Diagnostics of electrocatalytic systems by electrochemical impedance spectroscopy

The demand for new electrochemical reaction technologies and related engineering aspects is rising due to the current transition to green technologies and to use of renewable electricity sources. In this context, research of new electrocatalytic pathways to improve processes' efficiency and reduce their costs is essential. Electrochemical characterizations are usually employed in the study of new electrocatalysts and electrochemical systems. Among them, electrochemical impedance spectroscopy (EIS) is nowadays highly exploited to investigate charge transport and transfer phenomena. Nevertheless, EIS can be used for other purposes as well. This review will focus on the use of the EIS technique as a diagnostic tool in the electrocatalysis field. Surprisingly, among the numerous electrochemical reactions, the areas in which EIS is employed as a monitoring tool are very few. The most important are the ones with a high technological maturity level and, therefore, that are already employed in the industry or for commercial applications: e.g., batteries, fuel cells, and biosensors. Devices belonging to these groups need to control their working conditions with fast and reliable methods, even at the cost of losing a small amount of precision degree. In this perspective, EIS is often used in combination with machine learning algorithms to develop easy-to-use diagnostic devices that aim to a rapid indication of the system status rather than a precise understanding of all the underlying processes.