Supercapacitor Capacitance Exhibits Oscillatory Behavior as a Function of Nanopore Size

Supercapacitors composed of slit-shaped micropores ranging in size from 0.67 to 1.8 nm in a room-temperature ionic liquid were studied to investigate the dependence of capacitance (C) on the pore size (d) using molecular dynamics simulations. The capacitance versus pore size (i.e., the C-d curve) was found to exhibit two peaks located at 0.7 and 1.4 nm, respectively. Specifically, as the pore shrinks from 1.0 to 0.7 nm, the capacitance of the micropore increases anomalously, in good agreement with experimental observations. We report herein that the second peak within 1.0 to 1.8 nm is a new feature of the C-d curve. Furthermore, by analogy to the wave interference, we demonstrate that the interference of two electrical double layers near each slit wall does not only explain the entire C-d curve, including the anomalous character, but also predicts the oscillatory behavior of C-d curve beyond 1.8 nm.