Electronic Coupling and Dual‐Spillover Effect in Co/Co ₇ Fe ₃ Heterointerface for Boosting Nitrate‐to‐Ammonia Conversion

ABSTRACT

Rational design of dual‐site catalysts to decouple complex multi‐electron pathways is crucial for efficient electrocatalytic nitrate (NO ₃ ⁻ ) reduction reaction (NO ₃ RR). Here, we construct a Co/Co ₇ Fe ₃ heterojunction with strong electronic coupling that drives NO ₃ RR efficiently via an unconventional [4+4] tandem mechanism. In this [4+4] pathway, the first 4‐electron step reduces NO ₃ ⁻ to the *HNOH intermediate at the Fe sites. The second 4‐electron process involves the migration of *HNOH to adjacent Co sites, followed by a 4‐electron hydrogenation step. Experimental and theoretical investigations demonstrate that the interfacial electric field modulates the local water network, accelerating water dissociation and ensuring a robust proton supply via hydrogen spillover. Benefiting from well‐defined heterointerfaces, the adsorption energetics of key intermediates are favorably optimized, endowing Co/Co ₇ Fe ₃ with markedly boosted electrocatalytic activity for NO ₃ RR through synergistic dual‐spillover effects, and enabling it to achieve a near‐unity Faradaic efficiency of 99.16% ± 0.3% and a remarkable NH ₃ yield rate of 36.07 ± 0.52 mg h ⁻¹ cm ⁻² at −0.48 V versus RHE. Additionally, a rechargeable Zn‐nitrate battery featuring this material as the cathode delivers a peak power density of 18.15 mW cm ⁻² with excellent cycling stability. This study provides a novel paradigm for designing efficient tandem electrocatalysts.