The ac response of polyaniline thin films on platinum electrodes was measured at different dc potentials during the CO2 reduction in methanol/LiClO4 electrolyte with a small amount of 0.5 M H2SO4. The complex capacitance curves were simulated and the data obtained were used to calculate kinetic parameters, based on the assumption that the thermodynamic potential E-0(.) is in the region of -0.2- -0.1 V versus saturated calomel electrode (SCE). With E-0 = -0.2 V versus SCE and beta = 0.6, a j(0) value of ca. 10(-4) A cm(-2) was found for the electroreduction of CO2 on the polyaniline electrode. (C) 2003 Elsevier Science Ltd. All rights reserved.