CHLORIDE ADSORPTION ON CU(111) ELECTRODES IN DILUTE HCL SOLUTIONS

The adsorption of Cl- ions on a Cu(111) electrode was studied by UHV-b ased spectroscopies and by cyclic voltammetry. After standard UHV prep aration the sample was transferred to an electrochemical cell. The sha pe of the voltammograms can be explained by a superposition of Cl- ads orption/desorption and a hydrogen reduction current, if an enhancement of the hydrogen reduction by adsorbed Cl- is assumed. After backtrans fer to the UHV an additional peak was observed in the ultraviolet phot oemission spectrum. In combination with X-ray photoemission and low-en ergy ion scattering measurements this additional feature is unambiguou sly assigned to adsorbed CI. It is also evident from the spectra that the electrochemical double-layer does not remain intact in some cases during the transfer. A more detailed study of the surface structure as a function of the electrode potential was performed by in situ scanni ng tunneling microscopy. In situ STM images show a clear-cut transitio n from the (1 x 1) structure of the substrate to a (root 3 x root 3)R3 0 degrees adsorbate structure if the potential is scanned through the Cl- adsorption and vice versa if scanned through the desorption region .