Decoding Electrocatalyst Degradation Using Time-Resolved Electrochemical Impedance Analysis.

Evaluating the long-term stability of electrocatalysts under operational conditions is critical for understanding performance degradation in fuel cells, electrolyzers, and metal-air batteries. Conventional electrochemical techniques, such as chronoamperometry and chronopotentiometry, often rely on simple current or overpotential versus time correlations, offering limited insight into the evolving structure-performance relationships. In this study, we introduce a time-resolved electrochemical impedance analysis (tr-EIA) protocol that enables the real-time tracking of key electrochemical parameters, including current/overpotential, electrochemical double-layer capacitance, charge transfer resistance, electrolyte resistance, and process relaxation times, all in a single experiment. By applying tr-EIA to commercial RuO2 and Pt/C catalysts across representative electrochemical reactions, we reveal time-resolved structural dynamics and uncover distinct degradation pathways at different stages of operation. Notably, structural degradation tied to changes in the electrochemically active surface area is distinguished from kinetic factors, such as increased resistance, with quantitative insights provided by the proposed surface area contribution factor. This single-run tr-EIA approach delivers a comprehensive understanding of electrochemical and structural evolution, offering a powerful tool to decode the mechanisms governing electrocatalyst stability under realistic operating conditions.