Role of the\nIonomer in Supporting Electrolyte-Fed\nAnion Exchange Membrane Water Electrolyzers

While anion exchange membrane water electrolyzers (AEMWEs)\nhave\nachieved significant performance advances in recent decades, overpotentials\nremain high relative to their proton exchange membrane water electrolyzer\n(PEMWE) counterparts, requiring AEMWE-specific catalyst layer design\nstrategies to further advance this technology. In this work, the role\nof the ionomer in catalyst layer structure and quality, catalyst layer\nstability, and ion conduction for supporting electrolyte-fed AEMWEs\nis assessed for catalyst layers composed of NiFe<sub>2</sub>O<sub>4</sub> and PiperION TP85 from Versogen at variable ionomer contents\n(0–30 wt %) for tests up to 200 h. The results reveal that,\nfor supporting electrolyte-fed AEM devices, the ionomer is not required\nfor ion conduction through the catalyst layer. Instead, the ionomer\nis found to play a critical role in catalyst layer structure and stability,\nwhere intermediate ionomer contents lead to the lowest overpotentials,\nhighest effective surface areas, and lowest catalyst layer resistances.\nCatalyst layer stability is found to be a function of both catalyst\nadhesion and ionomer loss. These results show that an ionomer may\nbe selected which is not of the same chemistry as the anion exchange\nmembrane, mitigating ionomer stability concerns throughout the catalyst\nlayer and offering a pathway towards highly active and stable AEMWEs.