Elucidating Electrochemical Losses in Anion Exchange Membrane Water Electrolyzers via EIS-DRT Analysis

Electrochemical impedance spectroscopy (EIS) is a powerful technique for analyzing interfacial and transport processes in anion exchange membrane water electrolysis (AEMWE); however, overlapping phenomena at similar frequencies often hinder interpretation. The distribution of relaxation times (DRT) method addresses this limitation by separating overlapping electrochemical processes, particularly when combined with the use of a reference electrode that enables isolation of anodic and cathodic contributions. In this work, EIS coupled with DRT analysis was first applied to study the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in a conventional three-electrode electrochemical cell, and then detailed EIS was carried out in a customized AEMWE single cell equipped with a reference electrode chamber. EIS measurements were conducted in 1.0 M KOH at current densities of 2.5–25 mA cm–2 at 25 °C and at various temperatures of 25–45 °C at a constant current density of 15 mA cm–2. A commercial stainless-steel-based electrode, Catrode®, was used as the anode, commercial Pt/C-coated carbon paper as the cathode, and the FumaSep® FAA-3-50 anion-exchange membrane to represent a practical electrode configuration. By combining three-electrode, in-cell half-cell, and full-cell measurements, this work resolves and cross-validates the electrode-specific losses of an electrochemically activated stainless-steel-derived anode (Catrode®) during AEMWE operation. DRT analysis resolved up to five relaxation processes associated with ionic and interfacial transport, anodic and cathodic charge-transfer kinetics, and mass-transport limitations. The measured full-cell response was reconstructed from the independently measured half-cell spectra, validating the electrode-resolved decomposition. Three-electrode measurements identified the anode as the dominant source of charge-transfer resistance, while mass transport losses were primarily localized at the cathode. These results demonstrate the utility of combined EIS-DRT analysis for the in situ diagnosis of performance-limiting processes and guiding AEMWE cell design improvements.