Thermal properties of a modified MOF-stearic acid composite phase change materials

ZIF-67, a metal-organic framework (MOF), was grown on expanded graphite (EG) sheet by in-situ precipitation to obtain modified ZIF-67/EG, which, upon calcination, formed a hierarchical porous Co₃O₄/EG hybrid. By using a melting blending and vacuum adsorption methods, stearic acid (SA), SA/Co₃O₄/EG composite phase change material (PCM) was then prepared. The materials were characterized for their microstructure, phase, phase change enthalpy, phase change temperature and charging/discharging behavior. The influence of the microstructure of Co₃O₄/EG on the thermal properties of the SA/Co₃O₄/EG composite PCMs was analyzed. The results showed that the effect of Co₃O₄/EG on the phase transition temperature of SA/Co₃O₄/EG composite PCMs was small, and the phase transition temperature was independent of the amount of Co₃O₄/EG addition. However, the latent heat of the composites PCMs decreased with increasing Co₃O₄/EG content, consistent with the theoretical calculation. The Co₃O₄/EG hierarchical porous structure was shown to be able to prevent the agglomeration of Co₃O₄, providing a high specific surface area and pore volume adsorption of SA. The synergistic effect of the porous structure Co₃O₄ and high thermal conductivity of EG could increase the heat transfer of SA and improve the heat release rate.