Solar-powered water splitting is a dream reaction for constructing an artificial photosynthetic system for producing solar fuels. Natural photosystem II is a prototype template for research on artificial solar energy conversion by oxidizing water into molecular oxygen and supplying four electrons for fuel production. Although a range of synthetic molecular water oxidation catalysts have been developed, the understanding of O−O bond formation in this multielectron and multiproton catalytic process is limited, and thus water oxidation is still a big challenge. Herein, we report a trinuclear copper cluster that displays outstanding reactivity toward catalytic water oxidation inspired by multicopper oxidases (MCOs), which provides efficient catalytic four-electron reduction of O 2 to water. This synthetic mimic exhibits a turnover frequency of 20000 s −1 in sodium bicarbonate solution, which is about 150 and 15 times higher than that of the mononuclear Cu catalyst (F−N 2 O 2 Cu, 131.6 s −1 ) and binuclear Cu 2 complex (HappCu 2 , 1375 s −1 ), respectively. This work shows that the cooperation between multiple metals is an effective strategy to regulate the formation of O−O bond in water oxidation catalysis.

Water splitting is one of the most promising solutions for storing solar energy in a chemical bond. Water oxidation is still the bottleneck step because of its inherent difficulty and the limited understanding of the O−O bond formation mechanism. Molecular catalysts provide a platform for understanding this process in depth and have received wide attention since the first Ru‐based catalyst was reported in 1982. RuV=O is considered a key intermediate to initiate the O−O bond formation through either a water nucleophilic attack (WNA) pathway or a bimolecular coupling (I2M) pathway. Herein, we report a Ru‐based catalyst that displays water oxidation reactivity with RuIV=(O) with the help of a redox‐active ligand at pH 7.0. The results of electrochemical studies and DFT calculations disclose that ligand oxidation could significantly improve the reactivity of RuIV=O toward water oxidation. Under these conditions, sustained water oxidation catalysis occurs at reasonable rates with low overpotential (ca. 183 mV).

Molecular catalysis of water oxidation has been intensively investigated, but its mechanism is still not yet fully understood. This study aims at capturing and identifying key short-lived intermediates directly during the water oxidation catalyzed by a cobalt-tetraamido macrocyclic ligand complex using a newly developed an in situ electrochemical mass spectrometry (EC-MS) method. Two key ligand-centered-oxidation intermediates, [(L2–)­CoIIIOH] and [(L2–)­CoIIIOOH], were directly observed for the first time, and further confirmed by 18O-labeling and collision-induced dissociation studies. These experimental results further confirmed the rationality of the water nucleophilic attack mechanism for the single-site water oxidation catalysis. This work also demonstrated that such an in situ EC-MS method is a promising analytical tool for redox catalytic processes, not only limited to water oxidation.

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Herein we reported a molecular trinuclear nickel catalyst (defined as TNC-Ni) for water oxidation. This TNC-Ni catalyst exhibits high catalytic performance and stability under neutral conditions (pH 7). Electrochemical studies disclose that the cooperation among the three nickel sites plays a vital role in both charge accumulation and O-O bond formation. This trinuclear nickel catalyst can accomplish the 4eoxidation of water by involving all three nickel sites and the O-O bond formation is trigged by the charge distribution process from 5 to 5 dp via proton-coupled electron transfer.