g-C3N4@Co3O4 Nanocomposites: Effect of Nitrogen Annealing for Symmetric Supercapacitor Applications

Abstract

g-C₃N₄ nanosheets were synthesized by thermal polymerization of melamine followed by N₂ annealing, while Co₃O₄ nanoparticles were prepared via co-precipitation method. Nanocomposites of g-C₃N₄@Co₃O₄, with different g-C₃N₄ contents, were obtained using an annealing-assisted co-precipitation method. X-ray diffraction results confirmed single-phase formation of both materials, and SEM investigations revealed sheet-like and granular morphologies for g-C₃N₄ and Co₃O₄, respectively. Electrochemical performance was evaluated in a three-electrode system with Ni foam-supported electrodes in 1 M KOH electrolyte. Cyclic voltammetry (5–100 mV/s) showed distinct redox peaks, while galvanostatic charge-discharge (4–14 A/g) exhibited pseudocapacitive behavior. At 4 A/g, specific capacitances are 290 F/g (g-C₃N₄), 718 F/g (Co₃O₄), 720 F/g (10-g-C₃N₄@Co₃O₄), and 853 F/g (20-g-C₃N₄@Co₃O₄). A symmetric supercapacitor device, using 20-g-C₃N₄@Co₃O₄, delivered ∼131 Wh/kg at ∼2666 W/kg and retained over 95% capacitance after 10,000 cycles, effectively powering a light-emitting diode (LED).