Understanding the fingerprint region in the infra-red spectra of perfluorinated ionomer membranes and corresponding model compounds: Experiments and theoretical calculations

► We present an ATR-FTIR study of three major perfluorinated ionomers, Nafion, Aquivion and 3M, with focus on the C-O-C band absorptions. ► Band assignments were determined by FTIR spectra and DFT calculations of corresponding model compounds. ► The ATR-FTIR spectra of membranes and model compounds and the DFT calculations led to a re-examination and re-assignment of some bands for Nafion and Aquivion membranes, including the C-O-C bands. ► The low intensity of the spectral bands for the ether links in the membranes suggests that these bands cannot be used for the determination of the extent of degradation.