Accelerating Protonation Kinetics for Ammonia Electrosynthesis on Single Iron Sites Embedded in Carbon with Intrinsic Defects

Electrocatalysts play a vital role in electroreduction of N₂ to NH₃ (NRR); however, large-scale industrial application of electrochemical NRR is still limited by low selectivity and poor activity, owing to the sluggish reaction kinetics. Herein, a high-performance NRR catalyst consisting of atomically dispersed iron single site embedded in porous nitrogen-doped carbon nanofibers with abundant carbon defects (D-FeN/C) is reported. The D-FeN/C catalyst achieves a remarkably high NH₃ yield rate of ≈24.8 µg h⁻¹ mg_cat⁻¹ and Faradaic efficiency of 15.8% at −0.4 V in alkaline electrolyte, which outperforms almost all reported Fe-based NRR catalysts. Structural characterization manifests that the isolated Fe center is coordinated with four N atoms and assisted by extra carbon defects. In situ attenuated total reflectance-Fourier transform infrared results and kinetics isotope effects demonstrate that the intrinsic carbon defects dramatically enhance the water dissociation process and accelerate the protonation kinetics of D-FeN/C for NRR. Theoretical investigations unveil atomic Fe-N₄ catalytic sites together with intrinsic carbon defects synergistically reduce the energy barrier of the protonation process and promote the proton-coupled reaction kinetics, thus boosting the whole NRR catalytic performance.