Trilayer membranes with a methanol-barrier layer for DMFCs

Trilayer membranes (50 mum thick) composed of one central methanol- barrier layer and two conductive layers were developed to suppress methanol crossover in liquid-fed direct methanol fuel cells (DMFCs). Nafion-(poly) vinylidene fluoride (PVDF) was used as a central methanol- barrier layer with two outside Nafion layers. Both proton conduction and methanol diffusion were controlled by the properties of the Nafion- PVDF layer. The thickness of the barrier layer and the PVDF content affected methanol crossover and proton conductivity of the trilayer membrane. A 55 wt % PVDF, 45 wt % Nafion, 10 mum thick barrier layer with two outside 20 mm Nafion layers reduced methanol crossover by 64% compared to a 50 mum thick Nafion membrane. Membrane electrode assembly performance with the trilayer membrane was better than a 50 mum thick Nafion membrane because of lower methanol crossover and the presence of a good membrane/electrode interface for proton transfer. (C) 2004 The Electrochemical Society.