Photocatalytic reduction of CO2 is one of the most important chemical challenges of the modern times. Recent experiments suggested that Ru complexes attached to N-doped Ta2O5 can be efficient photocatalysts. The performance of these molecules was found to depend strongly on the nature of anchors connecting the Ru complex and the substrate. Nonetheless, the details of the mechanism of charge transfer in these systems and the factors that affect its efficiency in the photocatalytic CO2 reduction are not fully understood. To obtain a comprehensive description of the charge transfer dynamics in the Ru-complex/N-Ta2O5 system, we carried out the state-of-the-art nonadiabatic molecular dynamics simulations based on extended Hückel electronic structure method calibrated against the existing experimental and ab initio data. Our computations predict that the charge transfer is more efficient when the COOH anchor is used instead of PO3H2. This effect is in formal contradiction with the measured turnover numbers, yet we provide a strong support for the conclusions to be true, based on our atomistic nonadiabatic dynamics computations and literature review. We argue that the experimentally-observed turnover numbers are not necessarily indicative of the intrinsic photocatalytic properties of Ru complexes attached with different anchors, and can be affected by surface effects. Our predictions stimulated new set of experimental studies, which showed that the COOH anchor leads to higher efficiencies in electroneutral Ru complexes, thus confirming our computational prediction. In this presentation I will provide a qualitative discussion of our computational findings. In particular, I will focus on the role of the nonadiabatic coupling between donor and acceptor states, on the difference in the composition of the donor and acceptor wavefunctions, and the difference of their sensitivities to atomic motions. The role of quantum coherence and its interplay with the nonadiabatic coupling will be discussed. Special emphasis will be put on the role of surface coverage effects and partial self-reduction of Ru complexes with COOH anchors.

What makes the photocatalytic CO2 reduction on n-doped Ta2O5 efficient: insights from nonadiabatic molecular dynamics

251st National Meeting (2016)

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