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 int erface between a polycrystalline gold electrode and aqueous electrolyt e 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 PF 6-. The band intensity was found to be strongly dependent upon the ele ctrode potential, while the band positions exhibited almost no potenti al dependence. The bands, however, appeared at different frequencies d epending upon the electrolyte anions used, which strongly suggests tha t these water molecules should be in the hydration spheres of the anio ns. We also found that the potential dependent adsorption/desorption p rocess of halide ions dominated the spectral feature of interfacial wa ter, which was also supported by the double-layer capacitance measurem ents. (C) 1998 Elsevier Science S.A. All rights reserved.