Revisiting the Butler-Volmer Electrode Kinetics: Separating the Anodic and Cathodic Current Components of a Quasi-Reversible Electrode Reaction in Staircase Voltammetry

Abstract

A simple mathematical strategy is proposed to estimate anodic and cathodic current components in voltammetry by combining the basic mathematical model of a quasi-reversible electrode reaction at a conventional planar electrode with the Butler-Volmer electrode kinetics with a goal to simplify and facilitate the measurement of electrode kinetics. In spite of the fact that the separate anodic and cathodic current components are experimentally inaccessible parameters, it is demonstrated for the first time that they can be reliably estimated from the net (total) current over the whole potential interval of a common voltammetry, requiring only the current–potential relationship, without prior knowledge of any electrode kinetic parameter (i.e., the standard rate constant and the electron transfer coefficient). The mathematical procedure requires semi-integration of the current and previous knowledge of the formal potential of the studied redox couple. The theory predicts that very fast electrode processes, with an apparent electrochemical reversible behavior, are associated with anodic and cathodic current components the intensity of which is proportional to the standard rate constant. Thus, the proposed simple methodology provides a new perspective in analyzing voltammetric data and expands the accessible kinetic interval towards very fast electron transfer processes by means of simple voltammetry at macroscopic planar electrodes. The proposed methodology is experimentally illustrated with the electrode reaction of hexacyanoferrate(II) ion oxidation at platinum electrode.