g‐C ₃ N ₄ @Co ₃ O ₄ Nanocomposites: Effect of Nitrogen Annealing for Symmetric Supercapacitor Applications

ABSTRACT g‐C 3 N 4 nanosheets were synthesized by thermal polymerization of melamine followed by N 2 annealing, while Co 3 O 4 nanoparticles were prepared via co‐precipitation method. Nanocomposites of g‐C 3 N 4 @Co 3 O 4 , with different g‐C 3 N 4 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‐C 3 N 4 and Co 3 O 4 , 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‐C 3 N 4 ), 718 F/g (Co 3 O 4 ), 720 F/g (10‐g‐C 3 N 4 @Co 3 O 4 ), and 853 F/g (20‐g‐C 3 N 4 @Co 3 O 4 ). A symmetric supercapacitor device, using 20‐g‐C 3 N 4 @Co 3 O 4 , delivered ∼131 Wh/kg at ∼2666 W/kg and retained over 95% capacitance after 10,000 cycles, effectively powering a light‐emitting diode (LED).