Development of a new approach for the kinetic modeling of the lithium reactive hydride composite (Li-RHC) for hydrogen storage under desorption conditions.

[Display omitted] • Development of a comprehensive semi-empirical dehydrogenation kinetic model. • H 2 –release from MgH 2 and LiBH 4 decompositions and MgB 2 + LiH formation. • One-dimensional interphase-controlled decomposition of MgH 2. • Autocatalytic LiBH 4 decomposition based on novel Prout-Tompkins model approach. • Integral and differential form of the combined dehydrogenation rate model. • Application of the differential form of the developed model for FE simulations. Among some promising candidates for high-capacity energy and hydrogen storage is the Lithium-Boron Reactive Hydride Composite System (Li-RHC: 2 LiH + MgB 2 /2 LiBH 4 + MgH 2). This system desorbs hydrogen only at relatively high temperatures and presents a two-step series of reactions occurring in different time scales: first, MgH 2 desorbs, followed by LiBH 4. Hitherto, the dehydrogenation kinetic behavior of such a system has been described for different temperatures at specific values of operative pressure. However, a comprehensive model representing its dehydrogenation kinetic behavior under different operative conditions has not yet been developed. Herein, the separable variable method is applied to develop a comprehensive kinetic model, including the two-step dehydrogenation series reaction. The MgH 2 decomposition is described with the one-dimensional interface-controlled reaction rate Johnson-Mehl-Avrami-Erofeyev-Kholmogorov (JMAEK) with a (P equilibrium /P operative) pressure functionality and an Arrhenius temperature dependence activation energy of 63 ± 3 kJ/mol H 2. The LiBH 4 decomposition is modeled applying the autocatalytic Prout-Tompkins model. A novel approach to describe the Prout-Tompkins t 0 parameter as a function of the operative temperature and pressure model is proposed. This second reaction step presented a (P equilibrium – P operative /P equilibrium)2 pressure dependence and an Arrhenius temperature dependence with activation energy 94 ± 13 kJ/mol H 2. The proposed approach is experimentally and computationally validated, successfully describing the decomposition kinetic behavior of MgH 2 and LiBH 4 under three-phase gas, liquid and solid environment and shows good agreement between experimental and modeled curves. [ABSTRACT FROM AUTHOR]