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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}
}
  • 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 measurementsmore » 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.« less
  • The tetranuclear species [Mn[sup IV] [sub 4]O[sub 6] (bpy)[sub 6]] (ClO[sub 4])[sub 4][center dot]H[sub 2]O was isolated from an aqueous nitric acid solution (pH = 2) of Mn[sup III] (bpy) Cl[sub 3](H[sub 2]O) upon addition of NaClO[sub 4]. It crystallizes in the triclinic space group P[bar l] with a = 20.213(7) [angstrom], b = 13.533(7) [angstrom], c = 13.411(8) [angstrom], [alpha] = 112.01(8)[degree], [beta] = 96.72(11)[degree], [gamma] = 100.34(12)[degree], V = 3276.9 [angstrom][sup 3], and Z = 2. The cation has a nonrectilinear chain structure [(bpy)[sub 2]Mn[sup IV[sub a]]O[sub 2]Mn[sup IV[sub b]](bpy)O[sub 2]Mn[sup IV[sub c]](bpy)O[sub 2]Mn[sup IV[sub d]](bpy)[sub 2]][sup 4+].more » The metal-metal distances are Mn[sub a]-Mn[sub b] = 2.746(5) [angstrom], Mn[sub b]-Mn[sub c] = 2.760(5) [angstrom], Mn[sub c]-Mn[sub d] = 2.735(4) [angstrom], Mn[sub a]-Mn[sub c] = 4.899(10) [angstrom], Mn[sub b]-Mn[sub d] = 4.897(6) [angstrom], and Mn[sub a]-Mn[sub d] = 6.419(11) [angstrom]. The variable temperature magnetic susceptibility data for [Mn[sup IV[sub 4]]O[sub 6](bpy)[sub 6]](ClO[sub 4])[sub 4][center dot]H[sub 2]O in the range 12-294 K were fit using the spin Hamiltonian H[sub S] = J[sub ab]S[sub a]S[sub b] -J[sub bc]S[sub b]S[sub c] - J[sub cd]S[sub c]S[sub d], with J[sub ab] = J[sub cd] = -176 cm[sup [minus]1] and J[sub bc] = [minus]268 cm[sup [minus]1]. 55 refs., 11 figs., 3 tabs.« less
  • Solids of the composition La{sub 2{minus}x}Sr{sub x}Li{sub 1/2}Co{sub 1/2}O{sub 4} (x = 0, x {approx_equal} 0.2) crystallize in a superstructure of the K{sub 2}NiF{sub 4} lattice with a doubled unit cell in the (001) plane (space group Ammm; a = b = {radical}2a{sub 0}), caused by cation ordering between lithium and cobalt on the octahedral sites. The electronic structure of the Co{sup III}O{sub 6} and Co{sup IV}O{sub 6} polyhedra, which lie isolated in the lattice, were studied by various spectroscopic techniques (XANES, EPR, optical). The groundstates are low-spin in both cases (t{sub 2g}{sup 6} and t{sub 2g}{sup 5}, respectively), themore » ligand field parameters of Co{sup III} being close to those characterizing the high-spin/low-spin crossover.« less
  • Lanthanide {beta}-diketonates have been extensively reported and shown to exist as either Lewis base stabilized monomers, i.e. M(thd){sub 3}(L){sub n} or as dimeric or other oligomeric species. The majority of these studies yielded hydrated metal {beta}-diketonates. Herein, the authors report the reaction of [TbCl{sub 3}(H{sub 2}O){sub 6}] with [Na(hfa)]{sub n} in aqueous media, which produces a compound in high, reproducible yield that is characterized by X-ray diffraction as {l_brace}[Tb{sub 2}(hfa){sub 4}({mu}{sub 2}-O{sub 2}CCF{sub 3}){sub 2}(H{sub 2}O){sub 4}][Tb(fha){sub 3}(H{sub 2}O){sub 2}]{sub 2}{center_dot}H{sub 2}O{r_brace}.
  • The crystal structure of partially Pd{sup 2+}-exchanged zeolite X, dehydrated at 400 C in a flowing O{sub 2} stream (a = 24.982(4){angstrom}), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd{bar 3} at 21(1) C. The crystal was first Pd{sup 2+}-exchanged in a flowing stream of 0.05 M aqueous Pd(NH{sub 3}){sub 4}Cl{sub 2} for 3 days. After dehydration at 400 C in flowing oxygen, the crystal was evacuated at 21(1) C and 2 x 10{sup {minus}6} Torr for 2 h. The structure was refined to the final error indices R{sub 1} = 0.070 and R{submore » 2} = 0.051 for the 196 reflections for which I > 2{sigma}(I). In this structure, Pd{sup 2+} ions are found at four crystallographic sites: Na{sup +} ions fill just one, and nonframework oxygens are found at two. Eight Pd{sup 2+} ions and eight O{sup 2{minus}} ions fill the 16 double six-oxygen ring (D6R) centers (site I) per unit cell; this interpretation of the electron density at site I behaves well in least-squares refinement. Each of these Pd{sup 2+} ions is octahedrally coordinated by framework oxygens. Sixteen Pd{sup 4+} ions at site I{prime} (Pd-O = 2.103(13){angstrom}) lie in six-ring planes. With the eight oxide ions at site I at central positions and 16 more terminal, they form eight linear O-Pd-O-Pd-O clusters along 3-fold axes per unit cell. Each passes through the center of a D6R and extends into its two adjacent sodalite cavities. Considering bond lengths and charge balance, it is proposed that they are [HO-Pd{sup IV}-O-Pd{sup IV}-OH]{sup 4+} clusters with O-Pd-O-Pd-O linear. Thirty-two Na{sup +} ions fill site II and are recessed 1.03(1){angstrom} into the supercage from the single six-ring plane (Na-O = 2.258(11){angstrom}). About two Pd{sup 2+} ions at another site I{prime} (Pd-O = 2.371(11){angstrom}) are displaced 1.11 {angstrom} from six-ring plane into sodalite cages. About four Pd{sup 2+} ions lie at site III{prime} in the supercage (Pd-O = 2.16(5){angstrom}).« less