A yolk/shell strategy for designing hybrid phase change materials for heat management in catalytic reactions

Abstract

Thermal energy storage technology is a promising option for implementing thermal management in advanced chemical processes, and phase change materials (PCMs) are recognized as the ideal thermal storage materials due to their high heat storage density and moderate temperature variation in charging/discharging processes. Herein, a yolk/shell strategy is firstly introduced to encapsulate PCMs with catalytic materials to fabricate a thermal storage functional catalyst. Chemical looping combustion technology, which couples endothermic and exothermic reactions, is chosen as the model process to observe the thermal storage behavior of such catalysts at a micro level. A novel method was proposed to prepare a yolk/shell Al@Al₂O₃ phase change composite, where the Al₂O₃ shell is obtained by the catalytic oxidation of surface layer of Al microspheres by O₂ in the presence of Ni nanoparticles. After that, the Al@Al₂O₃ was coated with Fe₂O₃/Al₂O₃ to form an (Fe₂O₃/Al₂O₃)/(Al@Al₂O₃) thermal storage functional oxygen carrier. The Al@Al₂O₃ microspheres possess high latent heat (315 J g⁻¹) and superior thermal conductivity (1.5–2.7 W (m K)⁻¹). The voids between the yolk and the shell can serve as a buffering space for the volumetric changes of the Al core during the melting/freezing process, resulting in excellent charge/discharge stability. The heat released from the exothermic oxidation reaction can be efficiently absorbed by the PCM core to prevent thermal runaway. The thermal storage functional catalyst provides an intensive and practical approach for thermal management in complex chemical processes.