Rearrangement of Water Molecules Confined in 2D Nanochannels Regulates Ion Transport of Membrane towards Lithium Extraction

Abstract The manipulation and mechanism of monovalent and divalent ions (e.g., Li + , Na + , Mg 2+ ) transport through 2D channels remains elusive, limiting the development of 2D materials membranes for lithium extraction. Herein, a water molecules rearrangement strategy is proposed enabling selective transport of Li + over Na + and Mg 2+ through graphene oxide (GO) membrane. By rationally tuning the interlayer space and chemical environment of GO membrane, the distribution of interfacial bound water and non‐interfacial free water within confined channels is delicately manipulated. Characterizations (ion diffusion tests, electrochemical measurements, AFM‐IR, 1 H‐NMR, XPS, etc.) combined with computational simulations reveal that GO membranes with an effective transport space of ≈5.8 Å and O/C ratio of ≈30% exhibit a higher proportion of bound water than free water, facilitating water molecule rearrangement in the first ionic hydration shell and favorable ion–GO interactions. The optimal GO membrane achieves a Li + /Mg 2+ selectivity of 15.5 and Li + /Na + selectivity of 6, surpassing the state‐of‐the‐arts. The unique electronic and thermodynamic properties of ions differentiate their interaction strengths with GO, facilitating fast transport of Li + . This study deepens the understanding of hydrated ions transport through 2D channels, and would inspire the design of next‐generation ion transport membranes.