Structure and diffusion of molten alkali carbonate salts at the liquid-vacuum interface

Abstract

The liquid-vacuum interface of molten alkali carbonate salts is studied with molecular dynamics simulations. Three salts comprised of LixNayKzCO3 near their respective eutectic concentrations are considered to understand the distribution of ions relative to a liquid-vacuum interface and their diffusivity. These simulations show that each of the cations accumulate at the interface preferentially compared to carbonate. The cation ordering is found to inversely correspond to cation radius, with K being the most likely occupant at the surface, followed by Na, Li, and then the anion. Similar to other studies, the carbonate is found to diffuse more slowly than the cations, but we do observe small differences in diffusion between compositions that present opportunities to optimize ion transport. These results hold consequences for our understanding of ion behavior in molten carbonate salts and the performance of devices employ these electrolytes.

Long-ranged heterogeneous structure in aqueous solutions of the deep eutectic solvent choline and geranate at the liquid–vapor interface

“…Similar density oscillations induced by the interface have been observed in other systems. 13,15,[30][31][32] Furthermore, there are weak suggestions of density oscillations deeper in the liquid region, near 30 and 50 Å, but these are difficult to distinguish definitively from the noise in the curve. The signal and noise can be roughly distinguished by comparing the left and right sides of the density curve.…”

“…Such an approach provides a simple proxy for behavior at hydrophobic surfaces, which can be useful for deciphering the effect of CAGE solutions on lipid bilayers, on hydrophobic solutes with more complex geometries, or other heterogeneous systems containing CAGE. Similar approaches have been employed to study many other molecular systems 12,13 and on ionic liquid systems, 14,15 but, the tremendous diversity of ionic liquid-based solvents motivates this work, since different materials have subtle differences that affect their properties. These interfacial simulations permit evaluation of the effect of the liquid–vapor interface on the structure and orientation of each species as well as thermodynamic properties under idealized conditions.…”