Mg取代对LiBH_4(010)面结构和储氢性能的影响

Effects of Mg Substitution on Structure and Hydrogen Storage of LiBH_4 (010) Surface

采用基于密度泛函理论的第一性原理,研究了Mg取代Li原子对LiBH4(010)面的晶体结构、H原子解离能及H原子迁移的影响.结果发现,Mg取代后B—H键长增大,更易于H原子的解离.氢空位的出现也使其附近H原子的解离能减小.电子结构计算结果表明,Mg取代Li原子后,减弱了B—H之间的共价作用.通过对氢原子在[BH4]单元之间扩散能垒的计算发现,Mg取代Li原子后,H原子的扩散能垒由4.84 eV降为3.01 eV,表明H原子在体相内更容易迁移.

The geometry, electronic structure, dehydrogenation energy and hydrogen atom migration on the clean and Mg doped LiBH4（010） surfaces were studied with first-principles calculations based on density functional theory（DFT）. The lengths of B-H bond increase, and H atoms are easy to dissociate. Based on the H1 vacancy, we found that the presence of H vacancy is helpful to the formation of other kinds of H vacancy. Electronic structure reveals that the B-H bonds are weakened. By calculating the diffusion pathway of H atom from one [BH4] to the nearby [BH4] on the clean and Mg doped LiBH4（010） surfaces, we find that the migration barrier energy comes down from 4.03 eV to 3.09 eV. This indicates that the H atoms are easier to diffuse on the Mg doped LiBH4（010） surface.