Constructing new-generation ion exchange membranes under confinement regime

Abstract Ion exchange membranes (IEMs) enable the fast and selective ion transport and the partition of electrode reactions, playing an imperative role in the fields of precise ion separation, renewable energy storage and conversion, and clean energy production. Traditional IEMs form ion channels at the nanometer-scale via the assemble of flexible polymeric chains, which are trapped in the permeability/conductivity and selectivity trade-off dilemma due to the high swelling propensity. New-generation IEMs have shown great potential to break the intrinsic limitation by using microporous framework channels for ion transport under confinement regime. In this Review, we firstly describe the fundamental principles of ion transport in charged channels from nanometer to sub-nanometer scale. Then, we focus on the construction of new-generation IEMs and highlight the microporous confinement effects from sub-2-nm to sub-1-nm and further to ultra-micropores. The enhanced ion transport properties brought by the intensified size sieving and channel interaction are elucidated, and the corresponding applications including lithium separation, flow battery, water electrolysis, and ammonia synthesis are introduced. Finally, we prospect the future development of new-generation IEMs with respect to the intricate microstructure observation, in-situ ion transport visualization, and the large-scale membrane fabrication.