<i>In situ</i>STM studies of Cu underpotential deposition on Au(100) in the presence of sulfate and chloride anions

Abstract

The influence of anions on the underpotential deposition of Cu on Au(100) electrode surfaces has been investigated by in situ scanning tunneling microscopy. In pure ${\mathrm{Cu}}^{2+}$-containing ${\mathrm{H}}_{2}$${\mathrm{SO}}_{4}$ solution a (1\ifmmode\times\else\texttimes\fi{}1) lattice is observed in the entire potential range and interpreted in terms of an increasing population of the energetically most favorable lattice sites by mobile Cu adatoms with weakly repulsive interactions. In the presence of ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$ anions a one-dimensionally incommensurate (n\ifmmode\times\else\texttimes\fi{}2) structure is formed, coincident with a sharp peak in the current-potential curve. In this structure the adatoms are arranged in a quasihexagonal pattern with a spacing of 3.6 to 4.4 \AA{}, which is close to the diameter of the ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$ ion. The difference in the observed adsorption behavior corresponds well to the different shape of the corresponding electrochemical current-potential curves.