Voltage- and time-dependent valence state transition in cobalt oxide catalysts during the oxygen evolution reaction.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32332788.
- Also identified by DOI 10.1038/s41467-020-15925-2 and PMC identifier 7181785.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The ability to determine the electronic structure of catalysts during electrochemical reactions is highly important for identification of the active sites and the reaction mechanism. Here we successfully applied soft X-ray spectroscopy to follow in operando the valence and spin state of the Co ions in Li<sub>2</sub>Co<sub>2</sub>O<sub>4</sub> under oxygen evolution reaction (OER) conditions. We have observed that a substantial fraction of the Co ions undergo a voltage-dependent and time-dependent valence state transition from Co<sup>3+</sup> to Co<sup>4+</sup> accompanied by spontaneous delithiation, whereas the edge-shared Co-O network and spin state of the Co ions remain unchanged. Density functional theory calculations indicate that the highly oxidized Co<sup>4+</sup> site, rather than the Co<sup>3+</sup> site or the oxygen vacancy site, is mainly responsible for the high OER activity.