Nanofibrous Support With An Asymmetric Tiered Structure for High-Power-Density Pressure Retarded Osmosis Membrane

Pressure retarded osmosis (PRO) has the potential of capturing chemical potential difference created by salinity gradients and converting it into electricity. This work evaluates the performance of a novel electrospun nanofiber supported thin film composite (TFC) membrane platform for use in PRO. This new class of membrane employs a thin selective layer formed directly onto an electrospun nanofiber nonwoven support via in-situ interfacial polymerization. Investigation of the impacts of fiber sizes on membrane mechanical integrity and osmotic flux performance were first carried out. The nanofibrous support was then tailored with an asymmetric tiered structure which incorporated fibers of different size throughout the support. This structure enabled the TFC membranes to successfully withstand an applied hydraulic pressure up to 11.5 bar. In this work, two generations of nanofiber-supported thin film composite membranes were evaluated, each have a unique permselectivity. Testing the membranes in our customized benchtop PRO testing system, we found that these membranes exhibited a peak power density of 7.5 W/m² under real PRO conditions (using a seawater equivalent draw solution). This represents the highest reported empirical value in the peer reviewed literature at the time of this writing and exceeds the target performance of 5 W/m² necessary to make PRO economically viable.