The effects of two unsaturated hydrocarbons, C3H6 and C10H8, on the oxygen reduction reaction (ORR) at Pt/C electrodes were investigated using the rotating ring disk electrode (RRDE) method. Cyclic voltammetry (CV) measurements were performed to evaluate the electrochemical surface area losses. C3H6 coverage is found to be mass transfer and potential dependent. C10H8 is found to maintain high coverage across the whole potential range, independent of the mass transfer rates. The ORR kinetics is influenced by the hydrocarbon adsorption effect, and the mass activity decreases to lower values accordingly. The H2O2 collected on the ring also increases greatly due to the influence of the two contaminants, and this increase corresponds to an increase in the 2-electron O-2 reduction route. The increase in H2O2 production and decrease in the charge transfer number is ascribed to spatial limitations arising from the adsorption of the contaminants because the rupture of the O-O bond requires two adjacent Pt active sites. The ring current collected on the C3H6-contaminated Pt surface differs greatly for the forward and reverse scans due to the interference of C3H6 reduction and the change in electrode coverage. Increases in the Tafel slopes are observed to a different extent for the different contaminants, which indicates that electron transfer for ORR at the electrode surface is manipulated by contaminant adsorption. A nearly full recovery was achieved for the C3H6-contaminated surface, indicating that C3H6 can be sufficiently removed by stop injection in in situ cell tests. Only partial recovery was obtained for C10H8-contaminated electrodes, with the unrecovered performance due to the high affinity of C10H8 for the Pt/C electrode, which requires high potential for oxidative removal. (C) 2014 Elsevier Ltd. All rights reserved.