Probing the Fate of Mn Complexes in Nafion: A Combined Multifrequency EPR and XAS Study

Multifrequency electron paramagnetic resonance (EPR, 9.4 and 263 GHz) and X-ray absorption spectroscopy (XAS) were employed to study structural and electrochemical changes of selected Mn complexes in contact with dried Nafion films upon electro-oxidation and after long-term illumination. It was foun...

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Published in:Journal of physical chemistry. C 2016-01, Vol.120 (2), p.853-861
Main Authors: Schnegg, Alexander, Nehrkorn, Joscha, Singh, Archana, Calafell, Irati Alonso, Bonke, Shannon A, Hocking, Rosalie K, Lips, Klaus, Spiccia, Leone
Format: Article
Language:English
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Summary:Multifrequency electron paramagnetic resonance (EPR, 9.4 and 263 GHz) and X-ray absorption spectroscopy (XAS) were employed to study structural and electrochemical changes of selected Mn complexes in contact with dried Nafion films upon electro-oxidation and after long-term illumination. It was found that when in contact with Nafion the Mn-Me3TACN complexes are reduced into Mn­(II) complexes with an octahedral geometry (Me3TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane). The reduction process involves an intermediate product in which Mn has been reduced from the initial +III or +IV state of the precursor Mn complex but is still coordinated to the TACN ligand. Electro-oxidation yields a MnO x mineral with a birnessite structure, in which the Mn­(III) or Mn­(IV) ions exhibit very strong magnetic coupling. Long-term illumination of the oxide-containing Nafion film while it is exposed to an aqueous electrolyte partially decomposes the mineral and forms a Mn­(II) species with octahedral coordination.
ISSN:1932-7447
1932-7455
DOI:10.1021/acs.jpcc.5b10451