Clean power generation from salinity gradient using reverse electrodialysis technologies: Recent advances, bottlenecks, and future direction

• Salinity gradient power is an emerging affordable marine renewable energy technology. • RED has yet to attain high energy density and energy conversion efficiency at a field-scale. • Scalable IEMs with high mechanical strength and ion selectivity/conductivity enhance power generation of field-scale RED. • Process optimization of RED is a central key for fouling mitigation of IEMs and electrodes. • Efficient control of irreversible faradaic reactions is essential for sustainable operation of RED. Reverse electrodialysis (RED) is an emerging renewable energy technology that generates electricity by combining concentrated and diluted streams with varying salinities. Ion-exchange membranes (IEMs) have undergone significant advancements in RED, with an enhanced understanding of system configuration and operation conditions for increased power generation. This comprehensive review focuses on recent advances in IEMs, process design, and optimization of RED systems over the last five years. Challenges in the pilot-scale and field-scale systems are discussed, as well as practical limitations such as IEM fouling and electrochemical reactions on electrodes. Future research directions for enhancing overall performance, power generation, and economic feasibility of RED for salinity gradient power (SGP) generation are also proposed. Future advances in the following directions will increase the economic feasibility of RED application in SGP: 1) development of scalable IEMs with high anti-fouling efficiency, mechanical strength, and ion selectivity/conductivity, 2) process optimization (including pre-treatment) for IEM and electrode fouling mitigation, and 3) control of undesirable irreversible faradaic reactions.