Layered double hydroxide-coated silica nanospheres with 3D architecture-modified composite anion exchange membranes for fuel cell applications

A flower-like hierarchical structure consisting of a hydroxide ion conductor (layered double hydroxide, LDH) wrapped on hydrophilic SiO2 nanospheres (LDH@SiO2) was first prepared by an in situ co-precipitation method and then quaternized. This resulting nanocomposite (QLDH@SiO2) was used as a multifunctional additive to modify a quaternized chitosan/polyvinyl alcohol (QCS/PVA) blend matrix to prepare composite membranes. The surface modification of LDH@SiO2 with the silane coupling agent facilitates its dispersion within the blend matrix, which leads to the decreased degree of crystallinity and significant enhancement of mechanical properties of the composite membranes. Furthermore, in situ vertical growth of LDH on the surface of SiO2 cores can effectively avoid the ab-face stacking aggregation of LDH, which can take full advantage of the intrinsic hydroxide-conducting ability of LDH nanosheets. Compared to the ion exchange capability (only 2.09 mmol g(-1)) and effective ionic mobility (1.23x10(-5) cm(2) s(-1) V-1) of the pristine membrane, the two values for the composite membrane containing 6 wt% of QLDH@SiO2 increased to 2.63 mmol g(-1) and 1.50x10(-5) cm(2) s(-1) V-1, respectively. In alkaline direct methanol fuel cell tests at 60 degrees C, the QCS/PVA-6% QLDH@SiO2 composite membrane demonstrates peak power density of 64 mW cm(-2) which is 82% higher than that of the pristine membrane (only 35 mW cm(-2)). Moreover, the increased alkaline stability and decreased methanol permeability of the composite membranes also guarantee their satisfactory fuel cell stability.