Interfacial studies of sliver-aqueous electrolytes by optical second harmonic and differential capacitance

Abstract

Optical studies of the electrostatic and surface structure of the metal-liquid junction require probes which are insensitive to bulk phase properties yet sensitive to an atomic level to interfacial interactions. Second harmonic generation (SHG) is the unique probe for such measurements. In addition to the second-order effect intrinsically present at the symmetry breaking interface, an additional condition from the application of the dc electric field has also been recently demonstrated. Due to the high field strength present in the electrochemically double layer (107 V/cm), this third-order effect appears to dominate in the SH production here. To understand the relative contributions to SHG at the electrode surface, we have examined the effects of the excess surface charge, χm, as imposed by the dc field on the SH production. The experiments involved simultaneous measurement and comparison of the concentration of the specifically adsorbed ions by differential capacitance, and the SH signal on the same electrode surface. Various binary mixtures of electrolytes at constant ionic strength were used. The potential dependence of SH signals was monitored by applying linear potential sweep voltammetry within the ideally polarizable region on smooth and electrochemically roughened metal surfaces.