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采用基于密度泛函理论的第一原理平面波赝势方法,研究了MgH2, LiBH4,LiNH2,NaAlH4几种高密度储氢材料及其合金的释氢及影响机理.结果表明:高密储氢材料MgH2,LiBH4,LiNH2,NaAlH4都比较稳定,释氢温度都很高,合金化可以降低它们的稳定性,但系统稳定性不是决定高密度储氢材料释氢性质的关键因素;带隙的宽窄基本可以表征储氢材料成键的强弱,能隙越宽,键断开越难,释氢温度就越高;LiNH2价带顶成键峰主要由Li—N成键贡献,N—H键构成较低的峰,使得LiNH2储氢材料的带隙虽很窄释氢温度却较高,且放氢过程中有氨气放出;合金化使得几种高密度储氢材料的带隙变窄,费米能级进入导带,从而使它们的释氢性能大大改善;电荷布居分析发现LiBH4中B—H键最强,LiNH2中H—N键最弱,因此LiNH2中H相对容易放出.合金化后,各储氢材料中X—H键强度都有所降低,且LiMgNH2中N—H键强度最低,因此从降低释氢温度角度,发展LiNH2储氢材料最为有利.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 (MgH2, LiBH4,LiNH2 and NaAlH4) and their alloys. The results show that MgH2, LiBH4, LiNH2 and NaAlH4 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 LiNH2 is attributed mainly to the Li—N bonding, the N—H bond constitutes the low peak, which makes the dehydrogenation temperature of LiNH2 high, though LiNH2 has a narrow band gap in respect to LiBH4 and NaAlH4, 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 LiBH4 is the strongest, H—N bond in LiNH2 is the weakest, so LiNH2 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 LiMgNH2 is the lowest. Therefore, it is perspective to develop LiNH2 as hydrogen storage from the lowering of dehydrogenation temperature.
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[1] Bao D Y 1994 J. Power Sour. 16 1 (in Chinese)[鲍德佑 1994 新能源 16 1]
[2] Fang S S, Dong Y D 2001 Chinese Journal of Nature 23 259 (in Chinese)[方守狮、董远达 2001 自然杂志 23 259]
[3] Yao X D, Lu G Q 2008 Chin. Sci. Bull. 53 2421
[4] Zhuang P H, Liu X P, Li Z N, Wang S M, Jiang L J, Li H L 2007 Trans. Nonferrous Met. Soc. China 17 985
[5] Chen P, Xiong Z T, Luo J Z, Lin J Y,Tan K L 2002 Nature 420 302
[6] Zhang H, Qi K Z, Zhang G Y, Wu D, Zhu S L 2009 Acta Phys. Sin. 58 8077 (in Chinese)[张 辉、戚克振、张国英、吴 迪、朱圣龙 物理学报 2009 58 8077]
[7] Zhang H, Liu G L, Qi K Z, Zhang G Y, Xiao M Z,Zhu S L 2010 Chin. Phys. B 19 048601
[8] Segall M D, Lindan P J D, Probert M J, Pickard C J, Hasnip P J, Clark S J,Payne M C 2002 Phys. Condens. Matter 14 2717
[9] Vanderbilt D 1990 Phys. Rev. B 41 7892
[10] Hammer B, Hansen L B, Norkov J K 1999 Phys. Rev. B 59 7413
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