材料期刊网

Experiments on a ball milled mixture with a 1:1 molar ratio of LiNH(2) and LiH with a small amount (1 mol %) of Ti(nano), TiCl(3) and TiO(2)(nano) have revealed a superior catalytic effect on Li-N-H hydrogen storage materials. In the x-ray diffraction profiles, no trace of Ti(nano), TiCl(3) and TiO(2)(nano) was found in these doped composites, by which we deduced that Ti atoms enter LiNH(2) by partial element substitution. A first-principles plane-wave pseudopotential method based on density functional theory has been used to investigate the catalytic effects of Ti catalysts on the dehydrogenating properties of LiNH(2) system. The results show that Ti substitution can reduce the dehydrogenation reaction activation energy of LiNH(2) and improve the dehydrogenating properties of LiNH(2). Based on the analysis of the density of states and overlap populations for LiNH(2) before and after Ti substitution, it was found that the stability of the system of LiNH(2) is reduced, which originates from the increase of the valence electrons at the Fermi level (E(F)) and the decrease of the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap (Delta E(H-L)) near E(F). The catalytic effect of Ti on the dehydrogenating kinetics of LiNH(2) may be attributed to the reduction of average populations between N-H per unit bond length (nm(-1)), which leads to the reduction of the chemical bond strength of N-H.