Synthesis of Sn@SnO2 core-shell microcapsules by a self-oxidation strategy for medium temperature thermal storage

Abstract

• Sn@SnO 2 core-shell microcapsules are prepared by a facile two-step self-oxidation method. • The preparation includes vapor or water pretreatment and subsequent heat oxidation treatment. • The capsules exhibit a melting point of ~232 °C and latent heat of ~53 J/g. • The capsules show excellent thermal cycling stability, present no breakage after long term cycling. • The Sn@SnO 2 capsules are promising for application in medium-temperature thermal energy storage. Latent heat storage using metals as solid-liquid phase change materials (PCMs) have been concerned for medium-temperature thermal energy storage. However, due to the leakage and corrosion problems during phase transformation, the use of metallic PCMs are greatly limited. Encapsulation of PCM microparticles to form microencapsulated PCMs (MEPCMs) is an effective strategy, which is unfortunately technologically difficult for metallic PCMs. In this study, we develop metallic Sn MEPCMs coated by a stable SnO 2 shell through a facile self-oxidation method. Sn@SnO 2 core-shell MEPCMs are fabricated by two steps: firstly, Sn microspheres are pre-treated by vapor or water to form an oxide precursor shell on Sn microspheres; secondly, heat oxidation treatment under O 2 atmosphere is conducted to form a stable SnO 2 shell. The Sn@SnO 2 microcapsules exhibit a melting point of ~232 °C and latent heat of ~53 J/g. Importantly, the capsules present an excellent thermal cycling stability, in which after 100 cycles of melting-freezing the phase change properties and core-shell structure could be well retained. These results reinforce the promising application of microencapsulated Sn in medium-temperature thermal storage.