Abstract The adsorption of ethanol at a platinum electrode from a perchloric acid electrolytic solution has been investigated thoroughly, using infrared reflectance spectroscopy. Depending on the electrode potential, numerous infrared bands were detected, which could be attributed to various potential-dependent co-existing species. Among them, adsorbed CO, mainly linearly bonded to the surface, was detected unambiguously, giving rise to a strong absorption band at 2070 cm −1. when the potential range was chosen so that the CO species did not cover the whole surface, new bands appeared, due to various CH stretches together with a strong CO stretch at 1055 cm −1. Different models for the adsorbed species are discussed, including molecular adsorption of ethanol (evidence of weak infrared bands), adsorption of the ethoxy group [CH 3CH 2O] −, and the adsorbed ethylate species [CH 3CO] −.