The anodic Pt-Ru-Ni/C and the Pt-Ru/C catalysts for potential application in direct methanol fuel cell (DMFC) were prepared by chemical reduction method. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out by using a glassy carbon working electrode covered with the catalyst powder in a solution of 0.5 mol L-1 CH3OH and 0.5 mol L-1 H2SO4 at 25 degrees C. EIS information discloses that the methanol electrooxidation on the Pt-Ru-Ni/C catalyst at various potentials shows different impedance behaviors. The mechanism and the rate-determining step of methanol electrooxidation are changed with increasing potential. Its rate-determining steps are the methanol dehydrogenation and the oxidation reaction of adsorbed intermediate COads and OHads in low (400-500 mV) and high (600-800 mV) potentials, respectively. The catalytic activity of the Pt-Ru-Ni/C catalyst is higher for methanol electrooxidation than that of the Pt-Ru/C catalyst. Its tolerance performance to CO formed as one of the intermediates of methanol dehydrogenation is also better than that of the Pt-Ru/C catalyst. (c) 2006 Elsevier B.V. All rights reserved.