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

Unsaturated Ni single-atom catalysts (SACs), Ni-N (x=1,2,3), have been investigated to break the conventional Ni-N structural limitation and provide more unoccupied 3d orbitals for CO reduction reaction (CORR) 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-N atomic sites for efficient CO electroreduction to CO at industrial-level current. Density Functional Theory (DFT) calculations revealed that the incorporation of Ni nanocluster effectively stabilizes the unsaturated Ni-N atomic sites and modulates their electronic structure to enhance the adsorption of the key intermediate *COOH during CORR. Guided by these insights, we prepared an optimal composite catalyst, Ni@Ni-N, which features a NiN nanocluster surrounded by six Ni-N single atoms sites, through low-temperature pyrolysis. The morphology and coordinative structure of Ni@Ni-N were confirmed by an aberration-corrected transmission electron microscope (AC-TEM) and X-ray absorption spectroscopy (XAS). As a result, Ni@Ni-N demonstrated a remarkably high CO Faradaic efficiency (FE) of 99.7 % and a turnover frequency (TOF) of 83984.2 h at 500 mA cm under -1.15 V, much better than those of Ni-N with a lower FE of 86 % at 100 mA cm and a TOF of 39309.9 hunder identical potential. XAS analyses of Ni@Ni-N before and after long-term CORR 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 CORR.