Dehydration kinetics and thermodynamics of ZrO(NO3)2-doped Ca(OH)2 for chemical heat storage

Abstract

Long-term heat storage provides an efficient way to utilize solar energy. Hydroxides are potential candidates for this purpose by dehydration-hydration. In this study, we investigated the effect of doping calcium hydroxide with ZrO(NO3)2 on the thermodynamic and kinetic performance for heat storage. ZrO(NO3)2 improved the heat-storage performance of calcium hydroxide and significantly decreased the dehydration temperature. Differential scanning calorimetry and thermogravimetric data indicated that both the dehydration rate and heat-storage capacity of Ca(OH)2 at 310 °C notably increased by doping with ZrO(NO3)2. The Coats–Redfern integral method and Archar–Brindley–Sharp–Wendworth differential method were used to calculate the pre-exponential factor and the activation energy. The activation energy of the dehydration reaction decreased from 176 to 130 kJ/mol by doping with 10 wt% ZrO(NO3)2 (ZrO(NO3)2-Ca(OH)2-x composite, x = 10). The dehydration-mechanism functions for both the ZrO(NO3)2-Ca(OH)2-10 composite and pure Ca(OH)2 were determined to be the same. The kinetic control equation of the ZrO(NO3)2-Ca(OH)2-x composites was derived and tested. The cycling stability for heat storage was investigated. The results showed that these composites are promising materials for long-term heat storage.