Hydrogen storage properties and reaction mechanisms of K2Mn(NH2)4–8LiH system


Hydrogen storage properties of K2Mn(NH2)4–8LiH were investigated by considering its de/re-hydrogenation properties and reaction mechanisms. Experimental results show that the dehydrogenated K2Mn(NH2)4–8LiH can be almost re-hydrogenated completely at 230 °C and 50 bar of H2 with a hydrogenation rate more than 1.0 wt%/min. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and FTIR investigations reveal that during ball milling K2Mn(NH2)4 reacts with LiH to form LiNH2 and K–Mn-species1 which is probably a K–Mn-containing hydride. The ball milled sample releases hydrogen in a multi-step reaction with the formation of K3MnH5 and K–Mn-species2 as intermediates and Li2NH, Mn3N2 and MnN as final products. The full hydrogenated products are LiH, LiNH2, and K–Mn-species2. The K–Mn-species2 may play a critical role for the fast hydrogeneration. This work indicates that transition metal contained amide-hydride composite holds potentials for hydrogen storage.
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