Pore size and counterion effects on ionic transport of a ZnSO4 electrolyte in carbon slit pores via molecular dynamics

Abstract

Molecular dynamics simulations are used to study ion transport through nanometric slit pores made by parallel layers of graphene filled with a 3 M aqueous ZnSO₄ solution, under an external electric field applied perpendicular to the pore axis. After validating the force field with respect to bulk electrolyte properties at high concentrations, the effect of pore width and ion–counterion interactions on ion mobility is investigated with pore sizes ranging from 4.0 Å to 6.7 Å. A non-monotonic trend in ionic current is observed, with a peak at 5.0 Å exceeding those at 5.5 Å and 6.0 Å. The enhanced current is not due to reduced ion–counterion coordination, which remained consistent across these pore sizes. Instead, steric effects appear to enable a more efficient migration dynamic. Simulations performed at different applied electric fields confirm that this behavior is robust, with stronger fields enhancing flux while reducing the relative influence of ion–counterion interactions. These results highlight the importance of nanoscale confinement in optimizing ion transport and provide design guidelines for advanced electrochemical systems.