• Schnegg, A.; Nehrkorn, J.; Singh, A.; Calafell, I.-A.; Bonke, S.; Hocking, R.; Lips, K.; Spiccia, L.: Probing the Fate of Mn Complexes in Nafion: A Combined Multifrequency EPR and XAS Study. The Journal of Physical Chemistry C 120 (2016), p. 853–861


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.