The co-eletrodeposition of Pt-Ru on carbon electrodes was carried out using a double-potential pulse method in electrolytes containing varying concentrations of RuCl(3) + H(2)PtCl(6) in an attempt to deposit highly dispersed Pt-Ru electrocatalyst with a controlled composition. The amounts of the Pt and Ru deposited on the electrodes were analyzed using an inductively coupled plasma atomic emission spectrometer (ICP-AES). The results revealed that the Pt loading on the substrates increases linearly with H(2)PtCl(6) concentrations in the bath while the Ru loading is not related to the concentration of RuCl(3), indicating that the reduction of Pt ions is the dominant reaction in the cathodic deposition of Pt-Ru clusters on the substrate. The Pt-Ru/C electrodes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optimum Ru content in the deposited Pt-Ru electrode for promoting the electro-oxidation of MeOH and adsorbed Co was found to be 25 atm%, by CO-stripping measurements in 0.5 M H(2)SO(4) and by cyclic voltammography in a solution comprising CH(3)OH (2.0 M) +0.5 M H(2)SO(4) (0.5 M). SEM results showed that the generation of nucleation sites and growth of the deposits progresses continuously on carbon substrate and already deposited Pt-Ru particles. The particle size and loading amount of the deposits was found to increase with an increase in the number of cycles of the repeating double-potential pulse. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.