Ionic pair-interpenetrated anti-swelling hydrogel membranes for efficient osmotic energy conversion

Hydrogels hold great potential for osmotic energy conversion via reverse electrodialysis (RED). However, their lack of anti-swelling stability and sufficient ion-transport channels lead to unstable ion selectivity and low power output. Herein, an anti-swelling porous acrylamide/vinyl imidazole/methanesulfonic acid (AM/VI/MSA) hydrogel membrane (AVM-gel) was successfully fabricated via in situ polymerization for efficient osmotic energy conversion. Based on the AM hydrogel framework, ionic pairs were formed between basic VI and MSA, which not only reinforced the three-dimensional network structure but also regulated the charge characteristics, thereby improving the permeability and ion selectivity. The dense hydrogen bonding network and hydration sites introduced by MSA endow the membrane with superior water retention and anti-swelling capacity, effectively preventing structural collapse. Furthermore, incorporation of MSA generates imidazolium-sulfonate ionic pairs and creates uniform, interconnected micron-scale channels, in which the charged pore walls and interfacial electrical double layers regulate local ion distribution, thereby facilitating rapid and preferential cation transport. As a result, AVM-gel achieves a maximum output power density of 74.01 W·m −2 under a 50-fold NaCl (0.5/0.01 M) concentration gradient, surpassing most hydrogel-based generators while exhibiting excellent long-term stability. This work presents a robust strategy to address the dual bottlenecks of insufficient energy output and poor usage stability in hydrogels, advancing the practical implementation of osmotic energy harvesting.