Rapid electron transfer via dynamic coordinative interaction boosts quantum efficiency for photocatalytic CO2 reduction

Abstract The fulfilment of a high quantum efficiency for photocatalytic CO2 reduction presents a key challenge, which can be overcome by developing new strategies for dynamic attachment between photosensitizer and catalyst. In this context, we have for the first time exploited the use of coordinate bond to connect a pyridine-appended iridium photosensitizer (IrQPY) and molecular catalysts for CO2 reduction, which has been systematically demonstrated by 1H NMR titration, theoretical calculations, electrochemistry, and spectroscopic measurements. The mechanistic investigations reveal that the coordinative interaction between IrQPY and an unmodified cobalt phthalocyanine significantly accelerates the electron transfer and thus realizes a remarkable quantum efficiency of 10.2%±0.5% at 450 nm for photocatalytic CO2-to-CO conversion with nearly complete selectivity, over 4 times higher than a comparative system with no additional interaction (2.4%±0.2%). Moreover, the decoration of electron-donating amino groups on cobalt phthalocyanine has optimized the quantum efficiency up to 27.9%±0.8% at 425 nm, which is more attributable to the enhanced coordinative interaction rather than the intrinsic activity. The control experiments have indicated that the dynamic feature of coordinative interaction is important to prevent the coordination occupancy of labile sites and back electron transfer, also enabling the wide applicability on diverse non-noble-metal catalysts.