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he suppression of current exchange during the ethanol oxidation reaction on platinum supported on NbRuyOz (mixed metal oxide) has been investigated. 60% Pt/NbRuyOz was synthesized in a single step using aerosol spray pyrolysis, followed by reductive thermal post-treatment. Rapid cyclic voltammetry at a polarization rate of 1 V/s between anodic and cathodic potentials in 0.1M HClO4 and 1M KOH reveals the growth of a thin film of oxygen-rich niobia covering the catalyst and support particles. Step-increase cyclic voltammetry and chronopotentiostatic coulometry approaching, at, and above the oxygen evolution potential suggests that the mechanism of 3D film growth is oxygen-dependent. Density Functional Theory calculations indicate that the rate of oxygen diffusion across the Pt(111) surface is in good agreement with experimental observations of the period of catalyst deactivation (several weeks) when exposed to open atmosphere. This suggests that the mechanism of catalytic deactivation (passivation) could involve the capture and release of oxygen as Nb2O5 breaks down into reduced fragments of NbOx. [ABSTRACT FROM AUTHOR]