Structure and Dynamics of Aqueous Solutions in Carbon Nanotubes: Insights from First-Principles Simulations

Carbon nanopores underpin a large array of materials systems and technological applications, including supercapacitors and water desalination. In these devices, understanding of the ion solvation and dynamics is essential for predicting and optimizing the performance; however, many mechanistic details remain enigmatic. Here, we employ first-principles simulations to unravel key features of the solvation structure of several common ions confined within graphene slit pores and carbon nanotubes (CNTs). We find that polarizable ions exhibit a stronger adsorption at the interfaces and these effects are found to be significantly enhanced under confinement. In addition, we find that confinement significantly influences ion selectivity and transport, i.e., ions with a small radius are found to yield a notably larger energy barrier to reach the pore entrance. Our study points to the complex interplay between confinement and specific ion effects, which has broad implications in optimizing nanopores for ion selectivity and energy storage.

This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. Financial support is from CENT, an EFRC funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0019112.