Colour centre controlled formation of stable sub-nanometer transition metal clusters on TiO2 nanosheet for high efficient H2 production

Abstract The transition elements (Fe, Co, Ni) are important substitutes for noble metals as the co-catalysts in hydrogen evolution reaction. Enhancing the atom utilization efficiency is highly desirable, but preparation and preservation of the transition metal catalysts with the size downscaling to sub-nanometer are challenging. In this work, Fe, Co and Ni clusters with subnano size as co-catalysts are synthesized by controllable growth on 2D ultrathin TiO2(B) nanosheets for hydrogen evolution using a photo deposition method. The ultra-small Fe, Co, and Ni co-catalysts on the TiO2(B) nanosheets exhibit remarkably enhanced photo activities, compared to that with the best Pt loading. It is found that the oxygen bridge vacancies act as the colour centres locating at the position adjacent to the O1-Ti1 sites on the TiO2(B) (001) surface. The photo-colouration and photo-bleaching have significantly impact on the nucleation and growth of the metallic clusters. The high density and uniform dispersion of the sub-nano-sized transition metal clusters benefits for the photo reduction under light irradiation, as well as efficient carrier separation, leading to a great improvement of the photo activity.