Penetration and diffusion of hydrogen in Mg₂Ni: A first-principles investigation

First-principles calculations have been used to study the hydrogen adsorption and diffusion in both hexagonal Mg₂Ni surface and bulk Mg₂Ni, and the hydrogen diffusion rate in bulk Mg₂Ni is evaluated. The calculation shows that the adsorption energies on Mg₂Ni (100) surface are much higher than in bulk Mg₂Ni. For hydrogen diffusing from Mg₂Ni (100) surface to subsurface, three diffusion pathways have been studied, and the lowest energy barrier is found to be 0.64 eV. To study the hydrogen atom diffusion in bulk Mg₂Ni, nine possible diffusion paths have been considered. The results show hydrogen diffusion from Ni[sbnd]Ni bridge sites to the most nearby Mg[sbnd]Ni bridges site is energetically more favorable than the other paths. The energy barrier of this process is 0.34eV, which is close to experimental data of 0.28 ± 0.04 eV. The temperature dependence of the jump rates has been investigated in some details using harmonic transition state theory and semi-classically corrected harmonic transition state theory. The calculated diffusion constant is in good agreement with the experimental data.