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

•The Cu-doped, Ag-doped, and Au-doped m-WO3(001) and h-WO3(001) surfaces are n-type semiconductors.•The surfaces’ band gap is reduced upon atomic metal adsorption.•CO is adsorbed through a back-donation bond on both the clean and doped surfaces.•The changes in the band gap of the doped surfaces is more significant upon CO adsorption.