Waste-to-energy valorization of local Cydonia oblonga fruit waste into hierarchically porous activated carbon for high-performance electrochemical capacitor electrodes

The conversion of agricultural waste into high-value carbon materials represents an attractive strategy for simultaneously addressing biomass disposal and the growing demand for advanced energy-storage materials. In this study, locally sourced Cydonia oblonga (quince) fruit waste was precarbonized (QU) and converted to activated carbons through KOH-assisted chemical activation followed by controlled pyrolysis between 500 and 800 °C. The influence of activation temperature on physicochemical and electrochemical properties was systematically investigated using FTIR, SEM/EDX, XRD, BET, CV, GCD, and EIS. Increasing the activation temperature promoted the formation of a carbon-rich, hierarchically porous framework and improved ion-transport kinetics, with QU 800 exhibiting the most favorable performance. Based on electrochemical evaluation, QU 800 delivered 185.0 F g −1 at 0.5 A g −1 in 6 M KOH and exhibited lower resistance and superior rate capability, while electrochemical performance was consistently higher in KOH than in 1 M H 2 SO 4 . A symmetric QU 800 device operating over 0–1.0 V delivered a single-electrode capacitance of 95.2 F g −1 and retained approximately 80% capacitance at 2.0 A g −1 . The device achieved 2.29 Wh kg −1 at 208 W kg −1 and retained 92.6% of its initial capacitance after 5000 cycles. In support, BET revealed a high surface area of 1249 m 2 g −1 , micropore area of 888 m 2 g −1 , and a dominant pore width of 2.70 nm, confirming its micro-/mesoporous architecture. These findings demonstrate that quince fruit waste is a sustainable, inexpensive, and alternative abundant precursor for producing high-performance porous carbon electrodes and provide an effective waste-to-energy alternative material pathway source.