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Title: Electrochemical trapping of metastable Mn 3+ ions for activation of MnO 2 oxygen evolution catalysts

Abstract

Electrodeposited manganese oxide films are promising catalysts for promoting the oxygen evolution reaction (OER), especially in acidic solutions. The activity of these catalysts is known to be enhanced by the introduction of Mn3+. We present in situ electrochemical and X-ray absorption spectroscopic studies, which reveal that Mn3+ may be introduced into MnO2 by an electrochemically induced comproportionation reaction with Mn2+ and that Mn3+ persists in OER active films. Extended X-ray absorption fine structure (EXAFS) spectra of the Mn3+-activated films indicate a decrease in the Mn-O coordination number, and Raman microspectroscopy reveals the presence of distorted Mn-O environments. Computational studies show that Mn3+ is kinetically trapped in tetrahedral sites and in a fully oxidized structure, consistent with the reduction of coordination number observed in EXAFS. Although in a reduced state, computation shows that Mn3+ states are stabilized relative to those of oxygen and that the highest occupied molecular orbital (HOMO) is thus dominated by oxygen states. Furthermore, the Mn3+(Td) induces local strain on the oxide sublattice as observed in Raman spectra and results in a reduced gap between the HOMO and the lowest unoccupied molecular orbital (LUMO). The confluence of a reduced HOMO-LUMO gap and oxygen-based HOMO results in the facilitationmore » of OER on the application of anodic potentials to the d-MnO2 polymorph incorporating Mn3+ ions.« less

Authors:
; ; ; ; ; ; ; ; ORCiD logo
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Next Generation of Materials by Design: Incorporating Metastability (CNGMD)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1454752
Report Number(s):
NREL/JA-5F00-71730
Journal ID: ISSN 0027-8424
DOE Contract Number:  
AC36-08GO28308
Resource Type:
Journal Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 115; Journal Issue: 23; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; manganese oxide; polymorph; water splitting; catalysis; renewable energy storage

Citation Formats

Morgan Chan, Zamyla, Kitchaev, Daniil A., Nelson Weker, Johanna, Schnedermann, Christoph, Lim, Kipil, Ceder, Gerbrand, Tumas, William, Toney, Michael F., and Nocera, Daniel G. Electrochemical trapping of metastable Mn 3+ ions for activation of MnO 2 oxygen evolution catalysts. United States: N. p., 2018. Web. doi:10.1073/pnas.1722235115.
Morgan Chan, Zamyla, Kitchaev, Daniil A., Nelson Weker, Johanna, Schnedermann, Christoph, Lim, Kipil, Ceder, Gerbrand, Tumas, William, Toney, Michael F., & Nocera, Daniel G. Electrochemical trapping of metastable Mn 3+ ions for activation of MnO 2 oxygen evolution catalysts. United States. doi:10.1073/pnas.1722235115.
Morgan Chan, Zamyla, Kitchaev, Daniil A., Nelson Weker, Johanna, Schnedermann, Christoph, Lim, Kipil, Ceder, Gerbrand, Tumas, William, Toney, Michael F., and Nocera, Daniel G. Mon . "Electrochemical trapping of metastable Mn 3+ ions for activation of MnO 2 oxygen evolution catalysts". United States. doi:10.1073/pnas.1722235115.
@article{osti_1454752,
title = {Electrochemical trapping of metastable Mn 3+ ions for activation of MnO 2 oxygen evolution catalysts},
author = {Morgan Chan, Zamyla and Kitchaev, Daniil A. and Nelson Weker, Johanna and Schnedermann, Christoph and Lim, Kipil and Ceder, Gerbrand and Tumas, William and Toney, Michael F. and Nocera, Daniel G.},
abstractNote = {Electrodeposited manganese oxide films are promising catalysts for promoting the oxygen evolution reaction (OER), especially in acidic solutions. The activity of these catalysts is known to be enhanced by the introduction of Mn3+. We present in situ electrochemical and X-ray absorption spectroscopic studies, which reveal that Mn3+ may be introduced into MnO2 by an electrochemically induced comproportionation reaction with Mn2+ and that Mn3+ persists in OER active films. Extended X-ray absorption fine structure (EXAFS) spectra of the Mn3+-activated films indicate a decrease in the Mn-O coordination number, and Raman microspectroscopy reveals the presence of distorted Mn-O environments. Computational studies show that Mn3+ is kinetically trapped in tetrahedral sites and in a fully oxidized structure, consistent with the reduction of coordination number observed in EXAFS. Although in a reduced state, computation shows that Mn3+ states are stabilized relative to those of oxygen and that the highest occupied molecular orbital (HOMO) is thus dominated by oxygen states. Furthermore, the Mn3+(Td) induces local strain on the oxide sublattice as observed in Raman spectra and results in a reduced gap between the HOMO and the lowest unoccupied molecular orbital (LUMO). The confluence of a reduced HOMO-LUMO gap and oxygen-based HOMO results in the facilitation of OER on the application of anodic potentials to the d-MnO2 polymorph incorporating Mn3+ ions.},
doi = {10.1073/pnas.1722235115},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
issn = {0027-8424},
number = 23,
volume = 115,
place = {United States},
year = {2018},
month = {5}
}

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