Carbon functionalized with sulfophenyl moieties provides an interesting way to understand the interdependence between the ionic species of the electrolyte and the electrode materials in carbon-based electrochemical capacitors. In situ measurements of the ionic resistivity of the electrolyte upon polarization revealed that sulfophenyl grafted groups can provide the ionic species required for the formation of a novel type of electrical double layer. This charge storage mechanism can potentially lead to the development of electrochemical capacitors with smaller amounts of electrolyte. (C) 2008 The Electrochemical Society.