Unveiling the activity origin of ultrathin BiOCl nanosheets for photocatalytic CO2 reduction

Ultrathin layered semiconductors have attracted particular attention for various photocatalytic applications, while their surface-structure changes under reaction conditions have been rarely concerned. Herein, the dynamic evolutions of surface atomic and electronic structures on ultrathin BiOCl photocatalysts were firstly explored by combining synchronous-illumination X-ray photoelectron spectroscopy (SI-XPS) with X-ray diffraction (SI-XRD). The related results clearly reveal that the exposed {001} facets of ultrathin BiOCl are terminated with chlorine atoms instead of generally considered oxygen atoms. Under steady states, the outward migration of chlorine atoms on BiOCl (001) surfaces resulted in the formation of Bi, Cl, and O atoms with multiple-valence states and length decrease of ClO and BiO bond within the lattice phase. Under excitation states, the surface chlorine atoms return back to the lattice phase, leading to the elongation of BiCl and BiO bonds and the valence-state normalization of Bi, Cl, and O atoms. Owing to these significant atomic- and electronic-structure changes, ultrathin BiOCl nanosheets exhibit the prominent activity enhancement (21.4 μmol g−1 h−1) for CO2 reduction to CO compare with bulk BiOCl (3.3 μmol g−1 h−1).