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

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 (EM), the equilibrium potential (Eeq), and the potential of zero charge (Epzc) 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)64–) 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.