Curvature Balances CO₂ Electroreduction and Hydrogen Evolution over N atoms in Carbon Nanotubes

The planar carbon model is frequently employed to elucidate the electrocatalytic mechanism of CO2-to-CO conversion over defective nanocarbon materials; however, curved carbon microstructures are prevalent in carbon-based electrocatalysts. Herein, nitrogen-doped carbon nanotubes (N-CNTs) of varying diameters (4–50 nm) are chosen as model systems to investigate the curvature effect on electrochemical CO2 reduction (CO2RR) at nitrogen sites within the carbon layer. The curvature-dependent balance of the CO2RR and hydrogen evolution reaction (HER) yields a volcanic-type correlation between curvature and the intrinsic CO2RR activity. N-CNT with a moderate diameter of 30 nm delivered the highest CO selectivity and partial current density (JCO). Faradaic efficiency of CO surpassed 90% across a potential range from −0.13 to −0.94 V, with JCO reaching −124.5 mA cm–2. The density of nitrogen dopants is recognized as a descriptor for the curvature effect, and a similar volcanic trend is observed in the relationship between the curvature and pyridinic-N density. In situ spectra analysis and theoretical calculations revealed that curvature enhances the formation of *COOH, the rate-limiting step in CO2RR, and weakens the adsorption of *CO. However, excessively curved structures significantly promote HER, leading to diminished CO selectivity.