First-principles study on the crystal structure stability and hydrogen storage mechanism of hydrogen occupancy in interstitial sites in ZrCo compounds

Abstract

To study the properties of Zr 8 Co 8 H in the α-phase process of hydrogen storage, the effects of three types of H occupy sites in the ZrCo alloy on the crystal structure characteristics and their stability were investigated under the framework of a first-principles study. Two types of octahedral gaps were determined after crystal structure optimization, where the O1 octahedron was composed of two Co atoms and four Zr atoms, while O2 had two Zr atoms at its symmetry axis and four Co atoms in the middle vertical plane. The lattice constant, gap volume, and formation enthalpy results showed that Zr 8 Co 8 H O1 hydrides easily formed preferentially compared with Zr 8 Co 8 H O2 . By substituting the enthalpy changes into the pressure-composition isotherm (PCT) curve during the hydrogen absorption process, Zr 8 Co 8 H O2 facilitated the following hydrogen absorption process. In addition, the partial density of states (PDOS), charge difference density, the Mulliken population, the magnetic moment, and mechanical constants of three compounds were investigated to further verify that the O1 octahedral hydrogen placeholder had priority with superior lattice stability of the Zr 8 Co 8 H O1 structure.