Anodic film formation on osmium electrodes in strong acid solutions

Anodic film formation and reduction on electrodeposited Os was studied in strong HCl and HClO4 solutions. Significant voltammograms were obtained only after long pre-reduction of the electrode and at slow potential sweeps. The potentiodynamic curves reveal strong adsorption of oxygen with formation of OsO2 and further oxidation to OsO4 which goes into solution. In strong HCl solutions a corrosion step at high potential with formation of OsO2Cl42− is detected. The influence of scan rate on peak potential and current and the charge capacity of the electrode surface was investigated. Anion adsorption and increase in acid concentration was found to reduce the extent of the anodic film. The results are discussed in terms of the formation of thick surface oxides and compared with those for Ir and Ru.