Interfacial water in Nafion studied by infrared spectroscopy and computation methods

Interfacial interactions between water and the fluorinated proton exchange membrane material Nafion were studied by infrared spectroscopy and computational methods. Modern Fourier transform infrared spectra are reported that show features for H2O and the deuterium substituted HOD species that can be assigned to interfacial water interacting with sites on the ionomer. Relatively sharp features at 3667 cm-1 and 3710 cm-1 toward the high energy side of the fundamental O-H stretching modes of bulk liquid H2O, are associated with interfacial water inside membrane pores or channels. To interpret the measured infrared spectra, interfacial interactions between water and Nafion were modeled at the molecular-scale by applying classical and quantum chemical computational methods. The studies shed light on the structure of H2O at interfaces inside ion conducting membrane materials and have potential for application in elucidating structure at different types of water interfaces. Also, the studies herein provide a good guidance for materials scientists in designing and synthesizing novel polymer electrolytes arrived at improving the performance and efficiency of proton exchange membrane fuel cells.