Deciphering the Anomalous Acidic Tendency of Terminal Water at Rutile(110)–Water Interfaces
Yong‐Bin Zhuang, Jun Cheng
Abstract
Understanding the mechanism of the oxygen evolution reaction (OER) is essential to improve the efficiency of photocatalysis for TiO 2 . Previous studies have highlighted the importance of terminal hydroxide radical (TiOH • ) in the OER. Ab initio molecular dynamics simulations (AIMD) with hybrid functional have revealed that this radical readily loses its proton, creating the key intermediate, oxygen radical anion (Ti 5c O •– ). Herein, we combine machine-learning-accelerated molecular dynamics with density functional theory calculations to demonstrate that the Ti 5c O •– can alternatively be generated through the trapping of a hole in a terminal oxygen anion (Ti 5c O 2– ) at rutile(110)–water interfaces. Further examination reveals that the Ti 5c O 2– results from the deprotonation of Ti 5c OH – and remains stable at the charge-neutral interfaces for a transient time period of ca. 100 ps. The AIMD-based free energy perturbation method predicts that the acidity constant of Ti 5c OH – is even smaller than that of Ti 5c OH 2, thereby rationalizing the stability of Ti 5c O 2– . Structural analyses show that this anomalous acidic tendency of terminal water originates from the decrease of Ti–O bond length and the transition of Titanium’s coordination from octahedral to pyramidal in Ti 5c O 2– . Our findings provide valuable insights into the surface acid–base chemistry and a potential explanation for the pH-dependent behavior of photogenerated holes for TiO 2 .