Synthesis and characterization of Nafion/cross-linked PVP semi-interpenetrating polymer network membrane for direct methanol fuel cell

A novel semi-interpenetrating polymer network (semi-IPN) membrane composed by Nafion117 and cross-linked poly (vinyl pyrrolidone) (PVP) has been prepared to improve the proton selectivity of perfluorosulfonic acid (PFSA) membrane. Its physico-chemical properties are characterized using scanning electron microscopy (SEM), diffuse-reflection Fourier-transform infrared spectroscopy (DRFTIR), wide-angle X-ray diffraction (WAXRD), thermo-gravimetric analysis (TGA), thermo-gravimetric mass spectrometry (TG-MS) and solid-state nuclear magnetic resonance (NMR). Our results indicate that the introduction of the cross-linked PVP mainly affects the configuration of the Nafion side-chains and thus indirectly influences the formation and interconnection of ion clusters. It is shown that this new semi-IPN membrane exhibits a better proton selectivity as compared to the pristine membrane. Under the optimal condition, the semi-IPN membrane exhibits 53% lower methanol permeability but 38% higher proton conductivity as compared to Nafion117, thus resulting in a factor of two improvement on the relative proton selection coefficient. Such improvement can be attributed to the unique Grotthuss mechanism (hopping mechanism) of proton transfer, instead of the diffusion of methanol molecular.