Interfacial Charge‐Regulated Microenvironments Enabled by Ionic Organic Cages for Boosting Electrocatalytic Nitrate Reduction to Ammonia

Ammonia (NH₃) is essential for agriculture and industry, yet the Haber-Bosch process is energy-intensive and carbon-emissive. Electrochemical nitrate reduction reaction (NO₃RR) offers a sustainable alternative by coupling NH₃ synthesis with water remediation. However, challenges such as weak NO₃ ⁻ adsorption, competing hydrogen evolution, and suboptimal catalyst microenvironments hinder performance. Here, we report a family of electrocatalysts, Pd⊂QA-Cagex ⁺ (x = 24, 12, 6), constructed by encapsulating Pd clusters within quaternized organic cages. These discrete hosts enable uniform metal cluster confinement and precise control over the interfacial microenvironment. Increasing cage charge density enriches interfacial NO₃ ⁻ concentration, upshifts Pd d-band center, and enhances *NO₃ activation. Simultaneously, potential-driven electron transfer from the counterion (Cl⁻) to -NH₂ ⁺- generates stable radicals in the cage skeleton, which mediate water activation to form hydrogen radicals (H•) that spill over to Pd sites, accelerating intermediate hydrogenation. The optimized Pd⊂QA-Cage²⁴⁺ delivers a Faradaic efficiency of 95.44% and an NH₃ yield of 25.70 mg h⁻ ¹ mgcat ⁻ ¹ in neutral electrolytes, outperforming its lower-charge analogs. Moreover, it enables > 99.4% nitrate removal from eutrophic seawater, reducing NO₃ ⁻ concentrations below potable water standards. This work introduces ionic cages as programmable interfacial modifiers, offering a supramolecular strategy to regulate electrochemical microenvironments and boost electrocatalytic NO₃RR performance.