Surface X-ray diffraction study of Cu UPD on Au(111) electrode in 0.5 M H2SO4 solution:: the coadsorption structure of UPD copper, hydration water molecule and bisulfate anion on Au(111)

The structure of underpotential deposition (UPD) copper, a hydration water molecule, and a bisulfate anion on Au(111) surface in 0.5 M H2SO4 solution has been determined by in situ surface X-ray diffraction study. The bisulfate anion and the UPD copper form a root3 x root3R30degrees structure on an Au(111) electrode at a potential between 250 and 400 mV. At this potential range, UPD Cu, a bisulfate anion, and a hydration water molecule coadsorb on Au(111), while the coverages of copper and bisulfate anion are 0.6667 and 0.3333, respectively. The coadsorption structure is represented by Laue symmetry of P31m. On top of each copper atom, a hydration water molecule is accommodated to form a stable and closest-packed water adlayer with a large density. At a more positive potential than 940 mV, the bisulfate anion forms a root3 x root7 structure on a bare Au(111) surface. (C) 2002 Elsevier Science B.V. All rights reserved.