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 m2 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.