Demonstration of Mg₂FeH₆ as heat storage material at temperatures up to 550 °C

The storage of heat at high temperatures, which can be used to generate electricity after sunset in concentrating solar power plants, is one of the most challenging technologies. The use of metal hydride could be one possibility to solve the problem. During the endothermic heat storage process, the metal hydride is decomposed releasing hydrogen, which then can be stored. During the exothermic reaction of the metal with the hydrogen gas, the stored heat is then released. Previous research had shown that Mg and Fe powders can be used at temperatures up to 550 °C for heat storage and shows excellent cycle stability over hundreds of cycles without any degradation. Here, we describe the results of testing of a tube storage tank that contained 211 g of Mg and Fe powders in 2:1 ratio. Twenty-three dehydrogenations (storage) and 23 hydrogenations (heat release) in the temperature range between of 395 and 515 °C and pressure range between 1.5 and 8.6 MPa were done. During the dehydrogenation, 0.41–0.42 kWh_th kg⁻¹ of heat based on material 2 Mg/Fe can be stored in the tank. After testing, mainly Mg₂FeH₆ was observed and small amounts of MgH₂ and Fe metal can be detected in the hydride samples. This means that the heat storage capacity of the system could be further increased if only Mg₂FeH₆ is produced during subsequent cycles