Defect effects on H2 dissociative adsorption on the Ni(100) surface

Abstract

The dissociative adsorption of a hydrogen molecule on the nickel(100) surface with point defects is investigated using the embedded-atom method (EAM). The potential-energy surfaces (PES) for H2 dissociation on both perfect and imperfect Ni(100) surfaces are presented, based on total-energy calculations. it is clearly shown that as the H2 approaches the Ni(100) surface along the entrance channel, the H-H bond is progressively weakened while the H-metal bonds begin to form; finally the H2 is adsorbed on the surface in the form of two independent H atoms. This dissociation process is affected by the vacancy and impurity atoms existing in the Ni substrate. The activation barriers (Ea) for the dissociation of H2 through various pathways are calculated. The barriers for the dissociation of H2 on the perfect Ni(100) surface are found to be low (about 0.08-0.09 eV. corresponding to different dissociation pathways). The existence of vacancies enhances the dissociation of H2 by lowering the activation barrier height and providing more adsorption sites. However, the impurity atoms (Cu, Pd) can impede the dissociation of H2 on the Ni(100) surface by increasing the activation barrier height. The adsorption heat of H2 chemisorption on the contaminated Ni(100) surface is also calculated. It is found that the effects of impurities on the dissociation of H2 vary with the dissociation pathways and the impurity sites.