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

Abstract 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 CO 2 reduction reaction (eCO 2 RR). Operando X‐ray spectroscopy and microscopy unveil the transformation of asymmetric Cu–Ni dimers into fully exposed Cu x –Ni atomic clusters (Cu x –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 CO 2 intermediates as evidenced by operando measurements and theoretical analysis. Specifically, the tailored Cu 5 –Ni ACs formed at −0.9 V reduce the antibonding orbital occupancy between Cu 3 d and C 2 p states, facilitating CO 2 protonation and enhancing eCO 2 RR 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.