On the Differential Capacitance and Potential of Zero Charge of Au(111) in Some Aprotic Solvents

Abstract

Voltammetric and Gouy-Chapman capacitance minimum measurements were conducted on Au(111) and roughened Au(111) electrodes in aprotic electrolytes in the absence and presence of specifically adsorbed ions for concentrations ranging from 0.001 to 0.5 M. Negative of the point of zero charge (pzc), the capacitance maximum increases in the order Ca2+<Li+<K+, but the pzc value is independent of cation nature. The capacitance values have a slight dependence on cation type at a more negative potential. The pzc depends on the solvent and is influenced by the dielectric constant, metal-solvent interactions and donor number; it is shifted to more positive values with increasing water content. Specific anion adsorption shifts the pzc to more negative values. The pzc value is more negative for the roughened electrode compared to the single crystal electrode. Propylene carbonate (PC) adsorption in the presence of perchlorate and iodide was examined on gold film by surface-enhanced infrared absorption spectroscopy (SEIRAS). The potential dependent intensity is explained by a stronger electric field and thus a better alignment of the PC molecules when the absolute potential difference to the pzc is large. The capacitance curves were theoretically modelled. From the capacitance maxima on both sides of the pzc the ionic volume and thus the solvation numbers were estimated. The width of the capacitance minimum is believed to be related to the layer of adsorbed solvent molecules. © 2021 The Authors. ChemElectroChem published by Wiley-VCH GmbH