Nitrate reduction to ammonia using Cu–Fe nanoparticles†

Abstract

Ammonia, an important commercial compound, is traditionally produced via the energy-intensive Haber–Bosch process. Recently, there has been significant interest in developing electrochemical methods for ammonia synthesis, particularly through the nitrate reduction reaction (NO₃RR). In this study, we report the synthesis of copper-doped iron (Cu–Fe) nanoparticles via a galvanic exchange reaction for NO₃RR. The Cu₄Fe₉₆ particles, characterized by their low copper content, demonstrated a significant increase in both faradaic efficiency (78.3 ± 0.4%) and ammonia yield rate (11.53 ± 0.08 mg NH₃ per hour per mg of catalyst at −0.9 V vs. RHE), outperforming both pure iron and higher copper-loaded particles. The improvement in catalytic performance is attributed to the dual functionality of the active sites: iron facilitates nitrate adsorption, while copper promotes the generation of adsorbed hydrogen atoms (*H), which are critical for the reduction process. The careful balance between iron and copper on the particle surface is key to optimizing proton adsorption and reaction with nitrate species while suppressing unwanted hydrogen evolution. The Cu₄Fe₉₆ nanoparticles represent a promising and cost-effective alternative for sustainable ammonia production, combining high activity and stability under neutral pH conditions, addressing both environmental pollution and the need for efficient ammonia synthesis using earth-abundant materials.