Pyridine-grafted nitrogen-doped carbon nanotubes achieving efficient electroreduction of CO2 to CO within a wide electrochemical window

Abstract

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 (FE_CO) in the course of pursuing a commercial CO current density (j_CO) 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 FE_CO of 96% at −0.99 V (vs. reversible hydrogen electrode, RHE) with a desirable j_CO of 18.4 mA cm⁻², and FE_CO 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 j_CO 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.