Interface-engineered PBA-derived Cu/Co/Fe oxide heterostructures for d-band-center-regulated ampere-level tandem nitrate-to-ammonia electrosynthesis

Electrochemical nitrate reduction reaction (NO₃⁻RR) offers a sustainable route for ammonia production while simultaneously mitigating nitrate pollution. However, the simultaneous realization of near-unity selectivity and industrially relevant current density remains challenging because it requires precise regulation of multistep intermediate conversion and interfacial electronic structure. Here, we report a family of Prussian blue analogue-derived Cu/Co/Fe oxide heterostructures as compositionally programmable hybrid materials for high-rate nitrate-to-ammonia electrosynthesis. By tuning the Cu/Co ratio, the heterointerface coupling and associated d-band-center modulation can be rationally regulated to optimize *NO_x adsorption and sequential hydrogenation. Among them, the Cu₁Co₁FeO catalyst demonstrates exceptional performance, achieving a Faradaic efficiency toward NH₃ of 99.1%, a yield rate of 0.89 mmol h^{− 1} cm^{− 2} at − 0.25 V vs. RHE, while sustaining stable operation for 90 h at 2 A cm^{− 2}. Operando Raman and FTIR spectroscopy reveal the dynamic evolution of surface Cu–OH and Co(OH)₂ interfacial species under working conditions, which synergistically promote NO₃⁻ activation and *NO₂⁻ hydrogenation, respectively. Density-functional-theory calculations further indicate that heterostructure coupling together with Co incorporation shifts the d-band center to an optimal regime, balancing *NO_x adsorption, lowering the barrier for nitrate reduction, and suppressing poisoning and competitive hydrogen evolution under high-flux operation. This work establishes a structure-property-performance relationship for Cu–Co cooperative catalysis in multicomponent oxide heterostructures and highlights PBA-derived hybrid materials as a scalable platform for interface-engineered electrocatalysis and sustainable ammonia synthesis under industrially relevant current-density regime.