In situ synthesis and phase change properties of Na₂SO ₄·10H₂O@SiO₂ solid nanobowls toward smart heat storage

As one of the promising thermal energy storage materials, inorganic hydrate salts have long been suffering from two intrinsic drawbacks including phase segregation and supercooling in their heat storage applications. In this study, Na₂SO₄·10H₂O@SiO₂ solid nanobowls, structured as Na₂SO₄·10H₂O nanoclusters dispersed in SiO₂ matrix, were synthesized on a large scale through hydrolysis of tetraethyl silicate and 3-aminopropyltriethoxysilane synchronously in reverse-microemulsion. Microstress imbalance originated from the relative rotation of the growing nanoparticle inside the aqueous droplet leads to a whirlpool-like microreactor and thus results in the formation of brims of the solid nanobowls. Confined by SiO₂ matrix, heat storage properties of the hydrate salts are greatly improved. Their phase segregation is inhibited, and their supercooling is mitigated as well, which might originate from the mesoporous confinement effect. Their excellent cycling performance is of great importance in the prospective thermal energy storage application.