The electrooxidation of carbon monoxide on ruthenium modified Pt(110)

Abstract

The effect of adsorbed and incorporated (alloyed) sub-monolayers of Ru on Pt(110) on the electrooxidation of CO has been investigated using UHV-electrochemical transfer techniques. Overlayers of metal vapour deposited (MVD) Ru were characterised using LEED, XPS and LEISS. Both adsorbed and incorporated Ru overlayers were prepared, the alloy layers formed by annealing in the temperature range 400–1100 K. The reversible hydrogen adsorption characteristics of Pt(110) were suppressed in the cyclic voltammetry when Ru was adsorbed, incorporated in the top layer, or when absent from the top layer where there was a significant concentration of Ru in the second/third layers. Surfaces exhibited significant redox behaviour in the double layer region (0.3–0.6 V) of Pt(110) also when ruthenium was present in the adsorbed or top surface phases, but to a much lesser extent when incorporated in the second/third layer. CO electrooxidation, however, was promoted primarily by Ru incorporated in the top layer. Cycling to potentials of 1.2 V resulted in facile oxidative dissolution of adsorbed Ru, but only slow dissolution of Ru when incorporated in the top layer. The effect of cycling to 1.2 V on surfaces with negligible Ru in the top layer, but Ru in the second and third layers, was to modify the CO oxidation behaviour substantially, producing a significant coverage of a Pt(110)–Ru phase which promoted CO oxidation in a peak at 0.5 V.