The Yuan Ze University (Chung-Li, TW) investigators improved the ion conductivity of perfluorocarbon ionomer membranes used in fuel cells by aligning the nano-structure of ionic group aggregations using an electric field along the membrane thickness direction, which causes linear, less curved, and continuous proton transferring pathways. According to U.S. Patent Application 20090280385, the membranes are prepared by solution casting from the organic solvent which should be: (1) low boiling point so that it can be easily evaporated (or vacuum evaporated) at a temperature below T.sub.g of perfluorocarbon ionomers; (2) high dielectric constant so that the ionic groups of perfluorocarbon ionomers are in ionic state; (3) compatible with perfluorocarbon ionomers so that the ionomers can be easily dissolved in solvents. For preparing high ionic conductivity perfluorocarbon ionomer membranes, the preferred solvent is N,N'-dimethyl acetamide (DMAc), N,N'-dimethyl formamide (DMF), N-methyl formamide (NMF), glycerol, methanol, ethanol, isopropanol, and water, or mixtures of previous solvents.
The organic solvent is vacuum dried at a temperature below T.sub.g of perfluorocarbon ionomers, and then the membrane is annealed and aligned under an electric field at a temperature between T.sub.g and T.sub.m of perfluorocarbon ionomers. The nano-structure of perfluorocarbon ionomer membranes after applying with an electric field is identified by transmission electron microscopy (TEM) and is found to be aligned along the electric field. The ionic conductivity of membranes with aligned nano-structure along the membrane thickness direction is found to be improved.
The membrane electrode assembly (MEA) prepared from membrane with aligned nano-structure along the membrane thickness direction is found to have a better polyelectrolyte membrane fuel cell (PEMFC) performance than those prepared without nano-structure alignment and the commercial Nafion-117 membrane (Du Pont Co) according to inventors Tzyy-Lung Leon Yu, Hsiu-Li Lin, Shih-Hung Chan, Fang-Hsin Han, Kun-Sheng Shen, and Guo-Bin Jung.
