Reprogramming Impurity States from Carrier-Loss Centers to Electron-Relay States in Single-Atom Photocatalysts

Single-atom modification can endow semiconductor photocatalysts with well-defined active sites, but the accompanying impurity states often behave as trapping centers, causing severe carrier loss through multiphonon nonradiative recombination. Here we show that the binding and release of trapped photoelectrons, governed by the impurity-state charge localization, is a key factor controlling charge utilization in single-atom photocatalysts. As a demonstration, by introducing B atoms as hetero p-orbital ligands into the first coordination shell of Cu single atoms on TiO2, we construct O-Cu-B asymmetric coordination that delocalizes Cu-related impurity states through multicenter orbital hybridization. This delocalization lowers the effective barrier for thermally assisted detrapping, converting localized carrier-loss centers into electron-relay states. Photophysical analyses reveal reduced trap-mediated nonradiative loss, while light-field-assisted dynamic computation visualizes the ultrafast redistribution of photogenerated carriers mediated by the delocalized impurity states. Consequently, the engineered (Cu-O/B)TiO2 photocatalyst achieves a near-unity apparent quantum efficiency of 94.7% and delivers a 2.8-fold enhancement in H2 evolution relative to the localized-trap (Cu-O)TiO2 control. This work establishes nanoscale coordination engineering as a route to reprogram impurity states for efficient single-atom photocatalysis.