Diffusion of hydrogen, carbon and oxygen in the presence of hydrogen coadsorbed onto iron surfaces

Abstract

Density-functional theory calculations based on the GGA-PBE (generalized gradient approximation Perdew–Burke–Ernzerhof) exchange correlation functional were used to investigate the effect of hydrogen on the diffusion of adsorbed carbon, oxygen and hydrogen on the surface of Fe(100). The diffusion energy barrier was calculated for both clean surfaces and those with hydrogen, and it was found that hydrogen produced binding energies for carbon and oxygen. These bonds stabilized the binding of hydrogen with the Fe(100) surface. For all of the surface species studied here, the energy barrier was increased when hydrogen was coadsorbed, from 1.29 eV to 1.46 eV for C, from 0.33 eV to 0.53 eV for O and from 0.11 eV to 0.15 eV for H. An approximation of the diffusion coefficient was obtained from energy barrier calculations and a pre-exponential factor of diffusion was calculated. Carbon exhibited low diffusion at the surface under experimental temperatures, while oxygen diffusion was activated above 450 K and hydrogen was diffused in all the temperature ranges investigated.