Bridging the Gap Between Laboratory Catalyst Research and Practical Water Electrolyzer Commercialization.

Water electrolyzers are key technologies for enabling a carbon-neutral society by facilitating sustainable hydrogen production. Despite extensive efforts to develop highly active catalysts, a persistent gap remains between catalyst performance evaluated in rotating disk electrode (RDE) systems and that achieved in practical membrane electrode assembly (MEA) configurations. In this perspective, we highlight the origins of this discrepancy and emphasize that intrinsic catalytic activity alone is insufficient to predict electrolyzer performance. Using the acidic hydrogen evolution reaction (HER) as a model system, we demonstrate that apparent activity metrics such as mass activity and Tafel slope can be significantly influenced by catalyst loading, composition, and measurement conditions in RDE, often leading to misleading conclusions. In contrast, MEA performance is governed by complex interfacial phenomena including mass, electron, and charge transport. A similar behavior was also observed for alkaline HER and acidic oxygen evolution reaction (OER). We further present case studies illustrating the critical roles of electron transfer and durability in water electrolyzers. In addition, recent advances in proton-exchange-membrane water electrolyzer commercialization are discussed, highlighting the importance of system-level optimization, including ionomer distribution control and scalable manufacturing via slot-die coating, which enabled the deployment of a 2.5 MW system. Overall, bridging the gap between laboratory catalyst research and industrial water electrolyzer applications requires a shift from catalyst-centric design toward integrated system-level engineering.