Constructing built-in electric fields via interface engineering in (oxy)phosphides to boost electroreduction nitrate...

The synthesis of ammonia via the electrocatalytic nitrate reduction reaction (eNO₃RR) offers remarkable advantages due to its cost-effectiveness, operational simplicity, and low-carbon footprint. However, the ammonia yield and long-term stability in eNO₃RR are primarily limited by the sluggish transfer of active hydrogen (*H) and unregulated evolution of active sites under industrial-relevant high current densities. Herein, we fabricate a novel crystalline-amorphous CoNiFe oxides@phosphides (MO@MP) core-shell hybrid catalyst via in situ electrochemical reconstruction of a pre-synthesized CoNiFe phosphide precursor. Combined experimental characterizations and density functional theory (DFT) calculations verify that the Fe₃O₄ and Co/Ni(OH)₂ phases synergistically enhance NO₃^- adsorption and water dissociation for *H production, respectively. This unique crystalline-amorphous core-shell architecture not only mitigates the intrinsic rigidity of pure crystalline phases but also induces a localized built-in electric field at the heterointerfaces, which accelerates *H migration and inhibits the competing hydrogen evolution reaction (HER). Consequently, the optimized MO@MP-2 catalyst achieves a high ammonia yield of 3.69 mmol cm^-2 h^-1 and 99% Faradaic efficiency at -0.5 V, while maintaining long-term stability for over 100 h under industrial current densities in eNO₃RR. Furthermore, the MO@MP catalyst exhibits bifunctional catalytic activity in the coupled catalytic system of eNO₃RR and EGOR, delivering optimal performance and robust operation stability. This work establishes a universal strategy for the rational design of advanced catalysts with exceptional activity and stability for ammonia electrosynthesis and beyond, leveraging the in situ electrochemical reconstruction and interface engineering approach.