High Proton-Conducting Nafion/Calcium Hydroxyphosphate (CHP) Composite Membranes

High proton conducting Nafion/Calcium hydroxyphosphate (CHP) composite membranes were prepared using homogeneous dispersive homogenizing and solvent casting process for fuel cell applications. Crystallinity from decomposed X-ray diffractograms, increased whereas crystalline sizes gradually decreased in composite membranes with the CHP amounts. In X-ray profiles, new crystalline peaks were found in the original amorphous region of Nafion in composite membranes. It suggests that the incorporated CHP forms the crystalline structure within Nafion. It may allow composite membrane to have better thermal and mechanical stability by the virtue of a kind of nucleating agent in its crystallization process. In the analysis of water bending vibration at 1673 cm-1 by FT-IR, composite membranes showed lower water uptakes than in cast Nafion. It is also noteworthy that the disappearance of hydrated proton bending vibration at 1731 cm-1 might explain that less water is required for proton to transport in composite membranes. In FIB micrographs many holes, considering as clusters and channels in the surface of the all membranes, were shown. It is likely that these channels are connected three-dimensionally. The 5% composite membrane has not only higher conductivity but also lower activation energy than in the cast Nafion. We conclude that the structural modification in crystalline and cluster regions as well as the improvement of proton transport through three dimensional channels may cause higher conductivity and lower activation energy in composite membranes.