In situ S-scheme heterojunction of CuO islands on 2D N-TiO2 with dynamic Cu2+/Cu+ sites for selective CO2-to-C2H4 photoreduction

Selective solar-driven conversion of CO 2 into C 2 hydrocarbons under aqueous conditions is a promising route toward carbon neutrality. However, C 2 selectivity in water is severely constrained because the intrinsically slow C–C coupling requires sustained electron flux to build up coupling-relevant intermediates. This flux is readily depleted by the competing hydrogen evolution reaction and rapid carrier recombination. Here, we construct an in situ S-scheme heterojunction of CuO islands on two-dimensional (2D) N-TiO 2 (CuO/N-TiO 2 ) via a one-pot solvothermal strategy. The chemically anchored CuO islands on 2D N-TiO 2 nanosheets create a compact, coherent interface that facilitates interfacial charge transfer. Compared with an ex situ assembled counterpart, the in situ heterojunction shows more efficient S-scheme charge separation. In situ characterizations and theoretical calculations reveal that dynamically redox-cycling Cu 2+ /Cu + sites are beneficial for C 2 H 4 formation, with Cu + sites favoring *CO retention and Cu 2+ sites being more favorable for the subsequent asymmetric *CO–*CHO coupling step. Consequently, the as-prepared catalyst delivers 17.5 μmol g −1 ethylene in 4 h with 94.6% selectivity and robust cycling stability. This work establishes an in situ S-scheme heterojunction with oxide islands anchored on 2D nanosheets that integrates charge management with dynamic active sites for selective aqueous CO 2 -to-C 2 H 4 photoreduction. An in situ grown CuO-islands/2D N-TiO 2 S-scheme heterojunction promotes charge separation for aqueous CO 2 -to-C 2 H 4 photoreduction without sacrificial agents. The dynamic Cu 2+ /Cu + active sites favor *CO formation, asymmetric *CO–*CHO coupling, and ethylene selectivity. Download: Download high-res image (161KB) Download: Download full-size image