Fabrication of composite polymer electrolyte membrane using acidic metal-organic frameworks-functionalized halloysite nanotubes modified chitosan

Abstract

For the purpose of preparing high performance proton exchange membrane (PEM) with combined low cost and high selectivity, SO3H-UiO-66 coated halloysite nanotubes (SO3H-UiO-66@HNTs) was prepared by a facile one-pot in situ growth method, and then was employed as a multifuctional addtive into chitosan (CS) matrix to fabricate composite PEM. The coating of SO3H-UiO-66 provides SO3H-UiO-66@HNTs with satisfying compatibility and dispersibility with CS matrix. As a result, SO3H-UiO-66@HNTs dispersed homogeneously within CS matrix and thus composite membrane dispalys improved mechanical strength and methonal resistance. Incorporating 10 wt% of SO3H-UiO-66@HNTs into CS matrix results in 0.73-fold increased mechanical strength and 0.54-fold decreased methonal crossover. Due to the embedding of hierarchical core-shell nanobybrid comprising of one-dimensional halloysite nanotubes and a stable MOF with abundant functional –SO3H groups, composite membranes not only enhanced water absorpotion ability, which facilitates the formation of internal interconnected water networks for faster proton transfer, but also obtains additional proton-hoping sites and new channel-like proton-conducting pathway along CS–SO3H–UiO-66@HNTs interface, which is of benefit to the de-protonation/protonation procedure. CS/SO3H-UiO-66@HNTs-10 composite membrane obtains conductivity of 46.2 mS cm−1 (80 °C) and maximum power density of 84.5 mW cm−2 (70 °C), which are respectively 57.6% and 77.1% higher than the pristine CS membrane. Moreover, the durability test further proves the satisfactory stability of CS/SO3H-UiO-66@HNTs-10 composite membrane.