Deciphering the Anomalous Acidic Tendency of Terminal Water at Rutile(110)-Water Interfaces

YB Zhuang and J Cheng, JOURNAL OF PHYSICAL CHEMISTRY C, 127, 10532-10540 (2023).

DOI: 10.1021/acs.jpcc.3c01870

Understanding the mechanism of theoxygen evolution reaction(OER)is essential to improve the efficiency of photocatalysis for TiO2. Previous studies have highlighted the importance of terminalhydroxide radical (TiOH & BULL;) in the OER. Abinitio molecular dynamics simulations (AIMD) with hybridfunctional have revealed that this radical readily loses its proton,creating the key intermediate, oxygen radical anion (Ti5cO & BULL;-). Herein, we combine machine-learning- acceleratedmolecular dynamics with density functional theory calculations todemonstrate that the Ti5cO & BULL;- canalternatively be generated through the trapping of a hole in a terminaloxygen anion (Ti5cO2-) at rutile(110)-waterinterfaces. Further examination reveals that the Ti5cO2- results from the deprotonation of Ti5cOH- and remains stable at the charge-neutral interfacesfor a transient time period of ca. 100 ps. The AIMD-based free energyperturbation method predicts that the acidity constant of Ti5cOH- is even smaller than that of Ti5cOH2, thereby rationalizing the stability of Ti5cO2-. Structural analyses show that this anomalousacidic tendency of terminal water originates from the decrease ofTi-O bond length and the transition of Titanium's coordinationfrom octahedral to pyramidal in Ti5cO2-. Our findings provide valuable insights into the surface acid-basechemistry and a potential explanation for the pH-dependent behaviorof photogenerated holes for TiO2.

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