Locally Water-Rich Interfacial Microenvironment Enables Self-Powered High-Current Ammonia Electrosynthesis.

Electrochemical nitrate-to-ammonia conversion holds great promise for sustainable nitrogen fixation, yet its industrial‑level current density operation is limited by cathodic active hydrogen (*H) supply shortage and high energy consumption caused by anodic oxygen evolution reaction (OER). Here, we develop a bifunctional CoP electrocatalyst with engineered phosphorus vacancies that generate atomic-scale electric fields to enrich interfacial water molecules via enhanced hydrogen-bonding interactions, alleviating local water scarcity caused by double-layer compression under high nitrate concentrations and promoting *H generation for nitrate reduction reaction (NO3RR). Meanwhile, we replace OER with the thermodynamically favorable hydrazine oxidation reaction (HzOR), and the electrocatalyst promotes *OH adsorption to facilitate hydrazine dehydrogenation in HzOR. The resulting NO3RR||HzOR electrolyzer delivers an ammonia yield of 49.64 mg h-1 cm-2 at 500 mA cm-2 with a cell voltage of 0.962 V, and enables self-powered ammonia production at 0.769 g L-1 h-1 without external energy input. This work reveals atomic-scale electric field engineering as an effective strategy to modulate interfacial microenvironment for high-performance, low-energy ammonia electrosynthesis.