Preparation And Methanol-rejective Property Study Of Chitosan/Zeolite Beta Hybrid DMFC Membranes

Direct methanol fuel cell (DMFC) is considered to be one of the potential power sources, owing to its high power density, environmental benignity, simple structure, short starting time, high operation reliability and easy fuel storage, et al. However, the severe methanol crossover and high cost of perfluorinated sulfonic acid membranes such as Nafion^?, used as the proton exchange membrane in DMFC, limited their application. Thus, the study of methanol-rejective proton exchange membranes with low methanol crossover and low cost has important significance.Chitosan, which was usually utilized in the alcohol/water separation, was chosen as the organic matrix, and zeolite beta was chosen as the inorganic filler in this study to fabricate chitosan/zeolite beta hybrid membrane. Chitosan membranes filled by zeolite beta with different particle sizes were prepared. To improve the interfacial morphology and enhance the compatability between organic matrix and inorganic filler, zeolite beta was functionalized by different approaches. And the chitosan membranes filled by surface modified zeolite beta were prepared.Zeolite beta and hybrid membranes were characterized by SEM, TEM, FT-IR, XPS, XRD and TGA. The effects of particle size and surface modification of zeolite beta on the morphology and performances of hybrid membranes were systematically investigated. It was found that, chitosan membranes filled by zeolite beta with particle size about 800 nm (CS/Beta-2) exhibited lower methanol permeability, while chitosan membranes filled by 300 nm sized zeolite beta showed a little higher proton conductivity. When zeolite beta with particle size about 5μm was used, the separated organic and inorganic layers were formed due to the sedimentation of large sized zeolite beta during membrane preparation. Compared with CS/Beta-2 hybrid membranes, chitosan membranes filled by surface modified zeolite beta had lower methanol permeability owing to the better interfacial compatibility. Especially, chitosan membrane filled by 30 wt.% zeolite beta modified by 3-mercaptopropyltrimethoxysilane (CS/BetaSO₃H-3-30%) showed the lowest methanol permeability at 12 mol/L methanol concentration, which was less than 7% of Nafion^?117 membrane. Though the improvement of proton conductivity was not remarkable, the lowered methanol permeability enabled hybrid membranes improved selectivity, of which CS/BetaSO₃H-3-30% showed 4.6 times higher selectivity than that of Nafion^?117 membrane at 12 mol/L methanol concentration.