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

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• 作者：Alexander Schnegg ; Joscha Nehrkorn ; Archana Singh ; Irati Alonso Calafell ; Shannon A. Bonke ; Rosalie K. Hocking ; Klaus Lips ; Leone Spiccia
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：January 21, 2016
• 年：2016
• 卷：120
• 期：2
• 页码：853-861
• 全文大小：476K
• ISSN：1932-7455

文摘

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.