An interpretation of the different processes involved in the electroreduction of thick palladium oxide films

The electroreduction of palladium oxide films formed at high positive potentials in acid electrolytes was studied by voltammetry and potential step techniques. The anodic oxide layer can be described as a duplex layer, one inner in contact with the electrode surface, which is rather anhydrous and more compact, and a second one, thicker and rather hydrous which serves as a matrix for a fast electrochemical system. The electroreduction of the matrix-embedded fast electrochemical system follows the potentiodynamic and potentiostatic behaviour expected for a diffusion controlled process in a finite space. The electroreduction of the outer oxide layer can be described in terms of an instantaneous nucleation and 3-D growth with nuclei death. Both processes produce Pd2+ soluble species which can be detected by means of a rotating ring-disk electrode. At potentials lower than 0.7 V the electroreduction of O-2 formed during the growth of the Pd oxide layer can be detected. (C) 1997 Elsevier Science S.A.