First-principles Study On The Dehydrogenation Performance Of （Na,Li）AlH₄Systems

In present work, we performed first-principles calculations of the electronicstructures and the bonding characteristics of Li（Na） doped NaAlH₄（LiAlH₄） andNa₃AlH₆（Li₃AlH₆） to study the influence of dopant Li（Na） on the stability anddehydrogenation properties of the doped systems.Analysis of the electronic structures show that the dopant Li weakens theinteraction between atoms in NaAlH₄, while the Al-H bonding was weakly influencedby the dopant Na in LiAlH₄, however, the strength of the Li-H bonding was slightlyreduced by the dopant Na. The situation was changed for Li（Na） doping intoNa₃AlH₆（Li₃AlH₆）, the Li enhances both the Al-H and the Na-H bonds in Na₃AlH₆,while the Na weakens the Al-H bond but weakly affects the Li-H bond.The doping of Li（Na） influences the stability and the hydrogen dissoication energyof NaAlH₄（LiAlH₄）. Negative doping energy was obtained in Li-doped Na_1-xLi_xAlH₄,and the absolute value was reduced with the increasing of the concentration of dopant Li.The hydrogen dissociation energy of the doped systems is lower than the undopedsystem. For the Na doped Li1-xNaxAlH4, the doping energy is positive and its valueincreased with the increase of the concentration of the dopant Na, and the hydrogendissociation energy is larger than the undoped system. Therefore, Na does not enhancethe dehydrogenation properties of the LiAlH₄.The influence is different if Li（Na） doping into Na₃AlH₆（Li₃AlH₆）. The Listrengthens the interaction between atoms in Na_3-xLi_xAlH₆, while the Na unlikely toaffects the Li-H bond, but weakens the Al-H bond in Li_3-xNa_xAlH₆. Thus, the dopant Lidoes not improve the dehydrogenation properties of Na₃AlH₆, but the Na can improvethe dehydrogenation properties of Li₃AlH₆in some degree.