TiF_3对MgH_2体系解氢热力学影响的第一性原理研究  

First-principles investigation of TiF_3 solution hydrogen thermodynamic effects on MgH_2

作　　者：袁江[1,2] 周惦武[1] 魏红伟[2] 

机构地区：[1]湖南大学汽车车身先进设计制造国家重点实验室,长沙410082 [2]张家界航空工业职业技术学院航空维修系,张家界427000

出　　处：《中国有色金属学报》2016年第7期1480-1486,共7页The Chinese Journal of Nonferrous Metals

基　　金：国家高技术研究发展计划重点资助项目(2012AA111802);湖南大学汽车车身国家重点实验室自主课题(71075003);张家界航空工业职业技术学院资助项目(ZJJKT2014-008)~~

摘　　要：基于TiF_3作为催化剂提高MgH_2解氢性能的实验结果,采用基于密度泛函理论的Dmol3程序包,计算从MgH_2体系中移走H原子所需能量及几何、电子结构的改变,探讨TiF_3对MgH_2体系解氢热力学影响及提高其解氢性能的机理。结果表明:Ti替代Mg,体系中Ti—H的成键作用比Mg-H强,Ti将MgH_2中的H吸附到其周围,导致MgH_2中Mg周围的H减少;创造Mg空位,随着温度的提高,体系中H—H之间的键长变短,两者情形均利于提高MgH_2体系的热力学行为。创造Mg空位所需能量(6.65 eV)高于Ti替代Mg的能量(2.34 eV),表明低温下,Ti替代Mg对MgH_2体系解氢更为有利,至此TiF_3中的Ti替代MgH_2中的Mg,利于加快化学反应的进行,使结构稳定的MgH_2发生转变,生成结构不稳定的Ti H2,这样体系解氢过程不是通过MgH_2,而是转化为Ti H2进行,因此TiF_3可提高MgH_2体系的解氢性能。Based on experimental results in which the dehydrogenating properties of MgH2 systems was improved by the addition of TiF3 as the catalyst, the energy to remove H atoms, geometry and electronic structure of MgH2 systems were calculated by using Dmol3 program based on the density functional theory. Solutions for MgH2 hydrogen doping TiF3 thermodynamic effects were studied.The results show that the role of Ti—H bond is stronger than the effect of Mg—H bond, thus the H atoms around Mg atoms in MgH_2 phase diffuse to the Ti atom around, resulting in reduction of the H atoms around Mg. The formation of Mg vacancy can improve the thermodynamic behavior of MgH2 system. At low temperatures, the Ti atoms of TiF3 can substitution some Mg atoms of MgH2 system, which occupy the larger advantage for the formation of Mg vacancies. The dehydrogenating properties of MgH2 systems is improved with TiF3 because of the Ti atoms of TiF3 substitution the Mg atoms of MgH2 system formed Ti H2, the reaction of 2TiF3＋3MgH2→3Mg F2＋2Ti H2＋H2 during mill process is accelerated, and a stable structure MgH2 shift, generating unstable structure Ti H2, this system is not the solution process by MgH2, but converts to Ti H2, so TiF3 can improve the performance of hydrogen.

关 键 词：MgH2 TiF3 密度泛函理论 解氢性能 

分 类 号：TG146.2[一般工业技术—材料科学与工程]