The influence of poisoning of MoO x ePt catalyst by CO on the kinetics of H 2 oxidation reaction (HOR) at MoO x ePt electrode in 0.5 mol dm À3 HClO 4 saturated with H 2 containing 100 ppm CO, was examined on rotating disc electrode (RDE) at 25 C. MoO x ePt nanocatalyst prepared by the polyole method combined with MoO x post-deposition was supported on commercial carbon black, Vulcan XC-72. The MoO x ePt/C catalyst was characterized by TEM technique. The catalyst composition is very similar to the nominal one and post-deposited MoO x species block only a small fraction of the active Pt particle surface area. MoO x deposition on the carbon support can be ruled out from the EDAX results and from the low mobility of these oxides under used conditions. Based on TafeleHeyrovskyeVolmer mechanism the corresponding kinetic equations from a dualpathway model were derived to describe oxidation currentepotential behavior on RDE over entire potential range, at various CO coverages. The polarization RDE curves were fitted with derived polarization equations according to the proposed model. The fitting showed that the HOR proceeded most likely via the TafeleVolmer (TV) pathway. A very high electrocatalytic activity observed at MoO x ePt catalyst for the hydrogen oxidation reaction in the presence of 100 ppm CO is achieved through chemical surface reaction of adsorbed CO with Mo surface oxides.