Thermal-, photo- and electron-induced reactivity of hydrogen species on rutile TiO2(110) surface: Role of oxygen vacancy

Abstract

Interaction of hydrogen with TiO2 plays a vital role in TiO2-based photocatalysis and thermal catalysis. In this work, we compared thermal-, photo-, and electron-induced reactivity of various types of hydrogen species on a rutile TiO2(110) surface formed by atomic H exposure at 320 and 115K by means of thermal desorption spectroscopy, X-ray photoelectron spectroscopy and low energy electron diffraction. Atomic H interaction with rutile TiO2(110) at 115K forms surface TiH hydride, surface hydroxyl group, and chemisorbed water. Upon heating, surface TiH hydride reacts to produce H2 while surface hydroxyl groups react to form both water and H2. Atomic H interaction with rutile TiO2(110) at 320K strongly reduces TiO2 due to the continuous formation and desorption of water and forms surface hydroxyl groups and likely subsurface/bulk hydrogen species. Upon heating, hydrogen forms as the only gas-phase product and its desorption activation energy decreases with the subsurface/bulk reduction extent of rutile TiO2(110). Surface TiH hydride exhibits photo-induced reactivity while both surface TiH hydride and surface hydroxyl group exhibit electro-induced reactivity. These results have important implications for understanding the hydrogen-involved thermal and photo reactions on TiO2-based catalysts.