A CAPACITANCE AND INFRARED STUDY OF THE ELECTRICAL DOUBLE-LAYER STRUCTURE AT SINGLE-CRYSTAL GOLD ELECTRODES IN ACETONITRILE

The electrical double layer at Au(100) and Au(111) electrodes in acetonitrile containing tetraethylammoniumperchlorate (TEAP) was studied by means of differential capacitance and in-situ FTIR spectroscopy measurements. For both surfaces, a preponderant capacitance maximum was observed at a positive charge of about 8 mu C cm(-2). Two types of acetonitrile molecules were identified in the interfacial infrared spectra. One of these concerns adsorbed acetonitrile with a strongly blue shifted vCN mode at 2337 cm(-1). The potential dependence of the spectra provides a clear evidence for dielectric saturation of the solvent and specific adsorption of the ions at large electrode charges. The spectra also indicate that the maximum ability of the solvent to reorientate in the interfacial field is in an adsorption geometry with the molecular axis inclined with respect to the surface. The data are discussed in context of the current models of the double layer, and compared with the related literature data obtained in an aqueous electrolyte.