Ionomer Interphase Layers Enable Efficient Anion-Exchange Membrane Water Electrolyzer Operation at Low pH

Anion-exchange membrane water electrolysis (AEMWE) is an emerging green hydrogen technology. As of today, AEM water electrolyzers operate using highly alkaline electrolytes. Design strategies to operate AEMWE systems sustainably under lower alkalinity toward pure water conditions have become a scientific priority. Under low-alkaline conditions, the alkaline-exchange ionomer (AEI) is, in addition to the AEM, the key ion-transport medium inside the AEMWE cell. While prior work addressed ion transport and the ionomer-catalyst interface at the anode in low-pH AEMWEs, a thorough investigation at the cathode side, including different AEI architectures, received limited attention. In this contribution, we explore the impact of AEI architectures in AEMWE cathodes using an ionomer and a membrane that are both commercially available. We demonstrate separate ionomer top layer (ITL) interphases placed between the cathode catalyst layer and the membrane as the most effective strategy toward high cell performance under low pH feeding. ITLs enabled performance benefits even at pH 14, which leads us to perceive their mechanistic role as an ion-transport buffer enabling ready ion migration from the cathode to the anode. Our insights on the ITL architecture will aid the design of AEMWE cells for sustained efficient operation under pure water feeds.