Photoinduced processes on TiO2 electrodes

Due to their photoelectronic properties nanostructured semiconductors are employed for the decomposition of organic compounds in air or wastewaters and to the conversion of photon energy into chemical or electrical energy. However, the recombination of photo-generated charge carriers competes with the desired interfacial charge transfer to donor and acceptor molecules and causes low quantum efficiencies. A strategy to overcome this problem is to use nanostructured semiconductor films as electrode material in electrochemical cells. The application of an external potential then reduces the charge carrier recombination. This approach allows not only for the improvement of the overall quantum efficiency, but also offers a powerful approach for the investigation of photoinduced processes, which is needed in order to develop more efficient photoelectronic materials. The aim of the present project is to elucidate the structure-activity-relationship of TiO2 electrodes. For this purpose it will be investigated, how the surface modification of single crystalline electrodes affects the photooxidation of organic model compounds. For comparison well-defined nanostructured electrodes will be prepared and their structure and activity will be characterized. The results obtained from the two types of electrodes (single crystal versus nanostructured film) will be contrasted. Whereas electrochemical measurements will be carried out in order to study the integral properties of the respective electrode, spectroscopic "in-situ" techniques will be applied to characterize the stability, geometry and stoichiometry of adsorbed molecules and to address the interfacial charge transfer reaction on a molecular level.