Highly stable and nonflammable hydrated salt nanocapsules with inorganic-organic composite shell for sustainable building technology

Inorganic hydrated salts show great potential for use in low-temperature energy storage. Nevertheless, drawbacks, such as phase separation, liquid leakage , and inherent supercooling, restrict their application in sustainable building technology. Here, nanoencapsulated phase change materials (NePCMs) was designed by combination of hydrated salt and inorganic-organic composite shell to enhance the thermal energy storage of buildings. Using a two-step method, PMMA and TiO 2 , considered excellent shell materials, were harmoniously combined on the surface of Na 2 HPO 4 ·12H 2 O core. The latent heat of the nanocapsules was approximately 139.6 kJ/kg. After undergoing 500 heating and cooling cycles, the latent heat of nanocapsules only degraded by approximately 5 %. Leakage of water was not observed following heating of the NePCMs to 60 °C for 1 h. The supercooling degree of the nanocapsules decreased to around 0.7 °C. The hybrid PMMA-TiO 2 shell was designed to improve shape stability, reduce water loss, and enhance mechanical properties. Through burning experiments, it was confirmed that NePCMs had good flame-retardant properties. Thus, hydrated salt nanocapsules with inorganic-organic composite shell are an ideal candidate for use as building materials for effective thermal management and fire protection.