A method is herein described that allows the coverage of the two forms of oxide believed to form on polycrystalline Pt, Pt(poly), surfaces in aqueous solutions to be determined based on the analysis of in situ differential reflectance spectroscopy, AR/R, and voltammetric data recorded simultaneously. The model employed assumes AR/R can be expressed as the sum of contributions due to each type of surface site, i, represented by the product of their potential dependent coverage, θi(E), and a linear function of E obtained empirically. Values of θi(E) for the unoxidized and oxidized sites are calculated by solving a system of three non-linear equations that relate θi(E) to the charge associated with the formation of the oxide layer based on coulometric analyses and accepted values for the number of electrons transferred for each of the oxides. Data collected for Pt(poly) electrodes in aqueous 0.1 M HClO4 was found to be consistent with the coexistence of the two forms of Pt oxide and unoxidized sites on the surface over a potential range extending from ca. 1.0 to 1.25 V.
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