Review on thermal properties and reaction kinetics of Ca(OH)₂/CaO thermochemical energy storage materials

Abstract

Thermochemical energy storage technology is one of the most promising thermal storage technologies, which exhibits high energy storage capacity and long‐term energy storage potentials. The low‐cost, safe, and reliable calcium oxide/calcium hydroxide (CaO/Ca(OH)2) system has become the preferred thermochemical energy storage material system to solve the problem of renewable energy consumption. This study reviews the structural, thermodynamic, and kinetic properties influencing the absorption and desorption reactions of calcium oxide (CaO) and calcium hydroxide (Ca(OH)2) in thermal energy storage applications. It is found that the transformation of crystal structure from cubic to hexagonal upon hydration is attributed to volume expansion and crack formation facilitating diffusion. The specific heat capacities of CaO and Ca(OH)2, as well as reaction enthalpies, are studied across temperature ranges. Most studies on reaction kinetics are focused on the effect of factors such as temperature, particle size, and material content. Strategies to mitigate issues such as particle agglomeration and enhance reaction efficiency are discussed, including the incorporation of enhancing materials such as γ‐Al2O3. This study underscores the importance of the core reaction material content and the enhancing materials that are used to optimise energy density in thermal chemical water‐absorption and ‐desorption reactions.