Nucleation‐Controlled Reconstruction of CuO _x for Selective CO ₂ Electroreduction

ABSTRACT Copper‐based electrocatalysts are unique in reducing CO ₂ into multicarbon products. However, the reconstruction of CuO _x precatalysts into oxide‐derived copper (OD‐Cu) during the CO ₂ electroreduction reaction (CO ₂ RR) remains poorly understood, hindering rational catalyst design. Herein, we reveal that precursor Cu(OH) ₂ nucleation dynamics govern facet exposure of Cu ₂ O (111)/(200), and the oxygen vacancy (O _v ) formation in the CuO _x precatalysts, thereby influencing the competition between CO ₂ RR and hydrogen evolution reaction (HER) in the reconstructed OD‐Cu. Two types of CuO _x precatalysts are obtained by controlling the nucleation kinetics: slow‐nucleated CuO _x (CuO _xSN ) and fast‐nucleated CuO _x (CuO _xFN ). CuO _xFN with excess O _v and a lower ratio of Cu ₂ O (111)/(200) is generated by high‐index Cu(OH) ₂ facets, whereas low‐index Cu(OH) ₂ facets develop CuO _xSN with fewer O _v and a higher ratio of Cu ₂ O (111)/(200). CuO _xFN reconstructs to under‐coordinated Cu sites that enhance HER, while CuO _xSN reconstructs to higher‐coordinated Cu sites leading to greater CO ₂ RR selectivity (FE _CO2RR = 77% at −3.3 V _RHE , j = 359 mA cm ⁻² ). In‐situ and ex‐situ analyses confirm that a higher ratio of Cu ₂ O (111)/(200) and a lower ratio of O _v in the CuO _xSN facilitate selective CO ₂ RR. This work establishes an effective nucleation control strategy for O _v ‐related defects engineering and the facets exposure in CuO _x precatalyst in tuning OD‐Cu evolution for tailored CO ₂ RR.