The capacitive characteristics of activated carbons—comparisons of the activation methods on the pore structure and effects of the pore structure and electrolyte on the capacitive performance

Fir wood-derived carbons activated with steam, KOH, and KOH + CO2 were found to exhibit the high-power, low ESR, and highly reversible characteristics between −0.1 and 0.9 V in aqueous electrolytes, which were demonstrated to be promising electrode materials for supercapacitors. The pore structure of these activated carbons was systematically characterized by the t-plot method based on N2 adsorption isotherms. Activated carbons prepared through the above three activation methods under different conditions (i.e., the gasification time of CO2, KOH/char ratio, and activation time of steam) generally showed excellent capacitive performance in aqueous media, mainly attributed to the development of both micropores and mesopores (with the meso-pore volume ratio, Vmeso/Vpore, ranging from 0.18 to 0.52). Scanning electron microscopic (SEM) photographs showed that the surface morphologies of honeycombed holes were found to depend on the activation methods. The average specific capacitance of the activated carbon with a combination of KOH etching and CO2 gasification (with gasification time of 15 min) reached 197 F g−1 between −0.1 and 0.9 V in H2SO4. The capacitive characteristics of steam- and KOH-activated carbons in NaNO3 and H2SO4 could be roughly estimated from the pore structure and BET surface area although the correlation may be only applicable for the fir wood-derived activated carbons.