SURFACE CRYSTALLOGRAPHIC DEPENDENCE OF VOLTAMMETRIC OXIDATION OF POLYHYDRIC ALCOHOLS AND RELATED SYSTEMS AT MONOCRYSTALLINE GOLD ACIDIC AQUEOUS INTERFACES

The voltammetric oxidation in aqueous 0.1 M HClO4 of four polyhydric alcohols, ethylene glycol, glycerol, meso-erythritol, and d-mannitol, on seven oriented gold surfaces, Au(111), -(100), -(110), -(221), -(533), -(311), and -(210), is reported with the objective of assessing the role of surface crystallographic orientation on the catalytic electrooxidation of such polyfunctional reactants. (The atomically well-ordered nature of these gold surfaces has been scrutinized by in situ scanning tunneling microscopy.) In particular, the Au(221) and -(533) faces were selected since they provide stepped surfaces, 4(111)-(111) and 4(111)-(100), respectively. The results are compared with corresponding data for simple unifunctional reactants, specifically for formic acid oxidation and with results reported previously (ref 7) for carbon monoxide oxidation. In contrast to the last reaction, the electrooxidation rates for both the polyhydric alcohols and formic acid are greatest on Au(111), with Au(110) displaying unusually low activity. While formic acid electrooxidation is insensitive to the presence of monoatomic surface steps, the polyhydric alcohols (especially mannitol) are substantially less reactive on Au(221) and -(533) relative to Au(111). This behavioral difference is ascribed to stereochemical limitations on adsorption of the larger polyfunctional reactants imposed by the periodic surface steps. Such steps and other sites having low surface atomic coordination numbers are impotent for the alcohol oxidations, contrasting their strongly catalytic behavior for CO electrooxidation.