Redox mechanisms of NO with water on the Pt(111) electrode studied by in-situ STM and IRAS

NO (nitrogen monoxide) adsorption on a Pt(111) electrode surface yielded an STM image of 2 x 2-Pt(111)-NO structure. At a negative potential where no NO oxidation occurs, weak spots from water molecules were imaged between th e bright NO spots. Even at a positive potential where NO oxidation takes pl ace, a similar 2 x 2-Pt(111)-NO2 structure remained. Both images were repro duced reversibly by repeated potential cycles. This means that NO adsorptio n sites are preserved on the 2 x 2-Pt(111) surface sites during the redox p rocesses (NO reversible arrow NO2). At the point of NO saturation, NO molec ules in a 2 x 2 array were adsorbed exclusively on 'atop' sites of Pt(111). However, a new IR absorption band (NO2 band) began to appear and increased its intensity as the NO oxidation proceeded. An adsorbed H2O molecule adja cent to an adsorbed NO served as an oxygen source for the redox process and the oxidation reaction proceeded simultaneously with water decomposition o n the surface. (C) 1999 Elsevier Science S.A. All rights reserved.