Energetics of the lithium-magnesium imide–magnesium amide and lithium hydride reaction for hydrogen storage: An ab initio study

An ab initio study within the density functional theory of the recently described reversible hydrogen storage reaction Mg(NH2)2 + 2LiH ⇔ Li2Mg(NH)2 + 2H2 has been conducted. The electronic structure, structural parameters, vibrational spectra, and enthalpies of formation of all the reactants and products as well as the heat of the overall reaction at zero and finite temperature have been calculated in the generalized gradient approximation (GGA) to the exchange correlation potential. The heat of the overall reaction is calculated to be 53.4 kJ/mol H2 in contrast to the experimentally obtained overall heat of reaction of ∼44.1 kJ/mol H2. The difference of ∼20% between the experimental and calculated values is discussed.