99.7% Faradaic Efficiency in Nitrate Reduction Enabled by Defect-Rich Copper Nanoparticles

The electrocatalytic reduction of nitrate toward ammonia (NH 3 ) over Cu-based catalysts under mild conditions addresses many challenges of the Haber-Bosch reaction, providing a sustainable method for NH 3 synthesis, yet it is limited by low conversion rates and faradaic efficiency. In this study, an efficient copper nanoparticle (Cu NP) electrocatalyst was developed for the NO 3 – RR to synthesize NH 3 under mild conditions to enhance the efficiency of the NO 3 – RR. The Cu NPs were synthesized by a facile liquid-phase reduction method and are characterized by high specific surface area and abundant defects that synergistically enhance active site exposure and intermediate adsorption. Electrochemical testing exhibited high NO 3 – conversion and NH 3 selectivity along with a FE of 99.7% at −0.4 V (vs RHE) with 0.02 M NO 3 – . Notably, the catalyst was able to maintain >95% NO 3 – conversion and >90% NH 3 selectivity over a wide range of nitrate concentrations (0.01–0.5 M) at a voltage of −0.7 V (vs RHE). The catalyst also showed excellent stability over 10 cycles with negligible performance degradation. This work advances the progress of Cu-based catalysts for the NO 3 – RR while providing a sustainable pathway for nitrate wastewater remediation and green NH 3 production.