Developments and future prospects of reverse electrodialysis for salinity gradient power generation: Influence of ion exchange membranes and electrodes

Salinity gradient power can be a very attractive renewable energy system because electricity is generated by salt concentration difference between two solutions without any pollutant emission. The representative example of salinity gradient power is reverse electrodialysis (RED), in which there are many variables such as ion exchange membrane (IEM), electrode, stack configuration, the structure of flow pathway, spacer, and solution concentration. This paper focuses on IEMs and electrodes that have not been covered in the previous review papers, as well as on the fundamental of the RED system and plant development for commercialization. In the part of IEM, the characteristics that need to be intensively studied are analyzed and the studies have been conducted to improve membrane property are summarized. In addition, the properties of major commercial IEMs and tailor-made membranes are compared and analyzed, and the relationship between properties affecting membrane performance is studied. In the part of the electrode, the main issues and materials of the electrode part in the RED system are presented, and the recent researches related to the electrode of a large-scale RED system for commercialization are summarized. Finally, this review suggests the future prospects and expectations for salinity gradient power using the RED system.