Enhancement Effect of Bimetallic Amide K2Mn(NH2)4 and In-Situ Formed KH and Mn4N on the Dehydrogenation/Hydrogenation Properties of Li–Mg–N–H System.

In this work, we investigated the influence of the K₂Mn(NH₂)₄ additive on the hydrogen sorption properties of the Mg(NH₂)₂ + 2LiH (Li–Mg–N–H) system. The addition of 5 mol% of K₂Mn(NH₂)₄ to the Li–Mg–N–H system leads to a decrease of the dehydrogenation peak temperature from 200 °C to 172 °C compared to the pristine sample. This sample exhibits a constant hydrogen storage capacity of 4.2 wt.% over 25 dehydrogenation/rehydrogenation cycles. Besides that, the in-situ synchrotron powder X-ray diffraction analysis performed on the as prepared Mg(NH₂)₂ + 2LiH containing K₂Mn(NH₂)₄ indicates the presence of Mn₄N. However, no crystalline K-containing phases were detected. Upon dehydrogenation, the formation of KH is observed. The presence of KH and Mn₄N positively influences the hydrogen sorption properties of this system, especially at the later stage of rehydrogenation. Under the applied conditions, hydrogenation of the last 1 wt.% takes place in only 2 min. This feature is preserved in the following three cycles. [ABSTRACT FROM AUTHOR]