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 under potential deposition of Ag on polycrystalline Pt and polyfacetted Pt s ingle crystal substrates from 10(-3) M Ag salt in aqueous acid solutio ns has been studied by using potentiostatic and potentiodynamic techni ques complemented with Auger spectroscopy. The potential cycling betwe en E(r), the reversible potential of the Ag/Ag+ electrode reaction, an d 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 give s 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 ex change mechanism involving Ag and Pt surface atoms followed by a slow Ag atom diffusion into bulk Pt, the entire cyclic voltammetric feature s and Auger data can be accounted for.