High performance thin film composite pressure retarded osmosis (PRO) membranes for renewable salinity-gradient energy generation

Osmotic power generated from salinity gradients via pressure retarded osmosis (PRO) process has been identified as one of renewable green energy. However, the absence of effective PRO membranes with satisfactory power density hinders its advancement to commercialization. In this work, high performance thin film composite (TFC) PRO membranes have been successfully designed for osmotic power generation. The newly developed TFC-PRO membranes not only exhibit an excellent water permeability (A=5.3Lm^-2h^-1bar^-1) and membrane robust, but also overcome the bottlenecks of low power density. Under lab-scale PRO power generation tests, the membranes can withstand trans-membrane hydraulic pressures up 15bar and exhibit a power density ranging from 7 to 12W/m² using various synthesized seawater and brine as draw solutions. To the best of our knowledge, the developed PRO membranes are superior to other flat-sheet PRO membranes reported in the open literature in terms of the maximum operating pressure and power density. The newly designed PRO membranes consist of an aromatic polyamide selective layer formed by interfacial polymerization on top of a porous polyimide membrane support. The support layer shows a fully sponge-like structure with a small structure parameter and excellent mechanical robustness, while the polyamide selective layer was chemically modified using novel post-fabrication procedures to achieve desired water permeability. The impressive mechanical stability and attractive power density suggest the great practicability of the newly developed composite membranes for harvesting osmotic energy via PRO process.