First-principles study of the hydrogen adsorption and diffusion on ordered Ni_3Fe(111) surface and in the bulk

摘要

First-principles calculations based on density functional theory are performed to study the adsorption and diffusion of hydrogen on ordered Ni3Fe(111) surface and in the bulk. The adsorption of H_2 molecule on surface is weak, but the adsorption of H atom on surface is strong. H_2 decomposition on surface can easily take place and the largest barrier of H_2 decomposition is 0.25 eV. The adsorption of H on surface and in the bulk is both exothermic relative to isolated H atom. The minimum barrier for H diffusion between two nearest sites on surface is 0.11 eV, indicating the H has good mobility on the surface. The minimum barrier for H diffusion from surface to the first subsurface is 0.78 eV. Once H atom diffuses into the first subsurface, it can more easily further diffuse into bulk with barrier values in the range 0.22-0.46 eV, which are very close to those values obtained in ordered bulk Ni_3Fe. Moreover, the dependence of adsorption and diffusion properties on surface coverage is also discussed.