WATIO · Water on TiO2

Hydrogen produced by sunlight is a very promising, environmentally-friendly energy source as an alternative for fossil fuels, which are limited present on earth and produce green house gases by their combustion. Since the discovery of hydrogen production by photocatalytic water dissociation on a titanium dioxide (TiO2) electrode 40 years ago, much research has been performed to make the process more efficient mostly through a trial-and-error approach. However, fundamental knowledge of how water is bound to the catalyst, what the relation between structure and reactivity is, and what the dynamics of the photodissociation reaction are, is lacking up to now, because no suitable techniques were available. The aim of this proposal is to answer these fundamental questions by looking at specifically the molecules at the interface, before and during their dissociation. With the surface sensitive spectroscopic technique sum-frequency generation (SFG) we can look explicitly at the monolayer of water molecules at the interface. A recent expansion of this technique into two-dimensional SFG will allow us to determine the heterogeneity of the water molecules at the interface. Moreover, the dynamics of the photodissociation of water on TiO2 will be investigated by applying pump-probe sum-frequency generation spectroscopy. At variable delay times after the pump pulse the probe pulses will interrogate the interface and detect the reaction intermediates and products. Due to recent developments of this SFG technique it should now be possible to determine the structure of water at the TiO2 interface and to unravel the dynamics of the photodissocation process. The results will be essential for understanding the fundamentals of the water dissociation process at oxide surfaces and thus for developing cheaper and more efficient photocatalysts for the production of hydrogen.