Temperature-induced transformation of electrochemically formed hydrous RuO2 layers over Ru(0001) model electrodes

Abstract

Hydrous RuO₂ reveals excellent performance both as a supercapacitor and as a heterogeneous oxidation catalyst. Molecular understanding of these processes needs, however, a model system with preferably low structural and morphological complexity. This goal is partly accomplished here by using single crystalline Ru(0001) as a template on which hydrous RuO₂ is electrochemically formed. The hydrous RuO₂ layers on Ru(0001) and their temperature induced transformation under ultra high vacuum (UHV) conditions are comprehensively characterized by scanning electron microscopy and X-ray photoemission spectroscopy. The hydrous RuO₂ layer grows with an intricate morphology governed by the presence of step bunching regions of the Ru(0001) surface. Upon annealing to 200 °C in UHV the hydrous RuO₂ layer transforms mostly into flat metallic Ru islands and occasionally into (100) and (111) oriented RuO₂ particles aligned along the high symmetry direction of Ru(0001).