Construction and identification of highly active single-atom Fe1-NC catalytic site for electrocatalytic nitrate reduction

Atomically dispersed metal-N-C sites are highly active and selective for nitrate reduction reaction (NO3RR), while identifying their coordination and geometry structures remains significantly challenging. In this study, thermal-modulated single-atom Fe-based catalysts were fabricated and applied in NO3RR. The coordination and geometry structures of metal active-site in the Fe1/NC-X (X is the pyrolysis temperature) catalysts were elabo-rately dissected. The results disclose that Fe1/NC-900 with trigonal pyramidal Fe-N3 coordination exhibits the highest NO3RR performance with an ammonia yield rate (YR) of 18.8 mgNH3 h-1 mgcat-1 at -0.9 V, and a Faradaic efficiency (FE) of 86% at -0.7 V vs RHE. Electrochemical operando attenuated total reflection surface-enhanced infrared absorptive spectroscopy (ATR-SEIRAS) and density functional theory (DFT) calculation demonstrate that the Fe-N3 coordination in Fe1/NC-900 are responsible for the much higher catalytic activity in NO3RR due to their lone pair electrons, stronger charge transfer, and lower energy barrier of the rate-determining step.