Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 21, Issue 23, Pages 12485-12493Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c9cp01754b
Keywords
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Funding
- Posgrado en Quimica and Vicerrectoria de Investigacion (UCR)
- CONICIT-MICIT (Costa Rica)
- German Federal Ministry of Education and Research (Bundesministerium fur Bildung und Forschung
- BMBF
- CO2EKAT project) [03SF0523]
- Deutsche Forschungsgemeinschaft (DFG) [SP 1613]
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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. Co-3([(P/As)O](4))(2)center dot 8H(2)O 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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