Dynamic Crystal‐Structure and Active‐Site of Defective ZnAl‐Catalysts During CO 2 Photoreduction

Abstract Understanding of surface defects of a catalyst during the reaction process is critical to establish an accurate structure‐activity relationship. Herein, combining operando X‐ray diffraction/photoelectron spectroscopy with scanning probe microscope, we have first established the correlations between CO 2 photoreduction activities and crystal‐structure/active‐site of defective ZnAl layered double hydroxides (ZnAl‐LDH). Specifically, the introduction of oxygen vacancies in ZnAl‐LDH could effectively promote the selective adsorption of both CO 2 and H 2 O molecules on surface Al and Zn active sites, respectively, leading to opposite transition states and the evident shrinking of crystalline structures. Under light irradiation, the adsorbed CO 2 molecules transformed into *COOH intermediate on surface Al active sites, while the H 2 O molecules dissociated into OH group on Zn sites to provide proton, simultaneously leading to the expansion of crystalline structures and increase of layer spacing. Accordingly, these defect‐dependent evolutions of surface active sites and crystalline structure contributed to the significant improvement of CO 2 reduction to CO activity (17.2 µmol g −1 h −1 ), much higher than that of pristine ZnAl‐LDH (6.3 µmol g −1 h −1 ). This work provides new insights for in‐depth understanding of the electronic and crystalline changes of defective photocatalysts during the reaction process.