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Issue 23, 2019
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Structural and functional role of anions in electrochemical water oxidation probed by arsenate incorporation into cobalt-oxide materials

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Abstract

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.

Graphical abstract: Structural and functional role of anions in electrochemical water oxidation probed by arsenate incorporation into cobalt-oxide materials

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Article information


Submitted
29 Mar 2019
Accepted
10 May 2019
First published
10 May 2019

Phys. Chem. Chem. Phys., 2019,21, 12485-12493
Article type
Paper

Structural and functional role of anions in electrochemical water oxidation probed by arsenate incorporation into cobalt-oxide materials

J. Villalobos, D. González-Flores, K. Klingan, P. Chernev, P. Kubella, R. Urcuyo, C. Pasquini, M. R. Mohammadi, R. D. L. Smith, M. L. Montero and H. Dau, Phys. Chem. Chem. Phys., 2019, 21, 12485
DOI: 10.1039/C9CP01754B

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