Current status of ion exchange membranes for power generation from salinity gradients

Reverse electrodialysis (RED) is a non-polluting, sustainable technology used to generate energy by mixing water streams with different salinity. The key components in a RED system are the ion exchange membranes. This paper evaluates the potential of commercially available anion and cation exchange membranes for application in RED. Different membrane properties and characterization methods are discussed and a theoretical membrane model for RED was used to allow fair comparison of the characterization results for application in RED. The results of this study suggest that the membrane resistance should be as low as possible, while the membrane selectivity is of minor importance. Based on the results, the best benchmarked commercially available anion exchange membranes reach a power density of more than 5 W/m2 whereas the best cation exchange membranes show a theoretical power density of more than 4 W/m2. According to the membrane model calculations, power densities higher than 6 W/m2 could be obtained by using thin spacers and tailor made membranes with low membrane resistance and high permselectivity, especially designed for reverse electrodialysis. This makes RED a potentially attractive alternative for energy production.