| Abstract
| - Using high-resolution transmission electron microscopy (TEM), infrared reflection−absorptionspectroscopy (IRAS), and electrochemical (EC) measurements, platinum nanoparticles ranging in size from1 to 30 nm are characterized and their catalytic activity for CO electrooxidation is evaluated. TEM analysisreveals that Pt crystallites are not perfect cubooctahedrons, and that large particles have “rougher” surfacesthan small particles, which have some fairly smooth (111) facets. The importance of “defect” sites for thecatalytic properties of nanoparticles is probed in IRAS experiments by monitoring how the vibrationalfrequencies of atop CO (νCO) as well as the concomitant development of dissolved CO2 are affected by thenumber of defects on the Pt nanoparticles. It is found that defects play a significant role in CO “clustering”on nanoparticles, causing CO to decrease/increase in local coverage, which yields to anomalous redshift/blueshift νCO frequency deviations from the normal Stark-tuning behavior. The observed deviations areaccompanied by CO2 production, which increases by increasing the number of defects on the nanoparticles,that is, 1 ≤ 2 < 5 ≪ 30 nm. We suggest that the catalytic activity for CO adlayer oxidation is predominantlyinfluenced by the ability of the surface to dissociate water and to form OHad on defect sites rather than byCO energetics. These results are complemented by chronoamperometric and rotating disk electrode (RDE)data. In contrast to CO stripping experiments, we found that in the backsweep of CO bulk oxidation, theactivity increases with decreasing particle size, that is, with increasing oxophilicity of the particles.
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