Performance evaluation of sodium alginate–Pebax polyion complex membranes for application in direct methanol fuel cells

A novel polyion complex membrane was synthesized for direct methanol fuel cell application through the blending of the natural biopolymer sodium alginate (SA) with the synthetic polymer Pebax [poly(ether-block-amide)]. The blend was covalently crosslinked with glutaraldehyde (GA) and sulfonated with sulfuric acid (H2SO4), after which characterization by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffractometry, thermogravimetric analysis, and universal testing machine techniques was carried out. The SA–Pebax–GA–H2SO4 membrane exhibited a high ion-exchange capacity of 2.1 mequiv/g, an optimum water sorption of 17.3%, and a low methanol sorption of 9.5%. A desirably low methanol permeability of 9.25 × 10−8 cm2/s and a high proton conductivity of 0.067 S/cm were obtained as against corresponding values of 1.82 × 10−6 cm2/s and 0.077 S/cm reported for a commercial Nafion 117 membrane. Moreover, a high selectivity of 6.5 × 105 Ss/cm3 with a power density of 0.17 W/cm2 was achieved with the indigenous blend membrane at a potential of 0.34 V. Molecular dynamics simulation was performed along with the estimation of fractional free volume to explain the transport behavior of water and methanol molecules through the membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44485.