Charge-Transport Divergence in Ultrastable Heterometal-Oxo Clusters Exerting Significant Effect on Photoreactivity

The transfer path of photogenerated charges greatly affects the final photocatalytic performance, but this important fact has not been clearly demonstrated experimentally. Here, we construct an ultrastable crystalline catalytic system including three heterometal-oxo clusters, Bi₈M₇-TBC4A (M = group IVB metal-Ti/Zr/Hf), which include cubic metal-oxo cluster core with eight Bi atoms at the vertices, one M atom at the body center, and six M atoms above the cubic face centers. It is worth noted that the change of group IVB elements in Bi₈M₇-TBC4A can specifically modulate the LUMO-HOMO orbitals to distribute on different active metal atoms. This allows it to be an excellent model system to verify the effect of the transport paths of photogenerated charges on photoreactivity. In model reaction based on CO₂ photoreduction, Bi₈Ti₇-TBC4A displays superior photocatalytic CO₂-to-HCOOH conversion rate of 3580.02 µmol g^-1, which is twice that of Bi₈Zr₇-TBC4A and 4 times that of Bi₈Hf₇-TBC4A. In situ characterization accompanied by density functional theory (DFT) indicate that the difference in orbital hybridization between Bi and IVB group elements largely affects the orbital distribution of frontier molecular orbital levels in Bi₈M₇-TBC4A, leading to the transport of photogenerated charges to metal active sites with different reactivities, and thus widely differing photocatalytic performances. This is the first model catalyst system that explores the effect of different photogenerated charge transport pathways on photoreactivity.