First-principles studies on the structures and properties of Ti- and Zn-substituted Mg₂Ni hydrogen storage alloys and their hydrides

In order to study the improvement mechanism of transition metal elements on Mg-based hydrogen storage alloys, especially for the structures and properties of hydrogen storage alloy Mg₂Ni, Ti and Zn substituted alloys Mg_2-mM_mNi,Mg₂Ni_1-nM_n(M=Ti and Zn, m, n=0.1667), and their hydrides Mg₂NiH₄,Mg_2-mM_mNiH₄,Mg₂Ni_1-nM_nH₄(M=Ti and Zn, m, n=0.125) have been investigated by first-principles. Through analyzing the results of the crystal structure, electron density distribution and density of states, the changes of structures and properties resulting from the adding of transition metal elements Ti and V of intermetallic Mg₂Ni and its hydride Mg₂NiH₄were investigated. The results showed that the addition of transition metal elements can reduce the stability of the Mg₂Ni system to varying degrees and improve the dehydrogenation dynamics performance. Therefore, it may be considered that the substitution by transition metal elements in Mg-based hydrogen storage alloys is an effective technique to improve the thermodynamic behavior of hydrogenation/dehydrogenation in Mg-based hydrogen storage alloys (HSAs).