First Principles Study Of Cu Doping And Oxygen Vacancy Effect On TiO₂for Water Splitting

Titanium dioxide (TiO2) is widely regarded to be the most effective andsuitable photoactive material due to its non-toxicity, low cost, long-termchemical stability and strong oxidizing power. Currently, TiO2has beenstudied intensively for photoelectrochemical (PEC) water splitting generatinghydrogen and oxygen. However, the intrinsic band gap of TiO2is large and itcannot efficiently absorb visible light, which is the major part of the solarspectrum. Further, photoexcited electron-hole pairs tend to recombinerelatively easily in the bulk of TiO2and another issue is its poor electricalconductivity, which mitigates the photo-induced charge carrier migrationfrom body to surface for catalysis. These drawbacks have limited its extensiveapplications in photocatalysis. But doping with transition metals in TiO2is aversatile strategy for its band engineering. Here we investigate the crystalstructure, electronic structure, absorption properties and optical conductivityof Cu-doped TiO2by density functional theory (DFT) calculations. The Cudoping results in the formation of filled impurity bands lying above thevalence band of TiO2, leading to a much more effective band gap reduction. Cu doping is efficient to improve the optical absorption and opticalconductivity of anatase phase TiO2.Besides, TiO2with different contents of oxygen vacancy has also beensimulated based on DFT. Our results show that oxygen vacancies lead to theenhancement of donor density. The increased electron density is expected toshift the Fermi level of TiO2toward the conduction band, which facilitates thecharge separation and transportation. By introducing oxygen vacancy in thebulk TiO2, the light absorption has red-shifted and the conductivity hasimproved to some extent. Our calculation can give a reasonable explanationfor the effect of oxygen vacancy.At last, TiO2containing both Cu dopant and oxygen vacancy has alsocalculated by DFT. The results indicate that Cu dopant and oxygen vacancyshows the synergy effect: the band gap decreases and Fermi level shifts up. Tosum up, our calculation shows that introducing Cu dopant and oxygenvacancy in TiO2is a versatile strategy to design new kind of efficientphotocatalysts.