Trilayer Membranes with a Methanol-Barrier Layer for DMFCs

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Abstract
Trilayer membranes (50 μm 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 μm thick barrier layer with two outside 20 μm Nafion layers reduced methanol crossover by 64% compared to a 50 μm thick Nafion membrane. Membrane electrode assembly performance with the trilayer membrane was better than a 50 μm thick Nafion membrane because of lower methanol crossover and the presence of a good membrane/electrode interface for proton transfer. © 2004 The Electrochemical Society. All rights reserved.