Nation based organic/inorganic composite membrane for air-breathing direct methanol fuel cells

Membrane electrode assemblies (MEA) with organic/inorganic composite membranes were fabricated and tested in air-breathing direct methanol fuel cells (DMFCs). Various composite membranes based on Nation (R) ionomer with functionalized montmorillonite (MMT) were employed to reduce methanol cross-over without sacrificing proton conductivity by introducing sulfonic acid group at the MMT surface followed by blending with Nafion ionomer. Through a systematic investigation, the composite membrane containing 5 wt.% of MMT modified with 1,3-propane sultone was found to exhibit the best membrane selectivity among other membranes. Membrane-electrode interface of the composite membrane was improved by additional ionomer layer incorporated between membrane and catalyst layers. As a result, an improved DMFC performance was achieved compared to that with Nafion 112 or 115. Employing a self-humidifying diffusion layer, semi-passive DMFC tests were performed for various membranes, and it was confirmed that the composite membranes exhibit higher power density than the Nation membranes. In particular, MEA with a thin composite membrane showed the highest power density and fuel efficiency among the membranes tested in semi-passive DMFCs. (c) 2007 Elsevier B.V. All rights reserved.