Mg(OH)2/MgO has been attracting considerable interest as a viable candidate for thermochemical heat storage materials, particularly within the temperature range of 200-400 °C. Nonetheless, the typical dehydration temperature of Mg(OH)2, which occurs within the 300-400 °C range, needs to be reduced to enhance its effectiveness in various applications for thermal energy storage. While several studies have shown that heterospecies doping can lower the dehydration temperature, the fundamental mechanism underlying this effect still remains unclear. Here, we employed density functional theory calculations to elucidate the dehydration mechanism of Mg(OH)2, with a particular focus on the initial stage of the dehydration that determines the temperature beginning the reaction. Our findings indicate that the formation of water molecules on the (001) surface is critical in the early stages of the dehydration. This discovery provides a comprehensive explanation for the role of dopants (Na, Li, or LiCl) in reducing the dehydration temperature by decreasing the formation energy of paired H and OH defects and the migration barrier of H on the surface. The present study will significantly advance the development of novel dopants for Mg(OH)2, facilitating a lower dehydration temperature and, thereby, increasing its suitability for heat storage applications.
Keywords: dehydration temperature; density functional theory calculation; magnesium hydroxide; surface reaction; thermal storage material.