Evidence of Photocatalytic Dissociation of Water on TiO2 with Atomic Resolution

TL;DR

This study provides direct experimental evidence that water molecules adsorbed on TiO2 can be photocatalytically dissociated under UV light, clarifying a key step in the water splitting process relevant to hydrogen energy technology.

Contribution

It demonstrates the first direct observation of water dissociation on TiO2 surface under UV irradiation using atomic resolution microscopy.

Findings

Water molecules at Ti5c sites can be dissociated under UV light.

Dissociation results in hydroxyl groups at specific surface sites.

This reveals a crucial step in photocatalytic water splitting mechanism.

Abstract

Photocatalytic water splitting reaction on TiO2 surface is one of the fundamental issues that bears significant implication in hydrogen energy technology and has been extensively studied. However, the existence of the very first reaction step, the direct photo-dissociation of water, has been disregarded. Here, we provide unambiguously experimental evidence to demonstrate that adsorbed water molecules on reduced rutile TiO2(110)-1\times1 surface can be dissociated under UV irradiation using low temperature scanning tunneling microscopy. It is identified that a water molecule at fivefold coordinated Ti (Ti5c) site can be photocatalytically dissociated, resulting in a hydroxyl at Ti5c and another hydroxyl at bridge oxygen row. Our findings reveal a missing link in the photocatalytic water splitting reaction chain, which greatly contribute to the detailed understanding of underlying mechanism.