Transport properties of Nafion™ composite membranes for proton-exchange membranes fuel cells

The dielectric and electrical behaviors of a Nafion™ membrane, Nafion™/7SiO2–2P2O5–ZrO2 (SPZ), Nafion™/SiO2+H3PO4 (iHPO), Nafion™/SiO2+H3PW12O40 (iHPW) and Nafion™/ZrP composites were investigated using water desorption measurements and ac impedance spectroscopy as a function of time, relative humidity and temperature. The composite membranes except Nafion™/ZrP exhibited only marginally higher conductivity than Nafion™ at high temperature. Unlike the other membranes, the Nafion™/ZrP membrane showed reduced proton mobility with a higher activation energy. The results suggest that improvements in fuel cell performance, previously observed in Nafion™/SPZ and Nafion™/ZrP composite membranes, are not due simply to increased hydrophilic properties, but that there is an interplay between structure and proton mobility.