A Self-Recycling Ruthenium Incorporated CuFe₂O₄ Electrocatalyst for Efficient Neutral Ammonia Electrosynthesis.

Abstract

The high performance of Fe-based electrocatalyst for electrochemical nitrate reduction reaction to ammonia (eNO₃ ^-RR-to-NH₃) is currently constrained by low NH₃ selectivity and insufficient stability under high current density. Hence, the incorporation of ruthenium single-atom into the CuFe₂O₄ (Ru_SA-CuFe₂O₄) with self-recycling property is developed. The Cu and Ru sites synergistically promote the water dissociation and facilitate the redeposition of in situ adsorbed Fe²⁺ (Fe²⁺ _ad) as α-FeOOH by self-reinforcing local alkalinity at the Ru_SA-CuFe₂O₄ surface, thereby achieving high activity and robust stability for eNO₃ ^-RR-to-NH₃ process. The optimized Ru_SA-CuFe₂O₄ delivers excellent performance with a 97.9% NH₃ Faradaic efficiency and 99.8% NH₃ selectivity at -0.59 V versus RHE in neutral electrolyte. Remarkably, in a membrane electrode assembly (MEA) system, it achieves a large current density of 1000 mA cm^-2 at 2.5 V with robust stability, accompanied by >95% NH₃ selectivity, a nitrate removal rate of 4.17 mmol h^-1 cm^-2, and an NH₃ production rate of 3.97 mmol h^-1 cm^-2. Theoretical calculations have demonstrated that Ru site in the Ru_SA-CuFe₂O₄ significantly enhances NO₃ ^- adsorption and lowers the energy barrier for the potential determining step (*HNO₂ → *NO). This work offers valuable insights into designing autonomous local alkalinity microenvironments with self-recycling properties on cost-effective Cu/Fe oxides.