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Electrochemical trapping of metastable Mn3+ ions for activation of MnO₂ oxygen evolution catalysts

Chan, Zamyla Morgan ; Kitchaev, Daniil A. ; Weker, Johanna Nelson ; Schnedermann, Christoph ; Lim, Kipil ; Ceder, Gerbrand ; Tumas, William ; Toney, Michael F. ; Nocera, Daniel G.

Proceedings of the National Academy of Sciences - PNAS, 2018-06, Vol.115 (23), p.E5261-E5268 [Periódico revisado por pares]

National Academy of Sciences

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  • Título:
    Electrochemical trapping of metastable Mn3+ ions for activation of MnO₂ oxygen evolution catalysts
  • Autor: Chan, Zamyla Morgan ; Kitchaev, Daniil A. ; Weker, Johanna Nelson ; Schnedermann, Christoph ; Lim, Kipil ; Ceder, Gerbrand ; Tumas, William ; Toney, Michael F. ; Nocera, Daniel G.
  • Assuntos: Physical Sciences ; PNAS Plus
  • É parte de: Proceedings of the National Academy of Sciences - PNAS, 2018-06, Vol.115 (23), p.E5261-E5268
  • Notas: ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
    content type line 23
    Author contributions: Z.M.C., D.A.K., J.N.W., C.S., G.C., W.T., M.F.T., and D.G.N. designed research; Z.M.C., D.A.K., and C.S. performed research; Z.M.C., D.A.K., J.N.W., C.S., and K.L. contributed new reagents/analytic tools; Z.M.C., D.A.K., J.N.W., C.S., M.F.T., and D.G.N. analyzed data; and Z.M.C., D.A.K., C.S., and D.G.N. wrote the paper.
    Contributed by Daniel G. Nocera, April 16, 2018 (sent for review December 21, 2017; reviewed by Curtis P. Berlinguette, Charles Dismukes, and Mark S. Hybertsen)
    Reviewers: C.P.B., University of British Columbia; C.D., Rutgers; and M.S.H., Brookhaven National Laboratory.
  • Descrição: 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 oxygenbased HOMO results in the facilitation of OER on the application of anodic potentials to the δ-MnO₂ polymorph incorporating Mn3+ ions.
  • Editor: National Academy of Sciences
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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