Sustainable Chitin‐Derived 2D Nanosheets with Hierarchical Ion Transport for Osmotic Energy Harvesting

Abstract Generating electricity from salinity‐gradient waters with nanofluidic structures is a promising approach for achieving zero‐emission energy goals and addressing escalating energy crises. However, the ingenious design and development of biomass membranes that satisfy the requirements of sustainability, low‐cost, long‐term stability, and high output power density is a crucial challenge. This work reports two‐dimensional (2D) hierarchical‐structured chitin nanosheets (2D H‐CNS) with abundant micro‐/nano‐pore structures through chemical modification, acid vapor treatment, and ultrasound‐assisted exfoliation. The results showed that surface charge modification not only promotes the loosening and controllable exfoliation of the dense chitin structure into ultra‐thin 2D H‐CNS (1.34 nm) but also increases the porosity and enhances the ion transport flux and selectivity of the nanosheets. Furthermore, experimental and simulation confirm that hierarchical ion transport in nanosheet‐assembled membranes (2D‐HM) substantially enhances ion transport performance, with an 18.5 times improvement in ion conductance over dense nanosheet‐assembled membranes (2D‐DM). Furthermore, 2D‐HM embedded in an energy harvesting system achieved an output power density of 2.59 W m⁻², 2.51 times that of 2D‐DM. This study promotes the development of all‐biomass materials with high‐performance osmotic energy harvesting.