The oxygen-reduction kinetics on Vulcan XC-72 carbon-supported nanosized Pt-Cr alloy catalysts were studied using the porous rotating disk electrode technique in pure and methanol-containing electrolytes. The Vulcan XC-72 carbon-supported Pt-Cr alloy catalysts with different Pt/Cr atomic ratios were prepared via a Pt-carbonyl route. X-ray diffraction data showed that the as-prepared nanosized Pt-Cr alloy catalysts mainly have the disordered structures (solid solution) and that the lattice parameter decreases with the increase in Cr content. Energy-dispersive X-ray analysis indicated that the catalyst compositions are nearly the same as the nominal ones. The obtained Pt-Cr alloy nanoparticles are well dispersed on the surface of carbon with a relatively narrow size distribution. For example, the mean particle size of the as-prepared Pt-Cr (1:1)/C catalyst with 20 wt % metal loading is about 3.1 nm in diameter with a standard deviation of 1.3 nm, and the particle size distribution is relatively narrow. As compared to the Pt/C catalyst, the bimetallic alloy catalysts with the different Pt/Cr atomic ratios showed slightly enhanced mass activity (MA) for the oxygen reduction reaction (ORR); however, the significant enhancement in the specific activity (SA) by a factor of about 1.5-3 for the ORR was found on the Pt-Cr alloy catalysts in pure HClO 4 solution. This enhancement in SA of the Pt-based catalysts was correlated to the changes in the lattice parameter and Pt/Cr surface composition. Moreover, the bimetallic Pt-Cr alloy catalysts with the different Pt/Cr atomic ratios exhibited much higher methanol tolerance during the ORR than the Pt/C catalyst. Furthermore, the catalytic activity for methanol oxidation on the Pt-Cr alloy catalysts was much lower than that on the Pt/C catalyst. Thus, the high methanol tolerance of the carbon-supported Pt-Cr alloy catalysts for the ORR can be ascribed to the weak adsorption of methanol induced by the presence of Cr atoms in the alloys.

Carbon monoxide chemisorbed via methanol dissociative chemisorption onto commercial fuel-cell-grade carbonsupported nanoscale platinum electrocatalysts has been investigated by in situ subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy (SNIFTIRS). The infrared stretching frequency and the Stark tuning rate (i.e., the slope of stretching frequency vs electrode potential) show a strong dependence on platinum particle size. Five platinum particle sizes were analyzed; with average diameters 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 obtained by using solid-state 13 C NMR et al. J. Am. Chem. Soc. 2000, 122, 1123, showing that the particlesize-dependent variations in the infrared stretching frequency and the Stark tuning rate are due to the variation in the 2π* back-donation from metal to CO caused by strong interactions between platinum nanoparticles and the conductive carbon support.