Proton-conducting membranes with high selectivity from phosphotungstic acid-doped poly(vinyl alcohol) for DMFC applications

Abstract

Proton-conducting hybrid membranes composed of poly(vinyl alcohol) (PVA) and phosphotungstic acid (PWA) were prepared by solution-blending. The effect of PWA doping on the membrane properties such as water uptake, ion-exchange capacity (IEC), proton conductivity and methanol permeability was investigated. Up to 20 wt.% PWA content, both water uptake and methanol permeability slightly increased then decreased continuously until 90 wt.%. Fourier transform infrared spectra indicate that significant amount of PWA was maintained in the polymer matrix even after several hours of immersion in water. Combining FTIR results and the similarity in water uptake and methanol permeability of PVA/PWA hybrid membranes suggests that the variations in associated properties are ascribed to intermolecular hydrogen bonding interaction between hydroxyl groups of PVA and PWA. Methanol permeabilities of hybrid membranes were significantly lower than that of Nafion115. The proton conductivity of hybrid membranes was in the order of 10 −4 S cm −1 and generally increases with PWA content. Finally, the possibility of PVA/PWA hybrid membranes for use in PEMFC was explored. In H 2/O 2 mode, the performance increases with PWA content and a maximum current density of 46 mA cm −2 was obtained with PVA 20 wt.% and PWA 80 wt.% (PVA20PWA80) sample. Performance of DMFC with PVA20PWA80 increases with temperature and reached to 80 mA cm −2 at 80 °C.