fig6

Figure 6. (A) Proposed reaction steps of electrocatalytic reduction of CO₂ to CO over the Ni-N₄-O catalytic site; (B) Reaction paths and free energy diagrams of CO₂ reduction to CO over Ni-N₄ and Ni-N₄-O catalytic sites. Inset shows the side view of the optimized configurations of intermediates over the Ni-N₄-O catalytic site^[84]. Copyright 2022, American Chemical Society; (C) FE_CO at different potentials in H-cell^[86]. Copyright 2023, Wiley-VCH; (D) The Gibbs free energy diagrams of pathways I (from CO₂ to HCOOH) and II (from CO₂ to CO)^[87]. Copyright 2024, Wiley-VCH; (E) Comparison of FE_CO at different potentials for NSC, Pb-N₄ and Pb-N₂SV in CO₂-saturated 0.5 M KHCO₃; (F) Gibbs free energy profiles^[88]. Copyright 2024, Wiley-VCH. FE_CO: CO Faradaic efficiency; NSC: sulfur- and nitrogen-co-doped carbon.