Ultranarrow nanochannels in a staggered two-dimensional polymer membrane enhance electric double-layer coverage for osmotic energy harvesting

Abstract

Abstract Two-dimensional framework membranes (2DFMs) hold great promise for sustainable energy-harvesting technologies, yet their performance is often limited by low electric double-layer (EDL) coverage ( ƞ EDL ) arising from large channels and/or low charge densities. Here, we report an ultrathin ( ~ 50 nm), fully crystalline, ABC-stacked viologen-incorporated 2D polymer membrane (sV2DP) featuring vertically aligned triangular nanochannels ( D eff  = 1.36 nm) densely decorated with pyridinium sites ( + 22.4 mC m −2 ). Compared with its non-staggered AA-stacked analogue, sV2DP exhibits a 3.2-fold enhancement in ƞ EDL under a 50-fold KCl gradient, combining high anionic selectivity ( t −  = 0.85) with remarkable selective current density (14.6 kA m −2 ). Simulations reveal that spirally arranged charges generate a unique “screw-like” anion migration pathway, significantly enhancing transmembrane efficiency relative to non-staggered 2DP analogues. When integrated into micro-aperture osmotic power generators, the sV2DP membrane delivered a peak power density of 243 W m −2 under a 50-fold NaCl gradient, placing it among the highest-performing systems.