Limitations in Electrochemical Determination of Mass-Transport Parameters: Implications for Quantification of Electrode Kinetics Using Data Optimisation Methods

Abstract

Voltammetric quantification of the electrode kinetics for the quasi-reversible reaction requires detailed experiment–theory comparisons. Ideally, predicted data derived from the theoretical model are fitted to the experimental data by adjusting the reversible potential (E0), heterogeneous electron transfer rate constant at E0 (k0), and charge transfer coefficient α, with mass-transport and other parameters exactly known. However, parameters relevant to mass transport that include electrode area (A), diffusion coefficient (D), and concentration (c), are usually subject to some uncertainty. Herein, we examine the consequences of having different combinations of errors present in A, D, and c in the estimation of E0, k0, and α on the basis of the a.c. (alternating current) voltammetric experiment–theory comparisons facilitated by the use of a computer-assisted parameter optimisation algorithm. In most cases, experimentally reasonable errors (<10 %) in the mass-transport parameters do not introduce significant errors in recovered E0, k0, and α values. However, a pernicious situation may emerge when a slight overestimation of A, D or c is included in the model and results in erroneous identification of a reversible redox process as a quasi-reversible one with a report of apparently quantifiable kinetic parameters k0 and α.