Photocatalytic CO2 reduction over platinum modified hexagonal tungsten oxide: Effects of platinum on forward and back reactions

[Display omitted] •Pt species are homogeneously modified on h-WO3 and modulate the electronic structure of h-WO3.•Pt modified h-WO3 with improved charge separation and CO2 adsorption promotes photocatalytic CO2 reduction.•The back reactions of CO* and CH4 oxidation to CO2 are confirmed and accelerated with excess Pt modified on h-WO3.•The enhanced CO adsorption strength with excess Pt modification may contribute to the accelerated back reactions. Back reaction is an important factor hindering the efficiency of photocatalytic reaction in suspension system. Pt is an excellent cocatalyst that is widely used in photocatalytic CO2 reduction, however, its effects on the forward and back reactions have not been clearly clarified. Here, Pt modified hexagonal tungsten oxide (h-WO3) is prepared and the role of Pt is investigated based on the performance of CO2 reduction and its back reactions behavior. Appropriate amount of Pt modification proves not only to improve charge separation and transfer efficiency, but also to enhance CO2 adsorption and activation ability. Therefore, Pt modified h-WO3 promotes forward reactions of photocatalytic CO2 reduction to CO and CH4. Furthermore, the back reactions of CO* and CH4 oxidation to CO2 are confirmed and accelerated with excess Pt modified on h-WO3, which limit the further improvement of CO2 reduction performance. The enhanced CO adsorption strength and electronic localization with excess Pt modification may contribute to the accelerated back reactions.