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Title: X-ray spectroscopic characterization of Co(IV) and metal–metal interactions in Co 4O 4: Electronic structure contributions to the formation of high-valent states relevant to the oxygen evolution reaction

Abstract

In this paper, the formation of high-valent states is a key factor in making highly active transition metal-based catalysts of the oxygen-evolving reaction (OER). These high oxidation states will be strongly influenced by the local geometric and electronic structures of the metal ion, which is difficult to study due to spectroscopically active and complex backgrounds, short lifetimes, and limited concentrations. Here, we use a wide range of complementary X-ray spectroscopies coupled to DFT calculations to study Co 4O 4 cubanes, which provide insight into the high-valent Co(IV) centers responsible for the activity of molecular and heterogeneous OER catalysts. The combination of X-ray absorption and 1s3p resonant inelastic X-ray scattering (Kβ RIXS) allow Co(IV) to be isolated and studied against a spectroscopically active Co(III) background. Co K- and L-edge X-ray absorption data allow for a detailed characterization of the 3d-manifold of effectively localized Co(IV) centers and provide a direct handle on the ligand field environment and covalency of the t 2g-based redox active molecular orbital. Kβ RIXS is also shown to provide a powerful probe of Co(IV), and specific spectral features are sensitive to the degree of oxo-mediated metal-metal coupling across Co 4O 4. Guided by the data, calculations show electron-holemore » delocalization can actually oppose Co(IV) formation. Computational extension of Co 4O 4 to CoM 3O 4 structures (M = redox-inactive metal) defines electronic structure contri-butions to Co(IV) formation. Redox activity is shown to be linearly related to covalency, and M(III) oxo inductive effects on Co(IV) oxo bonding can tune the covalency of high-valent sites over a large range and thereby tune E 0 over hundreds of mVs.« less

Authors:
 [1];  [1];  [2];  [2];  [1];  [1];  [2];  [3]
  1. Argonne National Lab. (ANL), Lemont, IL (United States)
  2. Harvard Univ., Cambridge, MA (United States)
  3. Argonne National Lab. (ANL), Lemont, IL (United States); Northwestern Univ., Evanston, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1339577
DOE Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 138; Journal Issue: 34
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Hadt, Ryan G., Hayes, Dugan, Brodsky, Casey N., Ullman, Andrew M., Casa, Diego M., Upton, Mary H., Nocera, Daniel G., and Chen, Lin X.. X-ray spectroscopic characterization of Co(IV) and metal–metal interactions in Co4O4: Electronic structure contributions to the formation of high-valent states relevant to the oxygen evolution reaction. United States: N. p., 2016. Web. doi:10.1021/jacs.6b04663.
Hadt, Ryan G., Hayes, Dugan, Brodsky, Casey N., Ullman, Andrew M., Casa, Diego M., Upton, Mary H., Nocera, Daniel G., & Chen, Lin X.. X-ray spectroscopic characterization of Co(IV) and metal–metal interactions in Co4O4: Electronic structure contributions to the formation of high-valent states relevant to the oxygen evolution reaction. United States. doi:10.1021/jacs.6b04663.
Hadt, Ryan G., Hayes, Dugan, Brodsky, Casey N., Ullman, Andrew M., Casa, Diego M., Upton, Mary H., Nocera, Daniel G., and Chen, Lin X.. Fri . "X-ray spectroscopic characterization of Co(IV) and metal–metal interactions in Co4O4: Electronic structure contributions to the formation of high-valent states relevant to the oxygen evolution reaction". United States. doi:10.1021/jacs.6b04663.
@article{osti_1339577,
title = {X-ray spectroscopic characterization of Co(IV) and metal–metal interactions in Co4O4: Electronic structure contributions to the formation of high-valent states relevant to the oxygen evolution reaction},
author = {Hadt, Ryan G. and Hayes, Dugan and Brodsky, Casey N. and Ullman, Andrew M. and Casa, Diego M. and Upton, Mary H. and Nocera, Daniel G. and Chen, Lin X.},
abstractNote = {In this paper, the formation of high-valent states is a key factor in making highly active transition metal-based catalysts of the oxygen-evolving reaction (OER). These high oxidation states will be strongly influenced by the local geometric and electronic structures of the metal ion, which is difficult to study due to spectroscopically active and complex backgrounds, short lifetimes, and limited concentrations. Here, we use a wide range of complementary X-ray spectroscopies coupled to DFT calculations to study Co4O4 cubanes, which provide insight into the high-valent Co(IV) centers responsible for the activity of molecular and heterogeneous OER catalysts. The combination of X-ray absorption and 1s3p resonant inelastic X-ray scattering (Kβ RIXS) allow Co(IV) to be isolated and studied against a spectroscopically active Co(III) background. Co K- and L-edge X-ray absorption data allow for a detailed characterization of the 3d-manifold of effectively localized Co(IV) centers and provide a direct handle on the ligand field environment and covalency of the t2g-based redox active molecular orbital. Kβ RIXS is also shown to provide a powerful probe of Co(IV), and specific spectral features are sensitive to the degree of oxo-mediated metal-metal coupling across Co4O4. Guided by the data, calculations show electron-hole delocalization can actually oppose Co(IV) formation. Computational extension of Co4O4 to CoM3O4 structures (M = redox-inactive metal) defines electronic structure contri-butions to Co(IV) formation. Redox activity is shown to be linearly related to covalency, and M(III) oxo inductive effects on Co(IV) oxo bonding can tune the covalency of high-valent sites over a large range and thereby tune E0 over hundreds of mVs.},
doi = {10.1021/jacs.6b04663},
journal = {Journal of the American Chemical Society},
number = 34,
volume = 138,
place = {United States},
year = {Fri Aug 12 00:00:00 EDT 2016},
month = {Fri Aug 12 00:00:00 EDT 2016}
}