As the global demand for clean and renewable energy continues to rise, harvesting low-grade energy sources such as salinity gradients has attracted increasing attention. However, achieving both high ion selectivity and high ionic conductivity in ion-exchange membranes remains a major challenge, limiting practical power output. Now, researchers from Qingdao University, Beihang University, and the Chinese Academy of Sciences, led by Professor Xin Sui, Professor Lilong Gao, Professor Longcheng Gao, and Professor Kunyan Sui, report a breakthrough strategy based on high-density one-dimensional (1D) ionic wire arrays for efficient osmotic energy conversion. This work provides new insights into membrane design for next-generation blue energy technologies.
Why High-Density 1D Ionic Wire Arrays Matter
• Simultaneous High Selectivity and Conductivity: Precisely constructed 1D ionic wires enable efficient counter-ion transport while effectively excluding co-ions, overcoming the long-standing trade-off in conventional ion-exchange membranes.
• Ultrahigh Channel Density: The membrane achieves an areal ionic channel density of ~1012 cm-2, among the highest reported for upscaled polymeric membranes, ensuring large ion flux under salinity gradients.
• High Power Output: The optimized membrane delivers an ultrahigh power density of 40.5 W m-2 under a 500-fold salinity gradient, significantly advancing the performance of osmotic energy conversion systems.
Innovative Design and Features
• Self-Assembled Core–Shell Ionic Wires: Through molecular design, hydrophilic imidazole groups and hydrophobic alkyl chains are incorporated into homopolymer repeat units, forming 1D ionic cores protected by hydrophobic shells that suppress swelling.
• Anti-Swelling, High IEC Membrane: The membrane exhibits an ultrahigh ion-exchange capacity (~2.69 meq g-1) while maintaining minimal swelling (<10%), ensuring stable operation in aqueous environments.
• Advanced Structural Characterization: WAXD and AFM analyses confirm hexagonally packed, high-density ionic wire arrays, validating the controlled nanoscale organization of ion transport pathways.
Applications and Future Outlook
• Outstanding Ion Selectivity: The membrane shows near-ideal anion selectivity (Cl⁻/K⁺ selectivity ~0.99), as demonstrated by I–V measurements and fluorescence probe experiments.
• Practical Energy Harvesting: High power densities of 17.0–40.5 W m-2 are achieved across 50–500-fold concentration gradients, and a power density of 16.6 W m-2 is obtained using natural seawater and river water.
• Long-Term Stability and Recyclability: The membrane maintains stable performance over long-term operation and multiple recycling cycles, retaining over 90% of its initial power density.
• Antibacterial Functionality: Imidazolium groups impart excellent antibacterial properties, addressing biofouling concerns in real marine and riverine environments.
• Design Implications: This study highlights molecular self-assembly of 1D ionic wires as an effective route to break performance limits of conventional membranes. Future efforts will focus on further optimizing channel chemistry and extending this design concept to other membrane-based energy and separation technologies.
