Skeleton materials for shape-stabilization of high temperature salts based phase change materials: A critical review

Inorganic salts can be used as phase change materials (PCMs) for high temperature (>200 degrees C) thermal energy storage. Advantages of such PCMs include a wide range of phase change temperatures, high energy density, excellent physical/chemical stability and low price. However, applications of above salts based PCMs are greatly limited due to their corrosion to container materials and low thermal conductivity. These problems can be resolved by integrating salts to a porous skeleton, forming the so-called shape-stabilized PCMs (ss-PCMs). The ss-PCMs typically consist of an inorganic salt and a porous skeleton with the former for thermal energy storage and the latter both as a shape stabilizer and a thermal conductivity enhancer. The porous skeleton, made from packing of skeleton materials, is shown to effectively prevent leakage of loaded salts due to capillary force and surface tension. The generated porous skeleton also improves the thermal conductivity of ss-PCMs by providing a high thermally conductive heat transfer path. This review therefore focuses on the skeleton materials for high temperature salts based ss-PCMs, covering selection principles, types and current status of skeleton materials, formation mechanisms of porous skeletons generated from skeleton materials, and effects of different porous skeletons on mechanical and thermophysical properties of ss-PCMs, such as mechanical strength, phase transition temperature, latent heat, thermal conductivity, and cycling stability. Fabrication methods and applications of the ss-PCMs have been also summarized. To the best of our knowledge, this is the first profound review of skeleton materials for salts based ss-PCMs for high temperature applications.