Controlling conduction environments of anion exchange membrane by functionalized SiO2 for enhanced hydroxide conductivity

Alkaline anion exchange membrane (AAEM) attracts great attention as the key component of the sustainable AAEM fuel cell, while its design and development are still hindered by the structure-conductivity relationship of conducting group. Here three kinds of 200-nm SiO2 with imidazolium brushes tethered by -NH2, -OH, or -CO2H are synthesized and incorporated into chitosan matrix to prepare hybrid membranes. The microstructures of the hybrid membrane are investigated in detail. It is found that the hydrophilic brushes help the SiO2 to achieve uniform dispersion and well compatibility with chitosan matrix, thus resulting in abundant, distinct interfacial transfer pathways within hybrid membrane. Molecular simulation and conductivity measurement jointly reveal the structure-conductivity relationship of conducting group in AAEM: low electrostatic potential of imidazolium or bonding energy favors hydroxide conduction and vice versa. Thus the conduction ability of these three groups follows the order of QVI-NH2> QVI-OH> QVI-CO2H. The tunable chemical environment, excellent water bonding ability, and continuous transfer sites within these interfacial pathways endows the hybrid membrane with significant hydroxide conductivity enhancement by up to 130%, superior to other inorganic particles. Besides, the hybrid membrane achieves obvious improvement of fuel cell performance relative to chitosan control membrane.