Boosting NH3 production from nitrate electroreduction via electronic structure engineering of Fe3C nanoflakes

Clear structure-performance relationships are helpful for the design of efficient catalysts and the understanding of reaction mechanisms. The electrocatalytic nitrate reduction reaction (NO3RR) offers a sustainable route to ammonia (NH3) synthesis and nitrate mitigation. However, it suffers from poor nitrate adsorption, low NH3 selectivity and sluggish reaction kinetics. Herein, N-doped carbon nanosheets supported Fe3C nanoflakes featuring large surface areas (860.024 m(2) g(-1)) were prepared. Their NO3RR performances showed volcano-like relationships with the Fe3+/Fe2+ ratios and d-band centers. At -0.5 V, the NH3 yield, faradaic efficiency, selectivity and current density reached 1.19 mmol h(-1) mg(-1), 96.7%, 79.0% and 85.6 mA cm(-2), respectively, exceeding most reported results. Such exceptional performances mainly originated from the optimized electronic structures that boosted nitrate adsorption and reaction kinetics (Tafel slope: 56.7 mV dec(-1)). Mechanistic investigations revealed a NO3- -> NO2- -> NH3 reaction pathway with the chemical process following the fast electron transfer process as the rate-determining step.

Automated summary

This study demonstrates that N-doped carbon nanosheets supported Fe3C nanoflakes exhibit excellent NO3RR performance, mainly due to their optimized electronic structures that enhance nitrate adsorption and reaction kinetics. Mechanistic investigations reveal a reaction pathway of NO3- -> NO2- -> NH3.