Cs-Doped WO₃ with Enhanced Conduction Band for Efficient Photocatalytic Oxygen Evolution Reaction Driven by Long-Wavelength Visible Light

Cesium doped WO₃ (Cs-WO₃) photocatalyst with high and stable oxidation activity was successfully synthesized by a one-step hydrothermal method using Cs₂CO₃ as the doped metal ion source and tungstic acid (H₂WO₄) as the tungsten source. A series of analytical characterization tools and oxygen precipitation activity tests were used to compare the effects of different additions of Cs₂CO₃ on the crystal structure and microscopic morphologies. The UV–visible diffuse reflectance spectra (DRS) of Cs-doped material exhibited a significant red shift in the absorption edge with new shoulders appearing at 440–520 nm. The formation of an oxygen vacancy was confirmed in Cs-WO₃ by the EPR signal, which can effectively regulate the electronic structure of the catalyst surface and contribute to improving the activity of the oxygen evolution reaction (OER). The photocatalytic OER results showed that the Cs-WO₃-0.1 exhibited the optimal oxygen precipitation activity, reaching 58.28 µmol at 6 h, which was greater than six times higher than that of WO₃-0 (9.76 μmol). It can be attributed to the synergistic effect of the increase in the conduction band position of Cs-WO_3-0.1 (0.11 V) and oxygen vacancies compared to WO₃-0, which accelerate the electron conduction rate and slow down the rapid compounding of photogenerated electrons–holes, improving the water-catalytic oxygen precipitation activity of WO₃.