Electrooxidation of H2, CO and H2/CO mixtures on a well-characterized Pt-Re bulk alloy electrode and comparison with other Pt binary alloys

We report new results for the electrooxidation of Hz, CO and H-2/CO mixtures on a Pt75Re25 bulk alloy using surface preparation in a UHV chamber and characterization by X-ray photoelectron spectroscopy (XPS). Sputter-cleaned but not-annealed surfaces having the bulk composition were used. This alloy surface has unique properties for CO electrooxidation: finite current densities below 0.2 V (rhe), a positive reaction order in CO partial pressure of +0.5, but an unusually high slope in the log i vs E curve, about 220;mV per decade. Anodic stripping of the irreversibly adsorbed CO on this surface also occurs at an unusually low potential, initiating at about 0.15 V, but only about 1/3 of the total amount of CO on the surface is oxidized at 0.15-0.4 V, the remainder being oxidized at 0.6-0.8 V. The polarization curves for the oxidation of H-2/CO mixtures containing 0.1-2% CO are, however, very Pt-like. It appears that the low-potential oxidation of both dissolved CO and adsorbed CO on this surface occurs exclusively at Re sites, so that with the H-2/CO mixture the Pt sites remain fully covered (and thus deactivated) by COads. (C) 1998 Elsevier Science Ltd. All rights reserved.