Nanocellulose-based ion-exchange membranes for salinity-gradient osmotic energy conversion

Renewable salinity-gradient osmotic energy can be converted to electric energy by using the reverse electrodialysis (RED) technique, where the ion-exchange membranes (IEMs) play an important role in enhancing the output power for osmotic energy harvesting. To enhance the efficiency of the RED system, numerous advanced membrane materials have been investigated for fabricating high-performance IEMs. In recent years, nanocelluloses with abundant sources, active functional groups, and high-aspect-ratio have emerged as the ideal platform for developing various sustainable, high-performance nanocellulose-based IEMs used in the RED process. The review comprehensively summarized the current research progress of nanocellulose-based IEMs used in the RED process, from the preparation and modification techniques of nanocelluloses, manufacturing processes of nanocellulose-based hybrid/composite IEMs, to their RED performance, such as ion selectivity, output power density, and durability. We also discuss the operational principles of RED from the RED cell, the RED stack, and the property index of the RED process. We finally outline the perspective and challenges for RED-used nanocellulose-based IEMs for the potential practical application of the salinity-gradient osmotic energy conversion.