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 Cu_xO/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 Cu_xO/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 Cu_xO/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.