(401e) Development of SrBr2/SrCl2-MOF Composites with Enhanced Water Adsorption and Heat Storage through a Two-Stage Adsorption Strategy

Salt hydrates have been used as thermochemical storage materials through hydration and dehydration processes. Their heat storage capacity is related to water adsorption kinetics and capacity, and, of course, their hydration and dehydration enthalpy. However, these materials have either a fast water adsorption kinetics or a high water uptake capacity, but normally not both of them. In this study, a novel strategy has been proposed to combine the advantages from adsorbents with high adsorption dynamics at low water partial pressure with those with a high capacity at high water partial pressure to promote the water adsorption capacity and kinetics, therefore energy storage. Two type of composites have been developed based on this two-stage strategy, through incorporating SrBr₂ and SrCl₂ into the microporous metal-organic framework (MOF) MIL-101(Cr) with excellent pore volume and specific surface area properties. In these composites, SrBr₂ and SrCl₂ with a fast adsorption dynamics capture moisture from atmosphere rapidly playing as a moisture pump, while MIL-101(Cr) with high adsorption capacity functions as a water reservoir to take the water from adsorbents with fast adsorption dynamics, forming the two-stage adsorption effects. Through this design, the sorption capacities of the composite are much higher than the water uptake capacity of single components. SrBr₂/MIL-101(Cr) has a capacity of 0.54 g/g, SrCl₂/MIL-101(Cr) has a capacity of 0.73 g/g. The composites also present good heat storage capacities of 1526 J/g for SrBr₂/MIL-101(Cr) and 1462 J/g for SrCl₂/MIL-101(Cr), and good cycling stability after 15 repeating tests.