Efficient nitrate electroreduction to ammonia via synergistic cascade catalysis at Cu/Fe2O3 hetero-interfaces

Electrochemical nitrate (NO 3 − ) reduction offers a promising route for ammonia (NH 3 ) synthesis from industrial wastewater using renewable energy. However, achieving selective and active NO 3 − to NH 3 conversion at low potentials remains challenging due to complex multi-electron transfer processes and competing reactions. Herein, we tackle this challenge by developing a cascade catalysis approach using synergistic active sites at Cu-Fe 2 O 3 interfaces, significantly reducing the NO 3 − to NH 3 at a low onset potential to about +0.4 V RHE . Specifically, Cu optimizes *NO 3 adsorption, facilitating NO 3 − to nitrite (NO 2 − ) conversion, while adjacent Fe species in Fe 2 O 3 promote the subsequent NO 2 − reduction to NH 3 with favorable *NO 2 adsorption. Electrochemical operating experiments, in situ Raman spectroscopy, and in situ infrared spectroscopy consolidate this improved onset potential and reduction kinetics via cascade catalysis. An NH 3 partial current density of ~423 mA cm −2 and an NH 3 Faradaic efficiency (FE NH3 ) of 99.4% were achieved at −0.6 V RHE , with a maximum NH 3 production rate of 2.71 mmol h −1 cm −2 at −0.8 V RHE . Remarkably, the half-cell energy efficiency exceeded 35% at −0.27 V RHE (80% i R corrected), maintaining an FE NH3 above 90% across a wide range of NO 3 − concentrations (0.05−1 mol L −1 ). Using 15 N isotopic tracing, we confirmed NO 3 − as the sole nitrogen source and attained a 98% NO 3 − removal efficiency. The catalyst exhibit stability over 106-h of continuous operation without noticeable degradation. This work highlights distinctive active sites in Cu-Fe 2 O 3 for promoting the cascade NO 3 − to NO 2 − and NO 2 − to NH 3 electrolysis at industrial relevant current densities.