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In situ characterization of cofacial Co(IV) centers in Co_4O_4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts

Brodsky, Casey N. and Hadt, Ryan G. and Hayes, Dugan and Reinhart, Benjamin J. and Li, Nancy and Chen, Lin X. and Nocera, Daniel G. (2017) In situ characterization of cofacial Co(IV) centers in Co_4O_4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts. Proceedings of the National Academy of Sciences of the United States of America, 114 (15). pp. 3855-3860. ISSN 0027-8424. PMCID PMC5393202. https://resolver.caltech.edu/CaltechAUTHORS:20180612-101929196

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Abstract

The Co_4O_4 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. Spectroelectrochemical 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 Co_4O_4 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.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1073/pnas.1701816114DOIArticle
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5393202/PubMed CentralArticle
http://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1701816114/-/DCSupplementalPublisherSupporting Information
ORCID:
AuthorORCID
Hadt, Ryan G.0000-0001-6026-1358
Hayes, Dugan0000-0003-4171-5179
Chen, Lin X.0000-0002-8450-6687
Nocera, Daniel G.0000-0001-5055-320X
Alternate Title:In situ characterization of cofacial Co(IV) centers in Co4O4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts.
Additional Information:© 2017 National Academy of Sciences. Contributed by Daniel G. Nocera, February 7, 2017 (sent for review November 23, 2016; reviewed by Kyle M. Lancaster and James K. McCusker) This material is based upon work supported under the Solar Photochemistry Program of the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences of the US Department of Energy (D.G.N.) and the Solar Energy Conversion program in Chemical Sciences and Engineering Division at Argonne National Laboratory (ANL) under Contract DE-AC02-06CH11357. R.G.H. is an Enrico Fermi Fellow at ANL and D.H. is a Joseph J. Katz Postdoctoral Fellow at ANL. C.N.B. is a National Science Foundation Graduate Research Fellow at Harvard University. Use of beamline 12BM at the Advanced Photon Source at ANL was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-AC02-06CH11357. C.N.B. and R.G.H. contributed equally to this work. Author contributions: C.N.B., R.G.H., and D.G.N. designed research; C.N.B., R.G.H., D.H., and N.L. performed research; C.N.B., R.G.H., D.H., B.J.R., N.L., and L.X.C. contributed new reagents/analytic tools; C.N.B., R.G.H., D.H., N.L., and D.G.N. analyzed data; and C.N.B., R.G.H., and D.G.N. wrote the paper. Reviewers: K.M.L., Cornell University; and J.K.M., Michigan State University. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1701816114/-/DCSupplemental.
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-06CH11357
Argonne National LaboratoryUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:electrocatalysis; oxygen evolution reaction; renewable energy; solar-to-fuels; water splitting
Issue or Number:15
PubMed Central ID:PMC5393202
Record Number:CaltechAUTHORS:20180612-101929196
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180612-101929196
Official Citation: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 Proceedings of the National Academy of Sciences Apr 2017, 114 (15) 3855-3860; DOI: 10.1073/pnas.1701816114
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86999
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:12 Jun 2018 17:58
Last Modified:03 Oct 2019 19:51

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