A polyol reduction approach was employed to prepare carbon-supported PtOs/C electrocatalysts (PtOs-1/C was obtained via the co-reduction of H2PtCl6 and K2OsCl6 precursors and PtOs-2/C was obtained via a sequential deposition method in which Pt was deposited on the preformed Os nanoparticles). The home-made electrocatalysts were extensively characterized via transmission electron microscopy, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. The evaluation results of the catalytic activities obtained via cyclic voltammetry, CO stripping voltammetry, and chronoamperometry showed that the successively reduced PtOs-2/C out-performed PtOs-1/C in terms of specific/mass activity (528 mA mg(PtOs)(-1) and 0.98 mA cm(-2)) and CO tolerance in room temperature methanol electrooxidation reaction. The physical characteristics of the electrocatalysts correlated well with their electrochemical performances. The higher activity of PtOs-2/C was attributed to a combination of factors, such as a mix of nanoparticles (isolated Os, PtOs alloys or bimetallic nanoparticles), higher metallic Os content, and smaller particle sizes. (C) 2014 Elsevier B.V. All rights reserved.