Conversely, an endothermic phase transition is observed in the DSC scan of IL@CuBTC at 220 °C with no corresponding mass loss in the TGA prior to the final decomposition of the composite at 340 °C. To examine the reversibility of this endothermic transition, a cyclic DSC scan was conducted to a maximum temperature of 300 °C, shown in Figure . Following the endothermic transition upon heating at 220 °C, a corresponding exothermic phase transition occurs upon cooling at 195 °C. The temperature difference in these phase transitions is consistent with those observed in other metal-organic phase-change materials. Such a difference indicates a kinetic barrier, leading to an extended range of supercooling (a prerequisite for latent heat storage in PCMs).