Nanostructured Ionomeric Membranes for Direct Methanol Fuel Cell

Nanostructured ionomeric membranes for direct methanol fuel cell (DMFC) were prepared from polyethylene co-acrylic acid-based ionomer (Lotek 4200) with different proportions of functionalized multi-walled carbon nanotubes (f-MWNTs). The membranes (50-120 mu m in thickness) were examined in terms of water swelling, proton conductivity and methanol permeability. They were also fabricated in membrane electrode assemblies and tested in a DMFC at 60 degrees C. The proton conductivity and methanol permeability of the membranes were found to be dependent on f-MWNTs loading. The DMFC performance (maximum power density) of the membranes was comparable to that of a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (Nafion (R) 117) at 1.0 M methanol. It was found that the methanol crossover flux was 2.5 times lower than that of Nafion (R) 117. With the increasing methanol concentration (up to 10.0 M), the composite membranes exhibited superior DMFC performance and lower methanol crossover fluxes as compared to Nafion (R) 117. Significant cost savings may be attained by using the composite films which contain less expensive polymer, e.g., polyethylene co-acrylic acid-based ionomer (Lotek 4200) compared to Nafion (R) 117.