Coupling Atomically Dispersed Fe-N5 Sites with Defective N-Doped Carbon Boosts CO2 Electroreduction

Abstract

Atomically dispersed iron immobilized on nitrogen-doped carbon catalyst has attracted enormous attention for CO₂ electroreduction, but still suffers from low current density and poor selectivity. Herein, atomically dispersed FeN₅ active sites supported on defective N-doped carbon successfully formed by a multistep thermal treatment strategy with the aid of dicyandiamide are reported. This dual-functional strategy can not only construct intrinsic carbon defects by selectively etching pyridinic-N and pyrrolic-N, but also introduces an additional N from the neighboring carbon layer coordinating to the commonly observed FeN₄ , thus creating an FeN₅ active site supported on defective porous carbon nanofibers (FeN₅ /DPCF) with a local 3D configuration. The optimized FeN₅ /DPCF achieves a high CO Faradaic efficiency (>90%) over a wide potential range of -0.4 to -0.6 V versus RHE with a maximal FE_CO of 93.1%, a high CO partial current density of 9.4 mA cm^-2 at the low overpotential of 490 mV, and a remarkable turnover frequency of 2965 h^-1 . Density functional theory calculations reveal that the synergistic effect between the FeN₅ sites and carbon defects can enhance electronic localization, thus reducing the energy barrier for the CO₂ reduction reaction and suppressing the hydrogen evolution reaction, giving rise to the superior activity and selectivity.

Keywords: CO 2 electroreduction; Fe-N 5 active sites; defective N-doped carbon; single atom catalysts; synergistic effects.