Study of Thin Nafion® Films for Fuel Cells Using Energy Variable Slow Positron Annihilation Spectroscopy

Nafion® is one of the most popular proton conducting membranes for polymer electrolyte fuel cells (PEFCs). For the integration of Nafion® to the catalyst layers, very thin layers of the polymer are often formed on the catalysts of PEFC from dilute solutions. We applied energy variable positron annihilation to characterizing the structure of thin Nafion® films prepared by spin and dip coating from ethanol/water solutions of Nafion® on Si substrates. Experimental data suggest that the nano-structure of 23 nm thick spin coated Nafion® film is different from 220 nm thick film and also from 26 and 227 nm thick dip coated films, possibly due to the preservation of the unique rod-like structure of Nafion® in the dilute solution.