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

Electrocatalysts play a vital role in electroreduction of N-2 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 approximate to 24.8 mu g 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-N-4 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.

Automated summary

This study reports a high-performance NRR catalyst consisting of atomically dispersed iron single site embedded in porous nitrogen-doped carbon nanofibers. The catalyst achieves high NH3 yield and Faradaic efficiency in alkaline electrolyte, which outperforms almost all reported Fe-based NRR catalysts. Structural characterization and kinetics isotope effects indicate that carbon defects enhance the water dissociation process and protonation kinetics, promoting the NRR reaction. Theoretical investigations reveal that atomic Fe-N-4 catalytic sites together with carbon defects synergistically reduce the energy barrier of the protonation process and improve the NRR catalytic performance.