Compositional Tuning and Surface Restructuring Synergistically Enhance Perovskite Ferrite Catalysts for Hydrogen Evolution in a Membrane‐Less Electrolyzer

ABSTRACT Balancing stability and activity of the hydrogen evolution reaction (HER) electrocatalysis remains challenging for advanced electrolysis technologies. This work introduces a synergistic design strategy to tackle the challenge with in situ surface restructuring. Fe‐based double perovskite is developed with an optimal electronic structure for HER catalysis, delivering an overpotential of 325 mV in 0.1 m KOH and 184 mV in 1 m KOH at 10 mA/cm 2 , among the best reported. Additionally, the catalyst exhibited remarkable self‐improving stability, with specific activity increasing 1.98 times at 300 mV overpotential after 20 h, due to the restructuring of an amorphous layer confirmed with transmission electron microscopy. To demonstrate practical utility, the catalyst was integrated into an active flow membraneless electrolyzer (AFME), a promising technology that is currently limited by instability. The device demonstrated outstanding operational stability for 1000 h at 50 mA/cm 2 , with a minimal decay rate of 0.25 mV/h, establishing a new benchmark for membraneless systems. This work not only presents a powerful strategy for designing self‐improving catalysts but also validates its practical efficacy in next generation electrolyzer technologies, paving the way for cost‐effective green hydrogen production.