Exploring photocatalytic processes at the atomic scale

Limitations in the supply and environmental hazards related to fossil-fuels have stimulated intense research activities on renewable energies. A particularly interesting approach in this respect is the solar energy conversion into electrical or chemical energy, the latter being compatible with natural photosynthesis. In the technical analogue, natural light is exploited to split water into stoichiometric amounts of hydrogen and oxygen, a process that takes place on the surface of a suitable photocatalyst. Alternatively, more complex chemical reactions might be induced by the optical excitation, e.g. the dissociation or structural rearrangement of larger organic complexes. In both cases, the underlying mechanism is based on the generation of hot carriers by exciting an electron from the valence to the conduction band of a dielectric matrix with typically 1-3 eV band gap. The hot carriers then evolve towards molecular species bound to the surface, where they produce a local excitation that either leads to a chemical activation, a conformational change or a dissociation. Beyond this simplified picture, the fundamental processes involving a photochemical reaction are hardly understood, in particular when it comes to an atomic scale description. Moreover, numerous ways on how to enhance the photochemical response of a system are discussed in the literature, for instance by introducing sensitizers or dopants. However, a conclusive picture of the underlying processes only starts emerging in this field. In our project, we will use atomic scale microscopic and spectroscopic techniques, in order to add to the understanding of light-driven reaction mechanisms and to facilitate the rational design of photocatalysts.