Imidazolium-Functionalized Anion Exchange Polymer Electrolytes with High Tensile Strength and Stability for Alkaline Membrane Fuel Cells

This study reports novel kinds of high tensile strength alkaline anion-exchange membranes composed of imidazolium-functionalized anion exchange polymer electrolytes. The membranes were prepared by a combined thermal and chemical cross-linking of poly (vinyl alcohol) and poly (3-methyl-1-vinylimidazolium chloride)-co-(1-vinylpyrrolidone) (PMVIC-co-VP). Characterizations by AC impedance technique, mechanical property, FTIR spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), along with the water uptake, alkaline resistance and oxidation stability were carried out on the membranes consisting of different PVA/PVA-PMVIC-co-VP mass ratios to evaluate their applicability in alkaline fuel cells. The membrane in a mass ratio of 1:0.4 exhibited high tensile stress at break in the range of 59.3∼76.6 MPa, and the elongation at break around 9.2∼14.9%, depending on the annealing temperature from 130∼190 °C. The OH− conductivity of the membranes was found to be increased with increasing annealing temperature and mass ratio, and reached high up to 1.7 × 10−2 S cm−1. Besides, the membranes showed perfect oxidation stability in 30% H2O2 for 250 hours with no obvious weight loss was observed. XPS analysis indicated that some degradation occurred when the membrane was exposed to 8 M KOH at 85 °C for 312 h, but no lessened OH− conductivity was detected. SEM pictures revealed an ordered microvoid structure with pore size ca. 100∼150 nm uniformly dispersed on the membrane surface, which imparted the PVA/PVA-PMVIC-co-VP membrane with good OH− conductivity.