Operando Diagnosis of MEA-Type CO₂ Electrolyzer via Distribution of Relaxation Times Analysis

The membrane electrode assembly (MEA) electrolyzer stands out as the most practical design for CO 2 electrolysis. However, its compact configuration poses challenges in monitoring internal dynamic behaviors under real operating conditions. Here, we employ operando electrochemical impedance spectroscopy (EIS) testing and distribution of relaxation times (DRT) analysis to probe the complex charge-transfer and mass-transport processes within the MEA electrolyzer for CO 2 to CO conversion. By systematically varying assembly and electrolysis parameters, we successfully disentangle the parameter dependencies and identify specific processes in the DRT spectra. Furthermore, integrating DRT analysis with post-mortem characterizations, including scanning electron microscopy (SEM) and water contact angle measurements, reveals that the obstructed CO 2 mass transport is a significant factor contributing to performance failure in the stability test. These findings emphasize the reliability and practicality of operando EIS-DRT analysis in diagnosing the MEA electrolyzer and offer promising avenues for further improvements in the CO 2 electrolysis lifespan.