Yeon-Su Park, Jack H. Baricuatro, Mohammad A. Hossain, Manuel P. Soriaga
Ultrathin Pd films, with coverages from 0.5 monolayers (ML) to 8 ML, were prepared by potential-sweep deposition on well-defined Pt(111) surfaces. Analysis of the voltammetric peaks characteristic of hydrogen adsorption/desorption on Pd terrace and step sites revealed that, 1 ML coverage, the film remained step-free but, at higher coverages, formed 3D islands (Stranski-Krastanov growth mode). Corroborating evidences were provided by low-energy electron diffraction and Auger electron spectroscopy. Slight surface smoothening effects were observed after 4 ML films were electrochemically annealed in sulfuric acid between the hydrogen evolution region and the double-layer region. Bromine was used as a surface probe for the Pd films. Bromine chemisorption began at -0.20 V, and led to the formation of a (√3x√3)R30°-Br adlattice up to 0.50 V. Dissolution of films, however, commenced at the open-circuit potential (0.22 V) leading to a subsequent decrease in the surface coverage of bromine due to anodic oxidation that accompanied the stripping of Pd. At potentials E ≥ 0.60 V, a passivating PdBr2 layer was formed similar to that previously observed on bulk Pd(111) surfaces. ©The Electrochemical Society.
Department of Chemistry, Texas A and M University, College Station, TX 77843, United States; Department of Chemistry, University of San Carlos, Cebu City, Philippines
