Geometry-induced thermal storage enhancement of shape-stabilized phase change materials based on oriented carbon nanotubes

Abstract

Shape-stabilized phase change materials (PCMs) are promising in efficient utilization of solar energy, waste heat, and peak and valley power, etc. The structure of the supporting materials may have an important effect on the thermal energy storage properties of shape-stabilized phase change materials. However, there are almost no reports concerning this topic. Here, the geometry-induced thermal storage enhancement of shape-stabilized PCMs is first reported based on the comparison of aligned and disordered carbon nanotube (CNT) matrix, and this technique endows composite PCMs with thermal storage capacities exceeding the theoretical value. Polarizing microscopy and cryo-electron microscopy directly show that compared with randomly disordered nanotube (r-CNT), the aligned CNT (a-CNT) promotes a longer-range ordered arrangement of paraffin molecules and offers enhanced crystallization, which thereby result in increased thermal-storage capacities. Although the a-CNTs possess an open-porous architecture, the as-prepared paraffin@a-CNT nanocomposite PCMs displayed a 93 wt% mass loading of paraffin with no leakage and harvested a melting enthalpy of 218.56 kJ kg−1, which was increased by 19.6% compared with the theoretical value calculated from the mass ratio of the paraffin in the nanocomposite. Moreover, the nanocomposite PCMs exhibit excellent charging/discharging thermal stability (99% capacity retention for 500 cycles), high storage efficiency, and rapid response in thermal storage. The geometry-induced thermal-storage enhancement will have important implications for the fundamental understanding and designing of high-performance composite shape-stabilized PCMs.