Facile Synthesis of Al@Al2O3 Microcapsule for High-Temperature Thermal Energy Storage

Preparation of high-temperature encapsulated phase change materials (PCMs) is very challengeable due to the high chemical corrosion of liquid metal and the high thermal stress caused by volume expansion. We herein report a novel strategy for preparing high-temperature Al@Al2O3 PCM. In this method, nano Ni species are loaded on the surface of Al spheres, which could accelerate the oxidation of the surface Al layer during calcination in air. By monitoring the oxygen consumption and the exothermic changes during the oxidation process, it is found that the oxidation of Al follows a stepwise process which results in the formation of a layered Al2O3 shell. The high oxygen consumption and relatively low activation energy (149–156 kJ/mol) suggests that the surface nickel species significantly accelerate the low-temperature (<650 °C) oxidation of aluminum. The Al@Al2O3 composites show a well-formed core–shell structure with 60–68 wt % of core fraction, high latent heat (289–312 J/g), and mitigated supercooling performance. The layered structure of the shell and the presence of voids in the core together strongly improve the elasticity of the core–shell structure by tuning the thermal stress resulting from the volumetric expansion of the Al core during melting, obtaining a very high stability in long-term melting–freezing cycles.