Preparation And Characterization Of Nafion/Zeolites Composite Proton Exchange Membranes

Nowadays, significant efforts have been made on Nafion/inorganic compositeproton exchange membrane to improve its proton conductivity under elevatedtemperatures and reduced water activity which can result into better fuel cellperformance. Zeolites are a promising category of inorganic fillers to fulfill suchdemand of Nafion membrane due to the strong hydrophilic property and high ionicexchange capacity of most zeolites. In most cases, people focus on the area ofemploying zeolites as effective methanol cross-over barrier in direct methanol fuel cells.In this dissertation composite Nafion membranes were prepared using zeolite NaX andSAPO-5, these have high water capacity and showed enhanced proton conductivity.SAPO-5 and NaX with different crystal sizes were synthesized through variedhydrothermal methods. Their corresponding composite membranes were prepared usinga solution recasting approach. Various experimental techniques namely, X-raydiffraction (XRD), Scanning Electron Microscope (SEM), Fourier transform infraredspectra (FT-IR), Thermal Gravimetric Analysis (TGA) coupled with Differentialscanning calorimetry (DSC), Ion Exchange Capacity (IEC) and proton conductivitywere employed to characterize the synthetic NaX, SAPO-5 and composite protonconductivity membranes.The results show that pure NaX crystal with crystal size of 0.8~1.5μm (microNaX), 200~300nm(submicro NaX) and 30nm×100nm (nano NaX)are successfullysynthesized with controlled age time and reaction temperature. These zeolites addictivesare compatible with the matrix polymer after the recasting process. TGA results indicatethat the water uptake of these membranes are enhanced by the addition of three differentsizes NaX. Similar ionic exchange capacities are observed in all the three sized 10wt%NaX composite membranes which are 9% higher than the unmodified Nafion. At wateractivity lower than 0.5, an improvement of more than 100% in proton conductivity isboth shown in Nafion/SAPO-5 and Nafion/micro NaX membranes with powder loadingof 10wt% when compared to the blank Nafion one. This enhancement decreases to 18%and 28% for Nafion/micro NaX and Nafion/SAPO-5, respectively, when the wateractivity reaches to 0.8. This enhancement is based on the high hydrophilic property andionic exchange capacity of added zeolites. However, the dispersion of SAPO-5 particles in the membrane is an issue since its particles size are too large and have a negativeeffect on the mechanical property of the composite membrane. Combine these resultstogether, nano and submicro NaX composite membranes with desirable performancecan be expected.