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.