The synergistic effect of surface and bulk O vacancies in a WO3 photoanode to advance carrier separation and light harvesting for photoelectrochemical water splitting

It is critical to fabricate a photoanode with the virtues of high carrier separation efficiency and light harvesting to reduce the recombination of carriers and enhance the utilization of solar energy in photoelectrochemical (PEC) water splitting. In this work, WO3 nanoflake photoanodes with surface and bulk O vacancies (D-WO3-x) were fabricated via a hydrothermal method and H2WO4 etching to reveal the respective roles and collaborative effect of O vacancies in the surface and bulk. The surface O vacancies leave abundant active sites to reduce the redox barrier. Furthermore, the bulk O vacancies act as electron trap centers for heightening carrier separation efficiency. More importantly, the surface and bulk O vacancies in D-WO3-x reduce the band gap so that the resistance to electron jumping is reduced and light harvesting is increased. As expected, the photocurrent density of D-WO3-x is 0.98 mA cm-2 at 1.23 V vs. RHE, which is 5 times that of pristine WO3. Moreover, the carrier separation efficiencies in the surface and bulk are 2.38 and 2.26 times that of WO3. This work provides a promising method for the development of high-performance photoanodes via introducing surface and bulk O vacancies in semiconductors.