Construction of Tunable Single-Atom Sites on Metal-Oxo Clusters for Enhanced CO2 Photoreduction.

Single-atom catalysts are powerful and attractive materials capable of maximizing atomic efficiency and offering an alternative strategy to enhance the activity of catalytic reactions. However, developing atomically precise single-atom models that allow mechanistic investigation at the molecular level is still challenging. Herein, we demonstrate a series of atomically precise titanium-bismuth (TiBi) oxo clusters with open single-atom active sites fabricated via a two-step assembly: Bi₆@Ti₅Bi₃M (M = Ni for PTC-288, Co for PTC-289, Zn for PTC-290, and Mn for PTC-291), where the single-metal atoms share an identical coordination environment. The d-band centers for different single-metal sites allow tuning electron transfer efficiency and CO₂ activation energy. Single-Ni-doped PTC-288 achieved photoreduction of CO₂ to CO at a rate of 23.13 μmol·g^-1·h^-1 under visible-light irradiation without photosensitizers and cocatalysts, which is 12 times higher than that of non-single-atom-doped PTC-287. This work not only demonstrates an early example of TiBi single-atom clusters but also provides a comprehensive understanding of their structure-property relationships, guiding future designs of SACs with enhanced catalytic performance.