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 Li2Co2O4 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 Co3+ to Co4+ 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 Co4+ site, rather than the Co3+ site or the oxygen vacancy site, is mainly responsible for the high OER activity.
Highlights
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
We started by studying the pH-dependence of the oxygen evolution reaction (OER) activity, which can provide us with an initial overview of the possible active sites and reaction paths[14,32,33]
It was suggested that a conventional OER involving four concerted proton–electron transfer steps on a surface metalion center, exhibited pH-independent activity, while latticeoxygen oxidation from highly covalent oxides involving nonconcerted proton–electron transfer steps exhibited a strong pHdependent OER activity[14]
Summary
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. New materials need to be designed to replace the benchmark OER catalysts that typically consist of precious metal oxides such as IrO2 and RuO2. For this purpose, 3d transitionmetal (TM) oxides have recently emerged as promising candidates. 3d transitionmetal (TM) oxides have recently emerged as promising candidates They are inexpensive because they are earth abundant and environmentally friendly and have tunable chemical reactivities depending on the type of electronic and crystal structures. Anionic redox processes at lattice-oxygen sites were considered[14,15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
