Two-Sided Asymmetric Nanofluidic Membrane for Enhanced Ion Transport and Osmotic Energy Harvesting

Nanofluidic membranes holds great potential for osmotic energy conversion. Creating high-efficiency ion-permselective membranes with well-fit channel structure continues to pose a persistent challenge. In this work, we design a novel dual asymmetric nanofluidic membrane with MXene and Nafion separately on the two sides of anodic aluminum oxide (AAO) for enhanced ion selective transport. Driven by osmosis, cations are initially separated by Nafion layer with rich negative charges, then followed by accelerated transport due to the interface potential abruptness between AAO channels and MXene layer. Following that, MXene layer acts as the second cation selective layer and further achieve ion charge separation. Benefiting from the dual ion selectivity and accelerated ions transfer, high cation transfer number of 0.95 can be realized using the present membrane. In addition, photo-thermal property of MXene could generate an additional thermal gradient under light irradiation, further promoting ions transfer. Taking advantages of the present two-sided asymmetric nanofluidic membrane, the output power could be up to 65.6 W m-2 at 500-fold NaCl salinity gradient, which is much higher than the majority of previously reported RED membranes (3.0~35.0 W m-2). The present work opens up a new strategy for constructing novel asymmetric nanofluidic devices for enhanced ion transport and osmotic energy harvesting.