Density functional theory guide to structure and thermodynamics of metal hydrides – Case study of (Ti, Zr, Hf)Ni intermetallic compounds

Abstract

Thermodynamics of hydride formation is one of the key properties of metal-hydrogen system and determines its applicability. Therefore, numerous researches are focused on the use of first-principles calculations as the predictive tool when investigating the stability of the hydrides. In this paper we use density functional theory to address two-step process of hydride formation in the MNi (M = Ti, Zr, Hf). Through systematic study of experimentally verified and hypothetical hydride phases, we examine the influence of crystal structure and intermetallic composition on electronic structure, stability and bonding of the hydrides. The unique properties and advantages of γ-phase hydrides having orthorhombic crystal structure (space group Cmcm) for near-ambient hydrogen storage applications are pointed out, as well as the importance of further investigation of the crystal structure of the β-phase hydrides. Calculated enthalpies of hydride formation/decomposition and desorption temperatures show good agreement with the wide range of experimental data taken from literature, demonstrating predictive power of the used approach for addressing structure-property relationship and giving complete overview of the important representatives of AB class of intermetallic compounds.