Philippine Science Letters
vol. 4 | no. 1 | 2011
published online March 7, 2011


STM and DFT Studies of Anion Adsorption
at Well-defined Surfaces: Pd(111) in
Sulfuric Acid Solution

by Alnald C. Javier1, Youn-Geun Kim1, Joseph B. Soriaga1, Perla B. Balbuena2 and Manuel P. Soriaga1*

1 Department of Chemistry
2 Department of Chemical Engineering
Texas A&M University College Station, TX 77843



Density functional theory (DFT) has been employed to resolve compositional and structural issues related to the in situ (electrochemical) scanning tunneling microscopy (EC-STM) of a well-defined Pd(111) electrode surface in aqueous sulfuric acid solution. Fundamental concepts in inorganic chemistry had earlier been invoked to postulate that SO4 2+ anions, H3O+ counter-cations and H2O were the most likely constituents in the compact layer. However, while the STM images distinctly revealed ordered rows of anions interspersed with hydronium ions and water molecules, details such as the orientations, spatial configurations and adsorption-site locations of the interfacial species could not be unambiguously ascertained. The present DFT-based geometry-optimization and total-energy calculations indicate that two layers of water molecules and hydronium ions are assembled, non-co-planar with one another, between the rows of surface-coordinated anions; the layer that is slightly elevated is comprised of counter cations.

*Corresponding author
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Submitted: December 6, 2010
Revised: February 3, 2011
Accepted: February 10, 2011
Published: March 7, 2011
Editor-in-charge: Gisela P. Padilla-Concepcion