Electrode processes at graphite and hard carbon have been investigated in ionic liquid of 1,3-substituted imidazolium salt with and without organic solvents as a preliminary study for their application to energy storage devices. Acetonitrile solutions of imidazolium salts significantly promote a redox reaction, possibly assigned to reversible insertion and removal of imidazolium cation, for the graphite electrode. This redox reaction is sensitive to the kind of solvent, the bulk structure of graphite, and the chemical structure of cation. The intrinsic reversibility of this reaction is attractive for the use in electrochemical energy storage systems, while parasitic reduction process must be inhibited. (C) 2012 Elsevier B.V. All rights reserved.