Carbon electrodes have been modified with 2-nitro-1-naphthol with the aim of producing composite supercapacitor electrodes, which make use of both the electric double layer (EDL) capacitance of high surface area carbon and the redox capacity (pseudocapacitance) of the organic compound. In situ FTIR and cyclic voltammetric data confirm literature reports of the reduction of 2-nitro-1-naphthol to 2-amino-1-naphthol and the subsequent oxidation of the o-aminonaphthol to the corresponding o-naphthaquinoneimine in aqueous acidic media. The measurements also show that the quinoneimine is not stable and hydrolized in sulphuric acid electrolyte to 1,2-naphthaquinone. The chemically highly reversible o-naphthaquinone/o-naphthahydroquinone couple remains immobilized on the carbon electrodes during redox cycling. The organic redox couple contributes a capacity of 35mAhg−1 of the bare carbon to the overall charge storage capability of the composite electrode. Surprisingly, it does not affect the capacitance of the electric double layer of the carbon. During 1000charge/discharge cycles, the pseudocapacitance decreases by less than 20% in a normal large-volume electrochemical cell. Electrochemical impedance measurements show that the full capacity of the electrode is accessible at frequencies below 0.1Hz.