In situ infrared study of carbon monoxide adsorbed onto commercial fuel-cell-grade carbon-supported platinum nanoparticles: Correlation with C-13 NMRresults

Carbon monoxide chemisorbed via methanol dissociative chemisorption onto co mmercial fuel-cell-grade carbon-supported nanoscale platinum electrocatalys ts has been investigated by in situ subtractively normalized interfacial Fo urier transform infrared reflectance spectroscopy (SNIFTIRS). The infrared stretching frequency and the Stark tuning rate (i.e., the slope of stretchi ng frequency vs electrode potential) show a strong dependence on platinum p article size. Five platinum particle sizes were analyzed; with average diam eters of 2.0, 2.5, 3.2, 3.9, and 8.8 nm. The infrared stretching frequency was found to increase with increasing particle size, while the Stark tuning rate was found to decrease. These results were correlated with those obtai ned by using solid-state C-13 NMR (Tong, Y. Y.; ct al. J, Am. Chem. Soc. 20 00, 122, 1123-29), showing that the particle-size-dependent variations in t he infrared stretching frequency and the Stark tuning rate are due to the v ariation in the 2 pi* back-donation from metal to CO caused by strong inter actions between platinum nanoparticles and the conductive carbon support.