LiNH_2储氢材料中间隙H与掺杂原子交互作用对其释氢性能影响机理研究

Mechanism of the influence of the interaction between interstitial H atom and doped atom on the dehydrogenation performance of LiNH_2

采用基于密度泛函理论的赝势平面波第一性原理方法,研究了LiNH2缺陷及其掺杂原子交互作用对其释氢影响.通过对其进行优化求得它们的局域最稳定结构并计算了含间隙H原子缺陷的LiNH2及其掺杂合金的结合能、间隙缺陷形成能、态密度和电荷布居.结果表明:系统结合能不能反映LiNH2及其掺杂合金的释氢性质;平衡时,LiNH2中有一定的间隙氢原子存在,Mg,Ti掺杂使形成能大大降低,大大增大了间隙氢的浓度.间隙H原子在带隙引入了缺陷能级使带隙大大减小,提高释氢能力.间隙H原子导致[NH2]-中N—H原子间相互作用减弱,容易释氢.间隙H与[NH2]-中N存在共价作用,可以解释LiNH2释氢反应中NH3的放出.当存在掺杂时,N—H键的键强不均衡,部分较弱,部分较强,较弱的N—H键中H容易放出.

The first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the mechanism of the influence of interaction between interstitial H atom defect and doped atom on the dehydrogenation performance of LiNH2.We obtain the most stable structure of LiNH2 by geometrical optimization,and calculate the binding-energies,interstitial H atom defect formation energies,densities of states （DOSs）,and electric charge populations for LiNH2 and doped LiNH2.Studies show that the results of binding-energy cannot reflect the dehydrogenating properties of LiNH2 and doped LiNH2.In equilibrium,there are a number of interstitial H atom defects;the formation energy of interstitial H atom defect is reduced by doping Mg and Ti,which increases the concentration of interstitial H atoms.Interstitial H atoms can induce the defect energy level in the gap,which reduces the width of the gap,and improves the dehydrogenation performance of LiNH2.The strength of N—H bond in - is weakened by interstitial H atom,so that hydrogen atoms in LiNH2 is relatively easy to release.The covalent bond between interstitial H atom and N atom of - explains the escape of NH3 from the dehydrogenation reaction of LiNH2 system.The strengths of N—H bonds are not equal in doped LiNH2,a part of N—H bonds are weaker,and other N—H bonds are strong,the hydrogen atoms are easy to release from weaker N—H bonds.