Operando XAFS Deciphering Dynamic Evolution of Heteronuclear Cu‐Ni from Atomic Sites to Atomic Clusters for Enhanced CO2 Electroreduction

Revealing the dynamic evolution of atomic‐level active sites during catalytic reactions is critical for identifying true catalytic centers and optimizing the adsorption of reaction intermediates. However, elucidating the dynamic atomic/electronic transformation mechanisms of metal sites in multimetallic systems, and achieving atomic‐level control, remains challenging. Here, we report a potential‐dependent in‐plane atomic reconstruction intrinsic to Cu–Ni heteronuclear atomic sites during the electrocatalytic CO2 reduction reaction (eCO2RR). Operando X‐ray spectroscopy and microscopy unveil the transformation of asymmetric Cu–Ni dimers into fully exposed Cux‐Ni atomic clusters (Cux‐Ni ACs, x = 3–7) at potentials from −0.7 to −1.2 V versus RHE, anchored on porous carbon through N/S coordination. The Cu‐rich evolution reshapes geometric structures of active sites, inducing gradual electron localization, thereby optimizing the adsorption energy of CO2 intermediates as evidenced by operando measurements and theoretical analysis. Specifically, the tailored Cu5‐Ni ACs formed at −0.9 V reduce the antibonding orbital occupancy between Cu 3d and C 2p states, facilitating CO2 protonation and enhancing eCO2RR kinetics. These findings demonstrate high CO selectivity and catalytic stability, providing fundamental insights into the dynamic reconstruction and catalytic mechanism of atomic‐scale active sites.