Thermodynamic and Kinetic Investigations on Pure and Doped NaBH4鈭扢gH2 System

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• 作者：Chiara Milanese ; Sebastiano Garroni ; Alessandro Girella ; Gabriele Mulas ; Vittorio Berbenni ; Giovanna Bruni ; Santiago Surin虄ach ; Maria Dolors Baro虂 ; Amedeo Marini
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：February 24, 2011
• 年：2011
• 卷：115
• 期：7
• 页码：3151-3162
• 全文大小：1091K
• 年卷期：v.115,no.7(February 24, 2011)
• ISSN：1932-7455

文摘

In this work, a thermodynamic picture of the dehydrogenation mechanism of NaBH₄ in NaBH₄鈭扢gH₂ mixtures with 2:1 and 1:2 molar ratio is drawn, for the first time in literature, thanks to coupled manometric鈭抍alorimetric measurements up to 580 掳C. Such a new approach also allows, after the measurement of the borohydride melting enthalpy, the evaluation of the dehydrogenation enthalpy of the complex hydride in the mixtures. The thermodynamics of the 2:1 sample (where the borohydride decomposition takes place mainly in liquid state) is more favorable than that of the 1:2 mixture, where the process evolves fully in solid state. The kinetics of the systems is studied at 450 掳C, the minimum temperature at which the borohydride decomposition takes place. In these conditions, the 1:2 system is kinetically favored. Several additives (fluorides; chlorides; hydroxides) have been tested as possible destabilizing/catalyzing agents. These substances react with the component hydrides upon discharging, forming stable binary and ternary compounds that do not change the macroscopic desorption pathway of the composites (separate decomposition of the component hydrides) but lead to variations in the desorption temperature and kinetics. In particular, MgF₂ is found to improve the desorption kinetics of both the component hydrides and to reduce the decomposition temperature and enthalpy of NaBH₄ in the 2:1 system. On the contrary, none of the tested dopants exerts any positive effect on the 1:2 system.