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Physikgebäude (Neubau Otto-Hahn-Str. 4a) an der TU Dortmund © Nikolas Golsch​/​TU Dortmund
Research on Interfaces

How water accelerates chemical reactions

© Ahmed Ghalgaoui​​/​​TU Dortmund University
Researchers at the Technical University of Dortmund, in collaboration with Henan University, Université Paris-Saclay, Ruhr University Bochum, and Beihang University, have discovered how water promotes the decomposition of methanol on titanium dioxide (TiO₂) under realistic conditions. By combining surface-sensitive spectroscopy with theoretical calculations, they were able to show that water at the interface and hydroxyl groups facilitate proton transfer, stabilize localized charges, and lower reaction barriers. The results were published in *Angewandte Chemie International Edition*.

Methanol is an important liquid fuel and a promising hydrogen carrier. Understanding its reactions on photocatalyst surfaces is therefore crucial for developing more efficient approaches to energy conversion and sustainable chemical production.
TiO₂ is a stable and widely studied photocatalyst. However, to date, methanol reactions on TiO₂ have been studied under ultra-high vacuum conditions, which differ significantly from the hydrated environments in which photocatalysts typically operate. In the presence of water, surface-bound hydroxyl groups and water molecules form networks of hydrogen bonds that can fundamentally alter the reaction pathways at the surface.
To investigate these processes under more realistic conditions, the researchers combined surface-sensitive sum-frequency spectroscopy (SFG) with density functional theory (DFT) calculations.

The experiments identified methoxy as the dominant surface-bound species following methanol adsorption from solution. The calculations showed that surrounding water molecules and hydroxyl groups form cooperative hydrogen-bonding networks that facilitate proton transfer and stabilize key reaction states, thereby significantly reducing the energy required for methanol dissociation.

Under light irradiation, the surface-bound methoxy species is further oxidized. Here, too, interfacial water and hydroxyl groups play an active role by facilitating proton transfer and stabilizing localized charge carriers.

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“Our results show that water is not simply a passive solvent surrounding the catalyst,” says Dr. Ahmed Ghalgaoui. “Instead, interfacial water and hydroxyl groups actively reshape the reaction environment by facilitating proton transfer, stabilizing localized charges, and lowering the energy barriers for methanol conversion.”

The study bridges the gap between reaction mechanisms derived from idealized vacuum experiments and photocatalytic chemistry under realistic operating conditions. It illustrates how surface hydration, hydrogen bonding, and photoinduced charge carriers interact to control chemical reactions at oxide-liquid interfaces.

Under ambient conditions, adsorbed water molecules and hydroxyl groups (OH) cause hydration of the TiO₂ surface, making the initial step of methanol deprotonation virtually barrier-free compared to ideal ultra-high vacuum conditions. Under UV irradiation, this hydrated environment further promotes methoxy oxidation by stabilizing localized charge carriers and enabling cooperative proton transfer. Taken together, these effects illustrate how surface hydration enhances photocatalytic alcohol oxidation under realistic conditions.

These findings at the molecular level could help advance the development of improved photocatalytic systems for alcohol conversion, the production of solar fuels, hydrogen generation, and other sustainable energy applications.

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