In situ X-ray reflectivity and voltammetry study of Ru(0001) surface oxidation in electrolyte solutions

The electrochemical surface oxidation of Ru(0001) in acid solutions is limi ted to a one-electron process resulting in one monolayer oxygen uptake at p otentials below the onset of bulk oxidation at 1.35 V. In 1 M H2SO4, about (1)/(3) monolayer of bisulfate anions are coadsorbed with hydronium cations at low potentials. The spacing between the top two Ru layers is 2.13 Angst rom at 0.1 V and 2.20 Angstrom at 1.0 V, similar to those found in the gas phase for bare Ru (2.10 Angstrom) and for one monolayer of oxygen on Ru (2. 22 Angstrom), respectively. In contrast to Pt(lll) and Au(lll) surfaces, no place exchange is involved in the Ru(0001) surface oxidation. On the oxidi zed surface, the oxygen species stays on top of a smooth ruthenium surface causing a partial desorption of the bisulfate ions. The lack of subsurface oxygen on a Ru(0001) electrode is postulated to be the origin of its inacti vity for CO oxidation found in a separate study.