Accelerating water oxidation - a mixed Co/Fe polyoxometalate with improved turnover characteristics

Identifier:  imarina:9332003

Handle: https://hdl.handle.net/20.500.11797/imarina9332003

Authors:  Soriano-López, J; Steuber, FW; Mulahmetovic, M; Besora, M; Clemente-Juan, JM; O'Doherty, M; Zhu, NY; Hill, CL; Coronado, E; Poblet, JM; Schmitt, W

Abstract:
Water oxidation is a bottleneck reaction for the establishment of solar-to-fuel energy conversion systems. Earth-abundant metal-based polyoxometalates are promising heterogeneous water oxidation catalysts that can operate in a wide pH range. However, detailed structure-reactivity relationships are not yet comprehensively understood, hampering the design and synthesis of more effective polyoxometalate-based oxidation catalysts. Here we report the synthesis of an ordered, mixed-metal cobalt-iron Weakley archetype [CoII2(H2O)2FeIII2(CoIIW9O34)2]14− (Co2Fe2-WS), which unexpectedly highlights the strong influence of the central, coordinatively saturated metal ions on the catalytic water oxidation characteristics. The resulting species exhibits catalytic turnover frequencies which are up to 4× higher than those of the corresponding archetype tetracobalt-oxo species [CoII2(H2O)2CoII2(PW9O34)2]10− (Co4-WS). It is further striking that the system becomes catalytically inactive when one of the central positions is occupied by a WVI ion as demonstrated by [CoII2(H2O)2CoIIWVI(CoIIW9O34)2]12− (Co3W-WS). Importantly, this study demonstrates that coordinatively saturated metal ions in this central position, which at first glance appear insignificant, do not solely have a structural role but also impart a distinctive structural influence on the reactivity of the polyoxometalate. These results provide unique insights into the structure-reactivity relationships of polyoxometalates with improved catalytic performance characteristics.