Hydrous oxide growth on platinum

Shibata s experiment, involving the use of periodically interrupted cathodic current for the reduction of thick oxide films, is quite significant. The smaller potential variations observed during the reduction of the hydrous, as compared with the anhydrous, component of the surface layer clearly demonstrate that the reaction 

Formation and reduction of a hydrous oxide film on platinum resulted in an increase in the charge for monolayer oxide reduction in subsequent experiments. Obviously the metal surface was roughened as a result of formation and subsequent reduction of the phas, pxide. However, the roughness developed with this technique teMed to decay under open-circuit conditions (a process that was accelerated by occasional potential sweeps for monitoring purposes). Such decay was more rapid than with platinum black deposits prepared from conventional chloroplatinic add baths— evidence perhaps that in the former case the active metallic layer is of a more highly strained, finely divided character.  

An account of early work in this area, i.e., production of a yellowish brown layer of hydrated Pt02 at a platinum electrode in sulfuric add solution on imposition of an ac component on a dc current, has been given by Altmann and Busch. More recent work by Builre and Roche has demonstrated that quite thick films can be produced in both acid and base on cyding the electrode potential between suitable limits. In the initial work oxide growth 

this result may be rationalized by assuming that the layer produced on cycling is anionic, i.e., the reaction in question is assumed to be 

The asymmetry of the reduction peak may also be attributed to crystallization overpotential. At the peak the rate of production of Pt, and hence the crystallization overpotential (Tjcry) is at a 

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Work of a similar nature, involving hydrous oxide growth on platinum under square-wave perturbation conditions in acid, has been reported recently by Chialvo et al.137 Changes in real surface area were monitored by measuring the hydrogen monolayer charge before and after the hydrous oxide growth and reduction processes. The optimum limits observed in this case (especially the lower value... 

This system seems to be the only alloy to date whose hydrous oxide growth behavior under potential cycling conditions has been investigated.189 190 Burke and O Sullivan189 demonstrated that with an alloy containing 10% by weight of rhodium in platinum both components corroded on cycling between certain limits (0-1.5 V) in 1.0 mol dm-3 NaOH. However, while the platinum corrosion product was found to be soluble under these conditions the rhodium one was not—in fact the hydrous film developed on the surface in this case was apparently derived almost totally from the minor component in the alloy. 

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