Preparation And Characterization Of ZrP/Al₂O₃/PVA Combined Organic-inorganic Proton Exchange Membranes

Direct methanol fuel cells (DMFCs) possess the advantage of convenient fuelstorage and efficient and clean energy use which make DMFCs suitable as a mobile andportable power supply. The proton exchange membrane (PEM) is the key material in aDMFC and currently the preferred membranes are perfluorinated sulfonic acidmembranes, e,g, Nafion. The main disadvantage preventing the use of DMFCs in awide range of application is methanol permeability which lowers the batteryperformance.The research work reported here uses polyvinyl alcohol (PVA) as the polymermatrix and zirconia phosphate (ZrP) is added to act as the proton carrier. In order toimprove the interfacial connection between; PVA and ZrP, an alumina sol is added. Theswelling of PVA due to water uptake is restricted by cross-linking usingglutaraldehyde(G) as the cross-linking agent. However, if this composite membrane issoaked in solution, the IEC value of membrane deceases. It was found that, using amultiplayer membrane, the IEC value was stable. This article reports on a multi-layerproton exchange membrane using a single layer of50%ZrP/PVA covered on both sideswith a barrier layer of cross-linked PVA with alumina sol. The resulting compositemembranes were characterized using X-ray diffraction (XRD), scanning electronmicroscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermalgravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC). Theion exchange capacity (IEC) was measured by the equivalent weight method and thewater uptake by mass change. A UV-Vis spectrophotometer (UV-Vis) was used todetermine the methanol cross-over and so obtain a value for methanol permeability. Analternating current impedance method was used to obtain to measure protonconductivity of the membranes while the mechanical properties were measured using auniversal testing machine.The results show that by controlling the ZrP, alumina sol, PVA and glutaraldehyderatio, and ensuring an homogeneous blend, a compact composite membrane can beobtained. The multilayer composite membrane showed the outer layers are wellconnected to the middle layer and form a barrier layer (low methanol permeability) andmaintained a stable IEC value (IEC value is approximately0.75mequiv/g). Theoptimum mixture results in a composite membrane with an even distribution of ZrPwithin the polymer matrix and a degree of crosslinking that restricts excessive swellingand enhances the mechanical properties. The IEC value obtained is comparable toNafion115while the lower value of permeability points to a higher selectivity. Theseresults show the ZrP/Al2O3/PVA composite membrane is suitable for development foruse in DMFCs.