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 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 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.