Identification of the structure of a CO adlayer on a Pt(111) electrode

The structure of a Pt(111) electrode after treatment in an electrolyte and subsequent transfer to an UHV chamber was investigated ex situ by combined low energy electron diffraction (LEED), reflection high energy electron dif fraction (RHEED), and Auger electron spectroscopy (AES). Treatment of the s ample in a CO saturated 0.1 M HClO4 solution at potentials between -0.2 and 0.2 V versus Ag/AgCl caused a maximum CO coverage of about 0.75 as probed by cyclic voltammetry, which dropped by partial desorption to about 0.25 up on transfer to the UHV chamber. This adlayer exhibited a (distorted) root 3 x root 3 R30 degrees pattern by RHEED (but not with LEED) exhibiting an av erage domain size of 2.3 nm at room temperature. This is identified with th e same phase reported before from gas phase studies, as also corroborated b y the similarities of the vibrational spectroscopic data. The same structur e (albeit even more poorly ordered) was found after dissociative adsorption of methanol. (C) 1999 Elsevier Science B.V. All rights reserved.