Wurtzite CuGaS₂ with an In-Situ-Formed CuO Layer Photocatalyzes CO₂ Conversion to Ethylene with High Selectivity

We present surface reconstruction-induced C-C coupling whereby CO₂ 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 CO₂ to ethylene (C₂ H₄ ). Upon illumination, the catalyst efficiently converts CO₂ to C₂ H₄ 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 Cu²⁺ , 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 CO₂ reduction reaction pathway to selective formation of ethylene.