Optimization of UiO-66/CaCl2 composite material for thermal energy storage

Thermal energy storage technology can effectively solve the problems of mismatch between the supply and demand in solar thermal utilization. Injecting salt hydrates into porous matrices to develop composite materials could improve the thermal storage performance of pure salt hydrates. Recent studies have shown that UiO-66 could be a promising matrix of adsorption heat storage composite materials. In this paper, to optimize the UiO-66/CaCl2 composite material for thermal energy storage, a series of composite materials were prepared with injecting CaCl2 into UiO-66 of different crystal size and then characterized with various instruments. The results showed that the adsorption performance of the composites was determined by both the salt content and the crystal size of UiO-66. Among all the materials, it was found that U (100)-Ca30 had the best adsorption capacity, which was up to 1.80 g/g at 30 °C and 80% RH. The results of Kissinger equation fitting showed that the desorption activation energy of U (100)-Ca30 at low-temperature zone was lower than that of UiO-66. Moreover, the results showed that the thermal energy storage capacity of U (100)-Ca30 was up to 1416 J/g and it had also shown excellent stability with 16 times of cycling. All of the above results demonstrated that U (100)-Ca30 could be a potential candidate for adsorption thermal energy storage.