Development of hybrid photocatalysts with metal complexes and semiconductor for CO2 reduction

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The reaction profile over the entire course of the photochemical CO2 reduction proved higher TOFs for the supramolecular catalysts. It was therefore possible to demonstrate a highly potent supramolecular Ru(II)-Mn(I) catalyst, exceeding its single-unit pendant. At the same time, the Ru(II)-Mn(I) catalyst revealed a rapid degradation initiating after 1 hour diminishing its superior performance relative to the mixed system.In the case of the Ru(II)-Mn(I), it was found that over the course of the first hour, Ru-OERS accumulated in the reaction. Eventually, it was hypothesized that coordination of the Mn-formate intermediate might be too large for the confined space around the Mn-unit. Strong Brønsted acids were found to promote CO formation at fairly positive reduction potentials. Therefore, trifluoroethanol (TFE) was applied as Bronsted acid of choice.We were pleased to find that over the cause of 6 hrs the typical accumulation of Ru-OERS could not be detected. Moreover, the catalyst proved to show a much higher stability. Under identical conditions, the corresponding mixed system proved to be less efficient, demonstrating the advantage of supramolecular architectures.To investigate the reaction in more detail, UV-Vis spectra were recorded. It was found that in the case of Ru(II)-Mn(I), a new species with an absorption in the range of 450 nm was formed.Stronger light sources were screened to obtain representable TONs over 20 hrs reaction time. A stable CO-formation was obtained with a final TONCO of 250. No HCOOH or significant amounts of hydrogen could be detected.