Polarization-induced distortion of ions in the pores of carbon electrodes for electrochemical capacitors

This paper reports the effect of confining ionic species of the electrolyte inside the porosity of carbon electrodes during the performance of electrochemical capacitors. Solvent-free ionic liquids and a conventional organic medium were used as electrolytes, while two series of carbons with controlled pore sizes - one of them obtained from nanocasting procedure - were used as electrode materials. Our results demonstrate that under the effect of the electric field applied during the polarization of the electrodes, desolvated ions enter distorted in pores smaller than their limiting size. In such conditions of confinement, it is demonstrated that the traditional concept of an electric double-layer formed by solvated ions adsorbed on both pore walls does not apply for sub-nanometer size pores. (C) 2009 Elsevier Ltd. All rights reserved.