In situ IR spectroscopic study of water at a polycrystalline gold electrode surface

The effect of the electrolyte anions on the water structure at the interface between a polycrystalline gold electrode and aqueous electrolyte solutions was studied using in situ Fourier transform IR reflection absorption spectroscopy (FT-IRAS). Considerably sharp absorption bands due to OH stretching modes of water were observed in the 3600-3500 cm(-1) range in solutions containing F-, Cl-, Br-, I-, BF4-, ClO4- or PF6-. The band intensity was found to be strongly dependent upon the electrode potential, while the band positions exhibited almost no potential dependence. The bands, however, appeared at different frequencies depending upon the electrolyte anions used, which strongly suggests that these water molecules should be in the hydration spheres of the anions. We also found that the potential dependent adsorption/desorption process of halide ions dominated the spectral feature of interfacial water, which was also supported by the double-layer capacitance measurements. (C) 1998 Elsevier Science S.A. All rights reserved.