Hydrous oxide film growth on Pt.: I.: Type I β-oxide formation in 0.1 M H2SO4

The objective of this work has been to establish the compositional properties of hydrous oxide films formed at polycrystalline Pt electrodes in 0.1 mol/l sulfuric acid by multicycling to moderately positive potentials, i.e., less than 1.8 V vs. RHE. Under these conditions, both a compact (alpha) and an overlaying hydrous (beta) oxide film ("Type I") form. Both QCMB and ellipsometric methods have been used, along with electrochemical techniques, to characterize the alpha-oxide and the Type I beta-oxide film. It has been shown that the alpha-oxide films are non-hydrated under all conditions, being either PtO or PtO2. Very thin beta-oxide films formed in the first cn. 30 s of growth are suggested to be Pt(OH)(4). As the beta-oxide film thickens with time of growth, it becomes increasingly hydrated, particularly towards its outer surface, with a mass consistent with Pt(OH)(4). H2O and later with Pt(OH)(4). 2H(2)O. The increasing water content of the film with thickness can also be viewed as reflecting an increasing extent of film porosity in the outer regions of the film. (C) 1998 Elsevier Science Ltd. All rights reserved.