DFT+U study of the electronic structure changes of WO3 monoclinic and hexagonal surfaces upon Cu, Ag, and Au adsorption. Applications for CO adsorption

Abstract

A periodic DFT+U study about the adsorption of Cu, Ag, or Au on the monoclinic and hexagonal (001) surface of WO3 is presented. The scope is to elucidate the changes in the electronic structure of these materials upon adsorption of Cu, Ag and Au, and to provide some insights about the adsorption of CO. The adsorbed Cu, Ag, and Au atoms provokes the formation of positive charge on the surfaces by transferring electrons to the oxide. The charge is located at the bottom of the conduction band, which causes the Fermi level to move into the conduction band and the materials become semimetals. The CO molecule is weakly adsorbed on the clean surfaces. The adsorption provokes a compression of the surface's states at the conduction band due to the appearance of new states belonging to the CO molecule. This result is a slight stabilization of the bottom of the conduction band, which is translated into a reduction of the band gap upon CO adsorption on the clean surfaces. On the other hand, the CO molecule is also chemisorbed on the doped surfaces through a back-donation bond. The doped surfaces states at the conduction band are also compressed by the appearance of new states belonging to the CO molecule, and the states at the Fermi level seems to increase. The results provide good insights for the application of WO3 in gas sensing chemistry and photocatalysis.