A defect-free MOF composite membrane prepared via in-situ binder-controlled restrained second-growth method for energy storage device

Composite membranes with high selectivity and permeability are always essential in diverse fields including batteries and separation. Ultrathin highly-selective layers with well-defined porous structures are deemed as the priority for the composite membranes to break the trade-off effect between selectivity and permeability. Here, we report a binder-controlled restrained second-growth method (BRSM), which directly introduces continuous and uniform metal organic frameworks selective layers (UiO-66/-67) on porous polymer substrates (Daramic) to achieve defect-free composite membranes. In this method, the nucleation and growth of MOF can be well-tuned via controlling MOF nucleation density and the dissolution rates of binders. Composite membranes with UiO-66/-67 layers demonstrate well-controlled selectivities on different ions, confirming the key role of well-ordered pores of MOF. This is further highlighted by the coulombic efficiency (CE) enhanced from 88.4% to 94.5% at a current density of 80 mA cm−2 in zinc-iodine flow battery (ZIFB) demonstration. Additionally, a more even deposition of zinc is induced by MOF surface layer with uniformly pore size distribution, which can suppress the zinc dendrites effectively. This work demonstrates an effective and controllable way to introduce defect-free MOF selective layers on polymer substrates via tuning the MOF nucleation and growth, creating highly selective composite membranes.