The Interplay of Solvation and Polarization Effects on Ion Pairing in Nanoconfined Electrolytes

Abstract

The nature of ion–ion interactions in electrolytes confined to nanoscale pores has important implications for energy storage and separation technologies. However, the physical effects dictating the structure of nanoconfined electrolytes remain debated. Here we employ machine-learning-based molecular dynamics simulations to investigate ion–ion interactions with density functional theory level accuracy in a prototypical confined electrolyte, aqueous NaCl within graphene slit pores. We find that the free energy of ion pairing in highly confined electrolytes deviates substantially from that in bulk solutions, observing a decrease in contact ion pairing but an increase in solvent-separated ion pairing. These changes arise from an interplay of ion solvation effects and graphene’s electronic structure. Notably, the behavior observed from our first-principles-level simulations is not reproduced even qualitatively with the classical force fields conventionally used to model these systems. The insight provided in this work opens new avenues for predicting and controlling the structure of nanoconfined electrolytes.

PW-SMD: A Plane-Wave Implicit Solvation Model Based on Electron Density for Surface Chemistry and Crystalline Systems in Aqueous Solution

“…RDFs for surface systems are computed using an anisotropic correction described in a recent work . The correction accounts for the fact that water molecules cannot enter regions occupied by the Cu surface.…”

To Pair or not to Pair? Machine-Learned Explicitly-Correlated Electronic Structure for NaCl in Water

“…Beyond the bulk, confinement of electrolytes leads to interesting physics and unexpected phenomena that are highly relevant to a range of applications, including blue energy harvesting and desalination. , In particular, extension of our current models to explore the intriguing phenomenon of confinement-induced ion pairing is very attractive. Recent work has shown the assembly of confined ions in solution into long chains under an electric field, resulting in the so-called “memristor” effect, for which accurate atomistic insights are urgently needed …”

“…Recent work has shown the assembly of confined ions in solution into long chains under an electric field, resulting in the so-called “memristor” effect, 99 for which accurate atomistic insights are urgently needed. 100 …”