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

Hydrogen storage properties of K 2 Mn(NH 2 ) 4 –8LiH were investigated by considering its de/re-hydrogenation properties and reaction mechanisms. Experimental results show that the dehydrogenated K 2 Mn(NH 2 ) 4 –8LiH can be almost re-hydrogenated completely at 230 °C and 50 bar of H 2 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 K 2 Mn(NH 2 ) 4 reacts with LiH to form LiNH 2 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 K 3 MnH 5 and K–Mn-species2 as intermediates and Li 2 NH, Mn 3 N 2 and MnN as final products. The full hydrogenated products are LiH, LiNH 2 , 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. • K 2 Mn(NH 2 ) 4 is synthesized by ball milling metallic Mn with K under 7 bar of NH 3 . • K 2 Mn(NH 2 ) 4 –8LiH releases 6.0 wt% H 2 in an open system. • Dehydrogenated K 2 Mn(NH 2 ) 4 –8LiH has a fast absorption rate more than 1 wt%/min.