Abstract
Anodic oxidation of Ru and 
electrodes in 
has been investigated using x‐ray photoelectron spectroscopy. During 
evolution on Ru a highly defective hydrated oxide film is formed as a result of corrosion. At a temperature of 310°C in vacuum this film decomposes to metallic ruthenium. The surface of 
anodes prepared by thermal decomposition of 
contains some 
, which is stable during anodic polarization. A reaction path for 
evolution and corrosion on Ru and 
anodes is proposed.