Recycled blast furnace slag to form-stabilize NaNO₃ with high performance for high-temperature thermal energy storage

Large-scale use of renewable energy is an effective approach to solve the shortage and pollution issue of traditional fossil energy. This work concerns with heat storage materials for thermal energy storage, which play significant roles in copying with the intermittent and fluctuation of renewable energy. To realize the high-efficiency, low-carbon, and low-cost utilization of renewable energy, composite phase change materials (C-PCMs) with high performance were prepared from solid waste of blast furnace slag (BFS) and NaNO₃ salt. The results indicated that BFS was chemically compatible with NaNO₃. The pretreated BFS effectively form-stabilized 50 wt% NaNO₃ to contribute to a high energy density of C-PCMs of 369.10 J/g between 200 and 350 °C. The porous structure of pretreated BFS helped to improve the thermal stability of loaded salt, increased from 514 to 549 °C. The C-PCMs also performed an excellent cycling stability including chemical compatibility, phase transition temperature, and latent heat. Particularly, 7.5 wt% SiC nanoparticles greatly increased the thermal conductivity of C-PCMs up to 1.995 W/(m·K), 3 times higher than that of BFS or NaNO₃. Such C-PCMs could be also made into different shapes, which was easily integrated into renewable energy storage system in the form of packed bed or parallel channels. The economic analysis indicated that the prepared C-PCMs possessed extreme high market competitiveness. Such C-PCMs could be regarded as a promising heat storage material for high-temperature thermal energy storage.