Advanced Impedance\nAnalysis for Performance Degradation\nduring Low-Temperature CO<sub>2</sub> Electroreduction

Electrochemical impedance spectroscopy (EIS) is a powerful\ntool\ncommonly used to study electrochemical systems. Nevertheless, its\napplication in CO<sub>2</sub> electroreduction has been so far limited\ndue to its complex reaction mechanism and environment. Although initial\nfindings have demonstrated the viability of applying EIS analysis\nin CO<sub>2</sub> electrolyzers, the assignment of individual processes\nin the impedance spectra remains ambiguous. Therefore, a more detailed\ninvestigation, especially focused on its application in evaluating\ndegradation mechanisms, is essential. In this study, a stable gas\ndiffusion electrode (GDE) system was developed for a comprehensive\nEIS and distribution of relaxation time (DRT) evaluation to assess\nkey degradation mechanisms under accelerated stress conditions such\nas high current density and low operating temperature. Validated by\npost-mortem analysis and complementary methods, we demonstrate the\nviability of this approach for operando monitoring of CO<sub>2</sub> electroreduction by assigning individual mechanistic processes in\nthe GDE and linking them to performance degradation over time.