Simultaneously enhanced methanol barrier and proton conductive properties of phosphorylated titanate nanotubes embedded nanocomposite membranes

The current study aims at simultaneously enhancing the methanol barrier and proton conductive properties of membranes for direct methanol fuel cell (DMFC) by embedding phosphorylated titanate nanotubes (PTNTs) into chitosan (CS) membrane. The enhancement is most probably due to the intrinsic interfacial interactions between PTNTs and CS chains, which are verified by the increased thermal stability and homogeneous dispersion of the fillers. The influence of PTNTs incorporation conditions including acid concentration and filler content upon the resulting nanocomposite membrane performance is extensively investigated. Compared with plain CS membrane, the presence of PTNTs within chitosan matrix will lead to denser chain packing, thus reduce free volume cavity size and fractional free volume (FFV) according to positron annihilation lifetime spectroscopy analysis. The reduced FFV and more tortuous pathway significantly suppress the methanol crossover through the membranes. Meanwhile, the presence of PTNTs constructs an uninterrupted channel for proton migration via functionalized P–OH groups and adsorbed water, and therefore improving the proton conductivity substantially. As a result, the nanocomposite membranes exhibit desirable comprehensive performance, which is about ten times higher than that of Nafion 117. We envisage that the current observations hint the encouraging application promises of such nanocomposite membranes in DMFC.