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

doi:10.1073/pnas.1701816114

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

Chemistry

Research output: Contribution to journal › Article › peer-review

97 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 language	English (US)
Pages (from-to)	3855-3860
Number of pages	6
Journal	Proceedings of the National Academy of Sciences of the United States of America
Volume	114
Issue number	15
DOIs	https://doi.org/10.1073/pnas.1701816114
State	Published - Apr 11 2017

Funding

ACKNOWLEDGMENTS. 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.

Keywords

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

ASJC Scopus subject areas

General

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1073/pnas.1701816114

Cite this

Brodsky, C. N., Hadt, R. G., Hayes, D., Reinhart, B. J., Li, N., Chen, L. X., & Nocera, D. G. (2017). In situ characterization of cofacial Co(IV) centers in Co₄O₄ 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), 3855-3860. https://doi.org/10.1073/pnas.1701816114

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

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.",

keywords = "Electrocatalysis, Oxygen evolution reaction, Renewable energy, Solar-to-fuels, Water splitting",

author = "Brodsky, {Casey N.} and Hadt, {Ryan G.} and Dugan Hayes and Reinhart, {Benjamin J.} and Nancy Li and Chen, {Lin X.} and Nocera, {Daniel G.}",

year = "2017",

month = apr,

day = "11",

doi = "10.1073/pnas.1701816114",

language = "English (US)",

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Brodsky, CN, Hadt, RG, Hayes, D, Reinhart, BJ, Li, N, Chen, LX & Nocera, DG 2017, 'In situ characterization of cofacial Co(IV) centers in Co₄O₄ cubane: Modeling the high-valent active site in oxygen-evolving catalysts', Proceedings of the National Academy of Sciences of the United States of America, vol. 114, no. 15, pp. 3855-3860. https://doi.org/10.1073/pnas.1701816114

In situ characterization of cofacial Co(IV) centers in Co₄O₄ cubane: Modeling the high-valent active site in oxygen-evolving catalysts. / Brodsky, Casey N.; Hadt, Ryan G.; Hayes, Dugan et al.
In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 114, No. 15, 11.04.2017, p. 3855-3860.

Research output: Contribution to journal › Article › peer-review

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T1 - In situ characterization of cofacial Co(IV) centers in Co4O4 cubane

T2 - Modeling the high-valent active site in oxygen-evolving catalysts

AU - Brodsky, Casey N.

AU - Hadt, Ryan G.

AU - Hayes, Dugan

AU - Reinhart, Benjamin J.

AU - Li, Nancy

AU - Chen, Lin X.

AU - Nocera, Daniel G.

PY - 2017/4/11

Y1 - 2017/4/11

N2 - 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.

AB - 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.

KW - Electrocatalysis

KW - Oxygen evolution reaction

KW - Renewable energy

KW - Solar-to-fuels

KW - Water splitting

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