Self-Enhancing H2 Evolution from TiO2 Nanostructures under Illumination

Illumination of anatase in an aqueous methanolic solution leads to the formation of Ti3+ sites that are catalytically active for the generation of dihydrogen (H-2). With increasing illumination time, a light-induced self-amplification of the photocatalytic H-2 production rate can be observed. The effect is characterized by electron paramagnetic resonance (EPR) spectroscopy, reflectivity, and photoelectrochemical techniques. Combined measurements of H-2 generation rates and in situ EPR spectroscopic observation over the illumination time with AM1.5G or UV light establish that the activation is accompanied by the formation of Ti3+ states, which is validated through their characteristic EPR resonance at g=1.93. This self-activation and amplification behavior can be observed for anatase nanoparticles and nanotubes.