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.