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 oC) and maximum power density of 84.5 mW cm-2 (70 oC), 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.