Triggering Hard Lewis Acidity via Oxygen Vacancy Modulation in Cr ₂ O ₃ to Stabilize MnCoP for Seawater Splitting

Seawater electrolysis represents a sustainable frontier for green hydrogen production, yet its practical viability is severely hindered by the deleterious competition of chloride ions (Cl − ) and the detrimental accumulation of surface precipitates, both of which compromise reaction kinetics and electrode integrity. Here, we report an oxygen vacancy (O v )‐rich Cr 2 O 3 overlayer on MnCoP nanoarrays (MnCoP‐Cr 2 O 3 ‐O v ) that serves as a robust corrosion‐shield. O v ‐induced charge redistribution triggers Hard Lewis Acidity at the surface, amplifying hydroxide (OH − ) affinity to establish a localized alkaline buffer. This unique microenvironment accelerates reaction kinetics while creating a selective barrier that repels Cl − and inhibits precipitate nucleation. Consequently, the MnCoP‐Cr 2 O 3 ‐O v delivers exceptional bifunctional activity in alkaline seawater, requiring remarkably low overpotentials of 199 and 390 mV to reach an industrial current density of 500 mA cm −2 for hydrogen and oxygen evolution reactions, respectively. Furthermore, it demonstrates sustained stability (>100 h) at 200 mA cm −2 and achieves a 13% solar‐to‐hydrogen (STH) efficiency in a photovoltaic‐powered anion‐exchange membrane electrolyzer. This work provides a transformative strategy for tailoring surface Lewis acidity to construct durable, high‐performance electrodes for industrial seawater‐to‐hydrogen conversion.