Complex electron transfer kinetic data from convolution analysis of cyclic voltammograms. Theory and application to diamond electrodes

A new and versatile procedure, based on convolution analysis, for the evaluation of complex electron transfer kinetic data from cyclic voltammetnc experiments is proposed. Both the anodic and the cathodic partial reaction are analyzed independently by the use of a linearized form of the Butler-Volmer equation. It is shown that for both branches well-defined Tafel-type plots can be obtained even from quasireversible cyclic voltammograms. Processes inconsistent with Butler-Volmer kinetics can be analyzed. The approximations inherent in Tafel analysis associated with (i) concentration gradients in the solution phase and (ii) mixed anodic and cathodic processes close to the equilibrium potential can be overcome. Additionally, the sum of anodic and cathodic transfer coefficient needs not to be unity and may even change with potential. The analysis therefore provides a general tool for parametrization and for testing the validity of the Butler-Volmer expression for a given electrode process.The application of the new methodology is tested with simulated voltammograms and is demonstrated for the Fe(CN)₆^3-/4- redox system at a metal electrode, platinum, and at a polished highly boron-doped diamond electrode. At the diamond electrode both reduction and oxidation processes give linear Tafel-type plots with α = 0.29 ± 0.02 and β = 0.42 ± 0.03.