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Publication
JES
Paper
Kinetics of Oxygen Gas Evolution on Hydrous Rhodium Oxide Films
Abstract
The activity of rhodium for oxygen gas evolution in base is significantly enhanced by the presence of a thick, hydrous oxide film which is produced by repetitive potential cycling. An increase in oxygen evolution rate of up to three orders of magnitude was obtained on growing these films; the latter were found to be stable to dissolution (in short term tests) at potentials below ≃1.70V (RHE). A decrease in Tafel slope of 75 to 48 mV decade−1 was observed on going from a hydrous oxide-free to a hydrous oxide-covered rhodium surface at potentials less than ≃1.55V (RHE), while a slope of ≃120 mV decade−1 was observed in the linear Tafel region above 1.55V (RHE) in all cases. A reaction order with respect to hydroxide ion activity was also determined. A mechanism for oxygen evolution was proposed involving cyclical formation-decomposition of higher rhodium oxide species. A feature of the kinetic treatment was the incorporation in the rate equation of a term that took into account the variation of the Rh(IV) concentration at the interface, at constant overpotential, with change in solution pH. © 1990, The Electrochemical Society, Inc. All rights reserved.