Water Dissociation on Clean and Potassium Preadsorbed Transition Metals: A Systematic Theoretical Study

Abstract

It is crucial to control the O–H bond cleavage on metal surfaces with preadsorbed potassium atoms in heterogeneous catalysis. On the basis of the density functional theory (DFT) calculations, the adsorption and dissociation of water on clean and potassium preadsorbed transition metal surfaces, including group 11 (Cu, Ag, and Au) and group 8–10 metal (Co, Ni, Ru, Rh, Pd, Ir, and Pt) surfaces, have been investigated systematically. The calculation results show that the presence of potassium atom enhances the binding strength of H2O but weakens the binding strength of OH. More importantly, it was found that the preadsorbed potassium can promote the catalytic activity of various metals for H2O dissociation to varying degrees and the more promoting effect of potassium on the water O–H bond scission occurs on the less chemically active transition metals. On the basis of electronic and geometric analysis, the physical origin of the promotion effect can be attributed to the dipole–dipole interactions like ((Kδ+-OHδ−)-(Auδ+-OHδ−)), which stabilize the OH group and weaken the interaction between OH and H at the TS and thus facilitate the dissociation of water. The functional mechanism illuminated in this paper could be applicable to other electropositive additives like Na, Cs in the activation of the O–H bond involved in H2O or CH3OH.