Accurate Predictions of Ion Solvation Under Nanoconfinement

Understanding ion solvation and transport under confinement is critical for a wide range of emerging technologies, from water desalination to energy storage. Molecular dynamics simulations have been widely used to study the behavior of confined ions; however, considerable deviations between simulation results remain. To better understand the role of specific intermolecular interactions, we performed first-principles and classical molecular dynamics simulations of aqueous solutions confined in narrow carbon nanotubes with various diameters. The study shows that the inclusion of both polarization and cation-π interactions is essential for the description of ion solvation under confinement, particularly for large ions with weak hydration energies. Our simulations show slower ion dynamics in the CNTs with increasing degree of confinement, which is associated with the transition from Fickian to a single-file diffusion mechanism. Finally, we also demonstrate a clear correlation between ion dehydration, ion pairing and diffusion by including the polarization effects and cation-π interactions in the classical simulations.<br/>This work was supported as part of the Center for Enhanced Nanofluidic Transport (CENT), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE- SC0019112. The work at the Lawrence Livermore National Laboratory was performed under the auspices of the U.S. Department of Energy under Contract DE- AC52-07NA27344.