the highest specific surface area (2661 m² g -1 ) and a balanced micro/mesoporous structure. Electrochemical characterization in three- and two-electrode configurations revealed significant improvements in capacitance and conductivity for urea-impregnated ACs. CHKU2 achieved 329 F g -1 at 0.5 A g -1 and retained 255 F g -1 at 10 A g -1 , with 0.37 S cm -1 conductivity. Dunn’s analysis indicated that the capacitance in CHKU2 is predominantly driven by electric double-layer capacitance. Symmetric cell tests confirmed its superior energy and power densities and good cycling stability, retaining 105% of its capacitance after 3000 cycles at 2 A g -1 . These findings demonstrate that corn husk-derived ACs, optimized via urea-assisted activation, offer a promising route to sustainable and efficient energy storage.