Study of Fuel Cells Thin Film Morphologies by Grazing Incidence Small Angle X-ray Scattering (GISAXS)

摘要

Grazing incidence small angle x-ray scattering (GISAXS) experiments were performed on thin films of Nafion solutions as a function of temperature under humidity control, and as a function of humidity at constant temperature. The development and orientation of the structure and morphology in the thin films, at the free surface and in the bulk of the film, was characterized by the scattering below and above the critical angle. The scattering profiles indicated that Nafion thin film morphology was strongly influenced by the humidity and temperature as casting solvent is methanol/water. Nafion is a frequently used polymer for proton exchange membrane fuel cells (PEMFC) because of its excellent ionic conductivity, cation selectivity, chemical, thermal, and mechanical stability, at the aim of this is to manipulate the morphology that is generated by the use of different solvents. Regardless of the type of morphology that one has, it is of interest to be able to take these morphologies and optimize the orientation of these structures so as to optimize the rate of proton transport in order to increase the conductivity. To that end we investigated the thin film morphologies of these ionomers using grazing incidence small angle X-ray scattering using methanol/water, 2-propanol/water mixture and N,N’-dimethyl formamide (DMF) solvents. The scattering profiles indicated that Nafion thin morphology was strongly influenced by the characterictics of Nafion in solution and an applied electric field was found to markedly influence the orientation of the ion conducting domains in the films.