TiO(2) Nanotubes for Solar Water Splitting: Vacuum Annealing and Zr Doping Enhance Water Oxidation Kinetics

[Image: see text] Herein, we report the cooperative effect of Zr doping and vacuum annealing on the carrier dynamics and interfacial kinetics of anodized TiO(2) nanotubes for light-driven water oxidation. After evaluation of different Zr loads and different annealing conditions, it was found that both Zr doping and vacuum annealing lead to a significantly enhanced light harvesting efficiency and photoelectrochemical performance. The substitution of Zr(4+) by Ti(4+) species leads to a higher density of surface defects such as oxygen vacancies, facilitating electron trapping on Zr(4+), which reduced the charge recombination and hence boosted the charge transfer kinetics. More importantly, vacuum annealing promoted the presence of surface defects. Furthermore, the mechanistic study through impedance spectroscopy revealed that both charge transfer and surface conductivity are significantly enhanced due the presence of an oxygen-deficient TiO(2) surface. These results represent an important step forward in the optimization of nanostructured TiO(2)-based photoelectrodes, with high potential in photocatalytic applications, including solar fuel production.