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Sci Rep. 2019 Feb 6;9(1):1532. doi: 10.1038/s41598-018-37307-x.

Uncovering The Role of Oxygen in Ni-Fe(OxHy) Electrocatalysts using In situ Soft X-ray Absorption Spectroscopy during the Oxygen Evolution Reaction.

Author information

1
Operando Characterization of Solar Fuel Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany.
2
Free University of Berlin, Department of Physics, Arnimallee 14, 14195, Berlin, Germany.
3
Operando Characterization of Solar Fuel Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489, Berlin, Germany. Kathrin.lange@helmholtz-berlin.de.
4
Universität Bielefeld, Physikalische Chemie, Universitätsstr. 25, 33615, Bielefeld, Germany. Kathrin.lange@helmholtz-berlin.de.

Abstract

In-situ X-ray absorption spectroscopy (XAS) at the oxygen K-edge was used to investigate the role of oxygen during the oxygen evolution reaction (OER) in an electrodeposited Ni-Fe(OxHy) electrocatalyst in alkaline pH. We show the rise of a pre-peak feature at 529 eV in the O K-edge spectra, correlated to the appearance of a shoulder at the Ni L3-edge and formation of oxidized Ni3+/4+-O. Then, for the first time, we track the spectral changes in a dynamic fashion in both the soft and hard X-ray regimes during cyclic voltammetry (in situ CV-XAS) to obtain a fine-tuned resolution of the potential-related changes. The pre-peak feature at the O K-edge likely signifies formation of an electron deficient oxygen site. The electrophilic oxygen species appears and disappears reversibly in correlation with the Ni2+ ↔ Ni3+/4+ process, and persists during OER catalysis as long the metal is oxidized. Our study provides new insight into OER electrocatalysis: Before onset of the O-O bond formation step, the catalytic oxyhydroxide has accumulated electron deficiencies by both, oxidation of transition metal ions and formation of partially oxidized oxygen sites.

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