Redox-enhanced supercapacitors based on orange-peel-derived activated carbon with optimized redox-additive electrolyte
摘要
The design of green and high-performance supercapacitors requires optimization of both electrode materials and electrolyte chemistry. A systematic understanding of how redox additive concentration in highly concentrated electrolytes governs charge storage behaviour and device performance is still lacking. In this study, activated carbon derived from orange peel waste was employed as the electrode material, while the electrolyte was systematically engineered by introducing different amounts of p-phenylenediamine (PPD) (0–30 mg) into 5 mL of 6 M KOH solution. Physicochemical characterizations (BET, FESEM and Raman) confirmed the porous carbon structure with a high surface area of ~ 967.53 m2/g and partially graphitic domains suitable for double-layer charge storage. Electrochemical measurements demonstrated a strong dependence of capacitance on the concentration of the redox additive. The electrode tested in 6 M KOH containing 20 mg PPD delivered the highest performance, achieving a specific capacitance of 479.61 F g− 1 at 2 mV/s, with an energy density of 16.65 Wh kg− 1 at an average power density of 119.9 W kg− 1 in a symmetric two-electrode configuration. In contrast, both lower (≤ 15 mg) and higher (≥ 25 mg) PPD concentrations resulted in reduced performance, indicating an optimum redox contribution at intermediate loading. Long-term cycling confirmed 50% capacitance retention after 5000 charge-discharge cycles at 100 mV/s, which is comparable to other redox-additive-assisted aqueous supercapacitor systems where soluble redox species can introduce gradual degradation during extended cycling. These results establish that the synergistic interaction of orange-peel-derived carbon with an optimized redox-additive electrolyte can significantly boost supercapacitor performance, providing a sustainable and efficient route for advanced energy-storage devices.