The electrocatalytic oxidation of ethanol in proton exchange membrane fuel cells is of great interest. The oxidation of ethanol however is met with a number of challenges that result from activating the C-C bond. First-principle density functional theoretical calculations were carried out herein to investigate the oxidation of ethanol over Pt and different Pt-Mo alloy surfaces. The reaction energies and activation barriers for the main pathways involved in the complete oxidation to CO 2 were calculated to establish potential energy profiles and possible rate-limiting steps. The sluggishness of the carbon-carbon (C-C) cleavage reaction and the oxidative removal of poisonous single carbon (C1) intermediates, especially CO, have been probed in detail. It was found that by alloying Pt with Mo, the O-H bond could be selectively activated. The oxidative removal of poisonous C1 intermediates is promoted by adding Mo to the surface as well as to the subsurface. The computational results were calculated for a range of different Pt-Mo alloy surface ensembles and compared with results reported in the literature.