SURFACE CHARACTERIZATION OF MOLECULES AT PT(111) USING LEED, AUGER, HREELS AND ELECTROCHEMISTRY IN ULTRAHIGH-VACUUM

Reviewed in this article is surface characterization of organic molecules adsorbed at well-defined Pt(111) electrode surfaces from aqueous solution. Among the metal electrodes and surface-structure sensitive properties studied in this work are those involving electrocatalytic activity, such as platinum metal. Platinum is one of the most interesting materials for study in view of its exceptional spectrum of catalytic properties and its good stability in various electrolytic media. The compounds investigated were: (1) 4-Phenylpyridine (4PPY), (II) 4,4'-Bipyridyl (44BPY), (III) 2-Phenylpyridine (2PPY), (IV) 2-2' Bibyridyl (22BPY), (V) Pyridazine (PD), and (VI) 4-Pyridazinecarboxylic acid (4PDCA). For (I) and (II), the pyridine ring binds to the Pt(111) surface in a tilted, nearly vertical orientation having a pendant phenyl ring, and is virtually unreactive toward electrochemical oxidation. However, (III) and (IV) attach to Pt(111) with their pyridine ring vertically oriented and N-attached, while the other aromatic ring is oriented parallel to the electrode surface. Similarly, (V) and (VI) are attached to Pt(111) through their ring nitrogen atom, with a tilted-vertical orientation and average ring-to-surface angles ranging from 73-degrees to 86-degrees. Compounds (I-VI) were studied in order to understand the influence of molecular structure on surface bonding, molecular orientation, electronic structure, and electrochemical reactivity at well-defined surfaces such as Pt(111), as a function of pH, electrode potential and adsorbate concentration.