The currents at 600 s of the chronoamperometric curves vs. tin coverage are plotted in Fig. 7.7 for the two Pt nanoparticles samples used. Initially, currents increase with the addition of tin on the surface. For (100)Pt nanoparticles, at coverage values higher than 0.3, it diminishes, whereas for the (111)Pt nanoparticles, it reaches the maximum and stable value for coverages above 0.5. At higher tin coverages, currents increase but very slightly. Again, the competitive catalytic effect of tin for oxidation of CO and the oxidation of ethanol to acetic acid explains this behavior.