Boosting photoelectrochemical chlorine and hydrogen production with oxygen vacancy rich TiO2 photoanodes

Abstract

Photoelectrochemical chlorine (Cl2) evolution as the anodic reaction of solar hydrogen production is helpful for increasing the additional value of hydrogen and reducing production cost. In this work, chemically stable TiO2 nanotubes are used as the photoanodes for photoelectrochemical chlorine and hydrogen production. Oxygen vacancies (VO) are introduced by post-annealing in H2/N2 atmosphere. By controlling the post-annealing temperature, concentration of oxygen vacancies is tuned efficiently. Systematic photoelectrochemical measurements reveal that the oxygen vacancies significantly enhance the PEC performance for Cl2 production with respect to the pristine TiO2. The sample post-annealed at 450 °C in H2/N2 achieves the highest Cl2 production rate of 37.12 μmol h−1 cm−2 with a Faradaic efficiency of 73.2% that resulted in fast degradation of methyl orange at a speed of 5.73 mg h−1 cm−2. Furthermore, photocurrent of the two-electrode cell constructed with the VO-rich TiO2 is strongly increased by 250%, demonstrating that introducing oxygen vacancies is a promising way for promoting the photoelectrochemical performance for Cl2 and H2 production. By careful measuring the Faradaic efficiency of various photoanodes, it is revealed that the strongly boosted up Cl2 production is owing to enhancing utilization of photogenerated holes via the oxygen vacancies.