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

Abstract

AbstractElectrocatalysts 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 mgcat−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.