Strong Acid Modification Unlocks Synergy of Dissociation and Hydration in Hydrogels for High-Performance Osmotic Energy Conversion

Ion-selective membranes extract osmotic energy with reverse electrodialysis (RED) from salinity gradients, offering a highly promising renewable route to address energy scarcity. However, a key challenge of membrane-based RED is the relatively low power output density, which arises from high internal resistance, poor ion selectivity, and inadequate stability. Herein, a hydrogel with high conductivity, low internal resistance, and strong water retention is presented for efficient osmotic energy conversion. The hydrogels were rationally modified by utilizing the characteristic of strong acids undergoing high dissociation and hydration, resulting in pronounced improvements in electricity, ion transportation and water retention properties relative to those without acids. Under a 50-fold NaCl salinity gradient, the strong acid-modified hydrogel achieves a maximum output power density of 56.03 W/m 2, which far exceeds the commercial benchmark of 5 W/m 2 and capable of sustaining a stable output. Under the action of hydration, the swelling test shows a contracting behavior, indicative of a denser structure. In a 7 day evaporation test, due to the formation of bound water during hydration, the acid-modified hydrogel only lost 41.7% of its water, outperforming the nonacid hydrogel which dehydrated by 85.88%. This work provides a strategy for the fabrication of hydrogel cation-selectivity membranes, and holds broad application prospects in the field of osmotic energy harvesting.