The structure, growth and reactivity of electrodeposited Ru/Au(111) surfaces

In order to elucidate electronic effects on the oxidation of CO on small Ru clusters, we investigated this reaction on well defined Ru/Au(111) model s ystems via parallel in-situ STM studies of the structure and electrochemica l deposition of Ru on Au(111) in H2SO4 solution and cyclic voltammetry of C O monolayer oxidation on these surfaces. The Ru deposit consists of nanosca le islands, which coalesce with increasing coverage. The Ru saturation cove rage depends on the deposition potential, resulting in Ru submonolayer (> 0 .1 V), (defective) monolayer (greater than or equal to - 0.1 V), and multil ayer films (< - 0.1 V). At potentials > 0.6 V irreversible formation of Ru oxide/hydroxide species is observed, which can be partly reduced in the ran ge 0.4 to 0.0 V. CO stripping commences at approximate to0.1 V and occurs o ver a broad potential range. From the stripping charge a local CO coverage on the Ru monolayer islands of 0.7 ML was estimated. The observed influence of the morphology of the Ru deposit on the CO stripping voltammetry is exp lained by (local) variations in the CO adsorption energy due to electronic modifications of the Ru film. (C) 2001 Elsevier Science B.V. All rights res erved.