Mechanisms of homogeneous water oxidation

This review focuses on mechanistic insights into catalytic water oxidation, with an emphasis on elementary steps governing O–O bond formation and O 2 evolution in both thermal and photodriven systems. Particular attention is given to the generation and reactivity of high-valent metal–oxo and metal–hydroperoxo species formed via stepwise proton-coupled electron-transfer (PCET) processes. Kinetic analyses employing sacrificial oxidants and visible-light photoredox catalysts, such as [Ru II (bpy) 3 ] 2+ (bpy = 2,2’-bipyridine) and 2,3-dichloro-5,6-dicyano- p -benzoquinone (DDQ), elucidate rate-determining steps, redox potentials, and catalyst activation pathways. Mechanistic distinctions between water nucleophilic attack and radical coupling pathways are critically evaluated, along with evidence for dynamic catalyst evolution from molecular precursors to metal oxide nanoparticles under catalytic conditions. Time-resolved spectroscopic and electrochemical studies further reveal the role of transient intermediates in sustaining catalytic turnover. The broader oxidation chemistry of metal–oxygen species provides a unifying framework that connects water oxidation to diverse oxidative transformations. Together, these mechanistic insights establish structure–reactivity relationships that underpin efficient O₂ evolution and offer molecular-level design principles for next-generation water oxidation catalysts in artificial photosynthetic systems.