替代元素影响Mg_2Ni合金吸放氢动力学性能研究

Effects of Substitute Elements on Hydrogen Storage Properties of Mg_2Ni Alloy

采用基于密度泛函理论(DFT)的平面波赝势(PW-PP)方法,计算Mg2NixM(1-x)(0<x≤1)合金及氢化物Mg2Ni0.75M0.25H4(M=Ni,Cu,Mn)的晶体结构,生成焓和电子结构,研究替代元素(Cu,Mn)对Mg2Ni氢化物稳定性的影响。Cu,Mn取代使合金晶胞体积变大,合金晶胞体积的大小跟取代原子半径大小成正比,随着合金晶胞体积的增大,氢化物有不稳定的倾向。元素替代可以有效降低氢化物生成焓绝对值的大小,使得氢化物的稳定性降低,其中Cu元素的效果是最明显的。氢化物中H-Ni的相互作用强度是决定氢化物稳定性的主要因素,替代元素正是通过减弱H-Ni键强来改善合金的吸放氢动力学性能。

The electronic structures and formation enthalpies of Mg2NixM（1-x）（0 〈x≤ 1）alloys and Mg2Ni0.75M0. 25H4 （M = Ni, Cu, Mn） hydrides are investigated by using Plane-wave pseudo-potential method based on density function theory. The effects of substitute elements （Cu and Mn） on the stabilities of hydrides are studied. The substitutions of Cu and Mn increase the cell volumes of alloys, which vary directly proportional to the atomic radius of the substitute elements. With the increase of the cell volumes of alloys, the hydrides tend to be instability. Elements substitutions can effectively reduce the absolute values of formation enthalpies of the hydrides, which reduces the stabilities of hydrides, the substitution of Cu has produced an obvious result. The interactions of H-Ni in hydrides play a dominant role in the stabilities of hydrides, while the substitute elements just try to improve the hydrogen-adsorption and desorption properties by reducing the intensities of H--Ni interactions.