Room temperature formation, electro-reduction and dissolution of surface oxide layers on sputtered palladium films

Following storage under ambient conditions, peaks corresponding to sub-monolayer coverage of surface oxide and to chemisorbed oxygen were observed on linear sweep voltammograms measured on sputtered palladium films. Stepwise chronoamperometric desorption was used to decouple the contribution of the rapidly desorbed adsorbed oxygen from that of the more stable surface oxide layer. The technique was also used to determine the dependency of the oxide reduction peak position on oxide surface coverage.The position of the oxide reduction peak was used to monitor the growth of the surface oxide during room temperature storage in the period following manufacture. A growth curve was constructed in which there was an initial ‘lag’ period, during which surface coverage of chemisorbed oxygen was established. The growth of the oxide film then followed direct logarithmic kinetics, consistent with the place exchange mechanism known to operate on the case of surface oxides formed at elevated temperatures and at oxidising potentials.The oxide films formed on the surface of the sputtered palladium were found to be relatively insoluble in neutral conditions and in the absence of chloride ions, where dissolution was limited by the solubility of Pd2+. In hydrochloric acid the much greater solubility of PdCl42− allowed the oxide film to dissolve completely.Cyclic voltammetry of potassium ferricyanide on Pd electrodes with sub-monolayer oxide coverage was consistent with the PdO being spread uniformly over the electrode surface.