Hydrogen Desorption Properties of the MgH2–AlH3 Composites

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• 作者：Haizhen Liu ; Xinhua Wang ; Yongan Liu ; Zhaohui Dong ; Hongwei Ge ; Shouquan Li ; Mi Yan
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 9, 2014
• 年：2014
• 卷：118
• 期：1
• 页码：37-45
• 全文大小：508K
• ISSN：1932-7455

文摘

In this work, the hydrogen desorption properties of the novel Mg鈥揂l鈥揌 hydrogen storage composites prepared by ball-milling the as-received magnesium hydride (MgH₂) and the as-prepared aluminum hydride (AlH₃) with different molar ratios (1:1, 1:0.5, and 1:0.25) are investigated systematically. Nonisothermal desorption measurements show that more than 7.51 wt % of hydrogen is released from the Mg鈥揂l鈥揌 composites when they are heated from room temperature to 500 掳C. Thermal analysis by differential scanning calorimeter (DSC) and hydrogen desorption spectrum by mass spectrometer (MS-H₂) are used synchronously to study the desorption process of the Mg鈥揂l鈥揌. The onset hydrogen desorption temperature of MgH₂ in the MgH₂ + AlH₃ composite is dramatically reduced from 320 掳C for the pure MgH₂ to below 252 掳C. The DSC/MS-H₂ and the X-ray diffraction (XRD) analyses show that the desorption of MgH₂ in the Mg鈥揂l鈥揌 composite is composed of two steps with the reaction between MgH₂ and Al forming Mg₁₇Al₁₂ as the first step and the self-decomposition of the residual MgH₂ as the second step. Isothermal desorptions show that the desorption kinetics of the MgH₂ in the Mg鈥揂l鈥揌 composite is significantly improved. The apparent activation energy for the desorption of MgH₂ in the MgH₂ + 0.25AlH₃ is reduced to 144.6 kJ/mol, which contributes to the improvement in the desorption kinetics of MgH₂. The Johnson鈥揗ehl鈥揂vrami (JMA) kinetic studies indicate that the desorption kinetic model of MgH₂ in the Mg鈥揂l鈥揌 composite is different from the pure MgH₂. Concerning the reversibility, under the conditions of 300 掳C and 5 MPa H₂, MgH₂ in the Mg鈥揂l鈥揌 composite is almost fully recovered after absorption for 5 h while it is partially recovered for the pure MgH₂. Among the samples studied, the MgH₂ + 0.25AlH₃ composite exhibits the highest reversible hydrogen storage capacity of 6.10 wt % (H/M).