Overpressure Role in Isothermal Kinetics of H2 Desorption鈥揂bsorption: the 2LiBH4鈥揗g2FeH6 System

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• 作者：Michele Catti ; Mohammad R. Ghaani ; Ilya Pinus
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：December 19, 2013
• 年：2013
• 卷：117
• 期：50
• 页码：26460-26465
• 全文大小：337K
• 年卷期：v.117,no.50(December 19, 2013)
• ISSN：1932-7455

文摘

The rates of the irreversibile LiBH₄ +Mg₂FeH₆ 鈫?LiH + 2MgH₂ + FeB + 5/2H₂ and reversible (with significant sorption/desorption hysteresis) LiBH₄ + 1/2Mg 鈫?LiH + 1/2MgB₂ + 3/2H₂ reactions were measured by isothermal鈥搃sobaric experiments in a Sievert-type apparatus. Measurements were done at several temperature T and overpressure 螖p/p values, deriving the rate constants k(T, 螖p/p) by Avrami鈥檚 fitting of reaction advancement vs time. The results could be rationalized on the basis of the k = A鈥塭xp(鈭?i>E_a/RT) = A₀ exp[鈭扙_a⁰/RT + a(螖p/p)] kinetic formula, which couples the standard Arrhenius approach for thermal effects with an exponential dependence of the rate constant on overpressure. The empirical a coefficient varies with temperature in a way that requires the activation energy and entropy to depend linearly on 螖p/p. For the first of the above reactions, E_a = 鈭?51(螖p/p) + 118 kJ mol^鈥? and ln(A/min^鈥?) = 鈭?4(螖p/p) + 16; similar values are obtained for the second one. Relations of this kinetic model with the thermodynamic driving force 螖G and with equations of electrochemical kinetics, where overpressure is replaced by overvoltage, are discussed.