Deciphering interfacial charge transfer mechanisms in electrochemical energy systems through impedance spectroscopy

Electrochemical energy conversion and storage systems have become an integral part towards a sustainable future, where the goal is to achieve high energy efficiency for each targeted application. The output of these devices is governed by the material design and the underlying interfacial chemistry at the junction of the electrode and the electrolyte. Electrochemical impedance spectroscopy (EIS) is based on the response of applied frequency to the modulated potential and the decoupled capacitive and resistive components. It has emerged as a versatile non-destructive analytical tool endowed with the benefits of differentiating between multiple solid/electrolyte and solid/solid interfaces. In this perspective, the model-based and model-free approaches are elaborated along with relevant case studies for elucidating the charge transfer at multiple interfaces for water electrolysis, CO2 and N2 reduction to value-added fuels, and ammonia, respectively, in addition to the metal-ion, metal-air and photo-rechargeable batteries. The avenues to minimize the charge transfer resistance for boosting the overall device performance are also discussed. Employing electrochemical impedance spectroscopy as a non-destructive analytical tool for elucidating the interfacial charge transfer in electrochemical energy conversion/storage systems.