Oriented membranes with in-plane aligned nanosheets for high-energy-efficiency zinc-based flow batteries.

Mixed-matrix membranes (MMMs) embedded with two-dimensional nanosheets are expected to overcome the ubiquitous limitation of permeability-selectivity trade-off, showing great potential in various energy-related technologies. However, it remains challenging to synthesize high-aspect-ratio nanosheets and precisely manipulate their orientation in a polymer matrix to achieve long-range ordered membranes. Herein, we report a [100]-oriented, defect-free MMM incorporating in-plane aligned zeolitic imidazolate framework nanosheets with exposed (200) facets via a shear-flow-induced alignment technique. The high-aspect-ratio structure, in combination with highly aligned straight channels, enables efficient ion sieving and simultaneously builds an ion transport highway. Molecular dynamics simulations and experimental results corroborated that the [100]-oriented MMMs filled with nanosheets possess high ionic conductivity and ultralow active-species permeability. We further demonstrated their applications in alkaline zinc-iron flow batteries (AZIFBs), achieving an exceptionally high energy efficiency of 82.0% at a current density of 260 mA cm-2 and excellent stability over 200 cycles, which outperforms all commercial membranes and state-of-the-art membranes reported to date. This approach opens the door to the rational design of next-generation membranes with highly oriented channel architectures for other possible applications beyond energy-related technologies, such as gas separation and water treatment.