From Bulk to Surface: A First-Principles Study of Cu Doping in ZnO and Its Implications for Photocatalysis

High Resolution Image Download MS PowerPoint Slide Cu-doped ZnO has long been discussed for its optoelectronic properties, and, more recently, renewed interest has been prompted by applications in heterogeneous photocatalysis. In this study, we investigate copper defects, namely, substitutional (Cu Zn ) and interstitial (Cu i ), in bulk ZnO and at its (101̅0) surface using advanced electronic-structure calculations. In the bulk, Cu Zn and Cu i are found to feature deep donor and acceptor states, respectively. This explains why achieving p -type conductivity through Cu doping is highly unlikely, while the characteristic green luminescence of Cu-doped ZnO is induced by donor-related transitions involving Cu Zn . The physical picture appears remarkably different on the surface: by aligning the energy levels of Cu defects at the semiconductor–water interface, it is observed that surface Cu Zn, possessing both donor and acceptor states suitably aligned with the redox potentials of aqueous species, can promote both the reduction and oxidation processes of the water-splitting reaction. Instead, surface Cu i, while sizably stabilized at higher Cu concentrations, is predicted to have a less advantageous or even detrimental impact on the photocatalytic activity of ZnO. These results indicate that the relative population of substitutional and interstitial surface defects, tuned by the experimental conditions, is a key factor in determining the efficiency of Cu-doped ZnO for photocatalytic water splitting.