Solid hydride materials combining high gravimetric and volumetric hydrogen capacity, rapid hydrogenation and dehydrogenation kinetics, and low operating temperature are highly desirable for hydrogen storage on fuel cell vehicles. Recently, a material of nominal composition Li3BN2H 8, formed by combining LiNH2 and LiBH4 in a 2:1 ratio, has garnered much attention because of its high hydrogen release (up to 11.9 wt % hydrogen on heating above ̃200-250 °C). While the material is expected from previous experiments to exist in a single "Li 3BN2H8" α-phase, here it is shown that single-phase 2:1 Li3BN2H8 samples decompose with time into a combination of an R-phase composition enriched in LiNH2 compared to Li3BN2H8 and the 1:1 β-phase Li2BNH6. Through in situ X-ray diffraction of samples from the (LiNH2)c(LiBH 4)1-c system with c in the range 0.667-0.75 (corresponding to LiNH2:LiBH4 ) 2:1 to 3:1) prepared either by high-energy ball milling (HEBM) for 10 min (mixed) or HEBM for 300 min (milled), the equilibrium phase behavior of the quaternary α-phase was investigated. The complete equilibrium composition range of the α-phase at 50 °C was shown to be LiNH2:LiBH4 = ̃2.62:1-2.83:1 or c = 0.724-0.739. Also, an approximate phase diagram in the composition range c = 0.5-0.75 and temperature range T = 0-250 °C was generated.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films