Computational Studies of the Adsorption and Diffusion of Hydrogen on Fe−Co Alloy Surfaces

Studies of the dissociative adsorption of H 2 and surface diffusion of H atoms on FeCo(110) using periodic density functional theory and a slab model are reported. It is found that the bcc Fe−Co alloy in B2 phase favors the exposure of (110) plane under cleavage. The H 2 molecule is adsorbed on FeCo(110) via the dissociative mechanism where H−H bond scission over an OT-Co site kinetically is the most feasible, possessing an energy barrier of merely 1.5 kcal/mol, much lower than that for the corresponding H 2 adsorption on Fe(100) and Fe(110). Upon adsorption, H atoms prefer the TF-Co and TF-Fe sites so that the highest degree of coordination with the surface atoms can be achieved. The calculations reveal that H atoms may diffuse easily over the FeCo(110) surface; the rate-determining step is the migration across a SB site which requires that an activation barrier of about 4.2 kcal/mol be overcome. It is noticed that the diffusive motion TF-Fe → TF-Fe is dominant at room temperature, while at higher temperatures the diffusion TF-Fe → TF-Co prevails.