AN ELECTROCHEMICAL STUDY OF THE COMPOSITION OF THIN, COMPACT PD OXIDE-FILMS

An electrochemical study of the properties of thin, compact oxide film s (Pd alpha-oxides) formed at polycrystalline Pd wire electrodes and a t Pd-sputter-coated quartz crystals (to enable in situ mass measuremen ts) in alkaline and neutral sulfate solutions has been carried out. In alkaline solutions, the mass of the film is consistent with the forma tion and reduction of Pd(OH)(2) . H2O, in agreement with the ca. - 58 mV pH dependence observed over a narrow alkaline pH range using soluti ons that do not lead to competitive anion adsorption effects. This him can be transformed, without a change of oxidation state or significan t thickening, by a particular continuous potential cycling regime, to one which reduces at ca. 270 mV more negatively, consistent with the d evelopment of a deprotonated, charge compensated, hydrated oxide film, i.e., Pd(OH)(2) . yH(2)O . xOH(-). xNa(+). In neutral sulfate solutio ns, evidence for sulfate adsorption on the reduced Pd surface and in t he early stages of ct-oxide formation is seen. Nevertheless,the mass o f the alpha-oxide film could be measured, indicating it to be PdO . H2 O in this medium.