Electron delocalization engineering via hierarchical modulation in single-atom catalysts for highly efficient electrochemical CO2 reduction

• Ni-based SACs exhibit excellent FE in CO production, but their high overpotential requires high energy input. • By breaking the electronic symmetry of Ni active sites, we enhance the adsorption and desorption of intermediates at them. • A novel electron tug effect around Ni active centers is obtained by Oxygen coordination and loading Au nanoparticles. • The induced distortion in the electronic structure facilitates the desorption of intermediates and reduces overpotential. • This innovation broadens the applied potentials of CO 2 -to-CO conversion. Modulating the coordination of atomically dispersed MN 4 moieties to enhance electron asymmetry presents a promising strategy for improving catalytic performance in the electrochemical reduction of carbon dioxide (eCO 2 RR). By combining small amounts of Au nanoclusters with lateral oxygen coordination in the first coordination shell, the enhanced electron delocalization on Ni centers improves both activity and selectivity. Experimentally, the optimized catalyst demonstrates exceptional catalytic performance, achieving over 95% Faradaic efficiency (FE) for CO across a broad potential range from − 0.50 to − 0.85 V vs. RHE. It also achieves over 90% FE for CO at an overpotential of 340 mV, outperforming state-of-the-art Ni-based single-atom catalysts (SACs). Moreover, the catalyst shows promising potential at a higher current density (∼150 mA cm −2 ) in a flow cell, maintaining high CO selectivity (over 90%). Structural characterizations and theoretical calculations indicate that this structure enhances electron redistribution around Ni sites through a unique electron tug effect. This effectively stabilizes *COOH intermediates, favoring CO production during eCO 2 RR at low applied potentials. This work offers a valuable method that extends beyond the first coordination shell, augmenting the complexity of electronic distribution on metal centers, which could be adapted for further fine-tuning the catalytic behavior of SACs in various reactions.