Role of solute elements in Mg-Mg2Ni hydrogen storage alloys: A first-principles calculation study

• Roles of alloying elements in mg-mg 2 ni hydrogen storage alloys are investigated. • Qualitatively valid information on changes in plateau pressures are provided by DFT. • Effect of alloying elements on dilatation due to hydrogenation reaction is examined. • Site preferences of various alloying elements in Mg 2 Ni/Mg 2 NiH 4 are examined. • Electronic structure analyses are conducted to elucidate the detailed mechanisms. The effects of various alloying elements on the performance of Mg-Mg 2 Ni hydrogen storage alloys were investigated by performing first-principles density functional theory calculations. We examined the important characteristics of hydrogen storage alloys by considering both Mg-based solid solution and Mg 2 Ni-based intermetallic compound phases, where the hydride forms are MgH 2 and Mg 2 NiH 4 , respectively. In particular, qualitatively valid information for predicting changes in plateau pressures in the pressure-composition-temperature (PCT) curve was provided by calculating changes in the energy of related hydrogenation reactions. The effects of alloying elements on volume changes due to hydrogenation reactions were also obtained to provide additional criteria for the practical use of hydrogen storage alloys. For the Mg 2 Ni-based intermetallic compound, we examined the site preference of each alloying element, considering the designated stoichiometry of the base alloy. Based on the revealed site preferences, the effects of various possible alloying elements on the properties of Mg 2 Ni-based hydrides were also examined. Electronic structure analyses were further conducted to elucidate the detailed mechanisms underlying the role of the additional solute elements.