Dependence of NiTi hydride stability by co-substitution by (Zr,Mg) onto Ti and (Cr,Cu) onto Ni: first-principles study

ABSTRACT

The thermodynamics of hydride formation is one of the most important properties of the metal-hydrogen system, and states its potential for further uptake. For this reason, much research is focused on the use of first principle calculations as a predictive tool in the study of hydride stability. In this paper, First-principles density functional calculations were performed to predict the effect of co-substitution in NiTiH, Ti by Mg and Zr (x = 0.125, 0.25 and 0.375), as well as Ni by Cu and Cr (y = 0.125). Structural, thermodynamic stability and electronic properties were investigated. The formation enthalpy when Ti is substituted either by Mg or Zr with respect to their content is calculated and compared to the host NiTiH; it is found that the hydride stability decreases as Mg content increases while it increases when Zr content increases. The substitution of Ni by Cu destabilises the hydride while the stability of the hydride is enhanced when Ni is substituted by Cr. The simultaneous substitution of Ti by Mg (x = 0.375) and Ni by Cu (y = 0.125), leads to considerable destabilisation and an increase in cell volume of the hydride. The corresponding Ni_0.875Cu_0.125Ti_0.625Mg_0.375 compound is identified with optimum characteristics among the considered compositions, thereby can be considered as potential material for hydrogen storage.

KEYWORDS:

• Substitution
• hydride
• hydrogen storage
• NiTi
• Density functional theory
• NiMH batteries

Disclosure statement

No potential conflict of interest was reported by the author(s).