Reduced grey brookite for noble metal free photocatalytic H2 evolution

Abstract

Herein we introduce for the first time a reduced “grey” brookite TiO₂ photocatalyst, produced by thermal hydrogenation of brookite nanoparticles, that shows a remarkable noble metal free photocatalytic H₂ evolution. Its activity is substantially higher than that of other TiO₂ polymorphs, i.e. anatase or rutile, comparably sized and activated by hydrogenation under optimized conditions. Along with brookite powders, an oriented brookite single crystal was investigated as a defined surface to confirm the effects of the hydrogenation treatment. By a combination of electron paramagnetic resonance (EPR), electron and X-ray characterization techniques applied to the powders and single crystal, we find that hydrogenation forms in brookite a defective crystalline surface layer rich in Ti³⁺ states. Amorphization effects, i.e. forming the so called “amorphous shell” as reported in previous work for black anatase TiO₂, were not detected. Overall, we provide experimental evidence that hydrogenation forms in brookite a surface strained zone with point defects that are mediators for electron transfer to H₂O, leading to a significantly enhanced noble metal free photocatalytic H₂ evolution in comparison to anatase.