Anti-Swelling 3D Nanohydrogel for Efficient Osmotic Energy Conversion

Osmotic energy conversion based on reverse electrodialysis (RED) technology has attracted intense attention. As the key component, the ion-selective membranes should meet the basic requirements of high power density, high mechanical strength, and easy preparation. Polyelectrolyte hydrogel materials are good candidates, due to their high charge density. However, the severe swelling effect decreases the ion selectivity and mechanical strength. To solve this problem, an anti-swelling 3D nanohydrogel is demonstrated, which is in situ polymerized in the nanoporous polyimide (PI) membrane, exhibiting ultrahigh power density in osmotic energy conversion. Because of the nano-confinement of the PI matrix, the swelling ratio of the nanohydrogel decreases to 37.5% from 593.2% of the bulk hydrogel. Meanwhile, the hybrid membrane exhibits excellent mechanical strength (≈89.5 MPa). Under a 500-fold concentration gradient, the nanohydrogel generates a power density of up to 48.5 W m⁻², one order of magnitude higher than that of the bulk hydrogel. The anti-swelling 3D nanohydrogel introduces a new concept in designing separation membranes for osmotic energy conversion.