In Situ X-ray Diffraction Studies on the De/rehydrogenation Processes of the K2[Zn(NH2)4]-8LiH System

In this work, the hydrogen absorption and desorption properties of the system K2[Zn(NH2)4]-8LiH are investigated in detail via in situ synchrotron radiation powder X-ray diffraction (SR-PXD), Fourier transform infrared spectroscopy (FT-IR), and volumetric methods. Upon milling, K2[Zn(NH2)4] and 8LiH react to form 4LiNH2-4LiH-K2ZnH4, and then 4LiNH2-4LiH-K2ZnH4 releases H2 in multiple steps. The final products of the desorption reaction are KH, LiZn13, and Li2NH. During rehydrogenation, KH reacts with LiZn13 under 50 bar of hydrogen producing K3ZnH5. This phase appears to enhance the hydrogenation process which after its formation at ca. 220 °C takes place in only 30 s. The system 4LiNH2-4LiH-K2ZnH4 is shown to be reversible under the applied conditions of vacuum at 400 °C for desorption and 50 bar of H2 at 300 °C for absorption.