Nonlinear Ion Transport Within sub-1nm Radii Carbon Nanotubes

This is the authors' abstract. We don't add key points for this paper.

Ion transport within confinements, such as nanopores and nanotubes, plays a crucial role in advancing applications across various domains, including energy storage, seawater desalination, and neuromorphic computing. Despite the widespread societal impact of these applications, a comprehensive and accurate model to describe this transport mechanism remains elusive. In this study, we examine the role of the hydration layer—a critical factor influencing ion transport—as ions traverse carbon nanotubes. Utilizing molecular dynamics (MD) simulations, we discovered that the ion’s hydration layer exhibits both depletion and enhancement during transport, challenging the conventional view that transport is accompanied solely by dehydration. Further, by analyzing the pair distribution function (PDF) of ions within the carbon nanotube, we show the principle for these hydration layer changes, which stems from the alterations in the translational free energy of water molecules at specific locations. Our findings underscore the need for a new model that accounts for the variations in water’s translational free energy and the intricate many-body effects to provide a deeper understanding of the non-linearity of ion transport in carbon nanotubes with radii smaller than 1 nm.