Carbon supported Pt-Sn alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid and characterized by X-ray diffraction, high-resolution transmission electron microscopy, and X-ray absorption spectroscopy techniques. Their electrocatalytic activity for ethanol oxidation was compared with commercial Pt/C and Pt3Sn/C electrocatalysts and the differences discussed in terms of intrinsic properties of the materials. The activity for ethanol oxidation in linear sweep voltammetry experiments at room temperature is greatly enhanced, mainly at low potentials, on Pt-Sn (3:1) and Pt-Sn (2:1) catalysts prepared by the formic acid method, while only a slight improvement is observed on Pt-Sn (9:1) prepared with formic acid and on Pt3Sn from E-TEK. The commercial Pt3Sn catalyst showed a higher current performance as anode material in a direct ethanol fuel cell operating at 90 and 110 degrees C. At the low temperatures of the electrochemical experiments, the rate determining step (rds) of ethanol oxidation is the removal of CO-species, which is enhanced by the presence of Sn oxides. At the higher temperatures of the fuel cell, instead, the rds is the dissociative adsorption of ethanol and/or the oxidation of acetaldehyde to acetic acid: both these reactions are favored by an increase of the Sn content in the alloyed state. (c) 2006 The Electrochemical Society.