Enhancement of Hydroxide Conduction by Incorporation of Metal–Organic Frameworks into a Semi-Interpenetrating Network

Abstract

In order to overcome the trade-off barrier between conductivity and stability in anion exchange membranes and also to investigate the effect of the metal–organic framework (MOF) to resolve this limitation, two membranes (semi-interpenetrating network (semi-IPN) and semi-IPN MOF) were prepared through using the solution casting method. The membranes were characterized by FT-IR, 1H NMR, BET, scanning electron microscopy, and thermogravimetric analysis. Moreover, the effect of metal–organic frameworks was accurately investigated on the membrane features such as ion exchange capacity, water uptake, swelling ratio, hydroxide ion conductivity, thermal and mechanical properties, methanol crossover, single-cell performance, and alkaline stability. The results indicated that the enhancement of ion exchange capacity (1.92 mequiv·g–1 vs 2.40 mequiv·g–1) caused by increased quaternary functional groups resulted in higher water uptake (48% vs 73%). In contrast, the cross-linked networks along with the robust metal–organic frameworks prevented the membranes from the excessive swelling ratio (a swelling ratio of 7%). Finally, the robust, porous, and hydrophilic Cr-MIL-101-NH2 frameworks via the construction of well-connected hydrophilic nanochannels significantly enhanced and facilitated hydroxide ion conductivities (0.07 S cm–1vs 0.01 S cm–1 at 30 °C). This strategy is a promising method to resolve the trade-off issue between hydroxide ion conductivity and swelling in anion exchange membranes.