Hydrogen Release from Mixtures of Lithium Borohydride and Lithium Amide: A Phase Diagram Study

Abstract

We recently reported the synthesis of a new quaternary hydride in the lithium−boron−nitrogen−hydrogen quaternary phase diagram with the approximate composition LiB_0.33N_0.67H_2.67 having a theoretical hydrogen content of 11.9 wt %. This new compound forms by the reaction of appropriate amounts of lithium amide (LiNH₂) and lithium borohydride (LiBH₄) and releases greater than 10 wt % hydrogen when heated. A small amount of ammonia, 2−3 mol % of the generated gas, is also released. We now report a study of hydrogen and ammonia release from the series of reactant mixtures (LiNH₂)_x(LiBH₄)_1-x, where x = 0.667 corresponds to the composition LiB_0.33N_0.67H_2.67. We measured hydrogen and ammonia release amounts as a function of composition and found that maximum hydrogen and minimum ammonia release do occur for x = 0.667. We also present evidence for an additional new quaternary phase and for two possibly metastable phases in this system.