Chemical Dynamics of the First Proton-Coupled Electron Transfer of Water Oxidation on TiO₂ Anatase

Abstract

Titanium dioxide (TiO2) is a prototype, water-splitting (photo)catalyst, but its performance is limited by the large overpotential for the oxygen evolution reaction (OER). We report here a first-principles density functional theory study of the chemical dynamics of the first proton-coupled electron transfer (PCET), which is considered responsible for the large OER overpotential on TiO2. We use a periodic model of the TiO2/water interface that includes a slab of anatase TiO2 and explicit water molecules, sample the solvent configurations by first principles molecular dynamics, and determine the energy profiles of the two electronic states involved in the electron transfer (ET) by hybrid functional calculations. Our results suggest that the first PCET is sequential, with the ET following the proton transfer. The ET occurs via an inner sphere process, which is facilitated by a state in which one electronic hole is shared by the two oxygen ions involved in the transfer.

Chemical Transformations Approaching Chemical Accuracy via Correlated Sampling in Auxiliary-Field Quantum Monte Carlo

“…oxygen reduction on the surface of TiO 2 . [57] Hydrogen abstraction reactions are ubiquitous and play a major role in combustion and the oxidation of hydrocarbons, [58,59] diamond growth via chemical vapor deposition, [60] biochemical processes involving e.g. the antioxidant vitamin E [61] and various metalloenzymes, [62,63] industrial processes, [64] and organic synthesis.…”

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

“…TiO 2 is by far the most common choice for the semiconductor to be used in a dye-sensitized photoelectrochemical cell (DS-PEC) 8 , due to its excellent stability in combination with a high density of states of its conduction band, which allows for rapid electron injection rates [37][38][39] . The WOC considered in this system is the mono Ru-complex [(cy)Ru II bpy(H 2 O)] 2+ .…”

Water Oxidation Kinetics of Accumulated Holes on the Surface of a TiO2 Photoanode: A Rate Law Analysis

“…Some DFT studies have showed that the first PCET is sequential, with electron transfer following proton transfer, and at high pH was barrierless, where the rate was determined by the concentration of surface OH -. 63 However, to our knowledge, the energetics of successive oxidations of water on TiO2 have not been calculated. However, this study shows that a change in OH -concentration induces changes in the TiO2 surface, which changes the energetics of the surfaces holes and the mechanism by which water is oxidized.…”