Pressure Effect on the 2NaH + MgB2 Hydrogen Absorption Reaction

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• 作者：Claudio Pistidda ; Sebastiano Garroni ; Christian Bonatto Minella ; Francesco Dolci ; Torben R. Jensen ; Pau Nolis ; Ulrike Bsenberg ; Yngve Cerenius ; Wiebke Lohstroh ; Maximilian Fichtner ; Maria Dolores Bar
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：December 16, 2010
• 年：2010
• 卷：114
• 期：49
• 页码：21816-21823
• 全文大小：499K
• 年卷期：v.114,no.49(December 16, 2010)
• ISSN：1932-7455

文摘

The hydrogen absorption mechanism of the 2NaH + MgB₂ system has been investigated in detail. Depending on the applied hydrogen pressure, different intermediate phases are observed. In the case of absorption measurements performed under 50 bar of hydrogen pressure, NaBH₄ is found not to be formed directly. Instead, first an unknown phase is formed, followed upon further heating by the formation of NaMgH₃ and a NaH−NaBH₄ molten salt mixture; only at the end after heating to 380 °C do the reflections of the crystalline NaBH₄ appear. In contrast, measurements performed at lower hydrogen pressure (5 bar of H₂), but under the same temperature conditions, demonstrate that the synthesis of NaBH₄ is possible without occurrence of the unknown phase and of NaMgH₃. This indicates that the reaction path can be tuned by the applied hydrogen pressure. The formation of a NaH−NaBH₄ molten salt mixture is observed also for the measurement performed under 5 bar of hydrogen pressure with the formation of free Mg. However, under this pressure condition the formation of crystalline NaBH₄ is observed only during cooling at 367 °C. For none of the applied experimental conditions has it been possible to achieve the theoretical gravimetric hydrogen capacity of 7.8 wt %.