Enhanced Osmotic Energy Conversion through an Asymmetric Nanochannel Array Membrane with an Ultrathin Selective Layer

Osmotic energy, existing between sea water and river water, is a clean, renewable, and sustainable energy source that can be converted into electricity using ion-exchange membranes (IEMs) based on reverse electrodialysis. Asymmetric IEMs with thin selective layers have great potential in the osmotic energy conversion. However, there is still a tradeoff between ion selectivity and ion conductivity in the selective layer. Here, we demonstrate an up-scalable asymmetric nanochannel membrane with a crosslinked monomolecular selective layer that enhances osmotic energy conversion. A monomolecular layer of hyperbranched polyethyleneimine (h-PEI) is precisely grafted at the end of carboxylic nanochannels. The grafted h-PEI layer is fully expanded in the real aqueous condition, leading to unexpected permselectivity decrease. To avoid this, the h-PEI layer is in situ crosslinked with cyanuric chloride (CC), resulting in a dramatic decrease in thickness. The resultant asymmetric nanochannels with a crosslinked monomolecular h-PEI layer show increased Cl- permselectivity and conductivity, achieving enhanced osmotic energy conversion with a power density of 11.9 W/m(2) at a 500-fold salinity gradient, nearly twice as high as the pre-crosslinked membrane. The membrane design concept would pave the way for osmotic energy conversion and could be extended to other separation membranes.

Automated summary

Osmotic energy, existing between sea water and river water, can be converted into electricity using ion-exchange membranes (IEMs) based on reverse electrodialysis. An asymmetric nanochannel membrane with a crosslinked monomolecular selective layer is demonstrated to enhance osmotic energy conversion. The membrane design concept could pave the way for osmotic energy conversion and could be extended to other separation membranes.