Non-metal photochemical reduction of CO2 to formate with organohydride-recycle strategy

The increasing CO2 concentration in the atmosphere is an urgent social problem that has to be resolved. Reducing CO2 into compounds useful as energy sources and carbon materials is desirable. For the CO2 reduction reaction (CO2RR) to be operational on a global scale, the catalyst system must: (1) use only renewable energy, (2) be built from abundantly available elements, and (3) not require high-energy reactants. Although light is an alluring energy source, most existing methods utilize electricity. Furthermore, catalyst systems are based on rare heavy metals. Herein, we present a transition-metal-free catalyst system for CO2RR using visible light and containing a carbazole photocatalyst and an organohydride co-catalyst based on benzimidazoline. It produced formate with a turnover number exceeding 8000. No other reduced products such as H2 and CO were generated, confirming the high selectivity of the system. This finding is essential for operating artificial photosynthesis on a useful scale.