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

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.