Structural and functional role of anions in electrochemical water oxidation probed by arsenate incorporation into cobalt-oxide materials
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Date
2019Author
Villalobos Porras, Javier
González Flores, Diego
Klingan, Katharina
Chernev, Petko
Kubella, Paul
Urcuyo Solórzano, Roberto
Pasquini, Chiara
Mohammadi, Mohammad Reza
Smith, Rodney D.L.
Montero Villalobos, Mavis Lili
Dau, Holger
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Direct (photo)electrochemical production of non-fossil fuels from water and CO2 requires water-oxidation catalysis at near-neutral pH in the presence of appropriate anions that serve as proton acceptors. We investigate the largely enigmatic structural role of anions in water oxidation for the prominent cobalt-phosphate catalyst (CoCat), an amorphous and hydrated oxide material. Co3([(P/As)O]4)2·8H2O served, in conjunction with phosphate–arsenate exchange, as a synthetic model system. Its structural transformation was induced by prolonged operation at catalytic potentials and probed by X-ray absorption spectroscopy not only at the metal (Co), but for the first time also at the anion (As) K-edge. For initially isostructural microcrystals, anion exchange determined the amorphization process and final structure. Comparison to amorphous electrodeposited Co oxide revealed that in CoCat, the arsenate binds not only at oxide-layer edges, but also arsenic substitutes cobalt positions within the layered-oxide structure in an unusual AsO6 coordination. Our results show that in water oxidation catalysis at near-neutral pH, anion type and exchange dynamics correlate with the catalyst structure and redox properties.
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10.1039/C9CP01754BCollections
- Química [360]