Activated Carbon Framework From Carbon Nanospheres as Supercapacitor: Comparative Effects of Acidic, Alkaline, and...

Supercapacitors offer rapid charge-discharge rates and long cycle life, but their performance strongly depends on electrode design. Herein, carbon nanospheres (CNS) were synthesized by a hydrothermal method and activated using alkaline (KOH), acidic (H₃PO₄), and neutral (ZnCl₂) agents to study the effect of activation chemistry. The activating agents produced distinct pore structures and surface functionalities. KOH activation that proceeds through a strong redox process and intercalation-driven etching chemistry created a high surface area (1908 m²/g) with abundant microporosity and high electrical conductivity (1.5 × 10^-2 S/cm). This led to a remarkable specific capacitance of 603 F/g at 1 mV/s in three-electrode configuration and 82% retention after 10,000 cycles. ZnCl₂ activation resulted high pore volume (1.0 cm³/g) with mixed micro/mesoporosity, achieving 224 F/g, while H₃PO₄ activation introduced oxygenated groups and mesopores, yielding 219 F/g with the best rate capability (69.8%). Electrochemical impedance spectroscopy confirmed the lowest resistance for KOH-activated CNS, consistent with its superior double-layer capacitance. This study demonstrates that activation strategy governs pore structure, surface chemistry, and charge storage, providing guidelines for tailoring nanocarbon electrodes for high-performance supercapacitors.