A carbon supported Pt-Sn electrocatalyst in the Pt:Sn atomic ratio 75:25 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200 degrees C (Pt-Sn200) and 500 degrees C (Pt-Sn500). Thermal treatment at both temperatures gave rise to the formation of a predominant phase of cubic Pt3Sn and, to a lesser extent, a hexagonal PtSn phase. The amount of the hexagonal PtSn phase as well as the particle size increased with increasing thermal treatment temperature. The formation of some very large particles (size > 30 nm) was apparent in the Pt-Sn500 catalyst. The activity for the ethanol oxidation reaction (EOR) and the performance in a single direct ethanol fuel cell (DEFC) of the catalyst thermally treated at 200 degrees C were better than both the as-prepared catalyst and Pt75Sn25/C by ETEK. The higher activity for the EOR of the Pt-Sn200 sample was ascribed to the presence of the Pt3Sn phase and to cleaning effect of the thermal treatment at 200 degrees C. (c) 2006 Elsevier B.V. All rights reserved.