Hydrogen-Bond Network Promotes Water Splitting on the TiO₂ Surface

Area of Science:

• Surface science
• Photocatalysis
• Water splitting

Background:

• Breaking the O-H bond in isolated water molecules is challenging.
• Hydrogen-bonding networks significantly influence water molecule reactivity.
• Understanding these networks is key for natural photosynthesis and artificial photocatalysis.

Purpose of the Study:

• To investigate the role of hydrogen-bond networks in water splitting at the molecular level.
• To elucidate the mechanism of proton and hole transfer facilitated by these networks.
• To explore the impact of water coverage on hydrogen-bond network formation and function.

Main Methods:

• Utilized the prototypical photocatalytic H2O/anatase-TiO2(001)-(1×4) interface.
• Controlled water coverage to form hydrogen-bond networks above one monolayer.
• Employed ultraviolet (UV) light irradiation and in situ UV/X-ray photoelectron spectroscopy.
• Performed density functional theory (DFT) calculations.

Main Results:

• A hydrogen-bond network promotes coupled proton and hole transfer for water splitting.
• UV irradiation creates a channel for photoexcited hole transfer and proton release, forming hydroxyl groups.
• Hydroxyl groups supply electrons, reducing Ti4+ to Ti3+ and creating gap states.
• DFT calculations confirm water splitting is exothermic with the hydrogen-bond network's assistance.

Conclusions:

• The hydrogen-bond network is indispensable for water splitting, not just exotic photocatalyst activity.
• This internal network is crucial at practical aqueous/catalyst interfaces.
• The findings offer molecular-level insights into water splitting mechanisms.