Hydrogen storage properties of Li-Ca-N-H system with different molar ratios of LiNH_2/CaH_2

摘要

In this work, dehydrogenation and rehydrogenation of three LiNH_2/CaH_2 samples with LiNH_2/CaH_2 molar ratio of 2/1, 3/1 and 4/1 were systematically investigated. Remarkable differences were observed in the temperature dependence of hydrogen desorption and subsequent absorption. LiNH_2/CaH_2 in a molar ratio of 2/1 transforms to ternary imide Li_2Ca(NH)_2 after desorbing about 4.5 wt.% H_2 at 350 ℃. And it has a reversible hydrogen storage capacity of 2.7 wt.% at 200 ℃. As for the LiNH_2/CaH_2 mixture in a molar ratio of 4/1, it transforms to a new compound with a composition of Li_4CaN_4H_6 after being dehydro-genated at 350 ℃. The rehydrogenation of both LiCa(NH)_2 and Li_4CaN_4H_6 gives LiNH_2, LiH and the solid solution of 2CaNH-Ca(NH_2)_2.