Abstract
Pressure retarded osmosis (PRO) and reverse electrodialysis (RED) have been studied recently for their potential in salinity gradient energy generation, the Gibbs energy harvestable when solutions of different concentrations are mixed. Polymer-based membranes are key components of these systems and therefore, the properties of these membranes largely determine the performance and applicability of both PRO and RED. In this chapter, we will specifically elaborate on the mechanism, synthesis, and the state-of-the-art progress in the research field. Due to different operational principles, for PRO membranes, supporting layer design and highly functioning active layers are more important, while for RED membranes, ion permselectivity, and ionic conductivity are of greater concern.