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

Abstract

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.