THE ELECTROCHEMICAL-BEHAVIOR OF HYDROUS PALLADIUM OXIDE LAYERS FORMED AT HIGH POSITIVE POTENTIALS IN DIFFERENT ELECTROLYTE-SOLUTIONS

Several phenomenological aspects related to the anodization of Pd at potentials close to and more positive than the threshold potential of the oxygen evolution reaction (OER) in various acid electrolytes and in 1 M NaOH are described. At potentials located in the OER range, a fast redox electrochemical system as well as electrodichroism can be detected. These responses can be explained through anion injection and extraction coupled to changes of the water content in the anodic layer taking place during the oxidation-reduction cycles. The species formed at high positive potentials can be related to possible intermediates taking part in the OER. The voltammetric electroreduction of anodically formed Pd oxide layers exhibits several distinguishable processes within certain well-defined potential ranges, principally the electroreduction of the oxide layer, including phase changes. the formation of soluble Pd(II) species and finally Pd. The electroreduction process is influenced by the electrolyte composition.