Coupling Atomically Dispersed Fe-N 5 Sites with Defective N-Doped Carbon Boosts CO 2 Electroreduction.

Atomically dispersed iron immobilized on nitrogen-doped carbon catalyst has attracted enormous attention for CO 2 electroreduction, but still suffers from low current density and poor selectivity. Herein, atomically dispersed FeN 5 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N 4 , thus creating an FeN 5 active site supported on defective porous carbon nanofibers (FeN 5 /DPCF) with a local 3D configuration. The optimized FeN 5 /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N 5 sites and carbon defects can enhance electronic localization, thus reducing the energy barrier for the CO 2 reduction reaction and suppressing the hydrogen evolution reaction, giving rise to the superior activity and selectivity.