Structural and kinetic studies of Hg(UPD) on Au(111)

The UPD of mercury on Au(111) electrodes has been studied using cyclic voltammetry, surface x-ray scattering and potential step chronoamperometric techniques. Although interactions between mercury and the gold surface appear to play a dominant role, the presence of (bi)sulfate anions affects the initial and final stages of mercury deposition/desorption since ordered adlayers are formed, respectively, at potentials positive and negative of the main UPD peaks. At positive potentials, and prior to mercury deposition, previous STM and AFM studies revealed the existence of an ordered (bi)sulfate-water structure. At potentials negative of the main UPD peaks we have identified, by surface x-ray scattering techniques, a mercury-(bi)sulfate (probably in the form of Hg2SO4) distorted honeycomb adlayer. The formation/disruption of these adlayers occurs trough order-disorder transitions that give rise to sharp voltammetric peaks at the onset and final stages of mercury deposition, respectively. Kinetic measurements indicate that formation of the mercury(bi)sulfate adlayer takes place via nucleation and growth with a progressive nucleation mechanism.