Nonequilibrium Electrical Double Layer Effects on Unilateral Peak Suppression in Cyclic Voltammetry

Abstract

While equilibrium electrical double layer (EDL) effects on steady-state voltammetry have been studied, nonequilibrium transient EDL effects on cyclic voltammetry (CV) remain less understood. Herein, we report a combined theoretical and experimental study of nonequilibrium EDL effects on CV, focusing on their unequal influence over the cathodic and anodic peaks. The experiments are analyzed with the aid of a theoretical model coupling the Poisson–Nernst–Planck (PNP) theory and various electrode kinetic theories that can describe interfacial electron transfer reaction, EDL formation, and macroscopic mass transport in a unified framework. Consistent with experiments, the model predicts suppressed cathodic peaks for the CV of the [Fe(CN)6]3–/4– redox reaction and correlates them with the spatiotemporal distributions of electrical potential and reactant concentration in the EDL. The model is then utilized as an efficient computational tool for exploration in the vast parametric space, identifying parametric regions where pronounced nonequilibrium EDL effects could be observed in CV. A regime diagram of nonequilibrium EDL effects on CV is calculated and validated partly with experiments. In general, the unilateral suppression of CV peaks is more pronounced when the reactive ion is repelled from the like-charged electrode surface at a higher scanning rate.