The electrocatalytic behaviour of PtRu/C is modified by the addition of nickel. Results from X-ray photoelectron spectroscopy reveal that the amount of surface Ni is less than the expected from the bulk stoichiometry, especially in the used samples where Ni was not detected. The oxidation state of Ni plays a key role on the catalytic performance of PtRuNi/C electrocatalysts, particularly in the CO oxidation reaction due to the development of Pt-Ni electronic interaction. The influence of the nature of the carbon support was also evaluated. Electrocatalysts prepared on a carbon-modified substrate displayed higher activities in the methanol oxidation reaction than those prepared over non-treated carbon. For the Ni-containing samples, the preparation route determines the degree of interaction between Pt and Ni of the different samples and hence their catalytic performance. (c) 2006 Elsevier B.V. All rights reserved.