The effect of halide additives on the electrodeposition of Pb on polycrystalline Au

The growth of bulk (overpotentialdeposition – OPD) Pb layers on weakly textured polycrystalline Au surfaces from 100 mM ClO4- electrolytes with and without additional halide additives (20 mM Cl−, Br− and F−) was studied. We observed single broad cathodic and anodic underpotential deposition peaks in the cyclic voltammograms, the mean position of which was significantly more negative when Cl− or Br− was present. Ex situ atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that Pb forms a high density of small islands in the absence of strongly adsorbing anions, while in solutions containing Cl− or Br−, a low density of large Pb islands is formed. AFM and SEM further show that halide additives influence the shape of OPD Pb islands, being facetted when strongly adsorbing anions are absent but irregular in the presence of Cl− or Br−. In situ oblique incidence reflectivity difference (OIRD) measurements reveal qualitative differences in real time, during growth, between the structure of films grown at different potentials and in the presence of different additives. OIRD data further indicate that during dissolution of the OPD Pb, a single monolayer remains for a short time after the remaining Pb has dissolved. Similarities between the Pb/Cu and Pb/Au OPD systems are discussed.