SOLVENT EFFECT IN ELECTROCHEMICAL FORMATION OF ADATOM ARRAYS OF PB ON AU AND THE ROLE OF COADSORPTION OF ANIONS

In progression of underpotential deposition (UPD) of metal, M, adatoms on a noble metal substrate, from a coverage fraction, θM of zero to near unity, the deposition of the adatoms must involve a solvent-substitution adsorption process because new solvent-metal interactions are established, different from those between the solvent and the substrate when θM → 0. Such an effect does not arise in regular bulk metal deposition processes. The requirement of a solvent-substitution process provides a basis for expectation of a solvent effect in UPD of Pb on polycrystalline Au from water, methanol, acetonitrile, dimethylformamide and propylene carbonate using perchlorate and trifluoromethane sulfonate electrolyte salts. Substantial differences in UPD current vs. potential profiles, derived from cyclic voltammetry, are found for the various solvents. It is shown that the observed effects could arise from the "solvent-substitution" adsorption process, mentioned above but also, solvent-dependent, specific adsorption of anions can complicate the UPD behavior and must be taken into account. Effects arising in the presence of strongly adsorbed anions are demonstrated. © 1990.