Iodide adsorption at the Au(111) electrode surface

The adsorption of iodide at a Au(111) single crystal electrode has been inv estigated quantitatively using chronocoulometry. By analyzing the charge de nsity data thermodynamically, the following parameters were determined: the Gibbs excess, Gibbs energy of adsorption, the number of electrons flowing to the interface per one adsorbed iodide ion at a constant electrode potent ial (electrosorption valency), and at a constant chemical potential. The th ermodynamic data for iodide adsorption were compared to the results for bro mide and chloride adsorption. All the three halides form a chemisorption bo nd with the gold surface. The bond is quite polar at the negatively charged surface, however, its polarity drops significantly at the positively charg ed surface. At low charge densities and coverages. the bond polarity is det ermined by the ability of free electrons to screen the dipole formed by the adsorbed anion and its image charge in the metal. At high charge densities and coverages, the chemisorption bond has a predominantly covalent charact er. The strength of the halide adsorption and the covalent character of the chemisorption bond increase progressively by moving from chloride to iodid e. (C) 1999 Elsevier Science S.A. All rights reserved.