Experimental and computational modelling study of Ni substitution for Fe in Zr3Fe and its hydride

Abstract Zr 3 Fe and Ni-substituted Zr 3 Fe alloys with 30 and 50 at.% Ni were synthesized and their hydrogen absorption/desorption characteristics were compared experimentally (pressure–composition isotherms, thermal desorption spectroscopy, in-situ neutron diffraction) and by computational methods ( ab-initio molecular dynamics (AMD), nudged elastic band theory (NEB)). All the alloys absorbed hydrogen to a hydrogen-to-metal atomic ratio of about 1.7, but the hydrides formed were stable at room temperature. The Zr 3 Fe 0.5 Ni 0.5 alloy and its hydrided form were multi-phase. The Zr 3 Fe 0.7 Ni 0.3 alloy was single-phase and retained the C m c m structure of the parent intermetallic. In-situ neutron diffraction with D 2 in place of H 2 showed that the hydride formed in the isotherm measurements, Zr 3 Fe 0.7 Ni 0.3 H 6.88 , had the same structure ( C m c m ) as Zr 3 FeH 7 , while disproportionation was observed in the hydrogenation of Zr 3 Fe. The kinetics of hydride formation was slower in both the Ni-substituted alloys. Thermal desorption spectroscopy showed that substitution of 0.3Ni significantly destabilized the hydride, lowering the temperature of the principal desorption peak by about 300 K relative to Zr 3 Fe–H 2 , without loss of hydrogen capacity, and avoiding disproportionation. Based on the structures determined by neutron diffraction, AMD and NEB calculations were conducted to compare Zr 3 Fe and Zr 3 Fe 0.7 Ni 0.3 and their hydrides. The AMD calculations predicted that H diffusion was slower in Ni-substituted Zr 3 Fe, in agreement with the experimental observation of slower kinetics, implying a higher activation energy for H migration. The NEB calculations also predicted a higher energy barrier for H migration in Ni-substituted Zr 3 Fe.