Hybrid-DFT Molecular Dynamics Simulations of Photocatalytic Water Oxidation in a [Ru-bda]–Dye Complex

Abstract

In the past decade, Ru-bda (bda = 2,2′-bipyridine-6,6′-dicarboxylic acid) complexes have emerged as extremely effective water oxidation catalysts, rendering them a potential candidate for incorporation into dye-sensitized photoelectrochemical cells. However, the performance of these catalysts declines dramatically when anchored to a photoanode surface due to their catalytic mechanism involving the interaction of two metal centers (I2M). This reduced performance prompts an investigation into the catalytic cycle following an alternative mechanism in which the O–O bond is formed through a water nucleophilic attack (WNA). In this work, we have performed hybrid-DFT based molecular dynamics simulations of the rate-determining O–O bond formation following the WNA mechanism in a [Ru-bda]–dye dyad model in explicit water solvation. In addition, our study probes oxygen dissociation from the Ru^III–O₂ intermediate, and the equilibrium dynamics of the low-valent Ru^III–bda intermediate. Our simulations demonstrate that including a fraction of exact Hartree–Fock exchange impacts the electron and hole localizations in the catalyst–dye complex, which can in specific instances affect the dynamics of the system. This study contributes to a fundamental understanding of water oxidation catalysis with the Ru-bda catalyst family and highlights the relevance of modeling catalytic processes at the hybrid-DFT level.