Pivotal Role of Geometry Regulation on O-O Bond Formation Mechanism of Bimetallic Water Oxidation Catalysts.

In this study, we highlight the impact of catalyst geometry on the formation of O-O bonds in Cu ₂ and Fe ₂ catalysts. A series of Cu ₂ complexes with diverse linkers are designed as electrocatalysts for water oxidation. Interestingly, the catalytic performance of these Cu ₂ complexes is enhanced as their molecular skeletons become more rigid, which contrasts with the behavior observed in our previous investigation with Fe ₂ analogs. Moreover, mechanistic studies reveal that the reactivity of the bridging O atom results in distinct pathways for O-O bond formation in Cu ₂ and Fe ₂ catalysts. In Cu ₂ systems, the coupling takes place between a terminal Cu ^III -OH and a bridging μ-O⋅ radical. Whereas in Fe ₂ systems, it involves the coupling of two terminal Fe-oxo entities. Furthermore, an in-depth structure-activity analysis uncovers the spatial geometric prerequisites for the coupling of the terminal OH with the bridging μ-O⋅ radical, ultimately leading to the O-O bond formation. Overall, this study emphasizes the critical role of precisely adjusting the spatial geometry of catalysts to align with the O-O bonding pathway.
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