Design of an effective methanol-blocking membrane with purple membrane for direct methanol fuel cells

In this study, purple membrane (PM) was applied as a methanol-blocking agent on Nafion (R) membranes. A series of well-organized poly(diallyldimethylammonium chloride)/PM multilayer films were obtained on a Nafion (R) 212 surface (PDDA/PM/Nafion (R)) to form composite membranes by the electrostatic layer-by-layer (LbL) self-assembly method. The effect of the PDDA/PM/Nafion (R) heterogenic interface on proton conductivity and methanol permeability was studied by alternating the deposited surface. With five PDDA/PM bilayers, double-sided modification (PDDA/PM)(DF-5) and single-side modification (PDDA/PM)(SF-5) resulted in excellent methanol blocking with a 73.4% and 64.7% reduction in methanol permeability in comparison with unmodified Nafion (R) 212, respectively. Indeed, the involvement of PM suppressed the methanol crossover. With regard to the selectivity factor (PDDA/PM)(DF-1) composite membranes showed approximately 2-fold improvement as compared with unmodified Nafion (R) membranes. The cell performance of (PDDA/PM)(SF-1) composite membranes achieved a power density of 27.0 mW cm(-2) which is 48.4% increase compared to cells using unmodified Nafion (R) 212 membranes. Moreover, with (PDDA/PM)(DF-1), we achieved a power density of 34.4 mW cm(-2). This study highlights the potential application of PM as multifunctional protein membrane in direct methanol fuel cells. (C) 2010 Elsevier B.V. All rights reserved.