Structural and electrochemical investigation on re-cast Nafion membranes for polymer electrolyte fuel cells (PEFCs) application

Starting from a 5 wt% ion power Nafion® solution and dissolving the dry residue in a suitable solvent (10 wt% solution in dimethylacetammide), re-cast Nafion films were developed for polymer electrolyte fuel cells (PEFCs) application. The used Doctor-Blade casting technique allowed to prepare scaled-up membranes comparable to the commercial Nafion ones with good mechanical resistance, thickness homogeneity and an excellent reproducibility. The differences between the re-cast membrane nanostructure and that of the commercial Nafion were investigated by synchrotron small-angle X-ray scattering. The obtained re-cast membrane shows at ambient conditions a semi-crystalline structure with a typical correlation length of about 86 Å and an intercluster Bragg distance of 37 Å, quite different from the values of commercial film. Observation on the swelling of the films revealed that the semi-crystalline structure, once soaked in water, swells less than the ionomeric part, leading to an unusual small-angle X-ray scattering (SAXS) profile in which the matrix and the ionomer peak are significantly overlapped. The ionic conductivity measured at T = 80 °C shows slightly higher values for the re-cast Nafion membrane. A power density of about 0.490 W cm−2 at 0.6 V and at T = 80 °C in humidified hydrogen/air was obtained for the developed membrane.