Thermodynamics, Kinetics, and Modeling Investigation on the Dehydrogenation of CeAl4-Doped NaAlH4 Hydrogen Storage Material

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• 作者：Xiulin Fan ; Xuezhang Xiao ; Lixin Chen ; Leyuan Han ; Shouquan Li ; Hongwei Ge ; Qidong Wang
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：November 17, 2011
• 年：2011
• 卷：115
• 期：45
• 页码：22680-22687
• 全文大小：1032K
• 年卷期：v.115,no.45(November 17, 2011)
• ISSN：1932-7455

文摘

The CeAl₄-doped NaAlH₄ has been synthesized by mechanical milling NaH/Al mixture with 4 mol % CeAl₄ as catalyst under hydrogen pressure of 3 MPa. The hydrogen desorption thermodynamics and kinetics of as-synthesized NaAlH₄ were systematically investigated. The enthalpies for the first and second dehydrogenation steps of CeAl₄-doped NaAlH₄ system are estimated to be 40.56 卤 1.62 and 51.48 卤 1.92 kJ/mol H₂, respectively. By regulating the desorption temperatures, the two dehydrogenation steps were studied separately under a constant hydrogen backpressure of 0.1 MPa. The apparent activation energy, E_a, for the first and second step is estimated to be 87.9 and 103.6 kJ/mol, respectively, by using Arrhenius equation. Isothermal dehydrogenation measurements show that no induction period is observed in the first step or the second step under the measuring conditions. Both of the decomposition steps conform to the Johnson鈥揗ehl鈥揂vrami (JMA) formalism with Avrami exponent n 鈮?1, indicating that the nucleation of decomposition process is of the site saturation type. Detailed modeling study presents that the first-step dehydrogenation kinetics is most likely controlled by the reaction at a moving boundary, whereas the second-step decomposition follows the first-order reaction mechanism. Change in the dehydrogenation temperature does not alter the nature of decomposition mechanism.