Methoxy Photooxidation on Rutile TiO₂(110): The Role of Excess Electrons

Excess electrons are pivotal in titanium dioxide (TiO₂) photocatalysis. Understanding the role of excess electrons in photocatalytic reactions offers fundamental insights into the TiO₂ photocatalysis. Herein, we have investigated the role of excess electrons on rutile (R)-TiO₂(110) in the hole-mediated methoxy (CH₃O^-) photooxidation with the temperature-programmed desorption (TPD) method. By variation of the level of O₂ exposure, the concentration of excess electrons is tuned. As CH₃O^- coverage increases (the concentration of excess electrons decreases due to oxygen scavenging), the apparent rate parameter for CH₃O^- photooxidation almost scales linearly with initial CH₃O^- coverage, and the apparent rate parameter at 0.25 ML CH₃O^- coverage is about 4 times that on reduced R-TiO₂(110), indicating that CH₃O^- photooxidation is inhibited by excess electrons significantly. Furthermore, excess electrons originating from both surface and near-surface (not only several atomic layers) play similar roles in the hole-mediated reactions by trapping photogenerated holes. The results not only deepen our understanding of the photocatalytic reactions but also provide valuable insights into how excess electrons regulate photocatalytic reactions.