Illumination of anatase in an aqueous methanolic solution leads to the formation of Ti3+ sites that are catalytically active for the generation of dihydrogen (H2 ). With increasing illumination time, a light-induced self-amplification of the photocatalytic H2 production rate can be observed. The effect is characterized by electron paramagnetic resonance (EPR) spectroscopy, reflectivity, and photoelectrochemical techniques. Combined measurements of H2 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 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.

Department of Chemical and Materials Engineering Complutense University of Madrid Av Complutense s n 28040 Madrid Spain

Department of Chemistry and Pharmacy Inorganic Chemistry Friedrich Alexander University Erlangen Nürnberg Egerlandstrasse 1 91058 Erlangen Germany

Department of Chemistry King Abdulaziz University Jeddah Saudi Arabia

Department of Materials Science WW 4 LKO University of Erlangen Nuremberg Martensstrasse 7 91058 Erlangen Germany

Regional Centre of Advanced Technologies and Materials Department of Physical Chemistry Faculty of Science Palacky University Slechtitelu 11 783 71 Olomouc Czech Republic

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Metastable Ni(I)-TiO2-x Photocatalysts: Self-Amplifying H2 Evolution from Plain Water without Noble Metal Co-Catalyst and Sacrificial Agent