Tunable Na-doped MnO₂ Nanowires/g-C₃N₄ Composites for Efficient Energy Storage in Supercapacitors

Objectives This study aims to enhance the electrochemical performance of MnO₂-based supercapacitor electrodes by combining sodium (Na + ) doping with graphitic carbon nitride (g-C₃N₄). The goal is to improve electrical conductivity, structural stability, ion-diffusion behavior, specific capacitance, and long-term cycling efficiency. Material and Methods Na-doped MnO₂ nanowires were synthesized using a hydrothermal method at 180 °C for 16 hours. g-C₃N₄ sheets were prepared by thermal annealing of melamine followed by ultrasonication. The Na-MnO₂/g-C₃N₄ composite was formed by sonicating Na-MnO₂ with exfoliated g-C₃N₄. Structural and morphological analyses were performed using XRD, FTIR, SEM, EDX, and BET. Electrochemical performance was evaluated in 1 M Na₂SO₄ electrolyte using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). Results The Na-MnO₂/g-C₃N₄ composite exhibited significantly improved electrochemical properties, achieving a specific capacitance of 953 F g − 1 at 1 A g − 1 . It retained 89.83% of its capacitance at 9 A g − 1 and demonstrated excellent cycling stability with 96.2% capacitance retention after 6000 cycles at 12 A g − 1 . EIS analysis showed reduced charge-transfer resistance and enhanced ionic/electronic conductivity compared with pristine MnO₂ and Na-MnO₂. Conclusion The synergistic integration of Na + doping and g-C₃N₄ reinforcement significantly enhances the structural integrity and charge-storage capability of MnO₂ nanowires. The resulting composite shows high capacitance, strong rate capability, and outstanding long-term cycling stability, confirming its potential as a promising electrode material for next-generation supercapacitors.