Atomically defined Co on two-dimensional TiO2 nanosheet for photocatalytic hydrogen evolution

[Display omitted] •Edge-effect of ultrathin TiO2 nanosheet facilitates grafting of isolated Co atoms.•Isolated Co atom can steer the charge kinetics via Co-O electronic coupling.•Co-TiO2 produces excellent photocatalytic hydrogen evolution performance. Precisely constructed dispersion of well-defined single-atom active centers on the semiconductor could allow of the investigation of reaction mechanisms, yet targeted delivery of solar energy to steer the charge kinetics for hydrogen evolution remains challenging. Here we realize the location of isolated Co atoms on the TiO2 nanosheets with the thickness of 6 nm, providing highly active catalytic sites for the significantly boosted photocatalytic hydrogen evolution. X-ray absorption fine structure measurements verify that the atomically dispersed Co is successfully grafted on the surface of TiO2 nanosheets. Experimental exploration and theoretical demonstration not only confirm the isolated Co atoms perform as reactive sites, but also verify that the electron transfer and hydrogen adsorption/desorption processes can be greatly accelerated via the effective Co-O electronic coupling in atomic scale, thereby facilitating the hydrogen evolution.