What Makes the Photocatalytic CO₂ Reduction on N-Doped Ta₂O₅ Efficient: Insights from Nonadiabatic Molecular Dynamics

Recent experimental studies demonstrated that photocatalytic CO₂ reduction by Ru catalysts assembled on N-doped Ta₂O₅ surface is strongly dependent on the nature of the anchor group with which the Ru complexes are attached to the substrate. We report a comprehensive atomistic analysis of electron transfer dynamics in electroneutral Ru(di-X-bpy) (CO)₂Cl₂ complexes with X = COOH and PO₃H₂ attached to the N-Ta₂O₅ substrate. Nonadiabatic molecular dynamics simulations indicate that the electron transfer is faster in complexes with COOH anchors than in complexes with PO₃H₂ groups, due to larger nonadiabatic coupling. Quantum coherence counteracts this effect, however, to a small extent. The COOH anchor promotes the transfer with significantly higher frequency modes than PO₃H₂, due to both lighter atoms (C vs P) and stronger bonds (double vs single). The acceptor state delocalizes onto COOH, but not PO₃H₂, further favoring electron transfer in the COOH system. At the same time, the COOH anchor is prone to decomposition, in contrast to PO₃H₂, making the former show smaller turnover numbers in some cases. These theoretical predictions are consistent with recent experimental results, legitimating the proposed mechanism of the electron transfer. We emphasize the role of anchor stability, nonadiabatic coupling, and quantum coherence in determining the overall efficiency of artificial photocatalytic systems.