A High-performance Osmotic Energy Conversion Membrane Enabled by Cu2+-crosslinked Polyamide Acid

Abstract

Ion-selective membranes can convert osmotic energy into electrical energy through reverse electrodialysis, thus enabling the generation of sustainable blue energy. However, developing ion-selective membranes with excellent ion selectivity and fast ion transport rates, while also suitable for large-scale production, poses a significant challenge. In this study, we propose a feasible solution on a large scale: an amorphous polymer membrane with sub-nanopore channels made from Cu2+-cross-linked polyamide acid (PAA-Cu). The presence of inherent carboxyl sub-nanochannels in the PAA-Cu membrane (membrane area 390 cm2), combined with the three-dimensional porous interconnected structure formed through Cu2+ coordination, synergistically enhances ion propulsion and selective ion transport properties under the dominating influence of surface charge. By leveraging the energy gradient, the PAA-Cu membrane demonstrates an output power density of 187 W m-2 when subjected to a salinity gradient of 50-fold (0.5 M/0.01 M) KCl. Moreover, it can extract osmotic energy from the diffusion between saline solutions of the same concentration, offering a promising energy harvesting system for industrial wastewater treatment. These findings suggest that the self-supporting PAA-Cu membrane holds great potential for the practical implementation of osmotic energy conversion.