Self‐Enhancing H 2 Evolution from TiO 2 Nanostructures under Illumination

Illumination of anatase in an aqueous methanolic solution leads to the formation of Ti 3+ 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 AM 1.5G or UV light establish that the activation is accompanied by the formation of Ti 3+ 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.