The corresponding XRD pattern presented in Figure reveals the presence of crystalline metallic Cu, together with a residual amorphous phase. The initial crystalline pattern of the composite has disappeared completely after fivefold cycling to 300°C. Therefore, in order to avoid the decomposition reaction, the maximum cycle temperature was reduced to 260 °C in subsequent experiments. A 24-cycle DSC measurement with 20 K⸱min -1 heating/cooling rate to a maximum temperature of 260 °C is presented in Figure . ). From the apparent isobaric heat capacity observed in these scans, the thermal energy stored and released in each cycle (latent heat) was estimated. Integration of the apparent Cp data provided a latent heat of 16.8 Jg -1 for the IL@MOF transition reaction (8.9 Jg -1 in the cooling scan). These achieved values approach the lower end of benchmark materials such as soft paraffins, notably without any further optimization of the MOF:IL volume fraction or synthesis methodology. More importantly, as discussed below, the present material offers a geometrically constrained quasi-solid storage system without the need for a further matrix or scaffold support such as in PCMs involving solid-to-liquid phase transitions. The achieved performance is in the range of alternative solid-state PCMs (e.g., plastic crystals) operating at lower temperature. Considering upscaling ability, CuBTC and