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

Unsaturated Ni single-atom catalysts (SACs), Ni-Nx (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 (FECO) of 99.7 % and a turnover frequency (TOF) of 83984.2 h-1 at 500 mA cm-2 under -1.15 VRHE, much better than those of Ni-N4 with a lower FECO 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.