Surfactant‐Assisted Sulfonated Covalent Organic Nanosheets: Extrinsic Charge for Improved Ion Transport and Salinity‐Gradient Energy Harvesting

Abstract Charge‐governed ion transport is the vital property of nanofluidic channels for salinity‐gradient energy harvesting and other electrochemical energy conversion technologies. 2D nanofluidic channels constructed by nanosheets exhibit great superiority in ion selectivity, but a high ion transport rate remains challenging due to the insufficiency of intrinsic surface charge density in nanoconfinement. Herein, extrinsic surface charge into nanofluidic channels composed of surfactant‐assisted sulfonated covalent organic nanosheets (SCONs), which enable tunable ion transport behaviors, is demonstrated. The polar moiety of surfactant is embedded in SCONs to adjust in‐plane surface charges, and the aggregation of nonpolar moiety results in the sol‐to‐gel transformation of SCON solution for membrane fabrication. The combination endows SCON/surfactant membranes with considerable water‐resistance, and the designable extrinsic charges promise fast ion transport and high ion selectivity. Additionally, the SCON/surfactant membrane, serving as a power generator, exhibits huge potential in harvesting salinity‐gradient energy where corresponding output power density can reach up to 9.08 W m⁻² under a 50‐fold salinity gradient (0.5 m NaCl|0.01 m NaCl). The approach to extrinsic surface charge provides new and promising insight into regulating ion transport behaviors.