Introducing Oxygen Vacancies into a WO₃ Photoanode through NaH₂PO₂ Treatment for Efficient Water Splitting

WO₃, with a high light absorption capacity and a suitable band structure, is considered a promising photoanode material for photoelectrochemical water splitting. However, the poor photoinduced electron-hole separation efficiency limits its application. Herein, we report an effective strategy to suppress electron-hole recombination by introducing oxygen vacancies (O_V) on the surface of a WO₃ photoanode through NaH₂PO₂ treatment. An O_V-enriched amorphous surface layer with a thickness of 4 nm is formed after NaH₂PO₂ treatment, which increases the charge carrier density and enlarges the electrochemical surface area of the photoanode. The charge separation and surface injection efficiencies are both improved after NaH₂PO₂ treatment, and the charge transfer process of the photoanode is accelerated consequently. The current density of the modified WO₃ photoanode reaches 0.96 mA cm^-2 at 1.23 V.