Impedance Response of Electrochemical Interfaces: Part IV─Low-Frequency Inductive Loop for a Single-Electron Reaction

Abstract

The low-frequency inductive loop is usually attributed to relaxation of adsorbed intermediates of multistep reactions in electrocatalysis and corrosion. Herein, we report a low-frequency inductive loop for a single-electron reaction when the electrode potential (E M ), the equilibrium potential (E eq ), and the potential of zero charge (E pzc ) are different, namely, under nonequilibrium conditions. Interestingly enough, although both reactions involve only one electron, the metal deposition reaction (M + + e ↔ M) and the redox couple reaction (Fe(CN) 63− + e ↔ Fe(CN) 6 4−) show different impedance shapes. The low-frequency inductive loop is observed only for the M + + e ↔ M reaction in the oxidation direction because its faradaic current has a negative phase angle due to double layer effects. Moreover, we find that the low-frequency inductive loop occurs only when the polarization curve has no diffusion-limiting features.