An ab initio study of dissociative adsorption of H2 on FeTi surfaces

Dissociative adsorption of H2 on clean FeTi (001), (110) and (111) surfaces is investigated via ab initio pseudopotential-plane wave method. Adsorption energies of H atom and H2 molecule on Fe and Ti terminated (001) and (111) and FeTi (110) surfaces are calculated on high symmetry adsorption sites. It is shown that, top site is the most stable site for horizontal H2 molecule adsorption on (001) and (111) surfaces for both terminations. The most favorable site for H atom adsorption on these surfaces however, is the bridge site. In (110) surface, the 3-fold hollow site which is composed of a long Ti–Ti bridge and an Fe atom, (Ti–Ti)L–Fe, and again a 3-fold hollow site this time composed of a short Ti–Ti bridge and an Fe atom, (Ti–Ti)S–Fe, are the most stable sites for H2 and H adsorption, respectively. With the analysis of the above favorable adsorption sites, probable dissociation paths for H2 molecule over these surfaces are proposed. Activation energies of these dissociations are also determined with the use of the dynamics of the H2 relaxation and climbing image nudged elastic band method. It is found that H2 dissociation on (110) and Fe terminated (111) surfaces has no activation energy barrier. On other surfaces however, activation energies are calculated to be 0.178 and 0.190 eV per H2 molecule for Fe and Ti terminated (001) surfaces respectively, and 1.164 eV for Ti terminated (111) surface.