Effect of KOH impregnation conditions on the porosity and capacitance of coconut fiber–derived activated carbons

Abstract

The effect of the KOH impregnation with different experimental conditions on activated carbon derived from coconut fibers was studied. The molarity of the KOH solution, the temperature, and the pressure used during the impregnation process of the porogenic agent were varied. The synthesized activated carbons showed the formation of hierarchical porosity with a high microporosity and specific surface areas ranging from S_BET = 499 m² g⁻¹ up to S_BET = 1752 m² g⁻¹, maintaining a graphitic structure and showing good electrical conductivity despite the high porosity. The sample impregnated with the maximum molarity (6 M KOH) and treated by the hydrothermal method at 150 °C (6MhT) showed the highest specific surface area (S_BET = 1752 m² g⁻¹) and the highest gravimetric capacitance (236 F g⁻¹), while the samples impregnated with lower molarities or impregnated in room conditions showed smaller specific surface areas and lower gravimetric capacitance. Hence, a symmetrical supercapacitor (SC) was fabricated with the 6MhT sample, comparing its performance with a SC fabricated with a commercial activated carbon, both with similar specific surface area (XFP01, S_BET = 1800 ± 100 m² g⁻¹). It was observed that the 6MhT sample presents larger energy and power densities than the commercial activated carbon (6MhT, P_D = 41.6 kW kg⁻¹, E_D = 16.7 Wh kg⁻¹; XFP01 P_D = 32.6 kW kg⁻¹, E_D = 16.2 Wh kg⁻¹).