Adsorption and dissociation of hydrogen on MgO surface: A first-principles study

Periodic density functional theory (DFT) has been used to investigate the adsorption and dissociation of hydrogen on MgO surface. Weak molecular adsorptions were observed and the bridge site with the vertical mode was the most favorable molecular adsorption site. The reaction barrier along with dissociation of the hydrogen molecule on the MgO(001) surface has also been studied. Our results show the most favorable dissociation channel needs activation energy of around 2.2 eV at the bridge site which is in agreement with the previous results (2.34-2.94 eV). The minimum energy pathway for surface diffusion of atomic H indicates the existence of small classical barriers with a value of about 0.37 eV. And our calculations show that H atom can diffuse from the surface sites to subsurface and further into the bulk sites. The most stable absorption configurations are the interstitial octahedral sites in diffusion movements. The largest barrier in these processes is up to 1.52 eV in the diffusion step of surface to subsurface. Once atomic H penetrates the subsurface layers, the corresponding diffusion barriers decrease to 1.02 eV (from subsurface-1 (SB1) to subsurface-2 (SB2) site) and 1.2 eV (from SB2 to subsurface-3 (SB3) site), respectively. Our calculations indicate that dissociation of molecular hydrogen is strongly inhibited on the magnesium oxide surface during the hydrogenation on magnesium films. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.