The effect of adding various amounts of Rh to a carbon-supported Pt3Sn electrocatalyst for the electrooxidation of ethanol is evaluated by electrochemical methods and single potential alteration infrared reflectance spectroscopy (SPAIRS). This technique was used to identify intermediate species and the final products of ethanol electrooxidation and to track their evolution with the reaction potential. Rh addition to Pt3Sn/C was accomplished by impregnation, and this process resulted in Rh-modified catalysts of controlled composition. The Pt3Sn stoichiometry of the original sample was maintained after Rh addition, as demonstrated by analysis with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The selectivity for partially oxidized products, acetaldehyde and acetic acid is promoted on the Rh-PtSn/C electrocatalysts; however, the electrooxidation of ethanol to CO2 is only marginally promoted by the addition of Rh to PtSn/C. The higher production of acetic acid on the Rh-modified PtSn/C electrodes, rather than the production of CO2, is responsible for the higher current density recorded during the electrooxidation of ethanol on Rh-PtSn/C. (C) 2011 Elsevier B.V. All rights reserved.