Ion transport governed by water structure in nanoscale confinement

Water under nanoscale confinement exhibits structural, dynamical behaviors that differ profoundly from its bulk counterpart. Within angstrom-to-nanometer spaces, disrupted hydrogen bond networks, modified dielectric screening, and spatial ordering of water molecules give rise to unique hydration environments for ions. This review examines how the structural organization of confined water governs ion transport in nanochannels. We first discuss the emerging understanding of water structuring under confinement, highlighting the interplay between geometric restriction and interfacial chemistry. We then focus on the hydration structure of ions, including the suppression and deformation of hydration shells, the formation of layered solvation patterns, and their consequences on ionic mobility and selectivity. The discussion further extends to ion–ion interactions and collective transport phenomena that arise from reduced dielectric permittivity and electrostatic screening of confined water. Finally, we analyze how the hydrogen bond network topology and its dynamic fluctuations mediate proton and ion conduction in low-dimensional aqueous systems. Together, these insights reveal confined water as an active medium—rather than a passive solvent—that fundamentally shapes the physics of ion transport at the nanoscale, with implications for nanofluidics, energy conversion, and biomolecular interfaces.