Effects of nonmetal element (B, C and Si) additives in Mg₂Ni hydrogen storage alloy: A first-principles study

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• 作者：Hui Ding^a ; Shengli Zhang^a ; Yonghong Zhang^b ; Shiping Huang^a ; ^{huangsp@mail.buct.edu.cn} ; Peng Wang^c ; Huiping Tian^c
• 关键词：Hydrogen storage ; Mg2Ni alloys ; Density-functional theory ; Thermodynamic properties
• 刊名：International Journal of Hydrogen Energy
• 出版年：2012
• 期刊代码：42_03603199
• 类别：ch
• 出版时间：April, 2012
• 卷：37
• 期：8
• 页码：6700-6713
• 文件大小：2988 K

摘要

Nonmetal atoms (B, C and Si) are designed to add into Mg₂Ni hydrogen storage alloy and its hydride. First-principles density-functional theory calculations have been performed to investigate their crystal structures, electronic and thermodynamic properties. The calculation results present that nonmetal additions in Mg₂NiH₄ show more effective destabilization than metal additions. Especially for B and C, the decreases of formation enthalpies of Mg₂NiH₄ reach 0.19 and 0.21聽eV/atom. The NiH₄ structure near B or C in Mg₂NiH₄ hydride becomes the tripod-like NiH₃ structure. The results show that the thermodynamic stabilities of Mg₂Ni and Mg₂NiH₄ exhibit a nearly linear decrease with the increasing content of nonmetal atoms. The calculated dehydrogenation energies are 59.39, 58.12, 55.84 and 55.30聽kJ/mol H₂ for Mg₂NiH₄, Mg₂NiB_0.5H₄, Mg₂NiC_0.5H₄ and Mg₂NiSi_0.5H_4, respectively. It is found that the addition of nonmetal atoms favors the dehydrogenation reaction for Mg₂Ni hydrogen storage material. In addition, the effects of nonmetals to the heat capacities and vibrational entropies of Mg₂Ni and Mg₂NiH₄ are also analyzed.