Water Dissociation on MgO/Ag(100): Support Induced Stabilization or Electron Pairing?

Density functional theory is used to compare water splitting on MgO(100) and MgO/Ag(100). Adsorption is considered on terraces and step edges. On the terrace, the limits of low and monolayer coverage are explored. The metal support enhances the adsorption energies of isolated OH and H through electron exchange with the oxide/metal interface, forming either OH- or H+. As a consequence, the nature of the bonding of dissociated H2O on MgO(100) is different as compared to that on MgO/Ag(100). The bonding on MgO(100) is governed by electron pairing in the oxide whereas bonding to MgO/Ag(100) is determined by the interaction with the oxide/metal interface. The difference in bond character is manifested in a red shift (similar to 200 cm(-1)) of hydrogen-bonded O-H stretching vibrations when MgO is supported.