(546d) Nafion® Blend Membranes for the Direct Methanol Fuel Cell
The direct methanol fuel cell (DMFC) has the potential to replace lithium-ion rechargeable batteries in portable electronic devices. However, current DMFCs experience significant power density and efficiency losses due to high methanol crossover through polymer electrolyte membranes (PEMs), where Nafion® (DuPont) is the most frequently used PEM in the DMFC. In this study, solution-cast and heat-pressed Nafion® blend membranes were prepared with a variety of polymers, (poly(vinyl alcohol) (PVA), poly(acrylic acid), polyacrylonitrile, poly(ethylene oxide), and poly(ethylene glycol)), at various blend compositions and annealing temperatures. Transport properties (proton conductivity and methanol permeability), phase behavior (infrared spectroscopy and SEM), and DMFC performance were measured as a function of these blend parameters. Preliminary results show Nafion®/PVA blend membranes at high Nafion® content resulted in a similar proton conductivity, but three times lower methanol permeability compared to Nafion® 117 at a specific annealing temperature. In addition, an unusual trend was observed in Nafion®/PVA (1:1 wt ratio) blend membranes, where proton conductivity remained relatively constant, but methanol permeability decreased by approximately one order of magnitude with increasing annealing temperature. The role of methanol crossover was also addressed through DMFC performance tests, where improved performance was achieved with Nafion®/PVA blend membranes compared to Nafion® 117 at high methanol feed concentrations (>2M). Transport property trends, infrared spectroscopy, and SEM results coincide with DMFC performance data.