Design and optimization of salinity gradient energy harvesting system using symmetrical organic redox couples

Salinity gradient energy (SGE) is a rising source of renewable energy that commonly exists at the confluence of rivers and oceans and can be harvested by membrane-based technologies such as reverse electrodialysis (RED) process. However, unavoidable high external resistance and sluggish electrode kinetics in existing RED devices severely hamper power density and recovery efficiency. To solve the issue, aqueous organic species with fast redox kinetics were down-selected and adopted as a storage medium to be internally coupled with the RED module and directly transform SGE into chemical energy. Moreover, a temperature-responsive-fluid-imaging coupled 3D numerical simulation approach was also developed for further promoting the fluid state of the overall module. Owing to the systematic design and optimization, a high SGE harvesting power density of 0.29 W cm−2 and a recovery efficiency of 95.2 % were achieved, offering a promising process for large-scale SGE harvesting and integration into the future electric grid.