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 9.25x10(-8) cm(2)/s and a high proton conductivity of 0.067 S/cm were obtained as against corresponding values of 1.82x10(-6) cm(2)/s and 0.077 S/cm reported for a commercial Nafion 117 membrane. Moreover, a high selectivity of 6.5x10(5) Ss/cm(3) with a power density of 0.17 W/cm(2) was achieved with the indigenous blend membrane at a potential of 0.34V. 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. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44485.