Intrusion-extrusion of highly concentrated electrolyte solutions into nanoporous materials: Insights from Molecular Dynamics simulations*

Hydrophobic nanoporous materials hold promise for energy storage and dissipation applications. Water can be forced to intrude into the pores, storing energy that can be released during the extrusion process, which may occur at a different pressure [1]. The presence of dissolved salts dramatically influences intrusion and extrusion pressures. This has been related to an additional osmotic contribution which has to be overcome for the permeation of pure water into the material [2]. However, the intrusion and extrusion pressures are affected also by the type of ions in the solution [3], specially when the solution is highly concentrated.

Using Molecular Dynamics, we studied the intrusion into Silicalite-1 of solutions of NaCl and LiCl for a set of different concentrations. We observe an increase of intrusion pressure which can be related to the osmotic contribution at low concentrations, when only water intrudes. At higher concentrations, permeation of ions into the material influences the osmotic pressure balance, reducing the extrusion pressure. These findings shed light on the intrusion and extrusion mechanisms in presence of different ions.

[1] G. Fraux et al., Chem. Soc. Rev. (2017)

[2] M. Michelin-Jamois et al., PRL (2015)

[3] A. Ryzhikov et al., Phys. Chem. Chem. Phys. (2018)