Correlation between capacitance and porosity in microporous carbon monoliths

Specific capacitance of carbons in aqueous KOH electrolyte seems to have two contributions, a double-layer capacitance and a pseudocapacitance. Moreover, the specific capacitance increases as the specific surface area does. Here, we report that the pseudocapacitance is associated with the K+ ion and the double-layer capacitance with both K+ and OH- ions. The former ion dominates the capacitance of a real two-electrode supercapacitor. Two microporous carbon monoliths with surface areas similar for micropores below 0.63 nm but different for larger micropores are chosen. There is a correlation between the double-layer capacitance due to those ions and the surface areas due to micropores with sizes above a certain value. It provides information on the size of those ions as they are electroadsorbed at the double layer. The dielectric permittivity associated with the K+ and OH - ion is discussed in relation to the confinement of these electroadsorbed ions in the micropores. © 2014 American Chemical Society.Financial support through the projects MAT2011-25198 and MP 1004 is gratefully acknowledged. V.B. thanks MINECO for R&C contract.Peer Reviewe