Doping‐Engineered Fe‐Co Tandem Sites Balance Hydrogen and Nitrite Intermediates for Efficient Nitrate to Ammonia Conversion at Low Potential

ABSTRACT Electrocatalytic nitrate reduction (NO 3 − RR) offers a promising route for simultaneous nitrate remediation and sustainable ammonia (NH 3 ) synthesis. However, its efficiency is limited by low NH 3 selectivity, insufficient Faradaic efficiency (FE), and high overpotential, primarily due to inadequate active hydrogen (*H) supply and nitrite (NO2 − ) accumulation. Herein, we report an Fe─Co tandem catalyst (FeCo/C‐0.5) with an optimized Fe/Co ratio that achieves 98% NH 3 selectivity and 89.68% FE at −0.33 V vs. RHE, with a yield of 14.12 mg h −1 mg cat −1 . Combining in situ FTIR, Raman, DEMS, and DFT calculations, we demonstrate that Fe─Co synergy accelerates H 2 O dissociation and establishes a dynamic * H balance, suppressing the hydrogen evolution reaction (HER) while maintaining adequate * H supply for hydrogenation. Furthermore, NO 2 − generated at Fe sites is rapidly reduced to NH 3 at adjacent Co sites, thereby eliminating NO 2 − accumulation and enabling high NH 3 selectivity at low potentials. The catalyst also demonstrates robust stability in simulated wastewater containing Cl − and SO 4 2− , and achieves a power density of 6.63 mW cm −2 in a Zn‐NO 3 − battery, which underscores its practical potential.