Imaging Water Dissociation on TiO2(110): Evidence for Inequivalent Geminate OH Groups

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Abstract
Identical regions of partially reduced TiO2(110) surfaces with bridge-bonded oxygen vacancy (BBOV) concentrations of ∼10% ML (1 ML = 5.2 × 1014 cm-2) were imaged using scanning tunneling microscopy (STM) before and after dosing H2O at ambient temperature (∼300 K). Atomically resolved images confirm that H2O adsorbs dissociatively on the BBOV sites, producing two hydroxyl species, one positioned at BBOV and denoted OHV and the other, denoted OHB, formed by protonation at either of the two nearest-neighbor bridge-bonded oxygen atoms. Hydrogen hopping along the [001] direction is observed at ambient temperature, with a strong preference for OHB (∼10×) hydrogen motion. This powerful imbalance demonstrates the inequality of OHV and OHB and suggests differences in their charge and/or binding configuration.

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