材料期刊网

A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the dehydrogenation properties and its influence mechanics on several high-density hydrogen storage materials (MgH(2), LiBH(4), LiNH(2) and NaAlH(4)) and their alloys. The results show that MgH(2), LiBH(4), LiNH(2) and NaAlH(4) high-density hydrogen storage materials are relatively stable and have high dehydrogenation temperature. Alloying can reduce their stability, but the stability of a system is not a key factor to the dehydrogenation properties of high-density hydrogen storage materials. The width of band gap of hydrogen storage materials can characterize the bond strength basically, the wider the energy gap is, the harder the bond breaks, and the higher the dehydrogenation temperature is. The bonding peak of the valence band top of LiNH(2) is attributed mainly to the Li-N bonding, the N-H bond constitutes the low peak, which makes the dehydrogenation temperature of LiNH(2), high, though LiNH(2) has a narrow band gap in respect to LiBH(4) and NaAlH(4), which makes the ammonia release in the dehydrogenation process. Alloying makes the band gap narrow, and the Fermi level goes into the conduction band, which improves the dehydrogenation properties. It was found from the charge population analysis that B-H bond in LiBH(4) is the strongest, H-N bond in LiNH(2) is the weakest, so LiNH(2) is relatively easy to release hydrogen. After alloying, the bond strength of X-H is weakened in every hydrogen storage material, and the N-H bond strength in LiMgNH(2) is the lowest. Therefore, it is perspective to develop LiNH(2) as hydrogen storage from the lowering of dehydrogenation temperature.