Unveiling Ion-Transport Dynamics in 2D Nanofluidic Anion-Selective Membranes toward Osmotic Energy Harvesting

Two-dimensional (2D) nanofluidic architectures with nanoconfined interlayer channels and excess surface charges have revolutionized membrane-based reverse electrodialysis systems, demonstrating highly efficient osmotic energy collection through strong electrostatic screening of electric double layer (EDL). However, the ion-transport dynamics in 2D nanofluidic anion-selective membranes (2D-NAMs) still remain unexplored. Here, we combine density functional theory and molecular dynamics (MD) simulations to systematically explore ion transport in the 2D-NAMs. Ab initio MD simulations reveal that anions follow a rapid "sequential site-hopping" migration principle within the EDL-confined nanochannels. Classical MD simulations show that optimizing nanosheet layers, surface charge density, and migration pathways improves ion selectivity and permeability, boosting osmotic power output. Guided by these insights, a maximum power density of 5.86 W m^-2 is achieved under a 50-fold salinity gradient mimicking seawater/river water, exceeding the benchmark for commercial viability. This work provides an atomic-level understanding of ion transport in 2D-NAMs and theoretical guidance for designing high-performance membranes for scalable osmotic energy harvesting.