Photocatalytic CO2 reduction with a semiconductor/metal complex hybrid system: Toward visible light and water utilization

Photocatalytic artificial photosynthesis mimics its natural counterpart by converting solar energy into chemical energy, producing organic molecules from CO 2 and H 2 O. In particular, photocatalytic CO 2 reduction with water as the electron donor offers a clean alternative to fossil-fuel-based processes and considered as a promising strategy toward carbon neutrality and environmental sustainability. For example, the conversion of CO 2 and H 2 O to HCOOH and O 2 is thermodynamically uphill, with a standard Gibbs free-energy change of ΔG° ~ +250 kJ mol -1 . Early related studies mainly examined semiconductors or molecular metal complexes as standalone photocatalysts. More recently, increasing attention has focused on semiconductor/molecular-complex hybrid systems, which couple the strong water-oxidation activity and robustness of semiconductors with the high CO 2 reduction selectivity of metal complexes. Although particulate photocatalytic systems that use water as both the electron and proton source were once considered difficult to realize, recent studies have demonstrated highly selective C₁-product formation at appreciable rates by suppressing competing H 2 evolution. This minireview highlights recent advances in semiconductor/molecular-complex hybrid photocatalysts for CO 2 reduction, covering both half-reactions that use sacrificial electron donors and fully uphill overall reactions that use water. Photocatalytic reaction synthesizing organic compounds from CO₂ and H₂O using visible light energy via a hybrid photocatalyst composed of semiconductor particles and metal complexes