Unravelling the composition of the surface layers formed on Cu, Cu-Ni, Cu-Zn and Cu-Ni-Zn in clean and polluted environments

•Mixed oxides were detected over Cu-Zn while only Cu2O is detected over Cu-Ni surface.•Mixed oxides/hydroxides were detected on the surface of Cu-Ni-Zn.•Although ZnS is a wide bandgap semiconductor, it enhances the ionic conduction.•Both XPS and XRD analyses confirm the absence of any copper sulphide in case of Cu-Ni-Zn.•Polysulfide (S8) is formed on the surface of Cu-Ni and Cu-Zn.