Tungsten oxide in Catalysis and Photocatalysis: Hints from DFT

Despite the importance of tungsten oxide in various areas of materials science including catalysis and photocatalysis, relatively few systematic theoretical studies have been devoted to this system. In this review we report the results of first principle density functional theory calculations based on a hybrid functional that properly reproduces the band gap and other fundamental properties of WO3. We briefly describe the dependence of the band gap on the crystalline phase of WO3. Then, we address the nature of defects and dopants in bulk WO3. As WO3 can be easily reduced to WO3−x , we first discuss the nature of isolated O vacancies showing that three different situations arise from the removal of one O atom along each of the three crystallographic directions of RT monoclinic WO3. The data provide insight into the origin of electrochromism of this material. Then we discuss the role doping of WO3 with substitutional atoms in order to increase the activity for water splitting and we show that Hf is a promising dopant. The redox properties of WO3 are discussed also in relation to H2 adsorption on the WO3(001) surface. Finally, the role of nanostructuring is analyzed by studying the properties of (WO3)3 cyclic clusters deposited on the rutile TiO2(110) surface. Charge transfers at the (WO3)3/TiO2 interface and their role on the activity of this heterogeneous catalyst are discussed