Tandem Synergistic Effect of Cu‐In Dual Sites Confined on the Edge of Monolayer CuInP2S6 toward Selective Photoreduction of CO2 into Multi‐Carbon Solar Fuels.

One‐unit‐cell, single‐crystal, hexagonal CuInP2S6 atomically thin sheets of≈0.81 nm in thickness was successfully synthesized for photocatalytic reduction of CO2. Exciting ethene (C2H4) as the main product was dominantly generated with the yield‐based selectivity reaching ≈56.4 %, and the electron‐based selectivity as high as ≈74.6 %. The tandem synergistic effect of charge‐enriched Cu−In dual sites confined on the lateral edge of the CuInP2S6 monolayer (ML) is mainly responsible for efficient conversion and high selectivity of the C2H4 product as the basal surface site of the ML, exposing S atoms, can not derive the CO2 photoreduction due to the high energy barrier for the proton‐coupled electron transfer of CO2 into *COOH. The marginal In site of the ML preeminently targets CO2 conversion to *CO under light illumination, and the *CO then migrates to the neighbor Cu sites for the subsequent C−C coupling reaction into C2H4 with thermodynamic and kinetic feasibility. Moreover, ultrathin structure of the ML also allows to shorten the transfer distance of charge carriers from the interior onto the surface, thus inhibiting electron‐hole recombination and enabling more electrons to survive and accumulate on the exposed active sites for CO2 reduction. [ABSTRACT FROM AUTHOR]