Molecular and ionic adsorption on metal-solution interfaces

Investigations of sulfate/bisulfate and copper ions coadsorption on the surface of a Pt(111) single crystal electrode as well as the adsorption of pyridine (Py) and 4-cyanopyridine (4-CNPy) on the surface of Au(111) electrode are presented in this thesis. Thermodynamics of the so-called perfectly polarized electrode and the chronocoulometric technique were employed to determine the Gibbs excess of adsorbed sulfate/bisulfate and coadsorbed Cu adatoms. The Esin-Markov coefficient was used to estimate whether sulfate or bisulfate is the species predominantly adsorbed on the Pt(111) electrode surface. Quantum chemical calculations were performed to determine the driving force for Py and 4-CNPy adsorption on the Au(111) electrode and to discuss the differences and similarities in the coordination of these molecules to the gold surface.;Bisulfate was found to be the species predominantly adsorbed on the Pt(111) electrode surface in electrolytes containing sulfuric acid. In the potential range from 600 to 800 mV, the adsorbed bisulfate ions form an ordered overlayer with a coverage of 1/3 of a monolayer (ML) of platinum atoms on an ideal Pt(111) surface. This result is consistent with recent ex-situ LEED/Auger combined UHV-electrochemistry studies which have shown that in this range of electrode potentials the adsorbed bisulfate forms an ordered ;Quantum chemical calculations show that both Py and 4-CNPy form weak covalent bonds with the Au(111) electrode surface. At negative potentials with respect to the potential of zero charge (pzc), both molecules are adsorbed horizontally, while at potentials positive to pzc they are coordinated through the nitrogen atom of the aromatic ring and assume a vertical orientation. A change in the sign of the electrostatic field at the electrode surface causes a reorientation of the adsorbed molecules. The quantum chemical calculations explain why the reorientation is abrupt for Py molecules and gradual for 4-CNPy molecules.