Synthesis And Performance Of Composite Membranes Modified By Inorganic Nono-particles

As one of the key components in fuel cell, proton exchange membrane (PEM, such as Nafion(?)) provides the ionic pathway and acts as a gas separator. The conductivity of the PEMs is much related to the water content in the PEMs. Researchers had did may works to improve the hydrophilic capacity and water-retention capacity. Mixing hydrophilic particles (such as SiO₂, TiO₂ and other silicate particles) into PEM polymer is one of the most important ways. However, the water-retention capacity of the hydrophilic particles can not be efficiently achieved due to the random disperse of the particles in the PEM polymer, and these membranes usually had a biggish descend in mechanism strength. This paper pointed out that improving the dispersion of hydrophilic particles can improve the efficiency of that. The hydrophilic particles should be surround about the -SO3-, not the random dispersion in the PEM polymer. The hydrophilic particles should be controlled in nano size to decrease the damage in mechanism.There are two method are pointed out in this particle to control the dispersion of inorganic hydrophilic nano-particles in PEM membranes.(1) Intercalating the perfluorosulfonated resin into the interlayer of multilayered alumino-silicate mineral. In this particle, we used Nafion(?) ( Dupont) and montmorillonite(MMT)(2) The -SO_3- can be surrounded by nano-particles via electrostatic self-assembly technology. In this particle,we used SiO₂.We have made composite membranes in these ways.MMT/Nafion composite membranes were obtained in this way: first, the MMT was modified by dodecylamine, we get m-MMT from this. Then Nafion and m-MMT were in high pressure and temperature. At last ,we get intercalated membranes.Wide-angle X-ray diffraction (XRD) was used to analyze the d-spacing of MMT. The Differential Scanning Calorimetry (DSC) analysis had improved that the polymer molecules were limited by the interlayer of MMT. The test had proved that these composite membranes had revealed excellent water retention. The capacity of hydrophilic and water-retention had both increased, and these advantage had been reflected in the conductivity test and single cell test. But there is also some drawback found in the mechanical strength testing and H2 crossover test.The SiO₂/Nafion composite membranes was made based on the research in solution properties of Nafion. We changed the zeta Potential by adjusting the pH value. SiO₂ particles can be assembled into Nafion in this environment. The dependence of zeta potential of Nafion on pH value and concentration had been studied .But the polarity of zeta potential of SiO₂ can be changed depended on pH value. The zeta potential is positive while the pH value less than 2.0, and it changed into negative if the pH value over 2.0. The zeta potential increased as the pH value increased. So ,SiO₂ particles can be assembled into Nafion in the environment of pH value less than 2.0, then the -SO_3- can be surrounded by SiO₂ particles. The water of Nafion solution should be take out and the reaction shut be in organic environment to control the hydrolyze of TEOS. Then we can get nano-particle SiO₂.The SiO₂/Nafion composite membranes were analyzed by zeta potential test and transmission electron microscope(TEM) and other tests. The capacity of hydrophilic capacity and conductivity had also been tesed. These proved that the SiO₂/Nafion composite membranes had excellent performances.