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Abstract 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.

Attaining high selectivity for CO2 electroreduction in acid is usually difficult due to competing hydrogen evolution. Here, the authors demonstrate efficient CO2 reduction to multicarbon products in strongly acidic medium (pH ≤ 1) on a porous Cu catalyst by combining confinement and cation effects.

Electroreduction of CO2 on single atom catalysts is often hindered by electron delocalization of the metal sites. To improve CO2 activation, here the authors functionalize the carbon support with cyano moieties, thereby attenuating metal-substrate conjugation and improving CO2 to CO conversion.