Theoretical Study Of Hydrogen Adsorption On Ni And Fe Surfaces

The adsorption of gaseous molecules on transition-metallic surfaces has been an attractive field due to its importance in understanding the mechanisms of heterogeneous catalytic reactions. Theoretical study on the atomistic level can not only help understand the interaction mechanism between the absorbent and metallic atoms, but also obtain the kinetic information of surface adsorption and diffusion. The study on adsorption and dissociation of hydrogen on metallic stepped surfaces is of practical meaning. The adsorption of hydrogen on nickel and iron surfaces has been intensively studied in the past. In the present paper, the embedded-atom-method (EAM) is used to construct the many-body interaction potentials between hydrogen and hydrogen, metal and metal. A Morse potential is used to describe the interaction between hydrogen and nickel, and hydrogen and iron.The adsorption of atomic hydrogen on the stepped surfaces of nickel and iron has been studied with the EAM potential and Morse potential in this paper. The stable sites of hydrogen adsorbed are determined by the adsorption energies. The calculated results show that more active adsorption sites are found in the steps and the steps affect the adsorption properties of hydrogen seriously. On the low-index face of nickel, it is found that the stable sites exist at the ones with more coordinate atoms. The hydrogen atoms prefer to be adsorbed at the 4-fold hollow (H4) site, pseudo 3-fold hollow (H3') site and the bridge (B) site on the Ni (311) surface. There are three kinds of adsorption sites on the Ni (410) surface, i.e. B site on the step edge and pseudo 4-fold hollow (H1 and H2) site and long-bridge (LB) site at the bottom of the step. On Ni (511) surface, the adsorption sites are H1, H2 and bridge (B) sites on the step edge and H3' site on the step. On Ni (211) surface, the hydrogen atoms prefer to adsorb at H1 site and B site and pseudo 4-fold hollow (H5) site on the step. On Ni(320) surface, the hydrogen atoms prefer to adsorb at B, LB, LB' and SB sites. On the low-index surfaces of iron, the hydrogen atoms prefer to adsorb at hollow(H) site of Fe (001) surface and LB site of Fe(110) surface and B site of Fe(111) surface. On iron stepped surfaces, hydrogen atoms prefer to adsorb at B, H, H' and H3 sites of Fe (210), and H3 and B sites of Fe(211) respectively. The dissociative adsorption pathways of hydrogen molecules on the different nickel surfaces are also investigated. The dissociation of hydrogen is easier at the bottom of the step and the dissociated hydrogen atoms are more stable, thus the the steps are more active for hydrogen adsorption and...