Schnegg, Alexander, Nehrkorn, Joscha, Singh, Archana, Calafell, Irati Alonso, Bonke, Shannon A., Hocking, Rosalie, Lips, Klaus, and Spiccia, Leone (2016) Probing the fate of Mn complexes in Nafion: a combined multifrequency EPR and XAS study. Journal of Physical Chemistry Part C, 120 (2). pp. 853-861.

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Abstract

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 MnOₓ 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.

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