Impact of Confined and Exposed Nickel Nanoparticles on Electronic Modulation of Atomically Dispersed Nickel for Electrocatalytic Reduction CO2 to CO with an Ultra-Wide Voltage Range

The practical development of electrocatalytic CO₂ reduction requires high-performance electrocatalysts that can operate over a wide voltage range to accommodate the volatility of renewable electricity. Herein, the impact of confined and exposed nanoparticles on the voltage range of CO₂-to-CO are explored. A hybrid electrocatalyst consisting of Ni single-atoms (SAs) supported on carbon, modified with two types of Ni nanoparticles (NPs): confined nanoparticles (CP) and exposed nanoparticles (EP) is designed. Systematic investigations reveal that the confined Ni CP significantly enhances the CO₂-to-CO activity and selectivity of Ni SAs catalysts, while the exposed Ni EP exacerbates competitive hydrogen evolution, especially at a more negative potential. Density functional theory calculations indicate that introducing confined Ni CP effectively modulates the electronic structure of Ni SAs active sites, diminishing hydrogen evolution, lowering the free energy of *COOH formation, stabilizing the *COOH intermediate, and enhancing the reaction kinetics of CO formation. In an alkaline flow cell, the Faradaic efficiency for CO₂-to-CO (FE_CO) exceeds 93% across an ultra-wide voltage range of 1200 mV (from −0.37 to −1.57 V vs RHE), achieving a maximum FE_CO of ≈100% from −0.57 to −0.97 V. The mixed electrolyte (0.1 m KOH + 0.9 m KCl) significantly prolongs the stability of the catalyst.