LiNH2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

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. 关键词： 储氢材料 第一性原理 缺陷 释氢机理

Mechanism of the influence of the interaction between interstitial H atom and doped atom on the dehydrogenation performance of LiNH2

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 NH₂]^- 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 NH₂]^- 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.