Abstract
Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.
Highlights
Ion exchange membranes (IEMs) are actively used in modern technologies, including water purification, concentration, electrochemical synthesis, and sensors [1,2,3,4,5]
ConTchleusaiboonvse material indicates that the transport properties of ion-exchange membranes are deteTrmheinaebdopvreimmaartielyriablyitnhdeiicrastetrsutchtuatret,hwe htircahnsinpoirtst tpurronpedretpieesndofs oionn‐tehxecmhaenmgebrmaneempbrreapnaersataioren determined primarily by their structure, which in its turn depends on the membrane preparation method
As shown in a number of publications, there is a trade‐off between the membrane permeability/conductivity and the selectivity of the transfer rate of the target component
Summary
Ion exchange membranes (IEMs) are actively used in modern technologies, including water purification, concentration, electrochemical synthesis, and sensors [1,2,3,4,5]. Despite the fact that these processes proceed to a much less extent, they usually determine the decrease in the efficiency of electrodialysis, fuel cells and other devices based on ion-exchange membranes [16,28,29,30] That is why their understanding is so important for numerous membrane technologies. For the development of such technologies the selectivity between ions with different valences of the same sign (mono- and multivalent) is no less important [51,52,53,54] The processes of their separation have recently been extensively reviewed [55,56,57,58]. The main attention is paid to the selectivity of transport processes of ions with different charges and ions with neutral molecules
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