Engineered tungsten oxide-based photocatalysts for CO2 reduction: Categories and roles

Photocatalytic technology can convert CO2 molecules into clean fuels by solar energy, which can alleviate the energy and environmental crisis caused by the consumption of fossil fuels and the greenhouse effect. It is extremely challenging to develop semiconductor photocatalytic materials to achieve high-efficiency catalysis of CO2 reduction with a suitable band gap, effective use of sunlight, and better oxidation-reduction capability for photogenerated holes and electrons. Tungsten oxides mainly exist in the form of WO3, W18O49 (or WO2.72), WO3·0.33H2O, etc., and their visible light response and suitable band structure have certain potential in the photocatalytic CO2 reduction process. At the same time, in view of their shortcomings such as the negative conduction band position, the small amount of CO2 adsorption, and the serious recombination of photogenerated electron holes, the crystal plane/crystal phase/structure/defect/composition can be adjusted to treat their surfaces/interfaces to improve their catalytic activity. In this review, we first briefly introduce the different methods of controlling tungsten oxide. Then, the activities and mechanisms of different types of tungsten oxides-based photocatalysts in catalytic CO2 reduction are summarized. Finally, solutions to the problems for the material design and application of tungsten oxide-based photocatalysts in high-efficiency catalytic CO2 reduction are proposed, and future prospects are discussed.