Low-cost magnesium-based eutectic salt hydrate phase change material with enhanced thermal performance for energy storage

Low-cost salt hydrate eutectic phase change materials (EPCMs) are attracting increasing attentions and have shown good application prospects for medium-temperature solar thermal energy storage. Water control during sample preparation, supercooling inhibition, and cycle stability are crucial to ensure the thermal reliability of salt hydrate PCM-based thermal energy storage systems. In this study, a “differential scanning calorimeter (DSC) monitoring system evolution process” is developed to prepare MgCl2·6H2O and Mg-EPCM [MgCl2·6H2O (43.0 wt%)-Mg(NO3)2·6H2O (57.0 wt%)], in which unpurified industrial bischofite is used as a precursor. Melting enthalpy of the prepared MgCl2·6H2O can be raised from 125.6 to 164.2 J/g, which is higher than that of recrystallized MgCl2·6H2O and comparable to those of guaranteed reagent (GR), 3 N (purity: 99.9%), and 4 N (purity: 99.99%) MgCl2·6H2O. Furthermore, melting enthalpy of the prepared Mg-EPCM was improved by approximately 10%, from 126 to 140.1 J/g. The latent heat storage capacity is mainly affected by the preparation method, rather than by the small amounts of impurity elements arising from the precursor (impurity rate: ≤ 0.4%). Moreover, 0.5% Sr(OH)2·8H2O has inhibited the supercooling degree of Mg-EPCM within 1.0 °C, with a melting enthalpy of 139.5 J/g. It is found that Sr(OH)2·8H2O participates in eutectic formation and simultaneously nucleates the system to inhibit supercooling. Thermal cycle testing shows that there is almost no significant degradation after 500 thermal cycles. The low-cost Mg-EPCM developed here exhibits an excellent latent heat capacity and inhibits supercooling, showing great practical potential for latent heat storage systems.