EFFECT OF THE ELECTROLYTE-COMPOSITION ON THE ELECTROREDUCTION OF PALLADIUM OXIDE-FILMS

The voltammetric electroreduction of Pd oxide layers grown at 2.00 V ( RHE) was studied in H2SO4 and HClO4 solutions containing different con centrations of LiClO4, Na2SO4 and KHSO4. The voltammetric electroreduc tion profiles show two main regions; the first is in the range 1.2-1.6 V and is related to the electroreduction of a fast redox system; the second region extends through the range 1.1-0.40 V, where the electror eduction of the thick oxide matrix takes place. This latter process is strongly affected by the solution composition, including the pH, in a manner contrasting to the effect on Pd oxide growth. The thick oxide layer electroreduction charge increases as the solution pH is decrease d. These results are discussed in terms of specific interaction betwee n sulphate ions and the oxide layer, so that the electroreduction proc ess is favoured owing to the likely formation of sulphate-containing c omplex species.