Modified Al@Al2O3 phase change materials by carbon via in-situ catalytic decomposition of methane

The microencapsulated phase change materials (MEPCMs) are very promising in thermal storage due to the shape-stable structure that can prevent the leakage of liquid phase change materials during the solid-liquid phase transformation. However, the relatively low thermal conductivity significantly lowers the heat exchange efficiency. Herein, we proposed a new strategy to improve the stability and thermal conductivity by depositing carbon on the surface of Al@Al2O3 composite via in-situ catalytic methane decomposition. In this method, the Al spheres (20–50 μm) are firstly coated by a thin layer of nano Ni species which can promote the oxidation of the surface layer of Al to Al2O3 during the calcination in air. Thereafter, the carbon is produced on the surface of Al@Al2O3 composite when it is submitted to CH4 flow at relatively high temperature (e.g., 650 °C) due to the catalytic methane decomposition by Ni species, obtaining the Al@Al2O3–C composite. The Al@Al2O3–C composite exhibits high phase transition enthalpy (266 J g−1), high thermal conductivity (8 W (m K)−1), and low degree of supercooling in the exothermic process during cooling. In addition, the nesting of the deposited carbon on the surface of phase change material also contributes to obtain dense shell, owning excellent stability in multiple heating/cooling cycles. In the present work, we propose a novel method for preparing encapsulated Al@Al2O3–C phase change materials that an in-situ methane decomposition is proposed to deposit carbon on the Al@Al2O3 microcapsules to obtain high carbon dispersion. One molecule of methane will decompose into one molecule of carbon and two molecules of hydrogen. Ultimately, the carbon from methane decomposition will encapsulate Al@Al2O3 phase change materials and form Al@Al2O3–C phase change materials. During the phase change stage (solid-liquid) while heating or cooling, Al@Al2O3–C phase change materials possess very high heat storage capability, good thermal conductivity, denser structure and excellent cycle stability, which can promise the application of Al@Al2O3–C phase change materials in many chemical processes to balance the temperature of the reaction bed and improve energy efficiency. [Display omitted] •Carbon is deposited on the surface of Al@Al2O3 phase change composite via in-situ catalytic methane decomposition.•The Al@Al2O3-C PCM exhibits high phase transition enthalpy, good thermal conductivity and low degree of supercooling.•The nesting of the dep