Advances in nanotechnology have enabled precise design of catalytic sites for CO 2 photoreduction, pushing product selectivity to near unity. However, activity of most nanostructured photocatalysts remains underwhelming due to fast recombination of photogenerated electron−hole pairs and sluggish hole transfer. To address these issues, we construct colloidal CdS nanosheets (NSs) with the large basal planes terminated by S 2− atomic layers as intrinsic photocatalysts (CdS−S 2− NSs). Experimental investigation reveals that the S 2− termination endows ultrathin CdS−S 2− NSs with facet-resolved redoxcatalytic sites: oxidation occurs on S 2− -terminated large basal facets and reduction happens on side facets. Such an allocation of redox sites not only promotes spatial separation of photoinduced electrons and holes but also facilitates balanced extraction of holes and electrons by shortening the hole diffusion distance along the (001) direction of the ultrathin NSs. Consequently, the CdS−S 2− NSs exhibit superb performance for photocatalytic CO 2 -to-CO conversion, which was verified by the isotope-labeled experiments to be a record-breaking performance: a CO selectivity of 99%, a CO formation rate of 2.13 mol g −1 h −1 , and an effective apparent quantum efficiency of 42.1% under the irradiation (340 to 450 nm) of a solar simulator (AM 1.5G). The breakthrough performance achieved in this work provides novel insights into the precise design of nanostructures for selective and efficient CO 2 photoreduction.

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