Nickel Nanocluster-Stabilized Unsaturated Ni-N₃ Atomic Sites for Efficient CO₂-to-CO Electrolysis at Industrial-Level...

Unsaturated Ni single-atom catalysts (SACs), Ni-N_x (x=1,2,3), have been investigated to break the conventional Ni-N₄ structural limitation and provide more unoccupied 3d orbitals for CO₂ reduction reaction (CO₂RR) intermediates adsorption, but their intrinsically low structural stability has seriously hindered their applications. Here, we developed a strategy by integrating Ni nanoclusters to stabilize unsaturated Ni-N₃ atomic sites for efficient CO₂ electroreduction to CO at industrial-level current. Density Functional Theory (DFT) calculations revealed that the incorporation of Ni nanocluster effectively stabilizes the unsaturated Ni-N₃ atomic sites and modulates their electronic structure to enhance the adsorption of the key intermediate *COOH during CO₂RR. Guided by these insights, we prepared an optimal composite catalyst, Ni₆@Ni-N₃, which features a Ni₆N₆ nanocluster surrounded by six Ni-N₃ single atoms sites, through low-temperature pyrolysis. The morphology and coordinative structure of Ni₆@Ni-N₃ were confirmed by an aberration-corrected transmission electron microscope (AC-TEM) and X-ray absorption spectroscopy (XAS). As a result, Ni₆@Ni-N₃ demonstrated a remarkably high CO Faradaic efficiency (FE_CO) of 99.7 % and a turnover frequency (TOF) of 83984.2 h^-1 at 500 mA cm^-2 under -1.15 V_RHE, much better than those of Ni-N₄ with a lower FE_CO of 86 % at 100 mA cm^-2 and a TOF of 39309.9 h^-1under identical potential. XAS analyses of Ni₆@Ni-N₃ before and after long-term CO₂RR testing confirmed the excellent stability of its coordinative environment. This work highlights a generalizable approach for stabilizing unsaturated single-atom catalysts, paving the way for their application in high-performance CO₂RR.