Controlling Product\nSelectivity in Photochemical CO<sub>2</sub> Reduction with the Redox\nPotential of the Photosensitizer

The ability to selectively reduce CO<sub>2</sub> to a\nparticular\nproduct or mixture of products is expected to play a key role in mitigation\nstrategies aiming to alleviate the devastating impact of this greenhouse\ngas in our climate and oceans. Among those, the production of liquid\nsolar fuels from CO<sub>2</sub> and H<sub>2</sub>O will likely need\ncascade strategies involving multiple catalysts carrying out different\nfunctions. This will require that the catalysts doing the initial\nCO<sub>2</sub> reduction steps deliver the right product or products\nto downstream catalysts. CO, H<sub>2</sub> and formate are the most\ncommon products in CO<sub>2</sub> reduction by molecular catalysts.\nIn this work, we demonstrate control over the selectivity of C<sub>1</sub> products in photochemical CO<sub>2</sub> reduction with the\nsame catalyst, simply by changing the redox potential of the photosensitizer\nand/or the water concentration. Turnover numbers for CO generation\nwith one of the photosensitizers under anhydrous conditions reached\n85,000, one of the largest values reported to date. A combination\nof experimental results and DFT calculations show that control of\nthe selectivity is achieved, in part, due to the interplay between\nregimes under kinetic or thermodynamic control. These regimes are\nlargely dictated by the proton sources and the CO<sub>2</sub> reduction\nbyproducts generated.