
Reverse electrodialysis (RED) is an emerging sustainable energy technology that generates electric power from a salinity gradient without thermal pollution or CO2 emission. Theoretically, the energy generated by RED is estimated to be 1.7 MJ when 1 m3 of seawater is mixed with the same amount of river water [1–3]. RED systems consist of repeating cells of alternating anion exchange membranes (AEMs) and cation exchange membranes (CEMs), between which feed solutions flow through porous spacers. Counterions diffuse through the ion exchange membranes (IEMs) owing to concentration differences, leading to the generation of a membrane voltage that is converted to electric power by an electrochemical reaction at the electrodes. The membrane voltage increases proportionally with the number of cell pairs and thus a large-scale RED system with several hundreds of cell pairs produces a voltage on the order of tens of volts.
