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 limited to a one-electron process resulting in one monolayer oxygen uptake at potentials 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 Angstrom 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 oxidized 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 inactivity for CO oxidation found in a separate study.