Fig. 5: In situ ATR-IR spectra and DFT calculations.

a, b In situ ATR-IR spectra were recorded while ramping down the potential from +0.20 to −1.00 V on a Co-CNTs and b Co-CNTs-MW samples, respectively. c The charge density redistribution (charge transfer) of Co-N₂, Co-N₃, and Co-N₄ sites, respectively. Color code: Gray represents carbon atoms; Blue represents nitrogen atoms; pink represents cobalt atoms. The Cyan (yellow) region shows the electron loss (gain) and all the iso-surface values for these three models were 0.003 e bohr^‒3. d The calculated potential free energy diagrams for CO₂ electroreduction to CO on Co-N₂, Co-N₃, and Co-N₄ sites, respectively. Inset of d: Structural evolution of reaction intermediates on representative coordinatively unsaturated Co-N₃ site in electrochemical CO₂RR. Notes: solution environment and 6 × 6 unit cell are considered in the above data.