S. I. Orimo, N. Yuko, Tohoku University, Sendai, Japan
Li-based complex hydrides are of great interest for the application of hydrogen energy storage. We have studied structural and hydriding properties of Li-B- and Li-N-hydrides. In former case, volumetric and gravimetric densities of hydrogen in LiBH4 are reported to be 18.5 mass% and 121 kgH2m-3, respectively. In latter case, LiNH2 has been reported to exhibit reversible hydrogen storage properties about 10 mass% during 2 step reactions. A key issue is to destabilize the Li-based complex hydrides for lower dehydriding temperature. In this study, we clarify the correlation between B-H atomistic vibrations in [BH4]|-anion and melting temperatures of MBH4 (M = Li, Na, and K) as an index of dehydriding temperatures. Based on the experimental results, we propose that an effective method for destabilizing Li-based complex hydrides is to partially substitute Li by other elements with larger electronegativity, such as Mg. Next, as an example, the dehydriding properties of LiNH2 and its partial cation substitution are examined. At the start of the reaction, the dehydriding temperature drastically decreased to around 370 K with increasing Mg concentrations. The dehydriding reactions of LiNH2 with partial Mg substitutions are useful for fuel cell applications.
Summary: Based on the experimental results, we propose that an effective method for destabilizing Li-based complex hydrides is to partially substitute Li by other elements with larger electronegativity, such as Mg. Actually, at the start of the reaction, the dehydriding temperature of LiNH
2 drastically decreased with increasing Mg concentrations.
