High durable poly(vinyl alcohol)/Quaterized hydroxyethylcellulose ethoxylate anion exchange membranes for direct methanol alkaline fuel cells

Abstract

Novel alkaline anion-exchange membranes composed of chemically cross-linked poly(vinyl alcohol) modified quaternized hydroxyethylcellulose ethoxylate (PVA/QHECE) are prepared. The hydroxide conductivity (σOH−), water and methanol uptakes, ion exchange capacity (IEC), mechanical property, dimensional and alkaline stabilities of PVA/QHECE membranes are measured to evaluate their applicability in direct methanol alkaline fuel cells (DMAFC). The effects of cross-linking time, membrane composition and catalyst dosage (H+) on membrane OH− conductivity are studied using AC impedance technique. FTIR, SEM and TG analysis are used for structural characterization of these membranes. It is found that the OH− conductivity of the membranes increases with temperature and reaches up to 7.5 × 10−3 S cm−1 at 90 °C but no apparent changes on both water uptake and methanol uptake with temperature. The methanol permeability coefficients of the membranes are in the range of 1.26–1.72 × 10−7 cm2 s−1 at 25 °C. In addition, the PVA/QHECE membranes show the high alkaline stability in hot 6.0 M KOH at 80 °C without losing their integrity and OH− conductivity during a week of evaluation. The membrane electrode assembly (MEA) fabricated with PVA/QHECE (= 1:0.25 by mass) gives an initial power density of 4.6 mW cm−2 using 2.0 M methanol and 2.0 M KOH as the fuel and O2 as oxidant at room temperature.