ELECTROOXIDATION OF H-2, CO AND H-2 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 mi xtures on a Pt75Re25 bulk alloy using surface preparation in a UHV cha mber and characterization by X-ray photoelectron spectroscopy (XPS). S putter-cleaned but not-annealed surfaces having the bulk composition w ere used. This alloy surface has unique properties for CO electrooxida tion: 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 t he 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 l ow potential, initiating at about 0.15 V, but only about 1/3 of the to tal amount of CO on the surface is oxidized at 0.15-0.4 V, the remaind er being oxidized at 0.6-0.8 V. The polarization curves for the oxidat ion 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 w ith the H-2/CO mixture the Pt sites remain fully covered (and thus dea ctivated) by COads. (C) 1998 Elsevier Science Ltd. All rights reserved .