Biowaste-derived activated carbon from Dillenia Indica fruit for sustainable high-performance supercapacitor electrodes

In this work, we report for the first time the use of activated carbon (AC) derived from Dillenia Indica waste fruit for supercapacitor applications, adopting a sustainable “waste-to-wealth” approach that transforms an underutilized biomass into a high-performance energy storage material. The waste fruit collected from the University campus is treated with KOH, FeCl₃, and H₂SO₄ separately and carbonized at 500 °C. The morphological analysis revealed a porous and rough surface for all three samples. The AC-K has the highest surface area of 625.42 m² g⁻¹, followed by 521.21 m² g⁻¹ and 141.80 m² g⁻¹ for AC-S and AC-F. The AC-K electrode demonstrated a superior specific capacitance of 618.9 F g⁻¹ at 3 A g⁻¹ and exceptional cyclic stability of 107% after 7000 cycles. It also exhibited a low bulk resistance of 4.8 Ω with a 0.02-s relaxation time. An asymmetric supercapacitor (ASC) device, employing MnFe₂O₄ as the positive electrode, operated within an extended potential window of 1.2 V.