Bromide‐Mediated Low‐Energy Ru ^IV ═O Pathway of Stable Water Oxidation

ABSTRACT Mimicking natural photosynthesis to split water into oxygen and hydrogen represents a promising pathway for transitioning from fossil fuels to a sustainable energy future. It is extremely challenging to duplicate the efficient and elegant oxygen evolution complex of photosynthesis II of oxidizing water to O 2 being regarded as the bottleneck of water splitting. Cutting‐edge artificial molecular water oxidation catalysts (WOCs) with low overpotentials are highly desirable for efficient water oxidation. Here we report the design of a molecular water oxidation catalyst (WOC) RuN5 (Ru(N5)(pic) 2 ; N5 = 4‐tert‐butyl‐2,6‐di(1′,8′‐naphthyrid‐2′‐yl)pyridine, pic = 4‐picoline). Following electrochemical activation and bromide mediation, RuN5 achieves a high turnover frequency of 2604 s −1 with a low overpotential of 363 mV at pH 7. The catalyst is highly stable, maintaining a steady current density of 1.8 mA cm −2 over 200 h. Mechanistic studies reveal that activation and bromide mediation facilitate O–O bond formation via a ligand‐oxidized [Ru IV ═ O] 2+ intermediate through a low energy pathway, distinct from the classical [Ru V (O)] 3+ route. This work opens a new avenue for developing efficient molecular WOCs and advancing artificial photosynthesis.