Photocatalytic CO2 reduction in aqueous media using a silver-loaded conjugated polymer and a Ru(II)-Ru(II) supramolecular photocatalyst

Visible-light-driven conversion of CO2 to useful products is a promising process for a more sustainable energy system in a circular economy. Whilst highly efficient, durable, and selective systems have been reported in organic media, the photocatalytic process performing efficiently in aqueous media is highly desirable for the purpose of its practical application. However, efficiency and selectivity for CO2 reduction versus proton reduction in aqueous solution have proven challenging to date. Herein, this study demonstrates the enablement of highly efficient and durable visible-light-driven photocatalytic CO2 reduction to formate in aqueous media by a hybrid photocatalyst consisting of a silver-loaded conjugated polymer and a binuclear Ru(II) complex. The hybrid photocatalyst exhibited high activity and durability for formate production, with an apparent quantum yield of 4.2% at 460 nm and a turnover number of 38,000 (based on the amount of binuclear complexes adsorbed), both of which are the highest values reported amongst hybrid photocatalysts in aqueous media. Even though the conjugated polymer retains residual amounts of palladium from synthesis (which is an active site for H2 production in aqueous media), the loading of Ag nanoparticles onto the conjugated polymer enhanced the activity and selectivity for photocatalytic CO2 reduction by suppressing H2 production.