ELECTROOXIDATION OF H-2 CO MIXTURES ON A WELL-CHARACTERIZED PT75MO25 ALLOY SURFACE/

The electrochemical oxidation of hydrogen in the presence of carbon mo noxide (0.05-2%) on a well-characterized Pt75Mo25 alloy surface was ex amined using the rotating disk electrode technique in 0.5 M H2SO4 at 3 33 K. The surface composition of this alloy determined by low-energy i on scattering after sputter cleaning and annealing in UHV was essentia lly the same as the bulk. The shapes of the polarization curves are qu alitatively similar to those for the Pt50Ru50 alloy examined previousl y: a high Tafel-slope (ca. 0.5 V/dec) region at low overpotential foll owed by a transition to a highly actively state where the current appr oaches the diffusion-limiting current; the potential where the transit ion to the active state occurs decreases with decreasing CO concentrat ion, and the current in the low-overpotential region is roughly invers e half-order in the CO partial pressure. The magnitude of the current in the low-overpotential region on the Pt75Mo25 alloy is nearly the sa me as on the Pt50Ru50 alloy, but the potential for the transition to t he active state is about 0.15 V higher. The magnitude of the current a t 0.05-0.1 V with H-2 containing 100 ppm CO is sufficiently high that Pt-Mo alloy is of technical interest as an anode catalyst for low-temp erature fuel cells fed with a reformed hydrocarbon fuel.