Wurtzite CuGaS 2 with an In-Situ-Formed CuO Layer Photocatalyzes CO 2 Conversion to Ethylene with High Selectivity.

We present surface reconstruction-induced C-C coupling whereby CO 2 is converted into ethylene. The wurtzite phase of CuGaS 2. undergoes in situ surface reconstruction, leading to the formation of a thin CuO layer over the pristine catalyst, which facilitates selective conversion of CO 2 to ethylene (C 2 H 4 ). Upon illumination, the catalyst efficiently converts CO 2 to C 2 H 4 with 75.1 % selectivity (92.7 % selectivity in terms of R electron ) and a 20.6 μmol g -1  h -1 evolution rate. Subsequent spectroscopic and microscopic studies supported by theoretical analysis revealed operando-generated Cu 2+ , with the assistance of existing Cu + , functioning as an anchor for the generated *CO and thereby facilitating C-C coupling. This study demonstrates strain-induced in situ surface reconstruction leading to heterojunction formation, which finetunes the oxidation state of Cu and modulates the CO 2 reduction reaction pathway to selective formation of ethylene.