Potential modulated reflectance spectroscopy of Pt(111) in acidic and alkaline media: cyanide adsorption

The electroreflectance (ER) technique has been applied to the study of a Pt (111) electrode in different acidic and alkaline electrolytes. The variatio n in the normalised potential derivative of the reflectance signal, 1/R(dR/ dE) is observed in sulphuric and perchloric acid media as the potential is scanned 1.0 V positive from the hydrogen evolution region. In both these me dia, the usual hydrogen adsorption-desorption region corresponds to a zone in which the ER signal is practically zero and does not change with the pot ential. However, in the anomalous region, an increase in the ER signal was observed indicating that here, the adsorbed species increased the electron density of the platinum surface. The ER spectrum recorded for the cyanide-c overed Pt(111) surface showed a large decrease in the electron density of t he platinum surface and this is attributed to electron back-donation from t he platinum to the adsorbed cyanide. In alkaline solutions, the integrated ER spectrum showed relatively small changes which corresponded to the featu res in the cyclic voltammogram and were attributed to the reorientation of the hydrogen-bonded surface species and water dipoles. (C) 1999 Elsevier Sc ience S.A. All rights reserved.