Improved hydrogen storage performance of MgH₂-NaAlH₄ composite by addition of TiF₃

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• 作者：M. Ismail^a ; ^b ; ^{mohammadismail@umt.edu.my} ; Y. Zhao^a ; ^c ; ^{yue@uow.edu.au} ; X.B. Yu^a ; ^d ; S.X. Dou^a
• 关键词：MgH2 ; NaAlH4 ; TiF3 ; Catalytic effect
• 刊名：International Journal of Hydrogen Energy
• 出版年：2012
• 期刊代码：42_03603199
• 类别：ch
• 出版时间：May, 2012
• 卷：37
• 期：10
• 页码：8395-8401
• 文件大小：923 K

摘要

In a previous paper, it was demonstrated that a MgH₂-NaAlH₄ composite system had improved dehydrogenation performance compared with as-milled pure NaAlH₄ and pure MgH₂ alone. The purpose of the present study was to investigate the hydrogen storage properties of the MgH₂-NaAlH₄ composite in the presence of TiF₃. 10聽wt.%TiF₃ was added to the MgH₂-NaAlH₄ mixture, and its catalytic effects were investigated. The reaction mechanism and the hydrogen storage properties were studied by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), temperature-programmed-desorption and isothermal sorption measurements. The DSC results show that MgH₂-NaAlH₄ composite milled with 10聽wt.%TiF₃ had lower dehydrogenation temperatures, by 100, 73, 30, and 25聽掳C, respectively, for each step in the four-step dehydrogenation process compared to the neat MgH₂-NaAlH₄ composite. Kinetic desorption results show that the MgH₂-NaAlH₄-TiF₃ composite released about 2.4聽wt.%hydrogen within 10聽min at 300聽掳C, while the neat MgH₂-NaAlH₄ sample only released less than 1.0聽wt.%hydrogen under the same conditions. From the Kissinger plot, the apparent activation energy, E_A, for the decomposition of MgH₂, NaMgH₃, and NaH in the MgH₂-NaAlH₄-TiF₃ composite was reduced to 71, 104, and 124聽kJ/mol, respectively, compared with 148, 142, and 138聽kJ/mol in the neat MgH₂-NaAlH₄ composite. The high catalytic activity of TiF₃ is associated with in situ formation of a microcrystalline intermetallic Ti-Al phase from TiF₃ and NaAlH₄ during ball milling or the dehydrogenation process. Once formed, the Ti-Al phase acts as a real catalyst in the MgH₂-NaAlH₄-TiF₃ composite system.