Size-Tunable Alumina-Encapsulated Sn-Based Phase Change Materials for Thermal Energy Storage

The most commonly used phase change materials (PCMs), like organic compounds and inorganic salts, were limited in application by their low thermal conductivity. Herein, for the first time, alumina-encapsulated metallic Sn-based PCMs, named Sn@Al 2 O 3, were successfully fabricated with tunable size (60–2000 nm) by a facile process from low-cost chemicals. The robust fabrication process consists of a surfactant-free solvothermal synthesis of SnO 2 spheres, boehmite treatment on SnO 2 spheres, calcination in the air, and the final hydrogen reduction to transform SnO 2 to metallic Sn, endowing the PCMs with high potential for mass production. The as-obtained Sn@Al 2 O 3 showed a core–shell structure, in which a main metallic Sn core located in the center covered with an Al 2 O 3 shell with small Sn nanoparticles distributed inside. The boehmite treatment, in which the penetration of aluminum species into SnO 2 spheres played an important role, was found to be responsible for the unique structure formation of final Sn@Al 2 O 3 . The understanding of structure formation mechanism gives the possibilities of a new facile way for the synthesis of metal nanoparticles and particle-distributed nanostructures. The obtained Sn@Al 2 O 3 particles not only have high PCM content (92.37 wt %) but also show a stable thermal behavior and morphology during 100 melt–freeze cycles in the air atmosphere. Furthermore, the low melting temperature of the PCM core, combined with high thermal conductivity of both core material (Sn, 66.8 W m –1 K –1 ) and shell material (Al 2 O 3, 35 W m –1 K –1 ), makes Sn@Al 2 O 3 potentially suitable for rapid thermal energy storage in the range 100–300 °C.