Nanostructured Ionomeric Membranes for Direct Methanol Fuel Cell

Abstract

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 μm 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°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®117) at 1.0 M methanol. It was found that the methanol crossover flux was 2.5 times lower than that of Nafion®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®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®117.