Analysis of the solvation structure of rubidium bromide under nanoconfinement

Abstract

We report results from a molecular simulation study of aqueous rubidium bromide solutions confined in slit-shaped carbon pores 6.5–16 Å in width, which encompasses the range typically found in nanoporous carbon electrode materials. For each slit-pore model, the structure of the solvation shells surrounding the Rb+ and Br− ions in 0.1, 0.5 and 1.0 M solutions was examined using the ion–water radial distribution functions. The impact of pore geometry on solvation structure of ions was also investigated using a disordered carbon model that morphologically resembles real nanoporous carbon electrodes. Monte Carlo simulations were used to determine the propensity of ions to reside in pores of specific sizes in the model carbon, allowing the solvation structure of Rb+ and Br− ions to be analysed as a function of pore size. We find that a dramatic drop in the solvation number occurs in pore sizes below 10 Å for slit-shaped pores, while more complex geometries see a steady decrease in solvation number as pore size is decreased. Our results suggest that, when compared to the disordered carbon model, the slit-pore model may not provide qualitatively accurate predictions regarding the structural properties of electrolytes confined in complex electrode materials.