Boosting thermochemical performance of SrBr₂·6H₂O with a secondary salt hydrate

This work systematically investigates the effect of 9 inorganic salt hydrates on the performance of strontium bromide (SrBr₂) a thermochemical material (TCM). The goal is to boost the performance of this base salt by enhancing the reaction kinetics of the SrBr₂ 6-1 transition or by shrinking the reaction hysteresis. The study shows that the added salts that do not share a common ion with SrBr₂ (LiCl, LiF, ZnF₂, ZnI₂, K₂CO₃) give limited to no benefits. The lack of improvement is due to a side reaction between SrBr₂ and the added salt leading to the formation of new salt hydrate with low hygroscopicity that does not contribute to the thermochemical reaction. The addition of hygroscopic bromide salts with divalent cations (ZnBr₂, CaBr₂, MnBr₂) gave mixed results depending on the sample history. The most likely cause is cation exchange between bromide salts occurring during exposure to high vapour pressures which promote ionic mobility. The overall best performance was achieved with the addition of LiBr, which we attribute to its high hygroscopicity.