Insight into Alkali Cation Effect on CO₂ Electroreduction Catalyzed by Monodispersed Cu-N-C under Applied Potential

Atomically dispersed copper and nitrogen-doped carbon (Cu-N-C) materials are promising electro-driven CO₂ reduction (CO₂RR) catalysts. A comprehensive mechanistic understanding of Cu-N-C towards systematic improvement, however, is hampered by the complexity of electrode-electrolyte interface around Cu. Here, we adopted an electric double layer model to investigate the impact of alkali metal cations on the two-electron CO₂RR catalyzed by Cu-N₄-C under applied potential. The grand canonical density functional theory calculations show that, at U=−1.2 V vs. SHE, hydrated Na⁺ ions near the surface facilitate formation of bent CO₂⁻ bonding with Cu; with an increasingly negative potential, the electrosorption of CO₂ (Cu+CO₂+e⁻→Cu-CO₂⁻) instead of the formation of COOH becomes the presumable rate determining step for Na⁺-aided CO formation. Further, a possible Cu(I) may be vital for the adsorption of anionic COOH. Our study demonstrates the crucial role of alkali metal ion in the early stage of CO₂RR on Cu-N₄-C and the importance of explicit consideration of the applied potential in simulation for a better understanding of the reaction mechanism.