Boosting Tandem Nitrate-to-Ammonia Electrocatalysis via Phosphorus-Induced Active Hydrogen Modulation

The electrocatalytic nitrate reduction reaction (NO₃RR) offers a sustainable route for ammonia synthesis while addressing nitrate pollution, yet it faces challenges such as sluggish kinetics, competing hydrogen evolution reaction (HER), and poor selectivity under high current densities. Herein, we report a phosphorus-doped Co(OH)₂/Cu nanowire (P-Co(OH)₂/Cu NW) tandem catalyst engineered via in situ reconstruction, which achieves exceptional NO₃RR performance through synergistic dual-site mechanisms. The Cu phase promotes NO₃^- adsorption and activation, Co(OH)₂ facilitates ammonia formation, while P doping induces water dissociation to generate *H for hydrogenation instead of H₂ evolution. In 1 M KOH + 0.1 M NO₃^-, the catalyst delivers a record ammonia yield of 110.14 mg h^-1 cm^-2 with 95.13% Faradaic efficiency at -0.8 V vs RHE and industrially relevant current densities (-1 A cm^-2 at -0.55 V). In situ spectroscopic studies reveal that P doping modulates interfacial water structure, accelerating *H generation and optimizing the tandem pathway. Further, a Zn-NO₃^- battery integrating this cathode achieves simultaneous power output (28.4 mW cm^-2) and ammonia production (6.65 mg h^-1 cm^-2, FE: 90.8%), demonstrating its practical viability.