Structural changes of a Ru(0001) surface under the influence of electrochemical reactions

The structural properties of Ru(0001) surfaces after various electrochemical treatments were investigated by ex-situ electron diffraction [low-energy electron diffraction (LEED)/reflection high-energy electron diffraction (RHEED)] and Auger spectroscopy experiments in conjunction with cyclic voltammetry. At potentials of 0, 0.3 and 0.9 V s. Ag/AgCl in HClO4 solution, (2 × 2), (3 × 1) and (1 × 1)-O phases, respectively, are formed whereby the Ru surface remains smooth. On the other hand, an electrode previously roughened by argon ion bombardment becomes smoother (as reflected by a substantial increase of the mean terrace widths) by repeated cycles of CO adsorption and stripping. This effect of “electrochemical annealing” is attributed to the enhanced mobility of Ru surface atoms under the influence of the strong interaction with the CO adsorbate. Longer polarization (>1 min) at potentials above 1.1 V in HClO4 leads to the epitaxial growth of RuO2 islands on the Ru electrode surface. Oxidation/reduction cycles between −0.2 and 0.85 V in HClO4, on the other hand, lead to the formation of rough surfaces exhibiting the (1 × 1)-O phase, while the same procedure in the presence of CO causes transformation into the (2 × 2)-phase (with smaller O concentration) and the above-mentioned smoothing effect.