Synergistic Effects of Co‐Activation Agents on an MnO–Activated Carbon Composite Electrode for Electrochemical Supercapacitors

ABSTRACT Carbon materials synthesized from biomass are promising candidates for supercapacitor electrodes. Various activation processes for developing carbon materials with high surface areas have been investigated. Here, a manganese monoxide (MnO)–porous‐activated carbon (AC) composite was fabricated via the chemical activation of coconut shell by the co‐activation agents KOH and KMnO 4 . Besides influencing the physical properties, such as the specific surface area, pore size, and MnO particle size, co‐activation significantly influenced the chemical properties, such as the surface functional groups. These alterations in physical and chemical properties affected the electrochemical performance of a supercapacitor using the composite as an electrode. The fabricated MnO–AC samples exhibited unstable long‐term cycling properties due to MnO's structural instability during redox reactions. The samples fabricated by activation and in situ MnO formation using a co‐activation‐agent solution showed a better initial capacity and long‐term stability than those activated and metal oxide‐loaded exclusively with a KMnO 4 aqueous solution. This enhanced performance is attributable to the formation of MnO nanoparticles on AC with a large specific surface area owing to a microporous carbon structure and carbon vacancy creation within the carbon framework owing to sufficient K + ‐ion availability.