Unusual photoelectrochemical behaviour of nanocrystalline TiO2 films

Although photooxidation of water and numerous other species which are part of reversible redox couples is poorly efficient at nanocrystalline TiO2, conversely high photocurrent efficiencies are observed for the oxidation of various organic molecules. s associated with the fact that in most cases photooxidation of organic molecules does not produce species able to act as electron scavengers. The behaviour of nanocrystalline TiO2 photoelectrodes is clearly dominated by the indirect recombination or redox cycling where intermediates or products of the hole transfer act in turn as electron scavengers. These processes occur whatever the applied anodic bias showing that the actual potential in most of the nanocrystalline TiO2 film is disconnected from that imposed to the conducting substrate.