Nanofluidic channels based on 2D nanomaterials are promising for harvesting osmotic energy due to their high ion selectivity and osmotic conductivity [1]. Layered double hydroxide (LDH) nanosheets exhibit exceptionally high hydroxide ion (OH−) conductivity approaching 10−1 S cm−1 along the in-plane direction [2], making them attractive candidates for inorganic anion exchange membranes. However, their inherent 2D anisotropy results in a significantly low cross-plane conductivity of 10−5 S cm−1, which limits efficient ion transport across membranes composed of restacked nanosheets. In this study, freestanding composite membranes were constructed by integrating LDH nanosheets with porous imine-bridged covalent organic framework (COF) nanoparticles. The incorporation of appropriately sized COF nanoparticles effectively suppresses lamellar restacking and promotes varied orientation of LDH nanosheets within the composite membranes. This orientation modulation unlocks the fast in-plane ion transport pathways of individual LDH nanosheets, resulting in enhanced transmembrane ion conduction. As a result, the LDH/COF composite membranes demonstrate improved cross-plane ionic conductivity, reaching up to 10−2 S cm−1. Furthermore, under a 50-fold NaCl concentration gradient, these membranes deliver a high output power density of 4.5 W m−2, highlighting their potential for rapid ion transport and osmotic energy harvesting.

1. S. Qin, G. Yang, S. Wang, Y. Ma, Z. Wang, L. Wang, D. Liu, W. Lei, Small 20, 2400850 (2024), DOI: 10.1002/smll.202400850
2. P. Sun, R. Ma, X. Bai, K. Wang, H. Zhu, T. Sasaki, Sci. Adv. 3, e1602629 (2017), DOI:10.1126/sciadv.1602629