Application of Electrochemical Impedance Spectroscopy for Diagnostics in Fuel Cells, Electrolyzers, and Batteries

With global energy demand increasing alongside population growth, the importance of efficient, clean energy conversion systems like fuel cells and batteries intensifies. Fuel cells are recognized for their ability to generate electricity from hydrogen and oxygen, with water as the only byproduct, and can also function in reverse as energy storage systems by producing hydrogen. Batteries chemically store energy and enable zero‐carbon emissions through their closed‐loop functionality. As demand grows, electrochemical impedance spectroscopy (EIS) is more actively used for investigating various electrochemical and physicochemical properties within electrochemical systems. Furthermore, EIS can serve as an in situ analysis method during operation, making it even more impactful in the near future. This article reviews the studies and applications of EIS, an advanced technique that provides insights into the electrochemical reaction at the interfaces and charge transfer processes within these systems. In addition, it provides an overview of the electrochemical principles governing these technologies, with a focus on the distinct roles and mechanisms of their components. The review offers a deeper understanding of EIS applications for studying electrochemical performance and physicochemical properties while also covering advancements in state‐of‐the‐art technologies for fuel cells, electrolyzers, and batteries.