A Cu/FeO@CN tandem catalyst for efficient ammonia electrosynthesis from nitrate reduction.

Electrochemical nitrate reduction reaction (ENORR) is a green technology for value-added ammonia production meanwhile treating waste water at ambient conditions. However, it remains a great challenge to construct efficient catalysts due to the complex multiple proton and electron transfer process. Herein, we report a tandem catalyst Cu/FeO@CN composed of N-doped carbon layer coated Cu/FeO heterostructure toward highly efficient electrocatalytic nitrate reduction to ammonia production in alkaline medium. The catalyst can achieve an ammonia Faradaic efficiency and ammonia yield rate as high as 96.57 % and 22104.15 μg h mg at the optimal potential of -0.9 V vs. RHE in 0.1 M KOH. The outstanding ENORR performance outperforms the most of reported transitional metal-based ENORR electrocatalysts. More importantly, Cu/FeO@CN also exhibits excellent stability even under large current density of 200 mA cm, and long-time durability for continuous electrolysis for 36 h. The experimental and theoretical calculations verify the tandem catalysis mechanism of NO → NO → NH through the synergism of the two components Cu and FeO in Cu/FeO@CN. Specifically, Cu has strong NO adsorption capacity which can be reduced into NO, while FeO can boost water dissociation to generate abundant active *H, ensuring the smooth hydrogenation process while suppressing the occurrence of competitive hydrogen evolution reactions (HER). The heterostructure formation between Cu and FeO also significantly reduces the energy barrier of the rate-determining step (*NO → *NOH), which results in the high performance of Cu/FeO@CN.