Composite Proton Exchange Membranes Based on Chitosan and Phosphotungstic Acid Immobilized One-Dimensional Attapulgite for Direct Methanol Fuel Cells

Abstract

In order to obtain biopolymer chitosan-based proton exchange membranes with excellent mechanical properties as well as high ionic conductivity at the same time, natural attapulgite (AT) with one-dimensional (1D) structure was loaded with a strong heteropolyacid and also a super proton conductor, phosphotungstic acid (PWA), using a facial method. The obtained PWA anchored attapulgite (WQAT) was then doped into the chitosan matrix to prepare a series of Chitosan (CS)/WQAT composite membranes. The PWA coating could improve the dispersion and interfacial bonding between the nano-additive and polymer matrix, thus increasing the mechanical strength. Moreover, the ultra-strong proton conduction ability of PWA together with the interaction between positively charged CS chains and negatively charged PWA can construct effective proton transport channels with the help of 1D AT. The proton conductivity of the composite membrane (4 wt.% WQAT loading) reached 35.3 mS cm−1 at 80 °C, which was 31.8% higher than that of the pure CS membrane. Moreover, due to the decreased methanol permeability and increased conductivity, the composite membrane with 4% WQAT content exhibited a peak power density of 70.26 mW cm−2 fed at 2 M methanol, whereas the pure CS membrane displayed only 40.08 mW cm−2.