Bitter Apple Pulp-Derived Porous Carbon with Rich Oxygen Functionalities for High-Performance Zinc-Ion Storage

Enhancement of the energy-power performance of aqueous zinc-ion hybrid supercapacitors (ZIHSCs) relies on the development of high-performance carbon-based cathode materials. Porous carbon derived from plant-based biomasses is particularly attractive due to its rich surface functionalities, high specific surface area (SSA), tunable porosity, cost-effectiveness, and environmental sustainability. Here, bitter apple pulp (BAP) is explored as a green precursor to realize a novel activated carbon for ZIHSC applications. KOH activation at 900 °C results in a carbon (BAPC1-900) with an exceptionally high SSA of 3254 m² g^-1, pore volume of 1.8 cm³ g^-1, and rich oxygen functionalities (C─O, C─OH) significantly outperforming the non-activated counterpart (64 m² g^-1, 0.016 cm³ g^-1). Raman spectroscopy reveals that the high SSA and oxygen content facilitate the simultaneous adsorption/desorption of Zn²⁺ and desorption/adsorption of SO₄ ^2- ions, ensuring an impressive Zn-ion energy density of 162 Wh kg^-1 within a potential window of 0-1.8 V in an aqueous ZnSO₄ electrolyte for the optimized BAPC1-900-based cathode. Besides, the electrode demonstrates excellent reversibility over 50 000 cycles, retaining over 95% capacity retention. This study highlights the efficacy of pulp-based biomass-derived porous carbon and KOH-activation chemistry in maximizing the zinc-ion storage potential of carbon-based cathodes for next-generation energy storage.