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

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 molNH3 molMgCl2−1 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 kgMg(NH3)2Cl2−1, and 9.6 and 3.3 kW kgMg(NH3)2Cl2−1 on the 15th cycle. Using a cyclic chemical heat pump (CHP), a high energy density of over 1600 kJ kgMg(NH3)2Cl2−1 was achieved, demonstrating enough potential for CHP utilization of heat transformation from 90–120°C.