Heating Rate-Dependent Dehydrogenation in the Thermal Decomposition Process of Mg(BH4)2路6NH3

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• 作者：Yanjing Yang ; Yongfeng Liu ; You Li ; Mingxia Gao ; Hongge Pan
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：August 15, 2013
• 年：2013
• 卷：117
• 期：32
• 页码：16326-16335
• 全文大小：628K
• 年卷期：v.117,no.32(August 15, 2013)
• ISSN：1932-7455

文摘

The detailed mechanism of thermal decomposition of Mg(BH₄)₂路6NH₃ synthesized via a mechanochemical reaction between Mg(BH₄)₂ and NH₃ at room temperature was investigated for the first time. A six-step decomposition process, which involves several parallel and interrelated reactions, was elucidated through a series of structural examinations and property evaluations. First, the thermal decomposition of Mg(BH₄)₂路6NH₃ evolves 3 equiv of NH₃ and forms Mg(BH₄)₂路3NH₃. Subsequently, Mg(BH₄)₂路3NH₃ decomposes to release an additional 1 equiv of NH₃ and 3 equiv of H₂ to produce the [MgNBHNH₃][BH₄] polymer. And then, [MgNBHNH₃][BH₄] further desorbs 3 equiv of H₂ through a three-step reaction to give rise to the formation of the polymer intermediates of [MgNBHNH₂][BH₄], MgNBHNH₂BH₂, and MgNBNHBH, respectively. Finally, an additional 1 equiv of H₂ is liberated from MgNBNHBH to yield Mg and BN as the resultant solid products. In total, about 7 equiv of H₂ and 4 equiv of NH₃ are released together from Mg(BH₄)₂路6NH₃ upon heating. Moreover, there is a strong dependence of the gas compositions released from Mg(BH₄)₂路6NH₃ on the heating rate because the decomposition reaction of Mg(BH₄)₂路3NH₃ is sensitive to the heating rate, as the faster heating rate induces a lower ammonia evolution. The finding in this work provides us with insights into the dehydrogenation mechanisms of the metal borohydride ammoniates as hydrogen storage media.