Adsorption and Orientation of Aromatic Compounds at Smooth Polycrystalline Platinum Electrodes

摘要

A recent study has shown that aqueous solutions of weakly surface-active electrolytes such as Cl04(-), HSO4(-), H2PO4(-), PF6(-) and Cs(+) do not inhibit the spontaneous and irreversible oriented-adsorption of aromatic molecules at smooth ploycrystalline Pt electrodes. Studies using structurally well-defined Pt single-crystals have also demonstrated the inertness of irreversibly adsorbed layers towards these supporting electrolyte solutions. However, initial studies using iodide solutions have indicated that strongly surface-active electrolytes may exert profound influences on the adsorption characteristics of organic compounds. It was observed, for example, that when a layer of flat-adsorbed aromatic intermediates was exposed to dilute aqueous iodide, desorption and/or reorientation of the aromatic species occurred (depending on the nature of the adsorbate sna pH of the solution) along with adsorption of iodine. In ultra-high vacuum adsorbed molecule reorientation induced by coadsorption of iodine was indicated for dimethyl sulfoxide chemisorbed on Pt(III). In the present study, the effect of halide supporting electrolytes on the adsorption and orientation of hydroquinone (HQ) and 1,4-naphthohydroquinone (NHQ) at smooth polycrystalline Pt electrodes is examined in greater detail. This work focuses on competitive adsorption between halide and aromatic when both are present in the same solution in various proportions. Halide influences are indicated by differences in the adsorption profiles relative to the clean surface.