First-principles study of oxygen and hydrogen adsorption on Pt(111) and PtML/Pd(111) surfaces

In this paper, first-principles calculations based on density functional theory (DFT) have been performed to investigate the adsorption of oxygen and hydrogen on Pt(111) and Pd(111) surfaces covered by monolayer (ML) of Pt(Pt-ML/Pd(111)). The results have shown that the oxygen molecule tends to adsorb on fcc site on both surfaces at the coverage of 0.25 ML, which becomes degeneration with hcp site when the coverage increases to 1 ML. For both oxygen and hydrogen, the adsorption on Pt-ML/Pd(111) surface are stronger than those on Pt(111) surface. The adsorption energy difference for oxygen on the two surfaces is similar to 0.2 eV at the coverage of 1 ML, which increases to similar to 0.6 eV with the coverage decreasing to 0.25 ML. The similar energy difference was also found for hydrogen adsorption. The density of states analysis have demonstrated the chemical interaction of adsorbed oxygen with both pure Pt(111) and Pt-ML/Pd(111) surfaces with certain shift of O 2p states to lower level compared to isolated oxygen. For hydrogen adsorption, the hybridization of H 1s with Pt 5d states were observed for both surfaces, indicating the covalent bonding component of H-Pt bond.