Changing the hydrogenation dehydrogenation pathway of 2LiBH4+MgH2/2LiH+MgB2 via in-situ formed core-shell LixTiO2 nanoparticles.

One of the main constraints for the practical application of hydrogen as an energy carrier is the lack of an efficient and safe hydrogen storage system. Hydrogen storage in solid-state hydrides provides a potential alternative to address these problems. Aiming to improve the hydrogen storage properties of the 2LiBH₄+MgH₂/2LiH+MgB₂ (Li-RHC) system, the effect of the in-situ formation of core-shell nanoparticles Li_xTiO₂ on the Li-RHC is investigated. These nanoparticles markedly enhance the hydrogen storage properties of Li-RHC. This system has a gravimetric hydrogen capacity of about 10 wt. %. The presence of a small amount of Li_xTiO₂ enables the Li-RHC to reversibly store hydrogen through hydrogenation and dehydrogenation periods of just 25 and 50 minutes at 400 ºC, respectively. Upon hydrogenation/dehydrogenation cycling, the in-situ formed core-shell Li_xTiO₂ nanoparticles help refining and preserving the Li-RHC microstructure from coarsening. The kinetic modeling of the hydrogenation reaction shows that the presence of the core-shell Li_xTiO₂ nanoparticles accelerates the one-dimensional interface-controlled mechanism owing to the high Li⁺ mobility through the Li_xTiO₂ lattice. Upon dehydrogenation, the in-situ formed core-shell Li_xTiO₂ nanoparticles do not modify the dehydrogenation thermodynamic properties of the Li-RHC itself. A new approach based on the combination of two kinetic models evidence that the activation energy of both MgH₂ decomposition and MgB₂ formation are reduced. The presence of Li_xTiO₂ reduces the time required for the first dehydrogenation of the 2LiBH₄+MgH₂ by suppressing the side reaction leading from LiBH₄ to Li₂B₁₂H₁₂, thus enabling the direct formation of MgB₂. Moreover, after ten hydrogenation–dehydrogenation cycles starting with the 2LiH+MgB₂ the presence of Li₂B₁₂H₁₂ is still not observed by Raman spectroscopy. These improvements are due to the novel catalytic mechanism via Li⁺ source/sink reversible reactions.