TiF3对MgH2体系解氢热力学影响的第一性原理研究

来源期刊:中国有色金属学报2016年第7期

论文作者:袁江 周惦武 魏红伟

文章页码:1480 - 1487

关键词:MgH2;TiF3;密度泛函理论;解氢性能

Key words:MgH2; TiF3; density functional theory; dehydrogenating property

摘    要:基于TiF3作为催化剂提高MgH2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MgH2体系中移走H原子所需能量及几何、电子结构的改变,探讨TiF3对MgH2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MgH2中的H吸附到其周围,导致MgH2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MgH2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MgH2体系解氢更为有利,至此TiF3中的Ti替代MgH2中的Mg,利于加快化学反应的进行,使结构稳定的MgH2发生转变,生成结构不稳定的TiH2,这样体系解氢过程不是通过MgH2,而是转化为TiH2进行,因此TiF3可提高MgH2体系的解氢性能。

Abstract: 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 MgH2 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 TiH2, the reaction of 2TiF3+3MgH2→3MgF2+2TiH2+H2 during mill process is accelerated, and a stable structure MgH2 shift, generating unstable structure TiH2, this system is not the solution process by MgH2, but converts to TiH2, so TiF3 can improve the performance of hydrogen.

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