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Ionically cross-linked polyelectrolyte complex (PEC) membranes of cationic chitosan (CS) and anionic poly(acrylic acid) (PAAc) were synthesized and assessed for applicability in fuel cells. CS and PAAc were blended in different weight ratios and the resulting membranes were posttreated to enable the formation of the polyelectrolyte complex. The ionic cross-linking occurring on blending the polyelectrolytes excludes the need of using other cross-linking agents. These membranes were extensively characterized for morphology, their intermolecular interactions, thermal stability, and physicomechanical properties using SEM, FTIR, DSC, sorption studies, and tensile testing, respectively. Methanol permeability and proton conductivity were estimated and compared with respective values for Nafion 117. PEC membranes exhibited high ion exchange capacity (IEC), high proton conductivity, low methanol permeability, and adequate thermal and mechanical stability. Among the blends synthesized, the membrane blend with 50 wt % of CS and 50 wt % of PAAc, was identified as ideal for direct methanol fuel cell (DMFC) applications as it exhibited low methanol permeability (3.9 × 10-8 cm2/s), excellent physicomechanical properties and comparatively high proton conductivity (0.038 S·cm-1). Above all, the cost-effectiveness and simple fabrication technique involved in the synthesis of such PECs makes their applicability in DMFC quite attractive.

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The viability of using composite membranes of heteropolyacid (HPA)/polysulfone (PSF), HPA/sulfonated polysulfone (SPSF) for use in proton exchange membrane fuel cells (PEMFC) was investigated. PSF and its sulfonated polymer, SPSF was solution-blended with phosphotungstic acid, a commercially available HPA. Fourier transform infrared (FTIR) spectroscopy of the HPA-40/SPSF composite exhibited band shifts showing a possibility of intermolecular hydrogen bonding interaction between the HPA additive and the sulfonated polymer. The composite membranes exhibited improved mechanical strength and low water uptake. The conductivity of the composite membrane, HPA-40/SPSF, consisting of 40 wt % HPA and 60 wt % SPSF [with a degree of Sulfonation (DS) of 40%] exhibited a conductivity 0.089 S/cm at room temperature that linearly increased upto 0.14 S/cm at 120 8C, whereas the widely used commercial membrane Nafion 117, exhibited a room temperature conductivity of 0.1 S/cm that increased to only 0.12 S/cm at 120 8C. In contrast, the composite of HPA-40/PSF exhibited a proton conductivity of 0.02 S/cm at room temperature that increased only to 0.07 S/cm at a temperature of 100 8C. The incorporation of HPA into SPSF not only rendered the membranes suitable for elevated temperature operation of PEMFC but also provides an inexpensive alternative compared to Nafion. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: [1538][1539][1540][1541][1542][1543][1544][1545][1546][1547] 2005

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