Advancing ion-exchange membranes to ion-selective membranes: principles, status, and opportunities

Abstract Ion-exchange membranes (IEMs) are utilized in numerous established, emergent, and emerging applications for water, energy, the environment. This article reviews five different types of IEM selectivity, namely charge, valence, specific ion, ion/solvent, ion/uncharged solute selectivities. Technological pathways to advance selectivities through sorption migration mechanisms transport critically analyzed. Because underlying principles governing transport, efforts enhance selectivity by tuning membrane structural chemical properties almost always accompanied a concomitant decline permeability desired ion. Suppressing undesired crossover solvent neutral species is crucial realize practical implementation several technologies, including bioelectrochemical systems, hypersaline electrodialysis desalination, fuel cells, redox flow batteries, but ion/solvent relatively understudied, compared ion/ion Deepening fundamental understanding phenomena, specifically factors underpinning structure-property-performance relationships, will be vital guide informed development more selective IEMs. Innovations material design offer opportunities utilize ion discrimination that radically from conventional IEMs potentially depart putative permeability-selectivity tradeoff. Advancements can contribute meeting aqueous separation needs environmental challenges.