Three-dimensional graphitic hierarchical porous carbon/stearic acid composite as shape-stabilized phase change material for thermal energy storage

Abstract

Stearic acid (SA) is a promising phase change material (PCM) for thermal energy storage applications. In order to improve the shape stability and thermal conductivity of SA, a novel shape-stabilized PCM was prepared through incorporation of SA into a three-dimensional fluffy ultrathin-wall graphitic hierarchical porous carbon (GHPC) having large specific surface area and high pore volume in this study. The microstructure, chemical structure, thermal stability, thermal storage properties and thermal conductivity of GHPC and those of as-prepared SA/GHPC composites were determined using various characterization techniques. Furthermore, the effects of the content of GHPC on the thermal properties of SA/GHPC composite PCMs were investigated. The results show that GHPC efficiently enhances both the shape-stability of composite PCMs and their thermal conductivity. The maximumloading of SA in the composite is 85 wt% withoutanyliquidleakage. The prepared composite displays a lower melting temperature and a higher freezing temperature compared to those of pure SA. Meanwhile, the composite melts at 67.5 °C with a melting enthalpy of 171.5 J/g and solidifies at 68.4 °C with a freezing enthalpy of 170.0 J/g, which correspond to the thermal storage capabilities of 98.2% and 98.5%, respectively. In addition, its thermal conductivity was determined to be 0.879 W/m K, which is 3.502 times higher than the pure SA. More importantly, the composite possesses excellent thermal reliability after over at least 600 thermal cycles. Therefore, the as-prepared composite is a desirable candidate for low-temperature thermal energy storage applications.