Examination of the Electrochemical Interface between Two Immiscible Electrolyte Solutions by Second Harmonic Generation

The potential-induced accumulation of electrolyte ions at the water/1,2-dichloroethane (DCE) electrochemical interface has been examined by total internal reflection second harmonic generation (TIR SHG). TIR SHG experiments provide the first direct optical measurements of the accumulation of the base electrolytes, tetraphenylarsonium (Ph4As+) and tetraphenylborate (Ph4B-), in the interfacial region between two immiscible electrolyte solutions (ITIES). The standard Galvani potential for ion transfer across the water/DCE interface for the tetrabutylammonium (TBA+) is measured from the SHG data. Using the Ph4As+ ion as a reference, a value of 219 ( 5 mV is determined for TBA+. In addition, optically determined potential-dependent concentration profiles for the Ph4As+ and Ph4B- ions are correlated with the modified Verwey-Niessen model for surface excess. Results suggest that less than 10 % of the potential drop across the water/DCE interface occurs in the organic phase. I