Enhancing supercapacitor energy density via KMnO4-activated apple waste-derived carbon and aqueous trifluoroacetic acid electrolyte

Abstract

The conversion of biowaste into cost-effective porous carbons for electrode materials represents a promising strategy for sustainable energy storage. However, such materials often suffer from low specific capacitance and energy density. In this study, activated carbons (ACs) were synthesized from apple waste (AW) through chemical activation with potassium permanganate (KMnO<inf>4</inf>), followed by carbonization at 650–800 °C. The as-prepared AW AW-derived ACs were characterized and evaluated in both three-electrode and symmetric supercapacitor configurations across different electrolytes. The resulting AW-derived carbons exhibited a large specific surface area (>1000 m2 g−1) and demonstrated good electrochemical performance, with a specific capacitance of 360 F g−1 at 1 A g−1. The AW-based electrode using a trifluoroacetic acid (TFA) electrolyte exhibited a wide potential window (−0.5 V–1 V vs. Calomel), outperforming traditional electrolytes like KOH and H<inf>2</inf>SO<inf>4</inf>. The symmetric device had exceptional cycling stability, maintaining 93.5 % of its initial capacitance after 5000 cycles, and attained an energy density of 14.5 Wh kg−1 alongside a power density of 345.3 W kg−1. These results show the viability of biowaste-derived carbons as efficient, sustainable materials for next-generation supercapacitors.