Flexible core–shell structured Al-Cu alloy phase change materials for heat management

The development of core–shell structured phase change materials (PCMs) with tunable melting points has been attracted much attention for thermal storage of solar energy, and a flexible shell is crucial for their practical applications. Herein, we prepared microencapsulated Al-Cu alloy PCMs (MEPCMs) with a flexible shell by a deposition-oxidizing calcination method. The Cu nanoparticles are chemically deposited on the surface of Al powders by a rapid replacement reaction, which further promotes the formation of Al-Cu alloy microspheres and the oxidation of Al to form Al2O3 shell during oxidation calcination. The prepared MEPCMs show excellent thermal cyclic performance and tunable melting point (549–592 °C). The presence of a thin film between the Al2O3 shell and Al-Cu alloy core may act as a buffer to accommodate volume change during melting-freezing process, obtaining a flexible core–shell structure. The heat storage density of Al-Cu alloy MEPCMs decreases by only 0.09% after 100 melting-freezing cycles, indicating high thermal cycling stability. In addition, the microencapsulated Al-Cu alloys present high latent heat (208.6–222.3 J·g−1) and relatively high thermal conductivity (∼1.8 W·(m·K)−1), which makes it attractive for application in high-temperature thermal storage systems.