Understanding the cation selectivity and confinement in carbon-based nanopores from hybrid first-principles quantum-continuum simulation*

Understanding the cation selectivity under confinement in carbon nanopore is essential in environmental and energy technologies, such as water purification and capacitive energy storage. In this work, we investigate cation selectivity and confinement effects by using hybrid quantum-continuum simulation that provides a more realistic description of the ion-pore interaction than conventional classical force fields. By computing the change in the free energy of alkaline metal cations (Li⁺, Na⁺, K⁺, Cs⁺) during the intercalation process, we show that large cations are more preferable to enter the pore, but their relative selectivity can be manipulated by pore size and geometry. In addition to selectivity, the interfacial charge transfer, solvent number change and hydration structure of cations were also found to be significantly influenced by the pore size and geometry, indicating the complex interplay and competition between ion hydration and ion-pore interaction under confinement. Based on these results, we discuss possible application of specific type of nanopores for the separation of alkaline metal cations.