Near-frictionless ion transport within triazine framework membranes

• Published in: Nature (London) 2023-05, Vol.617 (7960), p.299-305
• Main Authors: Zuo, Peipei, Ye, Chunchun, Jiao, Zhongren, Luo, Jian, Fang, Junkai, Schubert, Ulrich S., McKeown, Neil B., Liu, T. Leo, Yang, Zhengjin, Xu, Tongwen
• Format: Article
• Language: English
• Subjects: 639/166/898; 639/301/299/1013; Diffusion barriers; Diffusion coefficient; Dilution; Electrochemistry; Energy efficiency; Humanities and Social Sciences; Hydration; Ion channels; Ion transport; Ions; Membrane resistance; Membranes; multidisciplinary; Permeability; Polymers; Rechargeable batteries; Rigidity; Science; Science (multidisciplinary); Separation; Separation processes; Triazine
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/s41586-023-05888-x

The enhancement of separation processes and electrochemical technologies such as water electrolysers 1 , 2 , fuel cells 3 , 4 , redox flow batteries 5 , 6 and ion-capture electrodialysis 7 depends on the development of low-resistance and high-selectivity ion-transport membranes. The transport of ions through these membranes depends on the overall energy barriers imposed by the collective interplay of pore architecture and pore–analyte interaction 8 , 9 . However, it remains challenging to design efficient, scaleable and low-cost selective ion-transport membranes that provide ion channels for low-energy-barrier transport. Here we pursue a strategy that allows the diffusion limit of ions in water to be approached for large-area, free-standing, synthetic membranes using covalently bonded polymer frameworks with rigidity-confined ion channels. The near-frictionless ion flow is synergistically fulfilled by robust micropore confinement and multi-interaction between ion and membrane, which afford, for instance, a Na + diffusion coefficient of 1.18 × 10 −9  m 2  s –1 , close to the value in pure water at infinite dilution, and an area-specific membrane resistance as low as 0.17 Ω cm 2 . We demonstrate highly efficient membranes in rapidly charging aqueous organic redox flow batteries that deliver both high energy efficiency and high-capacity utilization at extremely high current densities (up to 500 mA cm –2 ), and also that avoid crossover-induced capacity decay. This membrane design concept may be broadly applicable to membranes for a wide range of electrochemical devices and for precise molecular separation. The authors develop a strategy that allows the diffusion limit of ions in water to be approached for large-area, free-standing, synthetic membranes using covalently bonded polymer frameworks with rigidity-confined ion channels.