Imidazole-doped proton conducting composite membranes fabricated from double-crosslinked poly(vinyl alcohol) and zeolitic imidazolate framework

Abstract

Proton conducting membranes were fabricated from double-crosslinked poly(vinyl alcohol) and zeolitic imidazolate framework (ZIF). The effect of the ZIF type (ZIF-8, ZIF-67, and a 1:1 wt/wt. mixture (ZIF-mix)) on water uptake, ion exchange capacity, proton conductivity, and oxidative stability of the composite membranes was studied. The membrane comprising ZIF-mix exhibited the highest proton conductivity, suggesting a synergistic effect between ZIF-8 and ZIF-67. The influence of ZIF-mix content on the membrane properties was further investigated, and the optimum loading was 7.5%. The introduction of ZIF-mix provided an improvement in proton conductivity and mechanical strength. Moreover, all composite membranes demonstrated low water uptake, low methanol uptake, adequate thermal stability, and high oxidative stability. To the best of our knowledge, this was the first time a ZIF-mix composite membrane was doped with imidazole to improve proton conductivity under non-humidified conditions. The proton conductivity of the imidazole-doped 7.5%ZIF-mix membrane increased with increasing imidazole content and temperature.