Abstract

The Lithium–Boron Reactive Hydride Composite System (Li-RHC) (2 LiH + MgB2/2 LiBH4 + MgH2) is a high-temperature hydrogen storage material suitable for energy storage applications. Herein, a comprehensive gas-solid kinetic model for hydrogenation is developed. Based on thermodynamic measurements under absorption conditions, the system's enthalpy ΔH and entropy ΔS are determined to amount to −34 ± 2 kJ∙mol H2−1 and −70 ± 3 J∙K−1∙mol H2−1, respectively. Based on the thermodynamic behavior assessment, the kinetic measurements' conditions are set in the range between 325 °C and 412 °C, as well as between 15 bar and 50 bar. The kinetic analysis shows that the hydrogenation rate-limiting-step is related to a one-dimensional interface-controlled reaction with a driving-force-corrected apparent activation energy of 146 ± 3 kJ∙mol H2−1. Applying the kinetic model, the dependence of the reaction rate constant as a function of pressure and temperature is calculated, allowing the design of optimized hydrogen/energy storage vessels via finite element method (FEM) simulations.

Highlights

  • Driven by the necessity of reducing the impact of fossil energy consumption on the environment, researchers have been looking for suitable alternatives for generation, storage and use of renewable energies

  • Based on thermodynamic measurements under absorption conditions, the system’s enthalpy ∆H and entropy ∆S are determined to amount to -34 ± 2 kJ∙mol H2-1 and -70 ± 3 J∙K-1∙mol H2-1, respectively

  • The kinetic analysis shows that the hydrogenation rate-limiting-step is related to a onedimensional interface-controlled reaction with a driving-force-corrected apparent activation energy of 146 ± 3 kJ∙mol H2-1

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Summary

Introduction

Driven by the necessity of reducing the impact of fossil energy consumption on the environment, researchers have been looking for suitable alternatives for generation, storage and use of renewable energies. One of the most promising alternatives is the use of hydrogen as an energy carrier, which can significantly reduce the negative impact on the environment if the hydrogen is produced from renewable sources [1,2]. A considerable amount of the energy stored in hydrogen is required for its liquefaction [6,7] or its compression to increase the stored hydrogen density [6]. Chemical storage methods, such as hydrides, are an alternative to the physical methods mentioned above and show technological potential since they can work under much milder conditions of pressure and temperature [5]

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