Preparation And Characterization Of Nafion/NH₄-X Zeolite Composite Proton Exchange Membranes

Fuel cell, one novel energy conversion technology, has many advantages, such ashigh conversion efficiency, low pollution and low noise, etc. Direct methanol fuelcell(DMFC) converts methanol fuel into electricity directly, which can be widelyapplied in various applications, such as portable device, power supply, automobile, etc.The proton exchange membrane is the core component of direct methanol fuel cell andthe most popular membranes are Nafion membranes from the United States Dupontcurrently. However, Nafion membranes have some significant drawbacks, such ashigh methanol permeability and low proton conductivity at the conditions of hightemperature or low humidity, so it is necessary to modify the Nafion membranes tomeet the requirement for DMFC.Previously, the research team completed some research on zeolite compositemembranes. And they found that the sizes of filler particles plays a key role in theproton and mass transport behavior since it controls the morphology as well as thenature of water content at the Nafion-zeolite interphase region. The presence ofsubmicron Na-X zeolite embedded in Nafion matrix results in a significant reduction ofmethanol crossover due to the hidered transport of methanol through the zeolite.Combining the results together, submicron Na-X composite membranes with desirableperformance could be expected.This work presented here designs three kinds of zeolites: Na-X, NH4-X and H-Xzeolite. They shared the same structure but different balanced cation and were expectedto have the same methanol permeability as Na-X and higher proton conductivity thanNa-X. First, this work prepared nano size and submicron size Na-X zeolites byhydrothermal method. Then Na-X zeolites were converted to NH4-X zeolites. Thesezeolites were characterized and analyzed by X-ray diffraction (XRD), ScanningElectron Microscope (SEM), Fourier transform infrared spectra (FT-IR), ThermalGravimetric Analysis (TGA) coupled with Differential Scanning Calorimetry (DSC),BET analysis, etc. In addition, this work tried to convert NH4-X to H-X zeolites andfound the best method though the analysis of the converted zeolites.Furthermore, recast method was used to prepare Na-X/Nafion and NH4-X/Nafioncomposite membranes with the loading5wt%and10wt%respectively. Various experimental techniques namely: Scanning Electron Microscope (SEM), ThermalGravimetric Analysis (TGA) coupled with Differential Scanning Calorimetry (DSC),Ion Exchange Capacity (IEC), water uptake, methanol permeability, proton conductivityand selectivity were employed to characterize the Nafion composite membranes. Theresults showed that the water uptake, ions exchange capacity and proton conductivity ofNH4-X/Nafion composite membranes were not as good as Na-X/Nafion compositemembranes, but better than blank Nafion and the methanol permeability is muchlower than Na-X/Nafion composite membranes. Especially the SubmicronNH4-X/Nafion composite membrane, comparing with the blank Nafion, its methanolpermeability is only half and the selectivity is three times as high as the blank Nafion.