The study investigates the synthesis and electrochemical performance of Co3O4-g-C3N4 nanocomposites using the hydrothermal method. The weight percentage of g-C3N4 nanoparticles significantly influences the electrochemical performance of the composite. An electrode with 150 mg of g-C3N4 nanoparticles exhibited remarkable electrochemical performance, achieving a specific capacitance of 198 F/g in an aqueous electrolyte. The optimized electrode, combined with activated carbon and a polyvinyl alcohol gel with potassium hydroxide, was used to fabricate an asymmetric supercapacitor. The device demonstrated excellent energy storage capacity, with high energy density (11.86 Wh/kg) and power density (701 W/kg) at a current density of 5 mA/cm². The supercapacitor retained its capacity over 6,000 galvanostatic charge-discharge cycles, with minimal increase in series resistance and high columbic efficiency (99.97%). The results indicate that the Co3O4-g-C3N4 nanocomposite is a promising material for energy storage applications.The study investigates the synthesis and electrochemical performance of Co3O4-g-C3N4 nanocomposites using the hydrothermal method. The weight percentage of g-C3N4 nanoparticles significantly influences the electrochemical performance of the composite. An electrode with 150 mg of g-C3N4 nanoparticles exhibited remarkable electrochemical performance, achieving a specific capacitance of 198 F/g in an aqueous electrolyte. The optimized electrode, combined with activated carbon and a polyvinyl alcohol gel with potassium hydroxide, was used to fabricate an asymmetric supercapacitor. The device demonstrated excellent energy storage capacity, with high energy density (11.86 Wh/kg) and power density (701 W/kg) at a current density of 5 mA/cm². The supercapacitor retained its capacity over 6,000 galvanostatic charge-discharge cycles, with minimal increase in series resistance and high columbic efficiency (99.97%). The results indicate that the Co3O4-g-C3N4 nanocomposite is a promising material for energy storage applications.