Enhancement of CaCl2/silica gel composites sorbent stability for low-grade Thermal Energy Storage

This study explores the enhancement of a CaCl₂/silica gel composite sorbent for low-grade thermal energy storage (TES) and assesses its stability through modifications in the manufacturing process. Initially, the optimal calcium chloride concentration for incorporation into mesoporous silica gel via the DRY impregnation method was determined. Subsequently, the effects of three impregnation techniques (Dry (DRY), Wet (WET), and Airbrush (AB)) on the characteristics of the composite were investigated. Higher CaCl₂ concentrations reduced pore volume and surface area while increasing thermal storage capacity, though leading to structural instability due to deliquescence. The impregnation technique slightly affected the morphological and thermochemical properties of the composites. Due to the increased water volume, the WET and AB approaches enhanced salt distribution throughout the matrix, mitigating deliquescence and improving stability relative to the DRY method. The AB approach reduced surface salt crystallization by nebulization, promoting a more uniform distribution and fewer cracks; however, it slightly reduced salt content. Finally, the TES potential of these composites was assessed under conditions relevant to residential buildings. The maximum adsorption heat values were 887.77 ± 44.39 J/g (DRY), 938.39 ± 46.92 J/g (WET), and 867.38 ± 43.37 J/g (AB). The results underscore the impact of impregnation processes on composite performance, providing insights into the optimization of materials in TES applications.