Shearing metal-organic framework lattice defects create low-resistance reservoir channels for high-performance aqueous organic flow battery

Abstract

The efficiency of electrochemical storage devices, such as flow batteries, depends on the rapid and selective ion-transport capability of ion-conducting membranes. However, designing membranes with high selectivity and low resistance remains challenging. In this study, we propose a strategy that utilizes graded lattice differences to selectively shear the lattice-defective inner core form a hollow MIL-101 (HMIL-101) with ultralow-resistance reservoir transport channels and lattice-perfect ion-sieving outer shell. An approximately 1/8th-volume-ratio cavity can reduce proton transfer resistance by 86 %, and the HMIL-101 proton conductivity improves by roughly an order of magnitude (2.9 × 10⁻³ vs. 4.0 × 10⁻⁴ S/cm). Further membrane separation tests show precise and rapid selective ion transfer. The proton conductivity increased by 100 %, and the ion conductivity-selectivity increased 5.2 times, reaching 2.6 × 10⁷ S cm/min³. Additionally, a 7 % enhancement in voltage efficiency at a high current density (120 mA/cm²) in aqueous organic redox flow batteries further underscores the superiority of this high-selectivity and low-resistance metal-organic framework ion-conducting membrane. Our strategy offers a new direction for designing high-performance ion transport channels within membranes.