Reactivity Improvement of Magnesium Chloride by Ammonia Pre-coordination for Thermochemical Energy Storage at Approximately 100°C

Abstract

Thermochemical energy storage (TcES) is a promising technology for advanced energy storage. This study investigated the reaction of magnesium chloride (MgCl₂) and ammonia (NH₃) as TcES material at approximately 100°C. Activation through NH₃ absorption and desorption was confirmed to increase MgCl₂ surface area from 2.60 to 73.3 m² g⁻¹ and create mesopores. Superior NH₃ absorption reactivity was demonstrated with a maximum absorption rate of 0.019 mol_NH3 mol_MgCl2⁻¹ s⁻¹ at 100°C under 100 kPa of NH₃, compared to a nonactivated pure MgCl₂ material. In a cyclic experiment at 100°C, the activated sample achieved high energy densities and maximum thermal output/storage rates of 1720 kJ kg_Mg(NH3)2Cl2⁻¹, and 9.6 and 3.3 kW kg_Mg(NH3)2Cl2⁻¹ on the 15th cycle. Using a cyclic chemical heat pump (CHP), a high energy density of over 1600 kJ kg_Mg(NH3)2Cl2⁻¹ was achieved, demonstrating enough potential for CHP utilization of heat transformation from 90–120°C.