Tandem catalysis over Cu@Co/CoFe-P metal-alloy heterostructure achieving ampere-level nitrate-to-ammonia electrosynthesis

The electrocatalytic reduction of nitrate to ammonia (NO₃⁻RR) offers a sustainable alternative to energy-intensive industrial NH₃ synthesis. Tandem catalysis has shown promise in overcoming the multi-step complexity of NO₃⁻RR, yet challenges remain in optimizing performance and elucidating tandem mechanisms. Herein, we report a Cu@Co/CoFe-P tandem electrocatalyst featuring a phosphorus-doped heterostructure with dual active sites (Cu-P and Co/CoFe-P). This catalyst achieves an exceptional NH₃ yield of 175.40 mg h⁻¹ cm⁻² and a record-high current density exceeding 2 A cm⁻², with the electro-synthesized NH₃ directly converted into NH₄Cl. In situ spectroscopic analysis and density functional theory (DFT) calculations reveal a novel desorption-reactivation tandem mechanism: (1) the Cu-P domain preferentially reduces NO₃⁻ to *NO₂, which desorbs as stable NO₂⁻; (2) the Co/CoFe-P domain subsequently reactivates NO₂⁻, and converts it efficiently into NH₃. Moreover, phosphorus doping enhances *H supply, while Fe alloying with Co promotes NO₂⁻ hydrogenation, ensuring an efficient and synchronized tandem pathway for NO₃⁻RR. The proposed *NO₂ desorption-reactivation mechanism deepens the understanding of NO₃⁻RR tandem process, thereby paving the way for designing more efficient tandem electrocatalysts.