Halogen adsorption on crystallographic (1 1 1) planes of Pt, Pd, Cu and Au, and on Pd-monolayer catalyst surfaces: First-principles study

Abstract

Halogen (Cl, Br and I) adsorption on crystallographic (1 1 1) planes of Pd, Pt, Cu, Au and on palladium monolayer catalysts surfaces was investigated by DFT calculations. Palladium monolayer catalyst here denotes either the Pd monolayer deposited over (1 1 1) crystallographic plane of Pt, Cu and Au monocrystals (Pd ML/Me(1 1 1)), or the (1 1 1) crystallographic plane of Pd monocrystal with inserted one-atom thick surface underlayer of Pt, Cu and Au (Me UND/Pd(1 1 1)). The adsorption on the 3-fold sites was found to be the strongest, and adsorption energies decreased if the size of the halogen atoms increased. For the case of Pd-monolayer catalysts it was demonstrated that energy of adsorption of halogen atoms could be correlated to the position of the d-band of surface atoms. Charge states of halogen adatoms and work function changes were evaluated. On the basis of calculated data and both experimental and theoretical data available in the literature, the changes in the catalytic activity toward oxygen reduction reaction of the Pd ML/Pt(1 1 1) surface, caused by chloride adsorption, were discussed.