<p>This study focuses on the transformation of renewable agricultural waste (groundnut shell, sugarcane and corn cob) into eco-friendly porous activated carbon for use in renewable energy storage systems. The electrochemical behaviours of porous AC, synthesized through chemical activation methods, are examined in a 2.0&#xa0;M KOH electrolyte for supercapacitor applications. The activation and pyrolysis treatments are crucial for managing the microstructure of the AC, as well as enhancing the degree of graphitization and porosity. The activated carbon of corn cob exhibits a hierarchical porous structure, characterized by the largest pore volume of 0.85 cm³g^− 1 and the highest specific surface area of 937.44 m²g^− 1. The corn cob electrode demonstrates impressive capacitive performance of 496 Fg^− 1 at a current density of 1 Ag^− 1, showcasing superior rate characteristics and remarkable electrochemical stability. The two-electrode symmetric device demonstrated a specific capacitance of 161 Fg^− 1 at a current density of 1&#xa0;A g^− 1 in neutral aqueous gel electrolyte, achieving a high energy density of 21.2&#xa0;W h kg^− 1 attributed to an extended potential window. Corn cob carbon from agricultural waste presents a viable low-cost precursor for the development of supercapacitors.</p> Graphical Abstract <p></p>