Abstract
Reaction kinetic behaviour and cycling stability of the 2LiBH4–MgH2 reactive hydride composite (Li-RHC) are experimentally determined and analysed as a basis for the design and development of hydrogen storage tanks. In addition to the determination and discussion about the properties; different measurement methods are applied and compared. The activation energies for both hydrogenation and dehydrogenation are determined by the Kissinger method and via the fitting of solid-state reaction kinetic models to isothermal volumetric measurements. Furthermore, the hydrogen absorption–desorption cycling stability is assessed by titration measurements. Finally, the kinetic behaviour and the reversible hydrogen storage capacity of the Li-RHC are discussed.
Highlights
Hydrogen technologies, including the hydrogen generation from renewable energy sources, its storage by physical or chemical means, as well as the reconversion to energy using fuel cells, have been considered for a long time as a possible energy scenario for the future
The activation energy values during absorption have been determined as 104 ± 2 kJ mol−1 H2 at 50 bar of H2, and 160 ± 20 kJ mol−1 H2 at 30 bar, applying the Kissinger method to several HP-DSC
The second value at 30 bar H2 is in good agreement with 160 ± 20 kJ mol−1 H2, as calculated by the rate constant, taking into account the effect of the driving force
Summary
Hydrogen technologies, including the hydrogen generation from renewable energy sources, its storage by physical or chemical means, as well as the reconversion to energy using fuel cells, have been considered for a long time as a possible energy scenario for the future. By means of physical storage, hydrogen is either compressed up to 700 bar, or liquefied at −253 ◦ C These storage techniques, and in particular, the vessel structures and the gas processing, are relatively complex and energy demanding. Complex and intermetallic hydrides offer the possibility to increase the volumetric density of hydrogen considerably, for instance, LiBH4 possesses a volumetric density of 121 kg H2 m−3 [5] and Mg2 FeH6 has the highest known volumetric density of 150 kg H2 m−3 [6] In such metal hydrides, the chemical bonds with the metal atoms/ions allow interatomic distances, which are much shorter than in the molecular state of hydrogen, where repulsive forces are present. Considerable advancements have been achieved with the use of additives and catalysts (e.g., [12,13]), and the application of appropriate processing techniques, such as mechanical milling (e.g., [14,15])
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