2D Chitin Sub‐Nanosheets with Extreme Ion Transport for Nanofluidic Sensing

Nanofluidic membranes possess unique ion‐selective transport properties, offering considerable potential for energy harvesting and sensing applications. However, the scarcity of anion‐selective membranes has significantly hindered progress in these fields. Herein, the energy disparities among chitin crystalline planes are exploited to selectively cleave the low‐energy (020) plane, facilitating the directional exfoliation of Bouligand‐structured chitin into 2D sub‐nanosheets (CSs) with an average thickness of 0.7 nm and lateral dimensions of 50–100 nm. Simulations and experiments demonstrate that a reduction in thickness significantly enhances both the ion transport flux (1.53 times) and selectivity (1.14 times), which in turn boosts the power output density to 12.95 W m −2 under a 50‐fold salinity gradient surpassing all‐existing biomass‐based nanofluidic membranes (max. 2.87 W m −2 ) and the commercial benchmark (5.0 W m −2 ). Furthermore, the membranes' extreme ion management capabilities facilitate real‐time nanofluidic sensing, as demonstrated in jellyfish cultivation monitoring. This study presents a cost‐effective strategy for developing high‐performance, positively‐charged nanofluidic membranes with exceptional energy harvesting and sensing capabilities, laying the foundation for advanced energy and sensing technologies.