Theoretical and experimental study of the titanium substituted Mg2-xTixNi alloys and Mg2-xTixNiH4 hydrides

Abstract

The formation of the Ti substituted Mg2Ni alloys, a promising hydrogen storage material for various applications is studied in detail. Mg1.95Ti0.05Ni alloy and ribbons are successfully prepared by vacuum arc melting and melt spinning methods. The phases, microstructures, and thermal behavior of the alloys and ribbons are characterized by XRD, SEM, TEM, DTA/TG. Sievert-type apparatus is used to study hydrogen sorption properties. Apart from the dominant Mg2Ni phase, the formation of MgNi2, Mg, and Ni3Ti phases is seen in both Mg1·95Ti0·05Ni alloy and ribbons. During the initial three cycles, Mg1·95Ti0·05Ni ribbons showed 2 wt % hydrogen storage capacity. To explain the atomic-scale influence of Ti dopant in the studied alloys and hydrides, FP(L)APW + lo method based on Density Functional Theory (DFT) is applied to Mg2-xTixNi (x = 0.25 and 0.5) alloys and Mg2-xTixNiH4 (x = 0.25 and 0.5) hydrides. An increase in the Ti dopant on the Mg site leads to the hydrides destabilization. Bader's charge density topology analysis provides insight into the charge transfer and bonding between the constituent atoms.