(1. 湖南大學(xué) 汽車車身先進(jìn)設(shè)計(jì)制造國(guó)家重點(diǎn)實(shí)驗(yàn)室，長(zhǎng)沙 410082； 2. 湖南大學(xué) 材料科學(xué)與工程學(xué)院，長(zhǎng)沙 410082)
摘 要: 基于密度泛函理論的第一原理方法，通過計(jì)算清潔、空位缺陷Mg(0001)表面吸附氫分子(H2)前后以及Fe合金化鎂氫化合物(MgH2)體系的能量與電子結(jié)構(gòu)，對(duì)球磨條件下Fe合金化改善MgH2體系性能的原因進(jìn)行初步探討。結(jié)果表明：與清潔Mg表面相比，由于球磨改變了Mg顆粒的表面結(jié)構(gòu)，使Mg表面產(chǎn)生較多缺陷，而缺陷的存在增強(qiáng)了H2的物理吸附能力，并且Mg表面向H2轉(zhuǎn)移的電荷數(shù)增多，因而體系球磨后具有較好的吸氫性能；而在Fe合金化MgH2體系中，F(xiàn)e固溶于MgH2中形成(MgFe)H2固溶體和合金化形成少量Mg2FeH6相，MgH2系結(jié)構(gòu)穩(wěn)定性均降低，對(duì)應(yīng)體系解氫性能增強(qiáng)。分析電子結(jié)構(gòu)發(fā)現(xiàn)：空位缺陷有助H2吸附于Mg表面，與Mg(0001)表面最上層與H2直接產(chǎn)生吸附作用的金屬原子在費(fèi)米能級(jí)(EF)附近s軌道的成鍵電子數(shù)密切相關(guān)；在Fe合金化MgH2體系中，與合金化元素Fe近鄰的H原子形成空位的難度增加，H原子較難釋放；與Mg近鄰的H原子形成空位的難度減少，H原子容易釋放；Fe合金化導(dǎo)致Mg-H之間存在較弱的成鍵作用，因此，MgH2體系的解氫性能得到提高。
關(guān)鍵字: MgH2；Mg(0001)表面；吸附；形成熱
（1.State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China; 2. School of Materials Science and Engineering, Hunan University, Changsha 410082, China）
Abstract:The energy and electronic structure of the adsorption of H2 on the clean, vacancy defective Mg (0001) surfaces and iron alloying magnesium hydride were calculated by using a first-principles plane-wave pseudopotential method, the mechanism of improved properties on MgH2 systems were analyzed with milling and iron addition. The results show that the vacancy defect system benefits enhancing the physical sorption between Mg surface and H2 compared with the clean Mg (0001) surface, because the quantity of the charges transferring from Mg surface to H2 adsorbed may be increased significantly, the H2 adsorption properties are improved after ball milling. The structure stability of the alloying system is reduced when a little iron dissolves into the magnesium hydride, and is further reduced when the iron additions form Mg2FeH6 compound. The analyses of electronic structures shows that the catalytic reactivities for H2 adsorption of the different surfaces are dependent on the numbers of s orbital bonding electrons around Fermi level for the uppermost layer metal atoms which interact directly with H2. It is easy to form vacancy for hydrogen atoms next to iron atom, which indicates that hydrogen atom cannot be escaped, but it is difficult to from vacancy for hydrogen atoms next to magnesium atom, which indicates that hydrogen atom can be escaped. Hence it is thought that the change of dehydrogenating properties of MgH2 with or without a little iron addition attributes to the weakened bonding between magnesium and hydrogen.
Key words: magnesium hydride; Mg(0001) surface; adsorption; formation heat
