LDH nanosheets anchored on bacterial cellulose-based composite anion exchange membranes for significantly enhanced strength and ionic conductivity

Abstract

An optimal trade-off between ionic conductivity and mechanical properties is critical for ensuring high-performance applications of anion exchange membranes (AEMs). Herein, a bifunctional porous substrate with a nanoarchitecture morphology was prepared; it comprised a two-dimensional (2D) inorganic hydroxide ion conductor (layered double hydroxide, LDH) anchored on three-dimensional natural bacterial cellulose (BC) nanofibers (LDH@BC) and served as a strong reinforcing framework as well as an ion transport medium. The obtained LDH@BC can effectively prevent the layer stacking of LDH caused by space limitations and regulation functions of the BC fiber substrate, thus providing space for the inherent anion-transport ability of LDH. After quaternized chitosan (QCS) impregnation, the composite membrane showed a high OH− conductivity of 42.54 mS cm−1 (80 °C), while the conductivity of the QCS/BC membrane was only 27.90 mS cm−1. More importantly, owing to the synergistic reinforcing effect of LDH@BC, the mechanical strength of the resultant composite AEMs increased sharply to 64.3 MPa, which was nearly 2.5 times higher than that of the pure QCS membrane (only 18.4 MPa). Benefiting from the simultaneously improved anion conductivity and mechanical strength, the QCS-filled LDH@BC composite membrane demonstrated a superior peak power density of 84.2 mW cm−2, while for the fuel cell based on QCS/BC, this value was only 48.0 mW cm−2.