First-Principles Studies on Hydrogen Desorption Mechanism of MgnH2n (n = 3, 4)

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• 作者：Jianjun Liu ; James Tyrrell ; Lei Cheng ; Qingfeng Ge
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：April 25, 2013
• 年：2013
• 卷：117
• 期：16
• 页码：8099-8104
• 全文大小：323K
• 年卷期：v.117,no.16(April 25, 2013)
• ISSN：1932-7455

文摘

In an attempt to decrease the hydrogen desorption temperature of MgH₂, great efforts have been made to improve kinetic and thermodynamic properties by reducing the particle sizes. However, these improvements were impeded because the hydrogen desorption mechanism even for the small MgH₂ clusters is not clear. Herein, density functional theory studies have been performed to investigate hydrogen desorption mechanisms in Mg_nH_2n (n = 3, 4) systems. In both Mg₃H_x and Mg₄H_x systems, hydrogen desorption barriers are higher than hydrogen transfer ones and the first hydrogen desorption is the rate-determining step. Electronic structure analysis showed that many important intermediates along the minimum-energy pathways are combinations of metallic Mg and ionic MgH₂, suggesting that phase separation into metallic Mg and ionic MgH₂ may happen in a large nanoparticle. The overall hydrogen desorption process from the MgH₂ cluster comprises hydrogen transfer, phase separation, and hydrogen separation.