The direct methanol fuel cell (DMFC) has the potential to replace lithium-ion rechargeable batteries in portable electronic devices, but currently experiences significant power density and efficiency losses due to high methanol crossover through the polymer electrolyte membrane (PEM). In a previous study, poly vinyl alcohol (PVA), a selective polymer to water over methanol, was blended with Nafion� at various compositions (5-50 wt% PVA) in order to improve DMFC performance. Analysis of the transport properties (proton conductivity and methanol permeability), chemical bond interactions (FTIR), and DMFC performance as a function of blend composition and annealing temperature showed that Nafion�/PVA blend membranes exhibit improved membrane performance compared to Nafion�. Specifically, a Nafion�/PVA blend (5 wt% PVA) exhibited 3 times lower methanol permeability and similar proton conductivity compared to Nafion�. DMFC tests showed a marked improvement at 8M methanol feed concentration. Additionally, a Nafion�/PVA blend (50 wt% PVA) exhibited a constant proton conductivity, but a decreasing methanol permeability (by an order of magnitude) with increasing membrane annealing temperature 120-250 oC.

In an attempt to capitalize on the selective transport properties of the Nafion�/PVA blend (50 wt% PVA), we have partially sulfonated PVA (S-PVA) to enhance the overall ion exchange capacity (IEC) of the membrane. By increasing IEC, proton conductivity is increased, while low methanol permeability is maintained. The transport properties and DMFC performance of S-PVA and Nafion�/S-PVA blend membranes were measured. Preliminary results show conductivities 3 times higher than Nafion� with methanol permeabilities 2 fold lower than Nafion�. The effect of sulfonation level, blend composition, and annealing temperature on the transport and mechanical properties of the blend membranes will be presented.