Revealing the Kinetic Balance between Proton-Feeding and Hydrogenation in CO2 Electroreduction.

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Electrocatalytic reduction of CO2 to high-value-added chemicals provides a feasible path for global carbon balance. Herein, the fabrication of NiNP x @NiSA y -NG (x,y= 1, 2, 3; NG = nitrogen-doped graphite) is reported, in which Ni single atom sites (NiSA ) and Ni nanoparticles (NiNP ) coexist. These NiNP x @NiSA y -NG presented a volcano-like trend for maximum CO Faradaic efficiency (FECO ) with the highest point at NiNP2 @NiSA2 -NG in CO2 RR. NiNP2 @NiSA2 -NG exhibited ≈98% of maximum FECO and a large current density of -264 mA cm-2 at -0.98 V (vs. RHE) in the flow cell. In situ experiment and density functional theory (DFT) calculations confirmed that the proper content of NiSA and NiNP balanced kinetic between proton-feeding and CO2 hydrogenation. The NiNP in NiNP2 @NiSA2 -NG promoted the formation of H* and reduced the energy barrier of *CO2 hydrogenation to *COOH, and CO desorption can be efficiently facilitated by NiSA sites, thereby resulting in enhanced CO2 RR performance.