PLATINUM OXIDE FILM FORMATION REDUCTION - AN IN-SITU MASS MEASUREMENTSTUDY

The growth and reduction of oxide films at Pt was studied using the qu artz crystal microbalance technique. The compact alpha-oxide was shown to be anhydrous in nature (either PtO or PtO2). When the potential wa s extended into the hydrogen adsorption region, the electrode mass was seen to decrease, but then stabilized once the hydrogen evolution rea ction commenced. These results, as well as the effect of the addition of chloride and ferrous ions on the mass measurements, have been inter preted in terms of ion adsorption-desorption processes. The mass chang e during the reduction of thin hydrous beta-oxide films was also monit ored and yielded a mass-to-charge ratio consistent with a PtO(OH)2 fil m composition. Other mass data indicated that Pt dissolution can occur with repeated beta-oxide growth-reduction cycles and that some Pt may redeposit, given sufficient time at negative potentials.