Self-evolution induced CuxO/Fe3O4 heterogeneous interfaces enabling rapid nitrate reduction to ammonia†
Abstract
The electrocatalytic nitrate reduction reaction (eNO3RR) is a promising approach for sustainable ammonia (NH3) synthesis and wastewater treatment. In this work, a carbon-loaded Cu/Fe metal catalyst (Cu5Fe@NC) was synthesized via a solvothermal method followed by high-temperature carbonization. Electrochemically induced surface reconstruction led to the formation of a highly active CuxO/Fe3O4 heterojunction interface, which synergistically enhanced NO3− adsorption, facilitated electron and proton transfer, and accelerated the overall eNO3RR process. Electrochemical tests revealed that the Cu5Fe@NC catalyst exhibited excellent performance at an optimal potential of −0.7 V vs. RHE, achieving a NO3− removal efficiency of 98.93%, NH4+ selectivity of 92.61%, and a faradaic efficiency of 81.58%. The catalyst maintained 92% of its initial performance even after five consecutive electrolysis cycles, indicating remarkable durability and stability. In situ spectroscopic analysis and density functional theory (DFT) calculations further revealed the reaction mechanism. At the CuxO/Fe3O4 heterojunction interface, NO3− was adsorbed via a bridging mode, followed by a tandem reduction process, where NO2− migrated to the Fe3O4 surface, underwent hydrogenation, and ultimately converted into NH3. Gibbs free energy calculations confirmed that the CuxO/Fe3O4 interface significantly reduced the activation energy barrier for NH3 formation compared to Cu2O. This work provides valuable insights into the rational design of high-performance electrocatalysts for efficient nitrate reduction and sustainable ammonia production.