Investigating Performance Degradation in CO 2 Electrolyzers Using Impedance Spectroscopy and Distribution of Relaxation Times Analysis

The implementation of gas diffusion electrodes (GDE) in CO 2 electrolyzers is essential for achieving industrially relevant current densities 1 , but faces challenges in stability. These issues primarily stem from flooding in the catalyst layer and salt precipitation, which hinder CO 2 transport to the catalyst surface and favor the competing hydrogen evolution reaction (HER) 2 . To address these challenges, we applied hydrophobic pre-treatment to commercial gas diffusion layers (GDLs), followed by the incorporation of copper nanoparticles (CuNPs) as catalyst. The modified GDE demonstrated enhanced operational stability by mitigating flooding in a flow cell configuration. In this work, we employed nondestructive electrochemical impedance spectroscopy (EIS) combined with distribution of relaxation times (DRT) analysis to deconvolute overlapping electrochemical and physical processes 3 , including ionic and electronic conduction, faradaic reactions, and mass transport. Stability testing revealed shifts in DRT peaks, reflecting changes in timescales, and variations in peak areas, indicating increased resistances associated with electrode kinetics and mass transport upon flooding. These changes corresponded to reduced CO₂ availability at the triple phase boundary (TPB) and a subsequent decline in CO₂RR current density. These findings underscore the importance of maintaining an optimized TPB to enhance catalyst performance and stability in GDE-based electrolyzers. Furthermore, we highlight the effectiveness of EIS and DRT analysis as powerful diagnostic tools for monitoring electrolyzer performance. Wakerley, D. et al. Gas diffusion electrodes, reactor designs and key metrics of low-temperature CO2 electrolysers. Nat Energy 7 , 130–143 (2022). Leonard, M. E., Clarke, L. E., Forner‐Cuenca, A., Brown, S. M. & Brushett, F. R. Investigating Electrode Flooding in a Flowing Electrolyte, Gas‐Fed Carbon Dioxide Electrolyzer. ChemSusChem 13 , 400–411 (2020). Maradesa, A. et al. Advancing electrochemical impedance analysis through innovations in the distribution of relaxation times method. Joule 8 , 1958–1981 (2024).