Structure and thermodynamic studies of the LaMgNi4 compound and its hydrides by density functional theory

Mg containing intermetallic compounds are promising candidates for hydrogen storage. However, the thermodynamic data required to assess the hydriding/dehydriding enthalpies of these compounds are not available yet. In the present work, first principles density functional theory calculations were used to predict the crystal structure, stability, and reaction enthalpies of a LaMgNi4 compound. The cohesive energy (Ecoh) and enthalpies of formation (ΔH) of the corresponding hydrides were calculated. It was found that the structural stability order was γ-LaMgNi4H7 hydride > α-LaMgNi4H hydride > β-LaMgNi4H4 hydride. The reaction enthalpies (ΔHR) for dehydrogenation of the γ-LaMgNi4H7 hydride, α-LaMgNi4H hydride, and β-LaMgNi4H4 hydride were 32.67, 33.08, and 32.05 kJ/mol H2, respectively. The results proved theoretically that LaMgNi4 hydrides had a low dissociation temperature. The electronic structures of the LaMgNi4 compound and its hydrides were also calculated and the results indicated that LaMgNi4 hydrides were promising candidates for reversible hydrogen storage.