Sustainable conversion of alkaline nitrate to ammonia at activities greater than 2 A cm^-2

Nitrate (NO₃^‒) pollution poses significant threats to water quality and global nitrogen cycles. Alkaline electrocatalytic NO₃^‒ reduction reaction (NO₃RR) emerges as an attractive route for enabling NO₃^‒ removal and sustainable ammonia (NH₃) synthesis. However, it suffers from insufficient proton (H⁺) supply in high pH conditions, restricting NO₃^‒-to-NH₃ activity. Herein, we propose a halogen-mediated H⁺ feeding strategy to enhance the alkaline NO₃RR performance. Our platform achieves near-100% NH₃ Faradaic efficiency (pH = 14) with a current density of 2 A cm^-2 and enables an over 99% NO₃^--to-NH₃ conversion efficiency. We also convert NO₃^‒ to high-purity NH₄Cl with near-unity efficiency, suggesting a practical approach to valorizing pollutants into valuable ammonia products. Theoretical simulations and in situ experiments reveal that Cl-coordination endows a shifted d-band center of Pd atoms to construct local H⁺-abundant environments, through arousing dangling O-H water dissociation and fast *H desorption, for *NO intermediate hydrogenation and finally effective NO₃^‒-to-NH₃ conversion.