Solar Energy Storage in Phase Change Materials: First-Principles Thermodynamic Modeling of Magnesium Chloride Hydrates

Abstract

Thermal energy storage in salt hydrate phase change materials, such as magnesium chloride hydrates, represents an attractive option for solar energy applications. In this study, the structural, electronic, and thermodynamic properties of magnesium dichloride hexahydrate, MgCl2·6H2O, and its dehydrated phases, MgCl2·nH2O (n = 4, 2, 1), were computed within the framework of density functional theory. Densities of states were predicted, and phonon analysis using density functional perturbation theory was performed at equilibrium volume to derive isochoric thermal properties (i.e., Helmholtz free energy, entropy, and isochoric heat capacity). Isobaric thermal properties (i.e., Gibbs free energy, isobaric heat capacity, and latent heat) were also calculated within the quasi-harmonic approximation. Overall good agreement is observed between the computed thermodynamic properties and the scarce experimental data available for these materials.