A Dynamic View of Proton-Coupled Electron Transfer in Photocatalytic Water Splitting

Solar-driven water splitting is a key reaction step in a photoelectrochemical cell for solar fuel production. We propose a photoanode in which a TiO2 substrate is functionalized with a supramolecular complex consisting of a fully organic naphthalene-diimide (NDI) dye covalently bound to a mononuclear Ru-based water oxidation catalyst. By performing ab initio Molecular Dynamics simulations, we elucidate microscopic details of water oxidation at the photoanode induced by visible light absorption. The fast photoinduced electron injection from the NDI into the semiconductor provides the driving force for the activation of the Ru catalyst. The proton coupled electron transfer nature of this catalytic reaction path is unveiled through the explicit description of the water environment, which is essential to determine the proton diffusion channel and the free energy change along the reaction. The mechanistic insight into the photocatalytic processes obtained with our computational strategy can facilitate the design of new and efficient photoelectrochemical devices.