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 (NO3–RR) to ammonia (NH3) is an effective and sustainable method for NH3 synthesis and environmental remediation. However, the presence of numerous competing side reactions, especially the hydrogen generation reaction (HER), hinders the NO3–RR, resulting in slow reaction kinetics. Herein, a heterostructure catalyst, Fe2O3/NiFe2O4, is reported, that delivers a Faradaic efficiency of 94.10%, an NH3 yield rate of 47.47 mg·h–1·mgcat–1 and an NH3 energy efficiency of 41.00% and at −0.5 V vs RHE, which outperforms most of the reported NO3–RR electrocatalysts in neutral electrolyte. Experimental and theoretical calculations indicate that the interface effect caused by the strong interaction between Fe2O3 and NiFe2O4 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–NO3– battery assembled with the Fe2O3/NiFe2O4 cathode demonstrates an impressive output power density of 3.98 mW·cm–2. This study provides a new strategy for simultaneous NH3 production, water remediation, and energy storage at ambient conditions using heterostructure catalysts.