The reduction of oxygen on boron-doped diamond (BDD) and glassy carbon (GC) electrodes was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(2)mim][NTf2]. O-2 reduction at both electrodes was found to involve the 1e(-) reduction of oxygen to superoxide. The formation of superoxide was verified by repeating the oxygen reduction on BDD in the presence of benzoic acid, resulting in a shift from the 1e(-) reduction observed in the absence of benzoic acid to a 2e(-) reduction yielding the hydroperoxyl anion. The reduction of O-2 was found to be quasi-reversible on GC and irreversible on BDD. The significantly slower kinetics observed on the BDD electrode are likely due to the lower electronic density of states in BDD. (C) 2011 Elsevier B.V. All rights reserved.