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.