Highly Efficient Electrochemical Nitrate Reduction to Ammonia over a Fe ₂ O ₃ /NiFe ₂ O ₄ Heterostructured Catalyst

Under neutral electrolytes, the electrochemical reduction of nitrate (NO 3 – RR) to ammonia (NH 3 ) is an effective and sustainable method for NH 3 synthesis and environmental remediation. However, the presence of numerous competing side reactions, especially the hydrogen generation reaction (HER), hinders the NO 3 – RR, resulting in slow reaction kinetics. Herein, a heterostructure catalyst, Fe 2 O 3 /NiFe 2 O 4, is reported, that delivers a Faradaic efficiency of 94.10%, an NH 3 yield rate of 47.47 mg·h –1 ·mg cat –1 and an NH 3 energy efficiency of 41.00% and at −0.5 V vs RHE, which outperforms most of the reported NO 3 – RR electrocatalysts in neutral electrolyte. Experimental and theoretical calculations indicate that the interface effect caused by the strong interaction between Fe 2 O 3 and NiFe 2 O 4 modulates the electronic structure of active sites for optimized intermediate adsorption, reduces the energy barrier of the rate-determining step, and promotes the dissociation of water to generate abundant *H species, leading to the improved catalytic activity and selectivity. Furthermore, a Zn–NO 3 – battery assembled with the Fe 2 O 3 /NiFe 2 O 4 cathode demonstrates an impressive output power density of 3.98 mW·cm –2 . This study provides a new strategy for simultaneous NH 3 production, water remediation, and energy storage at ambient conditions using heterostructure catalysts.