Revealing the Kinetic Balance between Proton-Feeding and Hydrogenation in CO 2 Electroreduction.

Electrocatalytic reduction of CO 2 to high-value-added chemicals provides a feasible path for global carbon balance. Herein, the fabrication of Ni NP x @Ni SA y -NG (x,y = 1, 2, 3; NG = nitrogen-doped graphite) is reported, in which Ni single atom sites (Ni SA ) and Ni nanoparticles (Ni NP ) coexist. These Ni NP x @Ni SA y -NG presented a volcano-like trend for maximum CO Faradaic efficiency (FE CO ) with the highest point at Ni NP2 @Ni SA2 -NG in CO 2 RR. Ni NP2 @Ni SA2 -NG exhibited ≈98% of maximum FE CO 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 Ni SA and Ni NP balanced kinetic between proton-feeding and CO 2 hydrogenation. The Ni NP in Ni NP2 @Ni SA2 -NG promoted the formation of H* and reduced the energy barrier of *CO 2 hydrogenation to *COOH, and CO desorption can be efficiently facilitated by Ni SA sites, thereby resulting in enhanced CO 2 RR performance.