Tandem Synergistic Effect of Cu-In Dual Sites Confined on the Edge of Monolayer CuInP 2 S 6 toward Selective Photoreduction of CO 2 into Multi-Carbon Solar Fuels.

One-unit-cell, single-crystal, hexagonal CuInP 2 S 6 atomically thin sheets of≈0.81 nm in thickness was successfully synthesized for photocatalytic reduction of CO 2 . Exciting ethene (C 2 H 4 ) 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 CuInP 2 S 6 monolayer (ML) is mainly responsible for efficient conversion and high selectivity of the C 2 H 4 product as the basal surface site of the ML, exposing S atoms, can not derive the CO 2 photoreduction due to the high energy barrier for the proton-coupled electron transfer of CO 2 into *COOH. The marginal In site of the ML preeminently targets CO 2 conversion to *CO under light illumination, and the *CO then migrates to the neighbor Cu sites for the subsequent C-C coupling reaction into C 2 H 4 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 CO 2 reduction.