A study of the hydration and dehydration transitions of SrCl₂ hydrates for use in heat storage

We have experimentally determined the main thermodynamic properties of SrCl₂, a potentially promising salt for thermochemical heat storage. We found a high energy density of 2.4 ± 0.1 GJ/m³ and proved full cyclability for at least 10 cycles going from the anhydrate to the hexahydrate without chemical degradation. We have experimentally determined the thermodynamic equilibria for each individual transition and the corresponding metastable zones. We find that the metastable zone is widest for the anhydrate to monohydrate transition and decreases with each subsequent hydration step. We have also established that the observed nucleation kinetics are highly dependent on the preparation of the sample. Depending on the preparation conditions, some seeds of the precursor phase can remain in the sample thereby influencing the induction times for the transition. In heat storage applications we recommend selecting conditions well away from the phase transition lines (at least outside the metastable zone) and to leave some seeds of the phase to be transferred in order to increase the transition speed.