A critical review of salt hydrates as thermochemical sorption heat storage materials: Thermophysical properties and reaction kinetics

Salt hydrate-based thermochemical sorption heat storage is believed as one paramount technology for industrial waste heat and renewable energy such as solar energy recovery owing to the significant advantages of high heat storage density and long-duration storage capacity with negligible heat loss. As an advanced heat storage technology , it has aroused extensive interest in the past decade and lingers in the stage of laboratory-scale studies. The implementation of an efficient thermochemical heat storage system needs to ensure reliable thermodynamic properties and excellent reaction kinetics. The emphasis of this review is on the analysis of the thermodynamic characteristics and reaction kinetics of salt hydrates to evaluate the potential of thermochemical heat storage based on the salt hydrate sorption. In this work, the typical principle of thermochemical sorption heat storage, the selection criteria of sorption materials, thermophysical properties and reaction kinetics of salt hydrates were summarized. The thermodynamic data of salt hydrates including melting point, specific heat, density, as well as thermal conductivity were described. For the reaction kinetics, the desorption/sorption reaction rate models and dehydration/hydration behaviors of salt hydrates were summarized. Finally, the challenges and advanced designs of thermochemical sorption heat storage system were evaluated.