HYDROUS OXIDE FILM GROWTH ON PT - I - TYPE-I BETA-OXIDE FORMATION IN 0.1 M H2SO4

The objective of this work has been to establish the compositional pro perties of hydrous oxide films formed at polycrystalline Pt electrodes in 0.1 mol/l sulfuric acid by multicycling to moderately positive pot entials, 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 wi th 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 sugge sted to be Pt(OH)(4). As the beta-oxide film thickens with time of gro wth, 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 thicknes s can also be viewed as reflecting an increasing extent of film porosi ty in the outer regions of the film. (C) 1998 Elsevier Science Ltd. Al l rights reserved.