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

Abstract

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 Snbased PCMs, named Sn@Al 2 O 3 , were successfully fabricated with tunable size (60−2000 nm) by a facile process from lowcost 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.

Engineering the Thermal Conductivity of Functional Phase‐Change Materials for Heat Energy Conversion, Storage, and Utilization

“…Metal‐based PCMs possess superior thermal conductivities ranging from ≈10 to 400 W m −1 K −1 , which greatly enhance the exergetic efficiency of the thermal energy storage system . For example, the thermal conductivity of Sn is 66.8 W m −1 K −1 , and that of 88Al‐12Si is 181 W m −1 K −1 . Although carbon materials have higher thermal conductivities, there is a possibility that metal and carbon‐based additives can react to form carbide at a high temperature for high temperature metal‐based PCMs.…”

Micro- and nano-encapsulated metal and alloy-based phase-change materials for thermal energy storage

“…Previously, our group presented an encapsulation strategy, in which formation of oxide shell or other treatments were conducted on oxide shells before the formation of metal microparticles and nanoparticles. 88,89 By maintaining the designated form and avoiding the leakage or sintering of Sn-based PCMs at the nano-and micro-level, the isolation/protection of oxide structures effectively enhanced the thermal stability of PCMs in melt-freeze cyclic working conditions. SiO 2 (ref.…”

“…[83][84][85][86][88][89][90] The observation of the surface of the core suggests that oxidation of the core occurred slightly during and possibly aer the encapsulation. [83][84][85][86][88][89][90] The decrease of melting enthalpy of the encapsulated PCMs over melt-freeze cycle in the air to a certain extent indicates additional oxidation occurred, especially, when the core size is below 100 nm, 88 and the shell is not dense enough. 88,89 Thicker and denser shells with bigger core sizes show less oxidation (or not report and better cycle performance (LHS)).…”

“…[83][84][85][86][88][89][90] The decrease of melting enthalpy of the encapsulated PCMs over melt-freeze cycle in the air to a certain extent indicates additional oxidation occurred, especially, when the core size is below 100 nm, 88 and the shell is not dense enough. 88,89 Thicker and denser shells with bigger core sizes show less oxidation (or not report and better cycle performance (LHS)). [84][85][86]89 Meanwhile, coating with oxide is advantageous for the cycle test in air.…”

Molten Salt/Metal Foam/Graphene Nanoparticle Phase Change Composites for Thermal Energy Storage

“…There are three different methods for energy storage, including sensible heat storage, latent heat storage and chemical heat storage. Among them, latent heat thermal energy storage (LHTES) can provide a much higher energy storage density with a smaller temperature variation [3][4].…”