Electrochemical impedance spectroscopy studies of the Ag(111)/n-decanethiol monolayer/NaNO3 interface

Abstract

Surface properties of a modified single-crystal silver (111) face are studied in aqueous 1 M NaNO3 solutions with different acidity in the presence of a monolayer n-decanethiol (DT) film by the methods of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry that employs the meniscus contact technique. It is shown experimentally that in the potential range from 0 to −0.5 V, a DT-modified silver electrode in NaNO3 solutions with pH 6 behaves as an ideal capacitance in a wide frequency range (from 0.01 Hz to 100 kHz). It is found that with the increase in the solution acidity up to pH 4 and 2, the region of stable capacitance characteristics narrows down. The concomitant changes in the adsorbed monolayer structure lead to deviations of impedance characteristics measured using a low-frequency ac signal from those of the ideal capacitance. A potential shift to values more negative than −0.5 V leads to the destruction of the monolayer. Based on the analysis of experimental EIS characteristics, system’s deviation from the ideal behavior that may indicate violation of the layer continuity is assessed and the relaxation frequencies of the DT/Ag(111) interface in solutions of different acidity are calculated. Estimates of capacitance, resistance, and thickness of the adsorbed monolayer are obtained as a function of the solution pH.