Core-Shell Encapsulation of Salt Hydrates into Mesoporous Silica Shells for Thermochemical Energy Storage

The advent of thermochemical energy storage (TcES), that is, storage of thermal energy by means of reversible chemical reactions, incites finding pathways of stabilization of thermochemical materials for thermal batteries of the future. Currently, salt hydrates such as LiCl center dot H2O, CaCl2 center dot 6H(2)O, and SrBr2 center dot 6H(2)O are being actively studied for TcES in buildings due to both high energy storage density (1-2.5 GJ/m(3)) and high storage duration. In this work, we report the core-shell composites "salt in hollow SiO2 spheres with mesopores" (salt = LiCl center dot H2O, CaCl2 center dot 6H(2)O, SrBr2 center dot 6H(2)O) for domestic TcES. The salt hydrates were encapsulated into submicrometer-sized hollow SiO2 (HS) capsules as confirmed by transmission electron microscopy (TEM) and N-2 sorption analyses. High sorption/desorption rates due to mesopores of the shells were shown by thermogravimetric analysis (TGA). The sorption equilibrium for salt@HS was reported, and the applicability of the materials for domestic heat batteries was analyzed. As a result of almost the densest packing of salt@HS, the composites were shown to provide a state-of-the-art energy storage density up to 0.86 GJ/m(3) on the bed level for the high-temperature lift of 32-47 degrees C, showing high energy storage capacity. The stability in at least 50 charging/discharging cycles was confirmed by TGA and TEM.