THE ROLE OF SLOW SURFACE-ATOM REORDERING PROCESSES IN THE UNDERPOTENTIAL DEPOSITION OF METALS - SILVER UNDERPOTENTIAL DEPOSITION ON PLATINUM IN ACID-SOLUTIONS

The role played by slow surface-atom reordering processes in the underpotential deposition of Ag on polycrystalline Pt and polyfacetted Pt single crystal substrates from 10(-3) M Ag salt in aqueous acid solutions has been studied by using potentiostatic and potentiodynamic techniques complemented with Auger spectroscopy. The potential cycling between E(r), the reversible potential of the Ag/Ag+ electrode reaction, and 1.10 V (SHE) for 24 h resulted in the formation of a Ag + Pt surface alloy and the incorporation of Ag into the second layer of Pt atoms. The Ag electrodeposition/Ag anodic stripping on the Ag + Pt alloy gives rise to two new pairs of voltammetric peaks in the range 0.93-0.75 V, whereas the complete stripping of Ag occurs at 1.15 V. On the basis of surface-atom reordering processes which initiate through a place exchange mechanism involving Ag and Pt surface atoms followed by a slow Ag atom diffusion into bulk Pt, the entire cyclic voltammetric features and Auger data can be accounted for.