In situ characterization of cofacial Co(IV) centers in Co4O4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts

Casey N. Brodsky, Ryan G. Hadt, Dugan Hayes, Benjamin J. Reinhart, Nancy Li, Lin X. Chen, Daniel G. Nocera*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

50 Scopus citations

Abstract

The Co4O4 cubane is a representative structural model of oxidic cobalt oxygen-evolving catalysts (Co-OECs). The Co-OECs are active when residing at two oxidation levels above an all-Co(III) resting state. This doubly oxidized Co(IV)2 state may be captured in a Co(III)2(IV)2 cubane. We demonstrate that the Co(III)2(IV)2 cubane may be electrochemically generated and the electronic properties of this unique high-valent state may be probed by in situ spectroscopy. Intervalence charge-transfer (IVCT) bands in the near-IR are observed for the Co(III)2(IV)2 cubane, and spectroscopic analysis together with electrochemical kinetics measurements reveal a larger reorganization energy and a smaller electron transfer rate constant for the doubly versus singly oxidized cubane. Spectroe-lectrochemical X-ray absorption data further reveal systematic spectral changes with successive oxidations from the cubane resting state. Electronic structure calculations correlated to experimental data suggest that this state is best represented as a localized, antiferromagnetically coupled Co(IV)2 dimer. The exchange coupling in the cofacial Co(IV)2 site allows for parallels to be drawn between the electronic structure of the Co4O4 cubane model system and the high-valent active site of the Co-OEC, with specific emphasis on the manifestation of a doubly oxidized Co(IV)2 center on O–O bond formation.

Original languageEnglish (US)
Pages (from-to)3855-3860
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue number15
DOIs
StatePublished - Apr 11 2017

Keywords

  • Electrocatalysis
  • Oxygen evolution reaction
  • Renewable energy
  • Solar-to-fuels
  • Water splitting

ASJC Scopus subject areas

  • General

Fingerprint Dive into the research topics of 'In situ characterization of cofacial Co(IV) centers in Co<sub>4</sub>O<sub>4</sub> cubane: Modeling the high-valent active site in oxygen-evolving catalysts'. Together they form a unique fingerprint.

Cite this