Insights into the dehydrogenation reaction process of a K-containing Mg(NH2)2–2LiH system

Abstract

The thermal dehydrogenation process of the KOH-containing Mg(NH₂)₂–2LiH system was systematically investigated by identifying changes in the structure and composition of its components by XRD and FTIR. During ball milling, the added KOH reacts with Mg(NH₂)₂ and LiH to produce MgO, KH and Li₂K(NH₂)₃. During the initial heating process (<120 °C), the newly formed KH and Li₂K(NH₂)₃ react with Mg(NH₂)₂ and LiH to yield MgNH, LiNH₂ and Li₃K(NH₂)₄ along with hydrogen release. Raising the temperature to 185 °C results in a reaction between Mg(NH₂)₂, MgNH and LiH that gives Li₂Mg₂N₃H₃ as the product and further releases hydrogen. As the temperature is increased to 220 °C, Li₂Mg₂N₃H₃ reacts with LiNH₂ and LiH to produce Li₂MgN₂H₂ and H₂. Meanwhile, two parallel reactions between Li₂Mg₂N₃H₃, Li₃K(NH₂)₄ and LiH also generate additional hydrogen. Specifically, the KH and Li₂K(NH₂)₃, formed in situ during ball milling, serve as reactants in the dehydrogenation reaction of the Mg(NH₂)₂–2LiH system, which is responsible for the significantly improved thermodynamics and kinetics of hydrogen storage.