Combinatorial Use of Reference Electrodes and DRT for Disentangling AEM Electrolyzer Losses.

Abstract

Anion exchange membrane water electrolyzers (AEMWEs) offer a promising alternative to proton exchange membrane (PEM) electrolyzers, leveraging non-precious-metal catalysts and alkaline electrolytes for cost reduction. However, challenges persist in achieving long-term durability, high current densities, and stable membrane performance. While previous studies have examined AEM development, a comprehensive structural-electrochemical analysis of AEMWE components under prolonged operation remains limited. This study presents a detailed structural and electrochemical characterization of a commercial AEMWE, where its full-cell performance was matched with the intrinsic half-electrode performance through the use of dual reference electrodes. The electrochemical analysis was supported by a thorough tomographic and spectroscopic investigation of each electrode, thereby providing for the first time a complete materials analysis of the commercial NiFeO_x anode and Raney nickel cathode. Electrochemical characterization using LSV, EIS, and a dual reference electrode setup revealed full-cell performance of 1.0 A cm^-2 at 2.2 V (ambient) and 1.1 A cm^-2 at 2.0 V (60 °C), with an HHV efficiency of 74.5% at 1.0 A cm^-2. Long-term operation over 1000 h at 1.0 A cm^-2, 60 °C, in 1.0 M KOH resulted in a substantial polarization resistance increase beyond 230 h, despite an unexpected continuous improvement in MEA performance due to membrane degradation. DRT analysis, coupled with reference electrode studies, was critical in isolating losses. Low-frequency peaks (1.5-25 Hz) were linked to bubble formation, while intermediate-frequency (50-2000 Hz) and high-frequency (>2000 Hz) processes corresponded to charge transfer and ionic transport. The NiFeO_x anode exhibited better charge transfer, whereas the Raney nickel cathode showed higher polarization resistance.