Dehydration and hydration behavior of metal-salt-modified materials for chemical heat pumps

Lithium chloride (LiCl) modified magnesium hydroxide (Mg(OH)2) is a potential new material for chemical heat pumps. However, there is insufficient information concerning its dehydration and hydration behavior. In this study, the dehydration and hydration reactions, corresponding to the heat storage and the heat output operations, respectively, of authentic Mg(OH)2 and LiCl-modified Mg(OH)2 were investigated by thermogravimetric methods and near infrared spectroscopy. The dehydration of authentic Mg(OH)2 proceeded as a one-step reaction. In contrast, the dehydration of LiCl-modified Mg(OH)2 occurred in two steps. The dehydration reaction rates were increased by LiCl modification of the Mg(OH)2 surface, while the activation energy for the first-order dehydration reaction was lowered. The mechanism for the hydration reaction of magnesium oxide (MgO) was different to that for the hydration of LiCl-modified MgO. This difference was explained by the effect of the LiCl on the MgO particle surface. ► LiCl-modified Mg(OH)2 is a candidate material for chemical heat pumps. ► The dehydration reaction of LiCl-modified Mg(OH)2 is a two-step reaction. ► The dehydration reaction of Mg(OH)2 was enhanced by LiCl modification. ► The hydration mechanisms of authentic MgO and LiCl-modified MgO were different.