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

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 (H 3 PO 4 ), and neutral (ZnCl 2 ) 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 m 2 /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. ZnCl 2 activation resulted high pore volume (1.0 cm 3 /g) with mixed micro/mesoporosity, achieving 224 F/g, while H 3 PO 4 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.