Mathematical Analyses of AC Voltammetry of a Surface Confined Redox Process
W T. Yap
AC measurements have found wide application in various fields of research such as impedance spectroscopy in corrosion science and the familiar cyclic voltammetry (CV) in electroanalytical chemistry. Recently, sinusoidally modulated electrode potentials coupled with electro-optical reflectance (ER) measurements have been developed into a powerful analytical method for studying faradaic processes of surface-confined species, including surface-confined redox proteins used in biocatalysis and biosensors. Analytic solutions for the linearized kinetic model have been derived to interpret these measurements. Numerical solutions also have been obtained. These derivations were based on the fundamental harmonic of the CV or ER response. However, the non-linear and higher harmonic effects in these impedance measurements incorporate additional physical phenomena (e.g., the re-organization parameter in Marcus theory). We have recently obtained good quality second and higher harmonic responses, as well as the fundamental, for proteins confined at electrode surfaces. In this article, I present the derivations of analytical expressions for the various harmonic responses of a redox reaction of a surface confined species. Figure 1 illustrates the theory result of the fundamental mode of the current response from a cyclic voltammogram in which electrode voltage, E (t) varies sinusoidally about a DC component, EDC. The functionality of this fundamental mode is the same as that measured by Feng et al for a redox dye at a gold electrode (Feng Z.Q., Sagara T., Niki K., Anal. Chem. 67,3564,1995), and by Niaura and Gaigalas for azurin at a gold electrode (Niaura G. & Gaigalas A., J. Colloid Interface Sci., in press). This analysis significantly expands the amount of physical insight that can be obtained from impedance and electroreflectance measurements.
Journal of Electroanalytical Chemistry
AC voltammograms, harmonics, re-organization energy, surface-confined
Mathematical Analyses of AC Voltammetry of a Surface Confined Redox Process, Journal of Electroanalytical Chemistry
(Accessed December 7, 2023)