Unraveling Dynamic Interplay on Defective Indium Sites During CO ₂ Photoreduction

Defect engineering is a promising strategy in heterogeneous catalysis, while understanding how the defective sites affect reactivity still remains ambiguous. Herein, we demonstrated an in‐depth experimental study of dynamic interaction of CO 2 molecules on defective In 2 S 3 surfaces by integrating operando X‐ray photoelectron spectroscopy with infrared spectroscopy. More specifically, the formation of S vacancy could promote the electron enrichment on adjacent In sites for facilitating CO 2 molecule adsorption, accompanying with the emergence of high oxidation states of surface In sites. Upon light illumination, the adsorbed CO 2 molecules undergo a sequential transformation into *COOH and *CO intermediates. However, an unexpected upside‐down inversion of *CO species on defective In sites from In–*CO to In–*OC has been firstly observed, severely restraining desorption of CO product from In 2 S 3 surfaces. Further tailoring the electronic structure of defective In sites by substituting residual S atom with O atom for inhibiting *CO inversion, a significant improvement of CO evolution activity has been achieved (18.3 µmol g −1 h −1 ), nearly five times higher than that of pristine In 2 S 3 (3.77 µmol g −1 h −1 ). This work provides the new insights on dynamic roles of defect‐derived active sites in determining catalytic activity, which might offer opportunities for fine control of catalytic process.