Bridging Hydration-Shell Exchange Kinetics and Ion Translocation Energy Barriers across Graphene Nanopores

Ion transport across angstrom-scale graphene nanopores is governed by hydration-shell dynamics, yet the kinetic origin of the associated translocation energy barrier remains unresolved. Here, we bridge hydration-shell exchange kinetics and ion translocation energy barriers by resolving water residence events during pore crossing. Ionic conductance measurements establish the angstrom-scale confinement regime of graphene nanopores, within which molecular dynamics simulations are employed to analyze hydration-shell dynamics. We implement a residence-time analysis that decomposes hydration-shell water behavior into confinement-induced dehydration, regular water exchange, and thermal fluctuations. This analysis enables a quantitative determination of the number of hydration waters irreversibly removed during translocation. For both K⁺ and Mg²⁺, the extent of irreversible dehydration increases monotonically with the translocation energy barrier. These results identify hydration-shell exchange kinetics as the molecular-level determinant of ion transport barriers, providing a dynamically grounded and physically transparent picture of ionic transport under extreme nanoconfinement.