Membrane Development for Pressure-Retarded Osmosis

Salinity gradient energy (or osmotic power) has huge potential as a sustainable blue energy source. This chapter focuses on membrane development for osmotic power generation via pressure-retarded osmosis (PRO) processes. It discusses the concept of osmotic power generation and the fundamentals of PRO in terms of osmotic processes, water and salt permeabilities, concentration polarization, and power density. Theoretically, forward osmosis and PRO membranes share similar osmotic mechanisms, and both require highly selective membranes with high water and low salt fluxes. Materials with enhanced water transport properties and membranes with superior semipermeable characteristics and robust mechanical properties become absolutely necessary to harvest osmotic power from salinity gradient systems. The chapter reviews preferential types of PRO membranes and some recent exciting developments. The impressive mechanical stability and attractive power density suggest the great practicability of the newly developed composite membranes for harvesting osmotic energy via PRO processes.