Broad-Salinity Osmotic Energy Harvesting From Composition Tuned Laminar Membranes

Reverse electrodialysis (RED) is a promising pathway for blue energy generation from salinity gradients, yet its efficiency hinges on ion-exchange membranes that perform across widely varying environmental ionic strengths. In realistic high-salinity sources, large concentration fluctuations strongly influence ion transport and degrade energy output, posing a major challenge for membrane optimization under broad-salinity conditions. Here, we present a composition-tunable laminar composite membrane strategy that sustains high osmotic energy harvesting across diverse concentration regimes by adjusting the ratio between Ti₃C₂T_x and 1,4-phenylenediamine-2-sulfonic acid (DAS). Modulating the DAS fraction simultaneously regulates interlayer channel size and fixed charge density, systematically correlated with RED performance across varying concentrations spanning 0.05 to 5 m. We discovered that low DAS content membranes form narrower, highly selective channels optimal for high-salinity environments, whereas high DAS content membranes feature enlarged channels favoring low-salinity environments. Across all salinity regimes, membrane resistance emerges as the dominant factor governing energy output and is minimized through electrostatic control (via charge density) at high salinity and steric control (via free spacing) at low salinity. This composition-modulated strategy establishes a link between membrane formulation, nanochannel structure, and device-level performance, offering a versatile pathway for designing RED membranes capable of efficient broad-salinity operation.