UNDERPOTENTIAL DEPOSITION OF CU ON AU(111) IN SULFATE-CONTAINING ELECTROLYTES - A THEORETICAL AND EXPERIMENTAL-STUDY

We study the underpotential deposition of Cu on single-crystal Au(lll) electrodes in sulfate-containing electrolytes by a combination of com putational statistical-mechanics based lattice-gas modeling and experi ments. The experimental methods are in situ cyclic voltammetry and cou lometry and ex situ Auger electron spectroscopy and low-energy electro n diffraction. The experimentally obtained voltammetric current and ch arge densities and adsorbate coverages are compared with the predictio ns of a two-component lattice-gas model for the coadsorption of Cu and sulfate. This model includes effective, lateral interactions out to f ourth-nearest neighbors. Using group-theoretical ground-state calculat ions and Monte Carlo simulations, we estimate effective electrovalence s and lateral adsorbate-adsorbate interactions so as to obtain overall agreement with experiments, including both our own and those of other groups. In agreement with earlier work, we find a mixed (root 3 x roo t 3) phase consisting of 2/3 monolayer Cu and 1/3 monolayer sulfate at intermediate electrode potentials, delimited by phase transitions at both higher and lower potentials. Our approach provides estimates of t he effective electrovalences and lateral interaction energies, which c annot yet be calculated by first-principles methods. (C) 1996 American Institute of Physics.