Fig. 6: AIMD and GCP-K calculation of the process of CO₂RR to CO with K⁺.

a The radial distribution function g(r) and the corresponding integrated coordination number of the O-K⁺ pair in an equilibrated AIMD trajectory. b Evolution of the Ni-C distance, O-C-O angle, and K-O (CO₂) distance before and after the K⁺ ion left the active site. The purple dashed line represents the leaving of K⁺. In the left region, where K⁺ remains near the surface and interacts with chemisorbed CO₂⁻, the Ni-C distance maintains around 2 Å, and the angle of O-C-O keeps steady below 140°, which means the interaction exists all the time and chemisorbed CO₂⁻ never leaves. The left insert is a partial view of chemisorbed CO₂⁻ stabilized by K⁺. In the right region, as K⁺ moves away from the surface, the O-C-O angle becomes a right angle, and the interaction between K⁺ and CO₂⁻ disappears, then the CO₂ without stabilization from K⁺ leaves the active center. The right insert shows the partial view of spontaneous desorption of CO₂ as K⁺ departs. c Calculated partial current density for CO formation on Ni-N₂C₂ (green curve), Ni-N₃C₁ (blue curve), and Ni-N₄ (red curve) along with experimental data of this work (dotted curve) for comparison. The purple dotted line indicates the onset potential at the current density of 1 mA cm⁻², with the equivalent nickel site numbers. d Partial current density for CO formation on Ni-N₂C₂ (green curve), Ni-N₃C₁ (blue curve), and Ni-N₄ (red curve). The dotted blue curve following the blue curve is also the calculated prediction, indicating the RDS changes to the CO leaving the active site. e Faraday efficiency calculated for Ni-N₂C₂ (green curve), Ni-N₃C₁ (blue curve), and Ni-N₄ (red curve).