Kitchen waste-derived activated carbon from Murraya koenigii seeds as an electrode material for supercapacitors

The growing demand for sustainable, high-performance energy storage systems has spurred intensive research into biomass-derived carbon materials as environmentally friendly electrode candidates for supercapacitors. In this study, Murraya koenigii (curry plant) seed powder was employed as a novel biomass precursor for the synthesis of activated carbon in the presence of ferrous chloride (FeCl₂) as an activating agent (MKAC). The FeCl₂-mediated activation, followed by pyrolysis at 900 °C under an inert atmosphere, facilitated the formation of a hierarchically porous carbon structure rich in electrochemically active sites. Comprehensive structural and chemical characterisation via BET analysis, FTIR, XRD, SEM-EDAX, and Raman spectroscopy confirmed the formation of partially graphitised carbon with an enhanced surface area of approximately 1605.5 m² g^- 1. Symmetric supercapacitor cells were assembled using a conductive polymer gel electrolyte based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). Electrochemical evaluation demonstrated that FeCl₂ activation synergistically contributed to low internal resistance and a superior specific capacitance of 221.3 F g^- 1 at a current density of 0.5 mA cm^- 2, with an energy density of 15.37 Wh kg^- 1 at a power density of 217 W kg^- 1. The fabricated symmetric EDLC device retains ~ 88% of its initial capacitance after 10,000 consecutive charge-discharge cycles with a Coulombic efficiency of ~ 88%, confirming the long-term electrochemical stability and charge reversibility of the MKAC electrode. This green and economically viable approach not only adds value to agricultural waste but also offers a viable pathway toward developing advanced electrode materials for sustainable supercapacitor applications.