Pyridine-grafted nitrogen-doped carbon nanotubes achieving efficient electroreduction of CO₂to CO within a wide electrochemical window

Nitrogen-doped carbon nanomaterials for electrochemical reduction of CO2 (CO2ER) to CO have been extensively investigated, evaluated, and applied recently. Nevertheless, their weak adsorption capacity for CO2 usually results in a rapidly decayed CO faradaic efficiency (FECO) in the course of pursuing a commercial CO current density (jCO) by increasing the overpotential. Herein, we axially graft pyridine molecules on nitrogen-doped carbon nanotubes to construct a metal-free composite electrocatalyst (Py-N4CNTs-800) with enhanced CO2 affinity for CO2ER to efficiently generate CO. Py-N4CNTs-800 exhibits a prominent FECO of 96% at -0.99 V (vs. reversible hydrogen electrode, RHE) with a desirable jCO of 18.4 mA cm-2, and FECO can even be maintained above 90% in a wide electrochemical potential window (-0.79 to -1.19 V). In situ infrared spectra unambiguously indicate that grafted axial pyridine molecules can facilitate the CO2 adsorption and suppress the occurrence of competitive hydrogen evolution reaction (HER). Density functional theory (DFT) calculations enlighten that the introduction of pyridine molecules could dramatically stabilize the key intermediate ∗COOH, which effectively accelerates the reaction kinetics rate. Notably, Py-N4CNTs-800 delivers a promising jCO of 217 mA cm-2 at -0.9 V in a flow cell, showing a bright prospect of function strengthened carbon nanomaterial for industrial applications.