Photoelectrochemical water splitting has become one of the most reliable solar-energy conversion
technologies for clean hydrogen production. In the race of developing and understanding new
semiconducting materials for this application, several studies have been focused on the role of oxygen
vacancies, which are known to be defects with a high impact on the final optical and electrical
properties of the photoelectrodes. These oxygen defective states can introduce either favorable or
detrimental pathways to the overall PEC performance. The present topical review aims to summarize the
role of oxygen vacancies in four of the most studied semiconducting thin film oxides (BiVO4, Fe2O3, TiO2
and WO3) as photoanodes for solar water splitting
