Thin Film Morphological Characteristics of a Perfluorinated Anion Exchange Membrane

Abstract

Perfluorinated anion exchange membranes are promising materials for alkaline fuel cell applications. Our previous work indicates they have high conductivity of >100 mS/cm at 80ᵒC and 95%RH.(1) They have also displayed good fuel cell performance of 1W/cm2.(2) We have also performed transmission small- and wide-angle X-ray scattering (SAXS/WAXS) of the bulk membrane to understand the bulk morphology.(3) Properties of Perfluorinated sulfonic acid (PFSA) ionomers as thin films have been thoroughly investigated in the past.(4) However, there is no literature about thin film characterization of perfluorinated anion exchange polymer and hence there is a lack of understanding about the interfacial properties. Here, we have studied the structure of these materials using Grazing-incidence small-angle x-ray scattering (GISAXS). Polymer solutions of different concentrations were used to spin-cast the thin films onto silicon substrates with native oxide layer and also coated with silver and Platinum.. Ellipsometry was used to obtain a calibration curve of thin film thickness vs. concentration of the polymer solution (wt%). From GISAXS, we can conclude that the polymer chains align horizontally parallel to the plain silicon as well as silver substrate. This alignment becomes significant at higher film thicknesses. Understanding the interfacial alignments of polymer on potential catalyst surfaces will help us better design them for optimal fuel cell performance or other electro-chemical applications.