The influence of ruthenium and osmium spontaneous deposition on polycrystalline platinum in sulfuric acid was studied by conventional electrochemical techniques. The inhibition of the hydrogen adatom voltammetric profile by the foreign adatoms was used to calculate the degree of surface coverage of ruthenium, osmium, and a mixture of both metal ions front solutions of different composition. Methanol adsorption and oxidation were compared on bare platinum. platinum/ruthenium, platinum-Vosmium. and ternary compounds, considering the efficiency of methanol oxidation per hydrogen adatom displaced by the foreign metal on platinum. (c) 2005 Elsevier Inc. All rights reserved.