Unraveling oxygen vacancy changes of WO3 photoanodes for promoting oxygen evolution reaction

Oxygen vacancy (VO) on semiconductor photoanode plays an important role in enhancing photoelectrochemical water oxidation performances. Nonetheless, there is still a lack of definitive elucidation regarding the structural changes and their impact on charge transport during the oxygen evolution reaction (OER). Herein, oxygen vacancies were rationally introduced on WO3 nanoflake photoanodes via Ar-plasma engraving, resulting in a threefold increase in the photocurrent density of 2.76 mA cm−2 at 1.23 VRHE under AM 1.5 G solar irradiation compared to the pristine WO3 photoanode. Comprehensive experiments and theoretical calculations reveal that the self-healing process of surface oxygen vacancies on WO3 photoanodes should be more easily achieved by capturing oxygen atoms from adsorbed H2O molecules. However, some survived oxygen vacancies in the subsurface could effectively increase the charge carrier density and provide the additional driving force to accelerate the interfacial charge transport, leading to enhanced photoelectrochemical (PEC) activities. More importantly, the oxygen vacancy self-healing on metal-oxide semiconductors is a universal phenomenon, which might bring new insights for design and construction of highly efficient photoanodes for PEC water oxidation.