Ionic channel structure in perfluorinated membranes studied by small angle X-ray scattering, optical and Mössbauer spectroscopy

Small angle X-ray scattering optical and Mössbauer spectroscopy has been used to study ionic channels in perfluorinated Nafion$^{®}$-type membranes. X-ray scattering data have revealed the ordering of ionic groups of polymer chains at nanoscales into extended fine channels for proton conductivity. Then the membranes were saturated with Fe$^{3+}$ ions to probe their interaction with sulfonic groups. This remarkably changed electron properties of copolymer in which the energy of optical gap has decreased. The Mössbauer spectra have confirmed that even at ambient temperature in membrane, Fe$^{3+}$ ions are assembled into antiferromagnetic dimers with water shells and associated with sulfonic groups at the channel surfaces. The applied complementary methods allowed us to examine a short-range order of ionic groups forming a network of channels in membranes that provide their functional properties in hydrogen fuel cells.