In-Situ Monitoring of Electrochemical Oxidative Adsorption of Sulfur on Silver

Underpotential deposition of sulfur was studied on Ag(100) and Ag(110) from Na2S solution in 0.1M NaOH using in-situ STM. The cyclic voltammogram on Ag(100) presents two broad peaks, whereas three partial overlapping peaks and a more acute one are present for Ag(110). The STM investigation on Ag(100) proves the presence of a first square lattice adsorbed layer after the first peak that undergoes a phase transition towards a more compact structure constituted by couples of atoms after the second peak. On the other hand the process on Ag(110) starts with cluster deposition at the step edges and continues with aggregations of atoms in lines starting from the steps. Only after the acute peak a compact structure can be observed, of which a structure in register with the substrate is hypothesized.