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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.
The first principle plane wave pseudopotential method based on density functional theory (DFT) was used to study the hydrogen evolution and influence mechanism of several high density hydrogen storage materials such as MgH2, LiBH4, LiNH2 and NaAlH4 and their alloys. The results show that MgH2, LiBH4, LiNH2, NaAlH4 are relatively stable, high hydrogen release temperature, alloying can reduce their stability, but the system stability is not the key factor determining the hydrogen releasing properties of high-density hydrogen storage materials; the width of the band gap can be basically characterized The bond strength of hydrogen storage material, the wider the energy gap, the harder the bond is broken, the higher the hydrogen release temperature; the LiNH2 valence band bonding peak contributed mainly by the Li-N bond, the N-H bond structure is lower Of the peak, making the hydrogen storage material LiNH2 although a narrow band gap hydrogen release temperature is high, and the release of ammonia discharge process; alloying allows several high-density hydrogen storage materials narrow band gap, Fermi energy Level into the conduction band, so that their performance of hydrogen release greatly improved; charge population analysis found that LiBH4 B-H bond strongest, HN bond LiNH2 weakest, so LiNH2 in H relatively easy to release alloying, The X-H bond strength of each hydrogen storage material is reduced, and the N-H bond strength in LiMgNH2 is the lowest, so from the drop Temperature hydrogen-angle, the most favorable development LiNH2 hydrogen storage material.